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MERCURY CONTENTS IN THE UPPER HORIZON OF SOILS FROM THE IASSY MUNICIPALITY SURROUNDINGS

Mihaela Lungu1, Mihaela Monica Stanciu-Burileanu1, Ovidiu Gabriel Iancu2, Nicolae Buzgar2

1 National Research and Development Institute for Soil Science, Agrochemistry, and Environment (RISSA Bucharest)

61 Mărăşti Blvd., 011464 Bucharest (mihaelalungu.icpa@gmail.com) 2 “Al. I. Cuza” University, Iassy, 11 Carol Blvd., 700506

ABSTRACT

One hundred soil samples from the upper horizon of soils from the surroundings of Iassy municipality were taken in which mercury contents were determined, using cold vapor atomic absorption spectrometry, after digesting soil samples with a concentrated sulphuric and nitric acids mixture. The analytical data were statistically computed, spreading (σ, cv%) and grouping (average value , Me, Mo) parameters were calculated. Most of the determined values range in a 0.05-0.30 mg·kg-1 content interval, which includes the normal content value (0.10 mg·kg-1, according to the MAPPAM Order nr.756/1997 referring to the reference values for chemical elements traces in soil). Few values reach or exceed the alert threshold for a sensitive use (1 mg·kg-1, according to the same legislation), while the intervention threshold for a sensitive use (2 mg·kg-1 soil) is only exceeded in three out of the one hundred samples. These samples were taken from soils in the north-eastern surroundings of the Iassy municipality, a pasture (5,81 mg·kg-1) and a vineyard (2.71 mg·kg-1). The values distribution doesn’t differ in the Northern and Southern parts of the investigated area. Judging by soil types, no significant differences were noticed. The average value for forest soils was higher (0.37 mg·kg-1) than the values for other land uses. The high values proceed from pest control products, especially in the vineyard. From a statistical point of view, in spite of a few values exceeding the alert threshold for land sensitive use (11 out of 100), the soils of the Iassy municipality surroundings, most of them with agricultural use, don't raise problems of mercury contamination.

Key words: soil, mercury, Iassy Municipality

INTRODUCTION

Mercury has a calcophile geochemical affinity, which explains its association with antimony, selenium, silver, zinc, and lead in sulphide ores (Iancu and Buzgar, 2008). Mercury abundance in the Earth’s crust has been estimated at 30 g·kg-1 (Rudnick and Gao, 2003, cited by Iancu and Buzgar, 2008). Natural sources of mercury are represented by cinnabar (HgS) and many of the sulphides with various mercury contents, as well as fossil coals. Through their

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alteration mercury enters the environment as mercury protochloride (Hg2Cl2), mercury oxide (HgO), and in elementary form. It reaches the soils as mercury chloride (HgCl2) and the natural bodies of water as divalent cation (Hg2+): mercury hydroxide [Hg(OH)2] or chloride (HgCl2), and in elementary form. All these species confer upon mercury a relatively high mobility, limited by the solid organic matter absorption (Rose at al., 1979, cited by Iancu and Buzgar, 2008). Mercury is retained by soils mainly as slightly mobile organic complexes. According to Kabata-Pendias and Pendias (2000), mercury abundance in Earth’s crust is still uncertain. A much higher concentration is reported for sedimentary rocks, clay sediments, and organic-rich shale (usually 40-400 g·kg-1). Different mercury contents ranges are reported by Kabata-Pendias and Pendias (2000), from different sources, ranging, roughly, from 4 to 1,400 g·kg-1, depending on geographic area and soil types. Average values are very low, around 50-100 g·kg-1, only a few reach up to 410 g·kg-1. Mercury concentration in rocks is approximately 0.5 mg·kg-1. As it is not very soluble the natural concentrations in groundwater are less than 0.5 µg·l-1 (Jalgaonkar, 2008). The presence of mercury in the environment is interesting for its potential harmful effects on human health, as both the element and its soluble compounds are toxic. Its ready bioavailability creates an important health hazard. It also is one of the most common heavy metals that have a severe long term and short term effect on the groundwater quality (Jalgaonkar, 2008). Soil contamination with mercury itself is usually considered not to be a serious problem (Kabata-Pendias and Pendias, 2000). Nevertheless, even simple mercury salts or metallic mercury create a hazard to plants and soil biota from the toxic nature of mercury vapor. The mercury volatilization from contaminated soils can also have an adverse effect on human health when exceeding the EPA inhalation reference concentration of 300 ng Hg·m-3 (Henry et al., 1999, cited by Kabata-Pendias and Pendias, 2000). The mercury is very dangerous as vapors and in the form of its water soluble salts which attack the organisms’ membranes. Repeated ingestion over a long time of small quantities of the metal or its salts causes chronic intoxication which leads to irreversible brain, liver, and kidneys affectation (Encarta Encyclopedia 2000). As a consequence of the pollution phenomena intensification significant mercury quantities were determined in some fish species which gave rise to concern regarding uncontrolled discharge of this element in the environment. Methyl mercury ((CH3)2Hg) is the most dangerous compound of this element, as it accumulates excessively within certain fish, in amounts several hundreds times higher than its water concentration (Irwin et al., 1979, cited by Iancu and Buzgar, 2008). In highly contaminated areas, soil pollution with mercury determines groundwater pollution (Bequiraj et al., 2008) with obvious repercussions on human health.

