Science of the Total Environment 452-453 (2013) 28–39

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Pesticide management and their residues in sediments and surface and drinkingwater in the Mekong Delta, Vietnam

Pham Van Toan a,b, Zita Sebesvari a, Melanie Bläsing c, Ingrid Rosendahl c, Fabrice G. Renaud a,⁎a United Nations University, Institute for Environment and Human Security (UNU-EHS), Hermann-Ehlers-Str. 10, 53113, Bonn, Germanyb Department of Environmental Engineering, College of Environment and Natural Resources, Can Tho University, 3/2 street, Can Tho City, Viet Namc Institute of Crop Science and Resource Conservation (INRES), Division Soil Science and Soil Ecology, University Bonn, Nussallee 13, 53115 Bonn, Germany

H I G H L I G H T S

► Household level pesticide management remains suboptimal in the Mekong Delta, Vietnam.► A wide range of pesticides occurs in water, soil, and sediments of fields and canals.► Water for drinking is often derived from surface water by households in rural areas.► Environmental concentrations lead to chronic exposure of aquatic organism and humans.► Common treatment of surface water for drinking can enhance pesticide exposure.

⁎ Corresponding author. Tel.: +49 228 8150211; fax:E-mail address: renaud@ehs.unu.edu (F.G. Renaud).

0048-9697/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.scitotenv.2013.02.026

a b s t r a c t

a r t i c l e i n f o

Article history:Received 8 December 2012Received in revised form 31 January 2013Accepted 9 February 2013Available online xxxx

Keywords:Pesticide residuesPesticide managementSedimentSurface waterDrinking waterMekong Delta

Public concern in Vietnam is increasing with respect to pesticide pollution of the environment and of drink-ing water resources. While established monitoring programs in the Mekong Delta (MD) focus on the analysisof organochlorines and some organophosphates, the environmental concentrations of more recently usedpesticides such as carbamates, pyrethroides, and triazoles are not monitored. In the present study, householdlevel pesticide use and management was therefore surveyed and combined with a one year environmentalmonitoring program of thirteen relevant pesticides (buprofezin, butachlor, cypermethrin, α-endosulfan,β-endosulfan, endosulfan-sulfate, fenobucarb, fipronil, isoprothiolane, pretilachlor, profenofos, propanil,and propiconazole) in surface water, soil, and sediment samples. The surveys showed that household levelpesticide management remains suboptimal in the Mekong Delta. As a consequence, a wide range of pesticideresidues were present in water, soil, and sediments throughout the monitoring period. Maximum concentra-tions recorded were up to 11.24 μg l−1 in water for isoprothiolane and up to 521 μg kg−1 dm in sedimentfor buprofezin. Annual average concentrations ranged up to 3.34 μg l−1 in water and up to 135 μg kg−1 dmin sediment, both for isoprothiolane. Occurrence of pesticides in the environment throughout the year andco-occurrence of several pesticides in the samples indicate a considerable chronic exposure of biota andhumans to pesticides. This has a high relevance in the delta as water for drinking is often extracted from canalsand rivers by rural households (GSO, 2005, and own surveys). The treatment used by the households for pre-paring surface water prior to consumption (flocculation followed by boiling) is insufficient for the removal ofthe studied pesticides and boiling can actually increase the concentration of non-volatile pollutants.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

In Vietnam, the variety and amount of pesticides applied increasedrapidly from the end of the 1980s to 2010s (Ut, 2002). While 77 dif-ferent active ingredients (a.i.) were legally applied in 1991, nearly300 a.i. were in use in 2010 (Vien and Hoi, 2009; MARD, 2010; PAN,2010). As a result, the amount of imported pesticides increasedfrom 20,300 to 72,560 t (Huan, 2005; MARD, 2010). The reason be-hind this growth is the overlapping effect of the Green Revolution

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in rice production since the 1970s as well as of liberalization policies(Doi Moi) put in place from 1986 onward. The latter led to more re-sponsibility and planning security for individual farmers which inturn triggered higher farm-level investments, resulting in a high useof fertilizer and pesticides, agricultural intensification, and changesin production patterns (Dang and Danh, 2008). This increasing useof pesticides coupled with their widespread mismanagement (Thuyet al., 2012b) lead to considerable concerns with regard to environ-mental pollution and human health in the last decades (Dasguptaet al., 2005; Hoai et al., 2011).

Persistent organochlorine and organophosphate pesticides havebeen widely used in Vietnam's agriculture since the 1960s (Quyen

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et al., 1995; Sinh et al., 1999). From 1992, the use of these compoundsdecreased as a result of stepwise bans and restrictions of themost prob-lematic compounds (Gaston, 1994; Huan, 2005; Lensink and Nam,2008). Nevertheless, household surveys and environmental monitoringdata show continuous evidence of further use of some of these com-pounds (Berg, 2001; Dung and Dung, 2003; Hoai et al., 2011; Meisner,2005; Minh et al., 2007; Thuy et al., 2012b). Berg and Tam (2012) re-cently reported only marginal changes in the top ten list of the a.i.that were most frequently used in 1999 and 2007 in the MekongDelta. Themost commonly used pesticides in both yearswere the insec-ticide fenobucarb, the fungicides hexaconazole and propiconazole andthe herbicide pretilachlor. According to the study, the average numberof applications of insecticides per rice field and crop has decreased sig-nificantly from 1999 to 2007 (3.1 vs 1.4 applications on average for thefirst crop), while the amount applied per crop decreased less rapidly(0.93 vs 0.77 kg a.i. ha−1) (Berg and Tam, 2012), implying that thetreatment frequency decreased by increasing the amount sprayed pertreatment.

Once released in the environment, pesticides may harm non-targetplants and animals as well as human beings (Ohkawa et al., 2007).Although pesticide concentrations in surface water are routinely moni-tored and assessed in many countries (Azevedo et al., 2004; Ebbertand Embrey, 2002; Müller et al., 2002; Nakano et al., 2004), pesticidemonitoring is cost intensive and requires skilled laboratory staff andsophisticated equipment causing large differences between countrieswith regard to the extent and reliability of monitoring results. InVietnam, regular state-organized surface water monitoring programsare still focusing on organochlorines and organophosphates. Monitor-ing is very limited in terms of spatial coverage, sampling frequencyand compounds considered (authors' observations and discussionswith officers of the Department of Natural Resources and Environment(DONRE) of Can Tho and Dong Thap). Pesticides that are currently inuse are not monitored at all or are monitored at very low frequencies.

In addition to regularmonitoring programs, several scientific studieshave been conducted on pesticide occurrence. For example, DDT wasshown to still occur frequently in the environment. DDT concentrationsreported for soils and sediments in agricultural areas in North Vietnamranged from 5 to 28 ng g−1 dry weight (Viet et al., 2000). In theMekong Delta, DDT was detected in sediment with concentrationsranging from 0.01 to 110 ng g−1 dry weight (Minh et al., 2007). Againin the Mekong Delta among more than 70 monitored pesticides, diazi-non, fenitrothion and endosulfan were detected in the water, whileDDT, HCH, endosulfan and chlordane occurred in sediment and biota(Carvalho et al., 2008). Since the concentration of DDT was higherclose to settlements, Carvalho et al. (2008) attributed this to vector con-trol activities rather than to agricultural use. In contrast, endosulfanwasdetected in highest concentrations in rural areaswhere it has been usedfor agricultural purposes (Carvalho et al., 2008).

The studies of Hoai et al. (2011) and Lamers et al. (2011) areamong the few in Vietnam which monitored recently used pesticidesas opposed to the large amount of studies focusing on organochlo-rines and organophosphates. Hoai et al. (2011)monitored the occurrenceof fenobucarb, trichlorfon, cyfluthrin, and cypermethrin and detectedthem in environmental samples as well as in vegetable and fish. Lamerset al. (2011)monitored the loss of imidacloprid, fenitrothion, fenobucarb,and dichlorvos frompaddy ricefields at thewatershed scale inmountain-ous regions of North Vietnam and reported runoff losses in the range of0.4% (dichlorvos) to 16% (imidacloprid) of the total applied mass withmaximum concentration of 0.47 μg l−1 (fenitrothion).

In the rural areas of the Delta, surface water still serves as one ofthe main drinking water sources, especially during the dry season.Direct intake via drinking is one of the possible exposure routesto pesticides. In addition, surface water is widely used for personalhygiene and washing of food items, dishes, and clothes thus openingup another exposure pathway that potentially threatens humanhealth (US EPA, 2003).

In order to determine the extent of currently-used pesticide pollu-tion and resulting exposure of communities, the objectives of thisresearch were to (i) study the root-causes of pesticide contaminationof surface water by investigating pesticide use andmanagement prac-tices at the farm level, (ii) determine and assess the concentrations ofcommonly used pesticide residues in sediments and surface water, aswell as (iii) in drinking water derived from surface water after treat-ment as frequently applied by rural households.