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Sources of contamination of soils with mercury are mainly related to metal processing industries and some chemical works (chloralkali, in particular), as well as to earlier use of fungicides containing mercury (Kabata-Pendias and Pendias, 2000). Chemical fertilizer, especially phosphorous fertilizers, could influence the soil mercury. Still, minimal amounts of mercury result from applications of chemical fertilizers and organic manure, so they represent a very low risk to the food security of the agro-ecosystems in the terms of mercury inputs and contamination (Zheng et al., 2008). Extremely high concentrations of mercury were found in soils at a former battery recycling facility (Henry et al., 1999, cited by Kabata-Pendias and Pendias, 2000). In the topsoil of the town of Gyöngyösoroszi, with vegetables growing activities, located about 1,000 m far from the tailing dump of a flotation plant, mercury values exceed the threshold level only at a few sites, proceeded from geochemical features independent from mining. It is related rather to thermal springs (Gazdar and Sipter, 2008). Mercury occurs mainly in form of drops around the former geysers due to the latest hydrothermal phase at low temperature (at most 100°C). In postvolcanic activities the mercury drops can precipitate in the hydroquartzite and on the underlayers of the former thermal spring in the Toka Valley and of the geysers mostly around Asztag-kő, Hungary. Mercury is widely used in manufacturing thermometers, barometers, diffusion pumps, mercury-vapor lamps, advertising hoardings, mercury switches, and other electronic apparatus. It is also used in pesticides, fungicides, dental compounds, anti-fouling paint, batteries, and catalysts (Salaminen et al., 2005, cited by Iancu and Buzgar, 2008). The textile industry is considered to be the main source of mercury-related pollution in some Poland’s industrial areas (Lis and Pasieczna, 1995). The machine-building and electronic industries are identified as other sources of mercury-related pollution of water sediments. Kulikova and Nurgaleyeva (1979, cited by Kabata-Pendias and Pendias, 2000) described a short life of mercury residues in Chernozems proceeded from seed dressing. Most of the mercury pollution in the bay of Vlora, Albania, was caused by a chlorine-alkali unit where mercury cathode was used for sodium chloride (NaCl) brine electrolyses and by a polyvinyl chloride (PVC) unit where mercury cholride (HgCl2) was used as a catalyst for the chloretane (C2H3Cl) monomer synthesis (Bequiraj et al., 2008). The contamination of soil and water with mercury proceeded from technological looses and non controlled waste discharges. The situation triggered many researches, focussed on pollution of the marine environment, sediments, seawater, and biota (Babi, 1996; Çullaj et al. 2000; Lazo & Çullaj, 2002; Lazo et al. 2003, cited by Bequiraj et al., 2008). Researches regarding the surface (0-20 cm depth) soils’ mercury contents have been carried out by Lis and Pasieczna (1995), who draw up the mercury distribution map in Poland’s soils. On the average, the mercury content in Poland’s