2. Materials and methods

2.1. Study sites

The Mekong Delta is a low-lying area (b4.0 m above mean sealevel) with a complex network of rivers and canals. The Delta beginsin Cambodia, where the river splits into the Mekong (Tien River) andthe Bassac (Hau River). The Mekong subsequently splits into six maindistributaries while the Bassac splits into three, jointly forming theMD. The hydrology of the Delta is influenced by tides from theSouth China Sea as well as from the Gulf of Thailand (Tri, 2012). Theclimate is tropical monsoonal with one rainy season (May to Octo-ber). The average annual temperature is around 27 °C and the meanannual rainfall is ca. 1600 mm (>80% during the rainy season)(Statistical Office of Can Tho City, 2000, 2005, 2008). During the rainyseason, floods may cover up to 50% of the total area (39,000 km2) ofthe Vietnamese part of the MD (Deltares, 2011; Hung et al., 2012).

A survey on pesticide use and management as well as a year-roundmonitoring program was carried out in two study areas. The northernstudy site was located in An Long commune (Tam Nong District, DongThap Province, 10°43′9.15″N, 105°24′34.25″E) in the upstream part ofthe delta (Fig. 1). The southern study site was in Ba Lang (Cai RangDistrict, Can Tho City, 9°58′49.07″N, 105°43′52.20″E) in the center ofthe delta (Fig. 1). The study site in An Long represents an area of inten-sive paddy rice monoculture harvested twice a year. The winter–springcrop is cultivated from November/December until March/April, whilethe summer–autumn crop is grown from March/April to July/August.Most fields are flooded during the rainy season from July/August toNovember/December with flooding depths reaching 1 m and more.The tidal influence is moderate due to high dykes and a distance of3.5 km to the Tien River (Hung et al., 2012). The study site comprises13 fields on a total area of 8.5 ha. These fields are located on bothsides of an irrigation canal which is used for water intake and waterdischarge for the rice paddy. In the study period, the average rice yieldwas 5.5 tha−1 crop−1 in this area.

The southern study site is located in Ba Lang, a peri-urban areaof Can Tho City (the largest city in the MD). The site is character-ized by intercropping and a rotation of paddy rice, vegetables andfruit trees. Rice is harvested two to three times per year. Vegetablesare either rotated with rice in the same fields or grown on raisedbeds. Fruit trees are mainly grown together with rice or vegetables.Fig. 2 refers to the land use in Ba Lang during the monitoringperiod. The flooding period in Ba Lang is typically short (mainlyOctober) with flooding depths usually below 0.5 m. The area is ad-ditionally influenced by diurnal and semi-diurnal tides with tidal am-plitudes from1up to 1.3 m (Hung et al., 2012). The study site comprises13 fields on a total area of 5 ha. The average rice yield per crop was4.3 tha−1 in this area. As in An Long, the fields are located on bothsides of an irrigation canal which is used for water intake and waterdischarge.

The drinking water quality survey was carried out in Ba Lang, butthe geographical scope was extended to the downstream area of thestudy site. Households in this area do not have access to clean waterbut the majority of residents obtain water for domestic activitiesfrom surface water. These households are located along canals andrivers receiving field discharges from the Ba Lang study site.

Fig. 1. Location of the study sites.

Fig. 2. Land use in Ba Lang during the monitoring period.

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2.2. Pesticide management survey

Farmer's pesticide use and management practices at the studysites were investigated through household interviews and participa-tory rural appraisals (PRA). After pre-testing the questionnaire, a sur-vey was conducted with 35 households in Ba Lang in June 2008.In An Long, interviews were conducted in July 2008 and October2009 with 40 farmer households. The respondents were the ownersof the studied fields, and additional randomly selected farmers fromthe close neighborhood of the study sites. PRAs were conductedwith farmers who owned fields at the two study sites. Group sizefor the PRAs was around seven farmers per group. Farmers wereasked to provide information about land use, major pests and diseaseoutbreaks, pesticide application and water management practices intheir fields.

In addition, twenty-one household interviews were conducted inBa Lang from May to August 2009 as a screening survey on drinkingwater use. The survey aimed to identify households using surfacewater for drinking purposes located either within or downstreamfrom the Ba Lang study site. Furthermore, the survey enabled thecollection of information on household water sources, treatmentsapplied, and consumption patterns by using a structured questionnaire.Respondents were individuals involved in the process of obtainingdrinking water and/or responsible for the drinking water supplyof their families. The survey results were used to define the share ofhouseholds using surface water for drinking, to describe the commonmethods that households use to treat the surface water before con-sumption, and to identify suitable households for the screening studyon drinking water quality originating from surface water.

2.3. Monitoring campaign

2.3.1. Surface waterTo determine pesticide concentrations in surface water, water

samples were collected at both study sites from August 2008 toAugust 2009. Sampling was carried out every six weeks at the inten-sive rice growing site in An Long and every three weeks at the mixedcultivation site Ba Lang. Differences in the sampling frequencyresulted from logistical constraints as well as from the expectationthat the mixed cultivation site would show more fluctuation in thepesticide use pattern. A total of 109 water samples were collected inAn Long and 233 in Ba Lang. At both sites, grab samples were takenin glass bottles with PTFE sealed caps from inundated fields, field out-lets (discharged water) and from the irrigation canal. During theflooding season from end of August to end of November 2008, theentire study site was flooded in An Long (inundation depth>1 m).There was neither agricultural production nor agrichemical inputinto the system. Thus, both the number of samples taken and thesampling frequency was reduced during this period. Three samplingevents were carried out with three samples taken from the floodingwater inundating the site. All samples were transported on ice underdark conditions to the laboratory.

2.3.2. Drinking waterIn order to assess pesticide residues in drinking water derived

from surface water, a total of 54 water samples were collected attwo different time intervals from nine sampling points in May andJune 2009. An additional, third sampling event in August 2009 wasable to cover three of the above mentioned nine sampling pointsresulting in 63 samples in total. At each sampling points, three differ-ent types of samples were taken corresponding to the different stepsof water treatment applied by households prior to consumption. Theusual procedure for surface water preparation was found to be asfollows: 1) households collect water at high tide from the canalsand rivers using pumps or buckets, 2) this water is then stored inceramic jars, 3) the water is treated with aluminum sulfate in order

to flocculate the suspended matter, 4) it is then stored in ceramicjars (most often) covered by a lid, and 5) the water is boiled prior toconsumption. The first type of sample was taken from ceramic jarsshortly after the water was collected from the canals or rivers. The sec-ond type of sample was taken after an initial treatment of the surfacewater with aluminum sulfate. Acknowledging locally different proce-dures, samples were taken either some minutes, one day or one weekafter aluminum sulfate treatment. The third type of sample was takenafter boiling (30–40 min) of the flocculated water which was carriedout in situ. Samples were transported on ice under dark conditions tothe laboratory.

2.3.3. Soil and sedimentSoil and sediment samples were taken once in the dry and once in

the rainy season (March and July/August 2009) at both study sites.The sampling of the top soil/sediment layer was carried out usingpre-cleaned PET bottles fixed on a stainless steel rod of 1.5 m length.At every sampling point, three individual subsamples were taken togenerate one composite sample. In the small irrigation ditches, the sub-samples were taken at approximately 1, 2 and 3 m distances from theoutlet. However, during the sampling in March 2009 the fields in AnLong were already drained and rice was harvested. Thus, sedimentsamples were taken from the irrigation canal close to the outlet ofeach field. Within the main irrigation canal (at an upstream and down-stream point), three subsamples of sediments were taken along a crosssection of the canal. Soil and sediment samples were cooled for shortdistance transport (wet ice), frozen for the transport to Germany (dryice), and were stored at−20 °C until further analysis.

2.4. Studied pesticides and chemical analysis

Generally, the pesticide concentration in surface water dependslargely on the physico-chemical properties of the pesticides, environ-mental factors, water management practices, and pesticide application(Iwakuma et al., 1993; Nakano et al., 2004; Son et al., 2006). Thus, mon-itored pesticides were selected based on i) pesticide use (frequency,amount) as derived from literature and own household surveys, ii)expected fate in the environment as derived from physico-chemicalproperties such as solubility in water, hydrolysis half-life, octanol–water partition coefficient, soil sorption, soil degradation half-life(Table 1), iii) potential harm caused to the aquatic life and human health(Table 1), and analytical method availability. Applying these criteria, thefollowing fifteen pesticides were selected for monitoring: buprofezin,butachlor, cypermethrin, difenoconazole, α-endosulfan, β-endosulfan,endosulfan-sulfate, fenobucarb, fipronil, hexaconazole, isoprothiolane,pretilachlor, profenofos, propanil, and propiconazole.

All of the solvents and chemicals employed were of HPLC or resi-due grade (Merck, Darmstadt, Germany in Germany and J.T. Baker,Deventer, The Netherlands in Vietnam). Water was ultra pure grade(System Synergy 185, Millipore, Schwalbach, Germany) or HPLCgrade (J.T. Baker, Deventer, The Netherlands). All of the pesticidestandards employed, as well as the surrogate standard δ-HCH had a pu-rity>97% and were purchased from LGC Standards (Wesel, Germany)or from Dr. Ehrenstorfer (Augsburg, Germany). The internal standardfluorene-D10 was purchased from Cambridge Isotope Laboratories(Andover, USA). Pesticideswere extracted fromwater and analyzed fol-lowing a procedure modified from Laabs et al. (2007). Briefly, watersamples were passed through analytical grade glass wool (Carl Roth,Karlsruhe, Germany) and two layers of fiberglass filter with a poresize of 8 and 0.6 μm (Millipore AP 25 and AP 15, Millipore GmbH,Schwalbach, Germany) to remove suspended matters. The watersample (500 ml) was then adjusted to pH 3.5–4 using hydrochloricacid, and 15 g of NaCl were added. The samples were then solid phaseextracted with Strata C18-E cartridges (500 mg Phenomenex,Aschaffenburg, Germany) which were preconditioned with 3 ml ofn-hexane, 3 ml of ethylacetate, 1 ml of methanol and 1 ml water.

Table 1Monitored pesticides and their physicochemical properties, WHO toxicity class and fish acute toxicity.

Pesticides Solubility(20 °C)a

Hydrolysishalf-lifea

Octanol–water partitioncoefficienta

Soil sorptiona Soil deg.half-lifea

WHO toxicity classb Fish acutetoxicitya

Sw DT50, water LogKow Koc DT50, soil LC50, 96 h

(mg l−1) (av, days) (ml g−1) (ml g−1) (av, days) (mg l−1)

InsecticideBuprofezin 0.46 Stable 4.8 (high) 10,624 46.2 III 0.33 (Moderate)Cypermethrin 0.009 179 5.3 (high) 85,572 69 II 0.0028 (High)Endosulfan 0.32 20 3.13 (high) 11,500 86 II 49 (Moderate)Fenobucarb 420 c 2.78 (mod) 1068 c II 1.70 (Moderate)Fipronil 3.78 Stable 3.75 (high) 577 65 II 0.248 (Moderate)Profenofos 28 Stable 1.7 (low) 2016 7 II 0.08 (High)

HerbicideButachlor 20 c c 700 12 III 0.44 (Moderate)Pretilachlor 50 Stable 4.08 (high) c 30 U 0.9 (Moderate)Propanil 225 365 2.29 (low) 400 c II 2.3 (Moderate)

FungicideDifenoconazole 15 Stable 4.2 (high) 3760 85 II 1.1 (Moderate)Hexaconazole 18 30 3.9 (high) 1040 225 III 3.4 (Moderate)Isoprothiolane 54 Stable 3.3 (high) 1352 c II 6.8 (Moderate)Propiconazole 150 53.5 3.72 (high) 1086 214 II 1.3 (Moderate)

a Source: FOOTPRINT Pesticide database, 2009.b WHO toxicity classes: Class II: moderately hazardous, Class III: slightly hazardous, U: unlikely to present acute hazard (WHO, 2010).c Data not available.

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Cartridges were then washed (2 ml water) and dried using nitrogengas. Analytes were eluted from the cartridge using 6 ml ethylacetateand 6 ml n-hexane and the eluate was rotary-evaporated. The internalstandard was added and the extract was transferred to amber glassvials, filled up to 1 ml with toluene, transported to Germany on dryice and stored at−20 °C until analysis.

Extraction of the soil and sediment samples was carried out fol-lowing a method modified from Laabs et al. (1999). To this aim, sam-ples were freed from leaves, branches, stones and other debris andthe subsamples were combined, lyophilized (Gamma 1–16 LSC, MartinChrist Gefriertrocknungsanlagen GmbH, Osterode, Germany), groundthoroughly and sieved (mesh: 2 mm). Before using lyophilization asa standard sample preparation step, the absence of any influence oflyophilization on the stability and recovery of the pesticides was verified.A surrogate standard was added to the sample prior to extraction.Samples (20 g) were then shaken end-over-end for 4 h with 50 ml ofacetone:ethylacetate:water (2:2:1, v/v/v). The extract was then rotary-evaporated until the aqueous phase was left; the latter was thensubjected to four steps of liquid–liquid extraction using aliquots of25 ml dichloromethane. After a second step of rotary evaporation, sam-ples were cleaned up according to the solid phase extraction methodfrom Laabs et al. (2007). The extract was then reduced, spiked with theinternal standard, transferred to amber glass vials, filled up to 1 ml withtoluene and stored at−20 °C until analysis.

Pesticide residues were quantified using a gas chromatograph (GC)(Agilent Technologies 6890N, Böblingen, Germany) coupled with amass selective detector (MSD) (Agilent Technologies 5973) and equippedwith an Agilent 7683 automatic sampler. The GC was fitted with anOptima 5 Accent fused silica capillary column: 30 m length×0.25 mmID×0.5 μm film thickness (Macherey & Nagel, Düren, Germany). Heliumwas used as carrier gas with a constant flow rate of 0.8 ml min−1. Thefollowing oven temperature programwas used: 1) 85 °C initial tempera-ture for 2.5 min; 2) increase at 15 °C min−1 to 220 °C; 3) increase at10 °C min−1 to 280 °C, keep for 5 min; and 4) increase at 10 °C min−1

to 300 °C, keep for 5 min. The injector block temperature wasadjusted to 250 °C. The injection volume was 1 μl. The MSD wasoperated in the selected ion monitoring (SIM) mode. Quantitationof pesticides in samples was performed via the internal standardfluorene-D10.

2.5. Quality assurance and quality control

Laboratory blanks were regularly processed together with eachbatch of samples. The recovery of a surrogate standard, which wasadded to the samples prior to extraction, was used to monitor theextraction process. Surrogate standard recovery had to be between70 and 120% for the samples to be considered further. Results werenot corrected for the recovery of the surrogate standard.

Extraction efficiency was assessed via recovery experiments atthree concentration levels (0.1, 1.0, and 2.5 μg l−1 in water, n=2;and 0.2 and 2.5 μg for each pesticide in 20 g dry sediment, n=2).For water samples, the performance of the extraction method wasfound to be satisfactory (recovery 70–120%) for thirteen compounds(buprofezin, butachlor, cypermethrin, α-endosulfan, β-endosulfan,endosulfan-sulfate, fenobucarb, fipronil, isoprothiolane, pretilachlor,profenofos, propanil and propiconazole) while the recovery rate wasbelow 70% for difenoconazole (62%) and hexaconazole (68%). For sedi-ment samples, the recovery was between 70 and 120% for sevencompounds (buprofezin, cypermethrin, α-endosulfan, β-endosulfan,endosulfan-sulfate, fenobucarb and isoprothiolane). Pesticides failingto reach a recovery of 70% are not reported further.

The method detection limit (MDL) of each analyte was deter-mined via analysis of a series of water samples (n=9) spiked withan analyte concentration close to the expected detection limit (Ripp,1996). Analytical results below the calculated MDL are not reported.For soil and sediment analyses, the routine limit of quantification(RLOQ: the smallest detectable concentration of the external stan-dard) was used instead of the MDL.

2.6. Statistical analysis

Data were tested for normal distribution via Kolmogorov–Smirnovtest at p=0.05 level. In case of normal distribution and equal variance—depending on the number of groups—either a t-test, a Welch-test or aone-way ANOVA was applied. In case of non normal distribution—depending on the number of groups—either a Mann Whitney Rank Sumtest, a Mann Whitney U test, a Wilcoxon Signed Rank test, or a Kruskal–Wallis ANOVA on Ranks test was applied (Systat, 2008; Toutenburg,2002).

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3. Results and discussion

3.1. Pesticide use and management

The survey showed that more than 100 pesticide trade names cor-responding to more than 50 different active ingredients were used atthe two sites during the study period (Table 2).

Organochlorines and organophosphates were largely phasedout and are replaced by carbamates, pyrethroides and biopesticides.This development is beneficial from an environmental perspectivesince these substances tend to be less toxic and less persistentthan organochlorines. However, some of the compounds such ascypermethrin, propiconazole, profenofos, and propanil are toxic foraquatic animals, especially for fish (Cagauan, 1995; Cong et al.,2008; US EPA, 2009).

In rice fields, pesticides were applied eight times per cropping sea-son in An Long and six times in Ba Lang on average. Pesticide applica-tion patterns were strongly influenced by pest occurrence, e.g. by abrown plant hopper infestation in the winter–spring 2008–2009rice season in An Long. Furthermore, the lower pesticide use in ricefields in Ba Lang when compared to An Long was most probably par-tially influenced by the higher degree of crop diversification whichmight have allowed for the occurrence of natural enemies of pests,thereby reducing the need for intervention. Additionally, the exis-tence of more diverse agricultural income sources seems to lead toless overreaction in terms of preventive pesticide spraying, e.g. incase farmers have noticed pesticide application in neighboring fields.Preventive spraying was practiced regularly in An Long, while thispractice was atypical in Ba Lang where farmers acknowledged thatpest or disease occurring in rice fields might not affect the neighbor-ing vegetable fields.