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soils is low ( 50 g·kg-1) and comparable with the average mercury concentration in soils worldwide (60 g·kg-1, Freedman, 1989, cited by Lis and Pasieczna, 1995). Soil and crop heavy metal contamination were studied across China, focused on several heavy metals, among which mercury, in soils and vegetables in suburbs of four large cities (Dong et al., 2001). The results indicated that heavy metals, mercury included, levels in soils and some crops were greater than the Governmental Standards. Untreated sewage water irrigation, atmospheric deposition, industrial or municipal wastes, sewage sludge improperly used as fertilizers, and metal-containing phosphate fertilizers were named as important causes. The Order No.756/1997 of the Ministry of Waters, Forests, and Environment Protection establishes the mercury normal values and alert and intervention thresholds in Romania for sensitive and less sensitive use of the land, as follows (mg·kg-1):

Normal values

Alert thresholds Intervention thresholds Types of land use Types of land use

Sensitive Less sensitive Sensitive Less sensitive 0.1 1 4 2 10

In our Country researches regarding mercury contents in soils were carried out in the frame of a research project in the Iassy Municipality and surrounding areas, and the mercury tendency map was drawn (Iancu and Buzgar, 2008; Lungu et al., 2008) for the soils’ upper layer (0-25 cm depth). Most of the determined values (77%) belong to the normal content interval, ranging from 100 to 760 g·kg-1. Higher values, up to 5,810 g·kg-1, were registered in a meadow and a vineyard, the later proceeded from fungicide treatments.

MATERIALS AND METHODS

Soils from the Iassy Municipality and its surrounding area were sampled on a 256 km2 area, following a 500 m grid. The net initially included 588 points out of which 100 samples were chosen (Figure 1). The samples were taken from the upper soil layer (0-25 cm depth). The soil cover of the sampling area includes Chernozems, Luvic Chernozems and Phaeozems, Luvisols, Fluvisols, Regosols, Erodisols, and Anthrosols* (Iancu and Buzgar, 2008). The total mercury determination was done by atomic absorption spectrometry coupled with cold vapors technique, in the extract obtained after the soil samples digestion with a mixture of concentrated sulphuric and nitric acids. By this method concentrations ranging from 0.01 to 10 mg Hg/kg soil can be determined.

* WRB-SR, 1998

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The analytical data were statistically computed, spreading (σ, cv%) and grouping ( x average value , Me, Mo) parameters were calculated.

Figure 1. The sampling area

RESULTS AND DISCUSSIONS

Most of the determined values, 77%, range in the 0.01-0.76 mg·kg-1 dry soil content interval (Figure 2), which includes the normal content value, 0.10 mg·kg-1, according to the MAPPM Order nr.756/1997 regarding reference values for chemical elements traces in soil. Few values reach or exceed the alert threshold for a sensitive use (ATs, 1 mg·kg-1, according to the same legislation), and the intervention threshold for a sensitive use (ITs, 2 mg·kg-1) is only exceeded in three samples: two samples from pastures, one of them near the railway, and a sample from a vineyard, in which the high mercury quantity is proceeded from pest control products. Only the maximum value exceeds the alert threshold for less sensitive use (AT, 4 mg·kg-1). The average value of the determinations exceeds 4.6 times the upper limit of the soils normal content and the determined values scattering (the coefficient of variation is 163%) denotes an anthropic contribution to the high values. The distributions of the values from the North and the South of Iassy Municipality (Figures 3 and 4) are alike the general distribution (Figure 2), the difference

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between them consisting in the maximum values: 5.81 mg·kg-1 in the Northern area, registered in a pasture, and 2.46 mg·kg-1 in the Southern area, registered in the pasture near the railway.