In vegetable fields, farmers applied pesticides twelve times perseason on average (ranging from 3 to 17 times) depending on thetype of vegetables as well as on the severity of pest/disease infesta-tion. In Ba Lang, 37% of the farmers maintained some amount offruit trees in their production area. While similar pesticides wereused for rice at both study sites, pesticides of biological origin such

Table 2Pesticide use in An Long and Ba Lang in 2009 in percentage of all interviewed farmers. Onl

Pesticide group Trade name Active ingredient Chemicalgroup

Insecticide Abakill 1.8 EC Abamectin BiopesticideAbafax " "Difluent 10 WP Buprofezin Chitin synthesis inPenalty 40 WP " "Sấm sét 25 WP " "Applaud-Bas " "Dragon 585 EC Cypermethrin PyrethroidTungcydan 55 EC " "Serpal Super 55 EC " "Cyrux 25 EC " "Subside 505 EC " "Hopsan 75 ND Fenobucarb CarbamateAnba 50 EC " "Chief 520 WP Fipronil PyrazoleSespa gold 750 WG " "Selecron 500 EC Profenofos OrganophosphoruAntracol 70 WP Propineb Carbamate

Fungicide Tilt super 300 EC Difenoconazole TriazolePropiconazole Triazole

Anvil 5 SC Hexaconazole TriazolsFuan 40 EC Isoprothiolane PhosphorothiolateFuji-one 40 EC " "Filia 525 SE Propiconazole TriazoleValidan 5DD Validamycin Biopesticides

Herbicide Taco 600 EC Butachlor AmideSofit 300 EC Pretilachlor AmideButanil 55 EC Propanil Anilide

a WHO toxicity classes: Class II: moderately hazardous, Class III: slightly hazardous, U: u

as abamectin and validamycin were frequently sprayed in Ba Langfor vegetable treatment. Only 23% of those farmers stated that theyuse pesticides on fruits. In these farms, the number of pesticide appli-cations ranged from eight to twelve times per season (ten on aver-age). The reason that farmers do not use pesticides in orchards isthat the high diversity of fruit species on relatively small parcels ofland makes pesticide application inefficient. The amount of pesticidesapplied followed the same pattern as the application frequency: theintensive rice farming in An Long required higher pesticide inputswhen compared to the mixed cultivation in Ba Lang. On average,the total amount of pesticide active ingredient used per rice seasonwas 3.7 and 1.9 kg ha−1 in An Long and Ba Lang, respectively. Atboth study sites, the amount applied was higher in the summer–autumn crop than in the winter–spring crop which corresponds tohigher pest infestation in the summer–autumn crop when comparedto the winter–spring crop. The average amount of pesticide activeingredients reported per rice season in this study is higher than the av-erage of 1.02 kg a.i ha−1 reported by Dung and Dung (2003) for theMekong Delta as well as for some other developing countries such asthe Philippines and Bangladesh (both below 1.5 kg a.i.ha−1) (UNEP,2005). However, it was lower than in developed rice producingcountries such as Japan (14.3 kg a.i.ha−1) and Republic of Korea(10.7 kg a.i.ha−1) (UNEP, 2005).

Compared to the recommendation on the container label, farmersreported to favor the application of higher doses per hectare (AnLong: 45%, Ba Lang: 36% of the respondents) in order to be on thesafe side by protecting their crops. Furthermore, farmers often mixedtwo or more types of pesticides per application in order to—as theyclaim—(1) enhance the effectiveness of the treatment; (2) save timeand labor for spraying; (3) prevent and repel the many types of peststhat could develop after pesticide application; or (4) simply imitate anapplication method used by other farmers.

Only a minority of farmers (An Long 15%, Ba Lang 14%) appliedsome elements of integrated pest management methods (IPM) butno farmer followed IPM in full. These farmers used either pest resis-tant rice varieties (e.g. OM 2718, OM 1490), or followed the recom-mendation to avoid spraying in the first 30 days after seeding,

y formulations applied by more than 5% of the farmers are reported.

% of farmers in An Long % of farmers in Ba Lang WHO classa

0.0 84.6 NL0.0 15.4 "

hibitor 7.7 0.0 III7.7 0.0 "0.0 7.7 "0.0 7.7 "

69.2 0.0 II69.2 0.0 "15.4 53.8 "0.0 7.7 "0.0 15.4 "

15.4 7.7 II15.4 0.0 "7.7 0.0 II7.7 0.0 "

s 0.0 15.4 II15.4 0.0 U69.2 61.5 II69.2 61.5 II46.2 30.8 III38.5 38.5 II7.7 0.0 "

61.5 23.1 II38.5 69.2 U46.2 0.0 III46.2 53.8 U7.7 0.0 II

nlikely to present acute hazard, NL: not listed (WHO, 2010).

Fig. 3. Concentrations of pesticide residues in surface water at the two study sites a) AnLong and b) Ba Lang. The numbers above the box plots show the quantification fre-quency. The box plots show the statistical summary with five values (10th and 25thpercentile, median, 75th and 90th percentile); the two dots represent the 5th and95th percentile. The two figures have a different scale on the y-axis.

34 P.V. Toan et al. / Science of the Total Environment 452-453 (2013) 28–39

or—in vegetable fields—use plastic mulch to cover ridges in order toavoid weeds. Our larger scale follow-up surveys (yet unpublished)also show an inconsequent and less widespread application of IPMthan one might hope given that the successful application of IPMwas demonstrated manifold in the region (Escalada et al., 1999;Huan et al., 1999, 2004; Mai et al., 1994). The main reasons forthis weak uptake of IPM approaches at the studied sites were that(1) farmers did not officially attend an IPM training session and theytherefore did not clearly understand the relationship between pestsand natural enemies; (2) farmers did not want to apply IPM in theirown fields when it was not applied in surrounding fields; (3) pressurefrompesticide retailers togetherwith the outbreak of pests, for examplethe brown planthopper and (4) a low net profit was realized whenapplying IPM especially for farmers owning small fields.

Almost all (96%) farmers in An Long and 45% in Ba Lang discardedempty pesticide bags and containers directly in the fields. Wastescontaminated with pesticides easily pollute surface water as theyhave immediate contact with the water in the rice field during culti-vation or get washed away during the flooding season. Inappropriatedisposal of left-over pesticide solutions after spraying might also leadto pollution of water bodies. Half of the respondents (An Long 48%, BaLang 66%) used up the left-over pesticide solutions by spraying part oftheir crop one more time on the same application day. 43% of thefarmers in An Long and 23% in Ba Lang poured the left-over pesticidesolutions directly in fields. A minority of respondents (3% in An Longand 6% in Ba Lang) directly poured pesticide waste into canals. 81% ofthe farmers in An Long and 69% in Ba Lang cleaned the sprayers inirrigation ditches or ponds within their fields while others (10% inAn Long and 17% in Ba Lang) washed the equipment in canals outsidethe field. These practices, which are similar to those reported by Thuyet al. (2012b) in the Red River Delta, lead to an unfiltered and imme-diate point source pollution of surface water by pesticides and thus tothe exposures of aquatic organisms and humans.

3.2. Pesticide residues in surface water

3.2.1. Occurrence and concentration of pesticide residuesAt the study site in An Long, ten compounds were detected in

water samples during the monitoring (Fig. 3). Profenofos, α-, andβ-endosulfan were not detected in any of the samples. The maximumnumber of compounds detected in one single sample was ten whilethree or more compounds co-occurred in 90% of the samples.Among insecticides, fenobucarb was the most frequently detectedcompound (in 90.8% of the samples) with a median concentrationof 0.11 μg l−1 followed by buprofezin with a quantification frequencyof 58.7% and a median concentration of 0.19 μg l−1. Cypermethrinwas rarely detected in water samples. However, after heavy rains,cypermethrin concentrations occasionally reached up to 3.55 μg l−1

in surface water and were significantly higher than pre-rain samples(data not shown). This relates to cypermethrin's high potential for par-ticle bound transport (PPBT index) derived from the parameters DT50,KOC and aqueous solubility (Goss and Wauchope, 1990) which alsocauses enhanced aqueous concentrations via desorption processes.

Although the use of endosulfan was prohibited for agriculturalpurposes in 2005, its metabolite, endosulfan-sulfate, was detected in17% of the samples with a median concentration of 0.01 μg l−1. Amongherbicides, pretilachlor was most commonly detected (68.9%) with amedian concentration of 0.06 μg l−1. Butachlor and propanil were occa-sionally detected with median concentrations of 0.05 and 0.02 μg l−1,respectively. Isoprothiolane was themost frequently detected fungicide.It was omnipresent in the samples and it was quantified with both thehighest peak concentration (11.24 μg l−1) and the highest medianconcentration (2.72 μg l−1) among all detected compounds.

Similar to An Long, ten different pesticides were detected in thesamples from Ba Lang (Fig. 3) but residue concentrations were consid-erably lower. Cypermethrin, α-, and β-endosulfan were not found in

any of the samples. Isoprothiolane was detected most frequently(in 95% of the samples) with a median concentration of 0.16 μg l−1.The insecticide fenobucarb occurred in more than 80% of the samples,but concentrations were low (median 0.04 μg l−1). The metabolite ofthe prohibited insecticide endosulfan occurred in a few samples withmedian concentrations of 0.01 μg l−1. The herbicide pretilachlor wascommonly used and occurred in 31.4% of the samples in low concentra-tions (median 0.02 μg l−1).

3.2.2. Seasonality and the influence of farming patternsAverage concentrations of pesticides in surface water were several

times higher in An Long than in Ba Lang which is in line with the pes-ticide use data collected via household interviews at the two studysites. To take a closer look at the pollution patterns caused by differ-ent agricultural systems, a comparison between the two sites inthe winter–spring cropping season was undertaken. In 2009, the

35P.V. Toan et al. / Science of the Total Environment 452-453 (2013) 28–39

winter–spring crop was cultivated from December to March in AnLong and from November to February in Ba Lang. The number of pes-ticides detected at the more intensive rice producing site, An Long,was ten in this particular season and thus higher than in Ba Lang(five compounds) although all the studied pesticides applied in An Longwere also used in Ba Lang. This was seemingly due to the higher averageamount of pesticides used in An Long compared to the amounts usedin Ba Lang in this cropping season (1.7 kg a.i. ha−1 vs. 1.0 kg a.i. ha−1),so that pesticide residues were generally lower in Ba Lang (Figs. 3and 4) and thus not detectable for some of the applied compounds.

Based on the four pesticides which co-occurred at both siteswith a sufficient quantification frequency (pretilachlor, fenobucarb,isoprothiolane and propiconazole), a statistical comparison of pesticideconcentrations was undertaken between the study sites (Fig. 4). All me-dian concentrations of the pesticides detected in the samples collectedin An Long were higher than those in Ba Lang. Pretilachlor, fenobucarband isoprothiolane showed a statistically significant difference inmedianconcentrations with median concentrations in the samples collected inAn Long (0.17, 0.15 and 4.31 μg l−1) being higher than those in Ba Lang(0.01, 0.07 and 0.16 μg l−1, respectively). These results are in line withthe observations derived from the household surveys in terms of pesti-cide application patterns. This comparison demonstrates the higher im-pact of an intensive rice monoculture on the water quality as comparedto an area with mixed cultivation of rice, vegetables, and fruit trees.

Concentration of pesticides was ca. 40% lower in the canal waterthan in the field outlets in An Long and 23% lower in Ba Lang if averagedfor the entire year of monitoring. At both sites and for each and everysampling event, maximum concentrations were always associatedwith field outlets and not with canal water with the exception ofpretilachlor of which the maximum concentration was detected atboth sites in the canal water (0.21 μg l−1 in Ba Lang in July 2009and 1.05 μg l−1 in April 2009 in An Long). These sampling dates corre-spond with the beginning of the rice season (sowing) and thus withintensive and concerted application of herbicides in the rice fields bythe farmers. Simultaneous application of this pesticides lead to higherconcentration in the canal water than in the individual field outlets.

3.3. Pesticide residues in soils and sediments

Four out of seven monitored pesticides were detected in soils andsediments while α-, β-endosulfan, and endosulfan-sulfate did not

Fig. 4. Comparison of median concentrations of the pesticides detected in the samplescollected in An Long and Ba Lang in the winter–spring rice season. P-values indicateMann Whitney Rank Sum test results. The differences of median concentrations werecompared at a significance level of 5%.

occur. In An Long, buprofezin, fenobucarb, and isoprothiolanewere omnipresent; they were detected in all samples of both riceseasons. Cypermethrin showed a lower quantification frequency(13.3 and 40% respectively). The highest average concentrationswere recorded for buprofezin in the winter–spring rice season(116.1 μg kg−1 dm) and for isoprothiolane in the summer–autumnrice season (182 μg kg−1 dm). This relates to the frequent usage forthose two pesticides. Fenobucarb occurred in both seasons in con-siderably smaller concentration than the other pesticides (1.7 and4.3 μg kg−1 dm). The relatively fast breakdown of fenobucarb (DT506–14 days under paddy conditions; Tomlin, 2003) might account forthese differences. In An Long, pesticide concentrations in soils andsediments were subject to seasonality: in the summer–autumn riceseason all pesticide concentrations (with exception of cypermethrin)were detected in significantly higher concentrations than in thewinter–spring season (Fig. 5). These findings are not in line withthe results of the water samples, where pesticide concentrationswere higher in the dry season. This is likely due to the lower waterflows and thus lower degree of dilution in the dry season than inthe rainy season.

In Ba Lang, isoprothiolane and fenobucarb had the highest quanti-fication frequencies during both cropping seasons (80–93%, Fig. 6).Cypermethrin was only detected in the winter–spring rice season(in two fields), butwith the highest concentrations among all pesticides(average 34.8 μg kg−1 dm). A selective application of cypermethrinmight account for this patchy distribution but also discarded pesticidecontainersmight lead to this result. In Ba Lang, pesticide concentrationsdid not show significant differences between the rice-cropping seasons.A comparison between the two study sites shows higher pesticide con-centrations, higher quantification frequencies of pesticides and a highernumber of pesticides per sample in An Long which corresponds to theresults of the water samples and the household interviews.

3.4. Comparisons of residue concentrations with surface waterguideline values

Pesticide occurrence in surface water in itself does not neces-sarily cause adverse effects on aquatic ecosystems or human health.In order to assess the potential impact of the measured pesticide con-centrations on agricultural production and aquatic life, a comparison

Fig. 5.Median concentrations of pesticide residues in soils and sediments in An Long inthe winter–spring and in the summer–autumn rice season in 2009. The numbers abovethe bars show the quantification frequency of pesticides.

Fig. 6. Median concentration of pesticide residues in soils and sediments in Ba Lang inthe winter–spring and summer–autumn rice season in 2009. The numbers above thebars show the quantitation frequency of pesticides.

36 P.V. Toan et al. / Science of the Total Environment 452-453 (2013) 28–39

with published surface water and aquatic life guidelines or bench-marks was undertaken.

Vietnam's National Technical Regulation on Surface Water Quality(QCVN 08:, 2008/BTNMT) considers only endosulfan from our listof analyzed pesticides. The detected concentration exceeded the B1quality guideline of the above regulation (0.01 μg l−1) in 9.2 and1.3% of the samples in An Long and Ba Lang, respectively, meaningthat the water would not be suitable for irrigation purposes.

Similarly, the United States Environmental Protection Agency's(US EPA) compilation of national recommended water quality criteriafor the protection of aquatic life and human health in surface water(US EPA, 2006) considers only endosulfan among the analyzed pesti-cides. The water quality criteria (chronic level for aquatic life,0.056 μg l−1) were not exceeded in any of the samples.

EPA's Aquatic Life Benchmark Table (US EPA, 2009) lists con-centrations below which pesticides are not expected to harm aquaticlife. The table considers propiconazole, profenofos, propanil andcypermethrin with acute and chronic benchmarks for fish and inver-tebrates. Chronic invertebrate guideline values were exceeded for

Table 3Summary of parameters used for the assessment of sediment samples.Source: http://www.eu-footprint.org.

Pesticide Critical values for soil and sediment dwelling organism

μg kg−1 Type Organism

Buprofezin >100,000 Acute 14 days Eisenia foetLC50

170 Chronic 28 days ChironomuNOEC

Cypermethrin >500,000 Acute 14 days Eisenia foetLC50

16,000 EC50 Falsomia ca

Fenobucarb 107,000 Acute 14 days Eisenia foetLC50

Isoprothiolane 440,000d Acute 14 days Eisenia foetLC50

a Goss and Wauchope (1990).b Gustafson (1989).c Sangster (1997).d Tomlin (2003).

profenofos (0.2 μg l−1) in 0.9% of the samples in Ba Lang and in8.3% of the samples for cypermethrin (0.069 μg l−1) in An Long.Cypermethrin guideline values were regularly exceeded in samplestaken after rainfall events (Toan, 2011). In these cases, the detectedconcentrations of cypermethrin exceeded the toxicity guidelinevalues for both acute and chronic exposure of invertebrates as wellas of fish (acute fish 0.195 μg l−1, acute invertebrate 0.21 μg l−1).

In summary, for the few pesticides for which guideline valuesexist, these were exceeded in a limited number of samples for endo-sulfan, profenofos and cypermethrin when considering surface waterquality and individual pesticides. However, in 90% of the samplestaken in An Long, and in 50% of the samples from Ba Lang, morethan three different pesticides were detected at the same time whichmight put aquatic life at risk given the strong evidence that chemicalmixtures likely produce combination effects that are larger than theeffects of each of the components individually (Kortenkamp et al.,2009). Furthermore, the year-round prevalence of a pesticide mixturein the surface water deserves special attention in the context ofhuman exposure since a considerable proportion of the rural populationstill uses surfacewater as drinkingwater source, as well as for domesticpurposes. This is especially the case in the dry season, when rain waterharvested in the wet season is not available anymore (GSO, 2005, andown surveys).