0

10

20

30

40

50

60

70

80

90

Hg, mg•kg-1

Fre

qu

en

cy,

%

0.76 1.52 2.28 3.04 3.80 4.56 5.32 6.08

xmin = bdl

xmax = 5.81 mg•kg-1

x = 0.46 mg•kg-1

Me = 0.14 mg•kg-1

Mo = 0.44 mg•kg-1

normal values: 0.10 mg•kg-1

ATs

AT

n = 100

ITs

Figure 2. Total mercury contents distribution in the studied soils (bdl - below the detection limit of the analytical method)

0

10

20

30

40

50

60

70

80

90

Hg, mg•kg-1

Fre

qu

en

cy,

%

0.81 1.62 2.43 3.24 4.05 4.86 5.67 6.48

xmin = bdl

xmax = 5.81 mg•kg-1

x = 0.45 mg•kg-1

Me = 0.13 mg•kg-1

Mo = 0.46 mg•kg-1

normal values: 0.10 mg•kg-1

ATs

AT

n = 73

ITs

Figure 3. Total mercury contents distribution in the Northern studied area

(bdl - below the detection limit of the analytical method)

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0

2

4

6

8

10

12

14

16

18

Hg, mg•kg-1

Fre

quen

cy, %

0.05 0.47 0.89 1.31 1.73 2.15 2.57

xmin = 0.05 mg•kg-1

xmax = 2.46 mg•kg-1

x = 0.47 mg•kg-1

Me = 0.17 mg•kg-1

Mo = 0.31 mg•kg-1

normal values: 0.10 mg•kg-1

AT

n = 27

ITs

Figure 4. Total mercury contents distribution in the Southern studied area

(bdl - below the detection limit of the analytical method)

By soil types, the maximum total mercury values in soils exceed the alert threshold for sensitive use in Chernozems and Chernozems associated wit other soils (Table 1). In Regosols associated with other soils the maximum value exceeds the intervention threshold for a sensitive use, and in Fluvisols it also exceeds the alert threshold for a less sensitive use.

Table 1. Total mercury contents in the studied area, by soil types*

Soil type (WRB-SR 1998)

Statistical parameters

Fluvi-sols

Anthro-sols

Cherno-zems

Chernozems in association with Regosols and

Erodosols

Haplic Luvi-sols

Erodosols, Erodossols

in association

with Regosols

Phaeo-zems

Rego-sols

Regosols in association with Chernozems,

Erodosols, Phaeozems

n 15 7 21 11 2 6 7 9 11 xmin 0.06 0.08 0.02 0.01 0.09 0.07 0.09 0.01 0.13xmax 5.81 0.97 1.32 1.48 0.49 0.88 0.83 0.62 2.71

x 0.68 0.45 0.36 0.39 0.29 0.34 0.32 0.18 0.75 1.51 0.42 0.42 0.52 0.37 0.30 0.19 0.81xg 0.20 0.27 0.19 0.17 0.19 0.22 0.10 0.43

c.v. (%) 222 93 117 133 109 94 106 108Me 0.10 0.16 0.14 0.12 0.12 0.12 0.10 0.20Mo 0.70 0.20 0.14 0.18 0.19 0.20 0.10 0.52

* Soil types have been established according to the Soil Map of Romania, scale 1:200.000, published between 1964 and 1994, under the co-ordination of Nicolae Cernescu first and then Nicolae Florea (Munteanu et al., 2005)

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The other maximum values are lower, but they still exceed the soil normal content. The average values also exceed the normal soil content, but they are all bellow the alert threshold for a sensitive use. The coefficients of variation, with very high values, show a very scattered distribution, thus pleading for an anthropic contribution to the high mercury contents of some soil samples. The distribution of mercury total contents in the studied soils by land use (Table 2) seems more significant. Thus, it can be observed that the maximum value, 5.81 mg·kg-1, is registered in a meadow. A lower value, still exceeding the intervention threshold for a sensitive use, is registered in a vineyard, proceeded from the fungicide treatments.