In soil and sediment samples, critical concentrations for soil andsediment organism were only exceeded by buprofezin in An Long(Table 3). In two fields, recorded concentrations for buprofezinwere 1.3 and 3 times higher than the critical value. In two other fields,the concentrations were only marginally below the critical level.Similar to water samples, critical values were not exceeded in themajority of the samples, yet all samples contained two or more ofthe seven monitored pesticides.

The risk to contaminate the groundwater by leaching was eval-uated based on the Groundwater Ubiquity Score (GUS) leachingindex (Gustafson, 1989). According to the GUS, none of the pesticidesdetected in sediment samples has a high leaching potential, thus therisk for groundwater was estimated as low. The potential to contam-inate the surface water by particle bound transport was assessed ashigh for buprofezin and cypermethrin and medium for fenobucarbby using the Potential for Particle Bound Transport (PPBT) Index(Goss and Wauchope, 1990). In An Long, the risk was higher duringthe wet season due to higher pesticide concentrations in the sedi-ment and a higher frequency of run-off events.

The risk of bioaccumulation of these pesticides in plants or ani-mals was assessed by their respective LogP values which is the loga-rithm of the partition coefficient between n-octanol and water and

PPBT indexa GUS leaching indexb LogPc

ida High 0.96 4.93

s riparius

ida High −1.66 5.3

ndida

ida Medium 1.23 2.78

ida – 1.8 3.3

Fig. 7. Comparison of the median concentrations of pesticides in river and drinkingwater. P-values indicate Wilcoxon Signed Rank test results. The differences of medianswere compared at a significance level of p=0.05.

37P.V. Toan et al. / Science of the Total Environment 452-453 (2013) 28–39

is a suitable indicator for bioaccumulation in fatty tissues (Sangster,1997). It was evaluated as high because all pesticides (with theexception of fenobucarb) are classified as substances with a highpotential for bioaccumulation (i.e. having a LogP exceeding 3.0,Table 3). A high potential for bioaccumulation of these substance wasalso reported by other studies (buprofezin: Uchida et al., 1982;cypermethrin: Hoai et al., 2011; Muir et al., 1994, isoprothiolane:Tsuda et al., 1997). Bioaccumulation of pesticides not only poses a riskto the environment but pesticide residues can also enter the foodchain. This is a threat for the local population since wild capture offish, small scale aquaculture and livestock breeding within the riceand fruit fields is an important food source for a large part of the popu-lation (Bao et al., 2001; MRC, 2002). Bioaccumulation in fish, for exam-ple, might lead to concentrations exceeding acceptable daily intake(ADI) values as demonstrated in agricultural areas in North Vietnam(Hoai et al., 2011).

3.5. Pesticide residues in drinking water

3.5.1. Concentrations of pesticides in river and drinking waterResidues of thirteen pesticides were monitored in the samples col-

lected from rivers and in the samples of boiled aluminum-treatedwater (thereafter referred to as drinking water) taken from surfacewater by households. Fenobucarb, isoprothiolane, butachlor andpretilachlor were detected in river water during the three samplingevents. Isoprothiolane occurred in all samples, and its median con-centration was the highest among the four compounds detected(0.15 μg l−1). Fenobucarb was also quantified in a majority of samples(95%) with a median concentration of 0.04 μg l−1. The two herbicides,pretilachlor and butachlor occurred in 35% and 10% of the collectedsamples, respectively, with median concentrations of 0.01 μg l−1.

Table 4Quantitation frequency (%), median and maximum concentration (μg l−1), guideline compaIb: highly hazardous, Class II: moderately hazardous, Class III: slightly hazardous, U: unlike

Pesticide compounds Quantitation frequency[%]

Median conc.[μg l−1]

Isoprothiolane 100 0.17Fenobucarb 66.7 0.04Pretilachlor 47.6 0.01Butachlor 9.5 0.47Fipronil 9.5 0.16Buprofezin 4.8 0.12Profenofos 4.8 0.04

Sevenpesticideswere detected in drinkingwater. Isoprothiolanewasdetected in all samples with a median concentration of 0.17 μg l−1.Fenobucarb was quantified in 67% of the collected samples with a medi-an concentration of 0.04 μg l−1. Pretilachlorwas quantified in 48% of thesamples with a median concentration of 0.01 μg l−1. Butachlor, fipronil,buprofezin, and profenofos occurred occasionally (in 9.5, 9.5, 4.8 and4.8% of the collected samples) with median concentrations of 0.47,0.04, 0.12 and 0.04 μg l−1, respectively.

A statistical comparison of three pesticides (fenobucarb,isoprothiolane, and pretilachlor) in river and drinking water samplesis shown in Fig. 7. The quantitation frequency, and thus the number ofdata points, was not sufficient for a statistical analysis of butachlor. Incase of fenobucarb, there was no difference between its concentrationbefore and after treatment. The median concentration of pretilachlorwas significantly higher in drinking water than in river water (p=0.03). The median concentration of isoprothiolane was also higherin drinking water but the difference was not significant. Higherconcentrations of pretilachlor after boiling are related to the low vol-atility of this compound (according to Henry's Law constant; Linde,1994). Similarly, the fact that the number of detected pesticides washigher in drinking water samples when compared to river water(seven versus four) was mainly related to evaporation of waterduring boiling. Evaporation leads to an increased concentration ofcompounds with lower volatility than water (in this case fipronil,profenofos and buprofezin), increasing possibilities of detection.

3.5.2. Human health exposure to pesticide residues in drinking waterHuman exposure to pesticide residues was assessed via the diges-

tive route (i.e. oral intake of drinking water sourced from surfacewater). Observed concentrations were compared with the parametricguideline value of 0.1 μg l−1 set for single pesticides by the EuropeanCommission as well as with the World Health Organization (WHO)toxicity classes (Table 4).

None of these pesticides have guideline values in the VietnameseNational Technical Regulation for Drinking Water Quality (QCVN01:2009/BYT). The Health-Based Screening Level (HBSL) on drinkingwater quality established by the U.S. Geological Survey (USGS), setsguideline values only for profenofos (0.4 μg l−1), which was notexceeded in any of the samples. The WHO has also set guidelinevalues for a number of individual pesticides in drinking water, butthe pesticides in the present study are not listed. In the absence ofspecific health based guideline values, the parametric guidelinevalue of the European Commission (EC, 1998) and the respectiveWHO toxicity class (WHO, 2010) were used as a proxy for potentialhealth threats caused by pesticides. The parametric guideline valuefor total pesticide concentrations (0.5 μg l−1) was exceeded in 24%of the collected samples. The parametric guideline value for individu-al pesticides (0.1 μg l−1) was exceeded in 76.2%, 9.5%, 4.8% and 4.8%of the samples for isoprothiolane, butachlor, fipronil and buprofezin,respectively. While butachlor and buprofezin are slightly hazardous(WHO class III), fipronil and isoprothiolane have higher potentialtoxicity (WHO class II). Given that isoprothiolane is very abundantin both surface water and drinking water samples, further attention

rison, and toxicity of pesticides detected in drinking water (WHO toxicity classes: Classly to present acute hazard; WHO (2010)).

Max. conc.[μg l−1]

Samples above0.1 μg l−1 [%]

WHO toxicity class

0.67 76.2 II0.07 0.0 II0.03 0.0 U0.59 9.5 III0.28 4.8 II0.12 4.8 III0.04 0.0 II

38 P.V. Toan et al. / Science of the Total Environment 452-453 (2013) 28–39

is required in terms of drinking water risk assessment for this com-pound. Drinking water guideline values should be developed forthese pesticides, especially for isoprothiolane which, until recentlyhad a lower WHO toxicity class than now (the toxicity class wasrecently revised by WHO).

4. Conclusions

Pesticides are widely used in the Mekong Delta. Their manage-ment, in terms of application rate, frequency and disposal of con-tainers remains suboptimal. This research showed residues ofcurrently used pesticides in considerable concentrations in water,soils, and sediments of fields, field ditches and canals. These environ-ments are the most exposed to potential pesticide pollution due totheir proximity to application places; however our results also showthat this pollution partially persists and reaches larger canals whichare used by people for drinking and other domestic purposes aswell as for aquaculture production.

Most of the pesticides monitored in this study were moderately orslightly hazardous (WHO classes II and III). Where environmental andhealth guideline values existed (for only a few pesticides), their con-centrations occasionally exceeded these in surface water, and moreworryingly, in “ready to drink” water samples. The co-occurrence ofa wide range of pesticides in many of the samples and throughoutthe year hints to a chronic exposure of humans and aquatic organismsto pesticides. The surface water treatment used for preparing waterprior to consumption is insufficient for the removal of the studiedpesticides and boiling actually increases the concentration of someof them. Boiling is however essential for the treatment of pathogenssuch as bacteria, parasitic worms, worm eggs, etc. A compromisewith respect to boiling duration should be found to (1) achieve re-moval of pathogens and (2) limit the concentration effect on somepesticides. For example, rolling boiling for at least 1 min by using alid to avoid high evaporation could be recommended (CDC, 2009;WHO, 2004) as opposed to open boiling for 20–30 min as is oftenthe case in the region. There is also an urgent need for environmentaland health guideline values to be developed for all currently usedpesticides if we want to effectively protect populations and ecosys-tems exposed to these compounds. As long as pesticide managementremains suboptimal and water users are continuously exposed topesticide residues, more effective water treatment practices need tobe implemented at household level as well as in water treatmentplants. Flocculation, coagulation and disinfection are not sufficientto reduce the exposure to pesticides. Cheap and easy options for thedeveloping country context include, for example, the use of frequent-ly available adsorbents such us bamboo charcoal as suggested byThuy et al. (2012a).

However, more effective water treatment alone will not sufficebut more sustainable and strategic solutions are needed to addressthe root causes of pesticide pollution, which goes far beyond applica-tion rates and waste management at the household level in theMekong Delta (Berg and Tam, 2012; Sebesvari et al., 2011, 2012).Possible measures would include efforts to (i) reduce the use of agro-chemicals which might end up as pollutants in water (e.g. via aware-ness raising, education, incentives, enforcement of regulations),(ii) reduce the likelihood that these substances reach aquatic ecosys-tems (e.g. mode and time of application, buffer zones where possible),(iii) strengthen natural biocontrol mechanisms and thus allow for areduction on pesticide use (e.g. ecological engineering), (iv) enhancethe resilience of ecosystems to deal with pollution problems (e.g. in-crease biodiversity, wetlands for bioremediation), (iv) raise awarenessof the consumers and promote environmentally friendly products onthe market; and (v) accelerate programs which provide access to safefreshwater supplies to rural areas. In addition, given the shortcomingsin the implementation of previous IPM and other similar programs inthe region, new policies need to be embedded in a wider program of

water-related knowledge generation, information sharing and coopera-tion between the many stakeholders in the region (Renaud andKuenzer, 2012). Priority should be given to sustainably raising thecapacities of farmers and extension workers in the Mekong Delta.

Acknowledgements

The research was funded by the Federal Ministry of Education andResearch (BMBF), Germany through the Water-related InformationSystem for the Sustainable Development of the Mekong Delta(WISDOM) project in Vietnam. The authors would like to thank pro-ject members working on the water quality component of the projectin Vietnam and in Germany as well as the anonymous reviewers fortheir valuable comments.

Appendix A. Supplementary data

Supplementary data associated with this article can be found inthe online version, at http://dx.doi.org/10.1016/j.scitotenv.2013.02.026. These data include Google maps of the most important areasdescribed in this article.

References

Azevedo DDA, Gerchon E, Reis EO. Monitoring of pesticides and polycyclic aromatic hy-drocarbons in water from Paraiba do Sul river, Brazil; 2004. p. 10. [Rio de Janeiro].

Bao TQ, Bouhkhamvongsa K, Chan S, Chhuon KC, Phommavong T, Poulsen AF, et al.Local knowledge in the study of river fish biology: experiences from the Mekong.Mekong Development Series, No. 1; 2001.

Berg H. Pesticide use in rice and rice–fish farms in the Mekong Delta, Vietnam. CropProt Sci 2001;20:897–905.

Berg H, Tam NT. Use of pesticides and attitude to pest management strategies amongrice and rice–fish farmers in the Mekong Delta, Vietnam. Int J Pest Manag 2012;58(2):153–64.

Cagauan AG. The impact of pesticides on ricefield vertebrates with emphasis on fish. In:Pingali PL, Roger PA, editors. Impact of pesticides on farmer health and the riceenvironment. Manila: Kluwer Academic Publishers; 1995. p. 203–48.

Carvalho FP, Villeneuve JP, Cattini C, Tolosa I, Thuan DD, Nhan DD. Agrochemical andpolychlorobyphenyl (PCB) residues in the Mekong River Delta, Vietnam. MarPollut Bull 2008:10.

CDC, Centers for Disease Control and Prevention U.S. A guide to drinking water treatmentand sanitation for backcountry & travel use; 2009 [Available at http://www.cdc.gov/healthywater/drinking/travel/backcountry_water_treatment.html. Retrieved on 24August 2012].

Cong NV, Phuong NT, Bayley M. Brain cholinesterase response in the snakehead fish(Channa striata) after field exposure to diazinon. Ecotoxicol Environ Saf 2008;71:314–8.

Dang NH, Danh VT. An overview of the development of the agricultural economy in theMekong Delta. In: Lensink R, Mai VN, editors. Economic development of theMekong Delta in Vietnam, 27. CDS Research Paper; 2008. p. 31–50.

Dasgupta S, Meisner C, Wheeler D, Nhan LT, Khuc X. Pesticide poisoning of farmworkers: implications of blood test results from Vietnam. World Bank PolicyResearch Working Paper, 3624; 2005.

Deltares. Mekong Delta water resources assessment studies. Vietnam–NetherlandsMekong Delta Masterplan project; 2011.

Dung NH, Dung TTT. Economic and health consequences of pesticide use in paddy pro-duction in the Mekong Delta, Vietnam; 2003. p. 39.

Ebbert JC, Embrey SS. Pesticides in surface water of the Yakima River basin, Washing-ton, 1999–2000. Their occurrence and an assessment of factors affecting concen-trations and loads. Water resources investigations report 01–4211. Nationalwater quality assessment program; 2002. p. 39.

EC, European Commission. Council Directive 98/83/EC of 3 November 1998 onthe quality of water intended for human consumption. Off J Eur Communities1998;L 330:32–54.

Escalada MM, Heong KL, Huan NH, Mai V. Communication and behavior change in ricefarmers' pest management: the case of using mass media in Vietnam. J ApplCommun 1999;83:26.

Footprint Pesticide database. 2009. [Available at www.herts.ac.uk/aeru/footprint/].Gaston CP. Pesticide regulatory policies of selected countries Asia. Technical Report No.

2. Regional Agribusiness Project—RAP; 1994. p. 35.Goss D, Wauchope RD. The SCR/ARS/CES Pesticide Properties Database. II Using it with

soils data in a screening procedure. In: Weigmann DL, editor. Pesticides in the nextdecade: the challenge ahead. Blacksburg, VA, USA.: Virginia Resources ResearchCentre; 1990. p. 471–93.

GSO, General Statistics Office. Statistical yearbook. Hanoi, Vietnam: Statistical PublishingHouse; 2005.

Gustafson DI. Groundwater ubiquity score: a simple method for assessing pesticideleachability. Environ Toxicol Chem 1989;8:339–57.

39P.V. Toan et al. / Science of the Total Environment 452-453 (2013) 28–39

Hoai PM, Sebesvari Z, Minh TB, Viet PH, Renaud FG. Pesticide pollution in agriculturalareas of Northern Vietnam: case study in Hoang Liet and Minh Dai communes.Environ Pollut 2011;159:3344–50.

Huan NH. Review on pesticide use in pest management in Vietnam. Plant ProtectionDepartment, Ministry of Agricuture and Rural Development; 2005. p. 10.

Huan NH, Mai V, Escalada MM, Heong KL. Changes in rice farmers' pest management inthe Mekong Delta, Vietnam. Crop Prot 1999;18:557–63.

Huan NH, Thiet LV, Chien HV, Heong KL. Farmers' participatory evaluation of reducingpesticides, fertilizers and seed rates in rice farming in the Mekong Delta, Vietnam.Crop Prot 2004;24:457–64.

Hung NN, Delgado JM, Tri VK, Hung LM, Merz B, Bárdossy A, et al. Floodplain hydrologyof the Mekong Delta, Vietnam. Hydrol Process 2012;26(5):674–86.

Iwakuma T, Shiraishi H, Nohara S, Takamura K. Runoff properties and change inconcentrations of agricultural pesticides in a river system during a rice cultivationperiod. Chemosphere 1993;27(4):677–91.

Kortenkamp A, Backhaus T, Faust M. State of the art report on mixture toxicity. Finalreport of a project on mixture toxicology and ecotoxicology commissioned bythe European Commission, DG Environment; 2009.

Laabs V, Amelung W, Zech W. Multi-residue analysis of corn and soybean pesticides inBrazilian oxisol using gas chromatography and mass selective detection. J EnvironQual 1999;28:1778–86.

Laabs V, Wehrhan A, Pinto A, Dores E, AmelungW. Pesticide fate in tropical wetlands ofBrazil: an aquatic microcosm study under semi-field conditions. Chemosphere2007;67:975–89.