Table 2. Total mercury contents in the studied area, by land use

Land use Statistical parameters Arable

Gardens and

orchards Forests

Pastures and

meadows Vineyard Urban, roads

n 32 3 12 28 9 16

xmin 0,01 0,10 0,09 0,01 0,06 0,05

xmax 1,48 0,15 1,38 5,81 2,71 1,83

x 0,35 0,12 0,47 0,56 0,49 0,52

0,43 0,44 1,15 0,87 0,54

xg 0,17 0,31 0,21 0,20 0,28

c.v. (%) 123 94 205 178 104

Me 0,12 0,29 0,13 0,15 0,23

Mo 0,13 0,25 0,53 0,40 0,24

Values exceeding the alert threshold for a sensitive use is also registered in a forest and in an urban site, the latter proceeded from traffic emissions. The average values are rather low, but they still exceed the soil normal contents. The coefficients of variation show a large scattering of the values, just like the distribution by soil types. In both cases, the scattering and the high average values occur because of the few samples with very high concentrations.

CONCLUSIONS

Mercury total contents in the soils of the studied areas are, in a 77% proportion, in the normal values domain. Higher values, very few, rarely exceed the alert and intervention thresholds indicated by the MAPPM order nr.756/1997. By soil types, the mercury concentration registers the highest values in Fluvisols and Regosols associated with other soil types and the lowest in Regosols, but this distribution is not as significant as the distribution by land use.

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The distribution by land use shows higher values in a meadow and a vineyard, the latter due to organo-mercury pesticides use. High values also occur in the urban area. The mercury contents in the soils of the studied area don't represent a hazard for plant nutrition and nor for people, whether they live in the area and/or consume food (fish) produced in the area. Researches must be carried on in the areas where higher mercury values were registered to determine if the exceeding values are merely accidents, as the authors suppose, or more high values could be registered, in which case measures to reduce the impact or diminish the harmful emissions must be taken.

REFERENCES

1. Beqiraj Arjan, Çullaj Alqui, Kotorri Petrit, Gjoka Fran, 2008, High-contaminated soil with mercury in Bay Of Vlora (Albania) and its possible remediation, Carpathian Journal of Earth and Environmental Sciences, 3(2), 19-32.

2. Dong Wang Qingren Y., Cui Y, Liu X., 2001, Instances of Soil and Crop Heavy Metal Contamination in China, Soil and Sediment Contamination, 10(5).

3. Gazdag Enikö Rózsa, Sipter Emese, 2008, Geochemical background in heavy metals and humanhealth risk assessment at an ore mine site, Gyöngyösoroszi (North Hungary), Carpathian Journal of Earth and Environmental Sciences, 3(2), 83-89.

4. Iancu Gabriel, Buzgar Nicolae (Main Editors), 2008, The Geochemical Atlas of heavy metals in the soils of the Municipality of Iassy and its surrounding areas, "Alexandru Ioan Cuza” University Publishing House, Iassy (bilingual).

5. Jalgaonkar Aniket, 2008, Microanalysis of groundwater elements with respect to time and depth in the Hortobágy region in Hungary, Carpathian Journal of Earth and Environmental Sciences, 3(1), 39-47.

6. Kabata-Pendias Alina, Pendias Henryk, 2000, Trace Elements in Soils and Plants, CRC Press Boca Raton London New York Washington DC.

7. Lis Józef, Anna Pasieczna, 1995, Geochemical Atlas of Poland, Polish Geological institute, Warsaw.

8. Lungu Mihaela, Aldea Mihaela Monica, Iancu Ovidiu Gabriel, Buzgar Nicolae, 2008, Mercury contents in the upper horizon of soils from the surroundings of Iassy municipality, The 33rd International Geological Congress, Oslo, &-14 August, p.169.

9. Munteanu Ion, Dumitru Mihail, Florea Nicolae, Canarache Andrei, Lăcătuşu Radu, Vlad Virgil, Simota Cătăşin, Ciobanu Constantin, Roşu Constantin, 2005, Status of Soil Mapping, Monitoring, and Database Compilation in Romania at the beginning of the 21st Century, in: Soil Resources of Europe, Second edition, R. J. A. Jones, B. Houšková, P. Bullock, and L. Montanarella (eds), European Soil Bureau Research Report No.9, EUR 20559: 281-296.

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10. Zheng Y. M., liu Y. R., Hu H. Q., He J. Z., 2008, Mercury in soils of three agricultural experimental staitons with long-term fertilization in China, L. of Chemosphere, 72(9), 1274-1278.

11. * * * 2000, Encarta Encyclopedia, CD.