Lamers M, Anyusheva M, La N, Van Vien N, Streck T. Pesticide pollution in surface- andgroundwater by paddy rice cultivation: a case study from Northern Vietnam. CleanSoil Air Water 2011;39:356–61.

Lensink R, Nam MV. Economic development of the Mekong Delta in Vietnam. CDSResearch Paper No. 27; 2008 [Available at http://cds.eldoc.ub.rug.nl/FILES/root/ResRep/2008/CDS-27/CDS-27.pdf].

Linde CD. Physicochemical properties and environmental fate of pesticides. Environ-mental hazards assessment program. Environmental Protection Agency; 1994.p. 53.

Mai V, Huan NH, Heong KL, Escalada MM, Lazaro AA. Pest management perceptionsand practices of rice farmers in Long An Province, Vietnam. In: Heong KL, EscaladaMM, editors. In pest management of rice farmers in Asia. Manila (Philippines): Inter-national Rice Research Institute; 1994. p. 213–25.

MARD. Lists of pesticidepermitted, restricted andbanned foruse inVietnam(inVietnamese).The circular of theMinistry of Agricultural and Rural Development, promulgated in April2010; 2010. p. 231.

Meisner C. Poverty–environment report: pesticide use in the Mekong Delta, Vietnam.DECRG-IE; 2005. p. 19.

Minh NH, Minh TB, Kajiwara N, Kunisue T, Iwata H, Viet PH, et al. Pollution sources andoccurrences of selected persistent organic pollutants (POPs) in sediments of theMekong River Delta, South Vietnam. Chemosphere 2007;67:1794–801.

MRC, Mekong River Commission. Fisheries in the lower Mekong: status and perspec-tives. Mekong River Commission Technical Paper No. 6; 2002 [Cambodia].

Muir DCG, Hobden BR, Servos MR. Bioconcentration of pyrethroid insecticides and DDTby rainbow trout: uptake, depuration and effect of dissolved organic carbon. AquatToxicol 1994;29:223–40.

Müller K, Bach M, Hartmann H, Spiteller M, Frede HG. Point- and nonpoint-source pes-ticide contamination in the Zwester Ohm catchment, Germany. J Environ Qual2002;31:309–18.

Nakano Y, Miyazaki A, Yoshida T, Ono K, Inoue T. A study on pesticide runoff frompaddy fields to a river in rural region 1: field survey of pesticide runoff in theKozakura River, Japan. Water Res 2004;38:3017–22.

Ohkawa H, Miyagawa H, Lee Philip W, editors. Pesticide chemistry: crop protection,public health, environmental safety. Wiley-VCH; 2007. p. 538.

PAN Pesticides Database — Pesticide Registration Status. http://www.pesticideinfo.org/Detail_Country.jsp?Country=Viet%20Nam&offset=2002010. [Accessed 23.01.2013].

QCVN 01:2009/BYT. Circular enforced on “National Technical Regulation on DrinkingWater Quality”. Ministry of Health; 2009. p. 8.

QCVN 08:2008/BTNMT. Circular enforced on “National Technical Regulation on SurfaceWater Quality”. Ministry of Environment and Natural Resources; 2008. p. 8.

Quyen PB, Nhan DD, Sanh NV. Environmental pollution in Vietnam: analytical estima-tion and environmental priorities. Trends Anal Chem 1995;14:383–7.

Renaud FG, Kuenzer C. The water-development nexus: importance of knowledge, in-formation and cooperation in the Mekong Delta. In: Renaud FG, Kuenzer C, editors.The Mekong Delta system: the Mekong Delta system. Interdisciplinary analysesof a river delta, Springer Environmental Science and Engineering. Netherlands:Springer; 2012. p. 445–58.

Ripp J. Analytical detection limit guidance & laboratory guide for determining methoddetection limits. Wisconsin Department of Natural Resources Laboratory Certifica-tion Program; 1996. p. 33.

Sangster J. Octanol–water partition coefficients: fundamentals and physical chemistry.Wiley series in solution chemistry, vol. 2. United Kingdom, Chichester: John Wiley& Sons; 1997.

Sebesvari Z, Huong LTT, Renaud F. Climate change adaptation and agrichemicals in theMekong Delta, Vietnam. In: Steward M, Coclanis P, editors. The Mekong Delta: en-vironmental change and agricultural sustainability. Springer; 2011.

Sebesvari Z, Huong TTL, Toan PV, Arnold U, Renaud FG. Agriculture and water quality inthe Vietnamese Mekong Delta. In: Renaud FG, Kuenzer C, editors. The MekongDelta system: the Mekong Delta system. Interdisciplinary analyses of a riverdelta, Springer Environmental Science and EngineeringNetherlands: Springer;2012. p. 331–62.

Sinh NN, Thuy LTB, Kinh NK, Thang LB. The persistent organic pollutants and their man-agement in Vietnam. Proceedings of the Regional Workshop on the Managementof Persistent Organic Pollutant, POPs, United Nations Environment Programme,Hanoi, Vietnam; 1999. p. 385–406.

Son HV, Ishihara S, Watanabe H. Exposure risk assessment and evaluation of the bestmanagement practice for controlling pesticide runoff from paddy fields. Part 1:paddy watershed monitoring. Pest Manag Sci 2006;62:1193–206.

Statistical Office of Can Tho City. Statistical yearbooks Can Tho City, Vietnam; 2000.Statistical Office of Can Tho City. Statistical yearbooks Can Tho City, Vietnam; 2005.Statistical Office of Can Tho City. Statistical yearbooks Can Tho City, Vietnam; 2008.Systat. User's manual of Sigmaplot 11 for exact graphs and data analysis; 2008.Thuy PT, Anh NV, van der Bruggen B. Evaluation of two low-cost-high-performance ad-

sorbent materials in the waste-to-product approach for the removal of pesticidesfrom drinking water. Clean 2012a;3:246–53.

Thuy PT, Van Geluwe S, Nguyen VA, van der Bruggen B. Current pesticide practices andenvironmental issues in Vietnam: management challenges for sustainable use ofpesticides for tropical crops in (South-East) Asia to avoid environmental pollution.J Mater Cycle Waste Manag 2012b;14:379–87.

Toan PV. Pesticide use and management in the Mekong Delta and their residues insurface and drinking water. PhD thesis. University of Bonn. 2011.

Tomlin C. The pesticide manual. Farnham: British Crop Protection Council; 2003.Toutenburg H. Statistical analysis of designed experiments. Springer texts in Statistics;

2002.Tri VK. Hydrology and hydraulic infrastructure systems in the Mekong Delta, Vietnam.

In: Renaud FG, Kuenzer C, editors. The Mekong Delta system: the Mekong Deltasystem. Interdisciplinary analyses of a river delta, Springer Environmental Scienceand EngineeringNetherlands: Springer; 2012. p. 331–62.

Tsuda T, Kojima M, Harada H, Kakajima A, Aoki S. Acute toxicity, accumulation and excre-tion of isoprothiolane and its degradation products in Killifish. Water Res 1997;31:323–7.

Uchida M, Nishizawa H, Suzuki T. Hydrophobicity of buprofezin and flutolanil in relationto their soil adsorption and mobility in rice plants. J Pestic Sci 1982;7:397–400.

United Nations Enviromental Program (UNEP). Integrated assessment of the impact oftrade liberalization: a country study on the Viet Nam rice sector; 2005. p. 80.

US EPA, U. S. Environmental Protection Agency. ECOTOX database. 2006. [Available:http://www.epa.gov/ecotox. Retrieved on 16 June 2011].

US EPA, U. S. Environmental Protection Agency. Aquatic life benchmark table. 2009.[http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm. Retrievedon 17 May 2011].

US EPA, U.S. Environmental Protection Agency. Example exposure scenarios. EPA/600/R-03/036Washington, DC: National Center for Environmental Assessment; 2003[Available from National Information Service, Springfield, VA; PB2003-103280 andat http://www.epa.gov/nscep. Retrieved on 24 October 2012].

Ut TT. The impact of Green Revolution on rice production in Vietnam. Green Revolutionin Asia and its transferability to Africa; 2002. p. 32. [Tokyo].

Vien TD, Hoi PV. Pesticide dependence in agriculture: policy for productivity and policyfor security in Viet Nam. In: Umegaki M, Thiesmeyer L, Watabe A, editors. Humaninsecurity in East Asia. United Nations University Press; 2009. p. 22.

Viet PH, Hoai PM, Minh NH, Ngoc NT, Hung PT. Persistent organochlorine pesticidesand polychlorinated biphenyls in some agricultural and industrial areas in NorthernVietnam. Water Sci Technol 2000;42:223–9.

WHO, World Health Organization. Guidelines for drinking water quality. 3rd ed.Geneva: World Health Organization; 2004 [1].

WHO, World Health Organization. The WHO recommended classification of pesticidesby hazard and guidelines to classification 2009. Geneva: International Program onChemical Safety (IPCS) & World Health Organization (WHO); 2010 [Availeble athttp://www.who.int/ipcs/publications/pesticides_hazard_2009.pdf].