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Chemosphere 85 (2011) 1002–1009
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Chemosphere
journal homepage: www.elsevier .com/locate /chemosphere
Biotic and abiotic degradation of illicit drugs, their precursor, and by-productsin soil
Raktim Pal a,b, Mallavarapu Megharaj a,b,⇑, K. Paul Kirkbride c, Tunde Heinrich a,b, Ravi Naidu a,b,⇑a Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, Adelaide, South Australia 5095, Australiab CRC for Contamination Assessment and Remediation of the Environment, University of South Australia, Australiac Australian Federal Police Forensic and Data Centres, Canberra, Australia
a r t i c l e i n f o
Article history:Received 26 March 2011Received in revised form 23 June 2011Accepted 26 June 2011Available online 22 July 2011
Keywords:Illicit drugsMethamphetamineMDMAPseudoephedrineN-formylmethylamphetamine1-Benzyl-3-methylnaphthalene
0045-6535/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.chemosphere.2011.06.102
⇑ Corresponding authors at: Centre for EnvironmRemediation, University of South Australia, MawAustralia 5095, Australia. Tel.: +61 8 83025044; fax:
E-mail addresses: [email protected]@crccare.com (R. Naidu).
a b s t r a c t
This study presents the first systematic information on the degradation patterns of clandestine drug labo-ratory chemicals in soil. The persistence of five compounds – parent drugs (methamphetamine, 3,4-methy-lenedioxymethamphetamine (MDMA)), precursor (pseudoephedrine), and synthetic by-products N-formylmethylamphetamine and 1-benzyl-3-methylnaphthalene) – were investigated in laboratory scalefor 1 year in three different South Australian soils both under non-sterile and sterile conditions. The resultsof the degradation study indicated that 1-benzyl-3-methylnaphthalene and methamphetamine persist fora long time in soil compared to MDMA and pseudoephedrine; N-formylmethylamphetamine exhibits inter-mediate persistence. The role of biotic versus abiotic soil processes on the degradation of target compoundswas also varied significantly for different soils as well as with the progress in incubation period. The deg-radation of methamphetamine and 1-benzyl-3-methylnaphthalene can be considered as predominantlybiotic as no measureable changes in concentrations were recorded in the sterile soils within a 1 year period.The results of the present work will help forensic and environmental scientists to precisely determine theenvironmental impact of chemicals associated with clandestine drug manufacturing laboratories.
� 2011 Elsevier Ltd. All rights reserved.
1. Introduction
The use of illicit drugs has gained worldwide concern due to theirsignificant adverse impacts on human health and wellbeing of thesociety (Sloan, 2008; Rieckermann and Christakos, 2008). Illicitdrugs are those whose nonmedical use is prohibited by the interna-tional law, and mainly belong to the classes of opiates, cocaine,cannabis, amphetamines and ecstasy-group substances (UNODC,2007; Hall et al., 2008). Amphetamine, methamphetamine, and3,4-methylenedioxymethamphetamine currently demand the mostattention of all the synthetic illicit drugs (EMCDDA, 2008).
The amphetamines and ecstasy-group of illicit drugs (ATSs) areusually manufactured in clandestine laboratories. The chemicalsassociated with these illegal laboratories including precursors andby-products as well as the synthesized drugs are often illegally bur-ied in soil or public waste management facilities, or disposed of intosinks or toilets after which they enter the sewerage system (Januszet al., 2003; Scott et al., 2003). The degradation pattern of an illicit
ll rights reserved.
ental Risk Assessment andson Lakes, Adelaide, South+61 8 8302 3057.u.au (M. Megharaj), ravi.nai-
drug and a related precursor and manufacturing by-product in soilwas initially reported by our research group (Janusz et al., 2003).In this study, the persistence behavior of methylamphetamine sul-fate (MAS) and phenyl-2-propanone (P2P, a key precursor and by-product) in South Australian agricultural soils were presented. Itwas reported that P2P was rapidly degraded in all the test soils butthe degradation of MAS was very slow with the level remaining prac-tically constant over a period of 6 weeks.
Recently, the potential impacts of these toxic chemicals are beingrecognized as a growing concern among environmental scientistsand it is necessary to investigate the behavior of these compoundsin the environment. The majority of work so far has focused onanalytical detection techniques (Castiglioni et al., 2006; Sach andWoo, 2007), and chemical impurity profiling of the illicit drugs (Qiet al., 2006; Waddell-Smith, 2007). A series of reports have beenpublished on the presence of illicit drugs in surface and wastewaters from several countries (Jones-Lepp et al., 2004; Zuccatoet al., 2005; Hummel et al., 2006; Castiglioni et al., 2006, 2007;Bones et al., 2007; Boleda et al., 2007; Huerta-Fontela et al., 2007,2008; Kasprzyk-Hordern et al., 2008). Kaleta et al. (2006) reportedthe presence of amphetamine in the low ppb range in sewage sludgefrom Austria. There is a lack of information on the behavior of thesecompounds in the environment and there is no informationavailable in the scientific literature on the fate of these compoundsin soil.
Table 1General information on the target compounds in the present study.
Target compound full name Shortname
IUPAC nomenclature Molecularformula
Molecularweight
Molecular structure Solubility inH2O(mg L�1)
log Kow pKa
Methamphetamine MAP N-methyl-1 -phenyl-propan-2-amine C10H15N 149.24 NHCH3 1.33E + 04 2.07 9.87
3,4-methylenedioxy-methamphetamine
MDMA 1 -(benzo [ 1,3 ] dioxol-5 -yl-N-methylpropan-2-amine
C11H15NO2 193.25 NHCH 3O
OPseudoephedrine PSE (1S,2S)-2-methylamino-1 -phenylpropan-1-ol C10H15NO 165.23
NHCH 3
OH 1.06E + 05 0.89 10.3
N-formylmethylamphetamine FMA N,N-dimethyl-1 -phenyl-propan-2-amine C11H15NO 177.25
NCH3
CHO
l-benzyl-3-methylnaphthalene BMN l-benzyl-3-methylnaphthalene C18H16 232.32
R.Pal
etal./Chem
osphere85
(2011)1002–
10091003
Table 2Basic physico-chemical properties of the test soils.
Soil Short name pH (1:2.5 H2O) Electricalconductivity(lS cm�1)
Cation Exchangecapacity(cmol(p+) kg�1)
Organiccarbon (%)
Dissolvedorganiccarbon (lg mL�1)
Particle size distribution Textural class
Sand (%) Silt (%) Clay (%)
Mawson Lakes ML 8.91 159 19.24 1.11 8.71 55.0 25.0 20.0 Sandy loamSturt Gorge SG 5.98 36 6.30 2.88 5.84 60.0 25.0 15.0 Sandy loamWaite campus WC 5.64 965 17.42 2.26 3.90 42.5 42.5 15.0 Loam
1004 R. Pal et al. / Chemosphere 85 (2011) 1002–1009
The research we present here was designed to understand thedegradation pattern of ATS chemicals in soils with contrasting phys-ico-chemical properties, and in particular, understand the soil fac-tors controlling the degradation of those potential pollutants in soil.
2. Materials and methods
2.1. Target compounds
The target compounds selected for study were the parent drugs(methamphetamine (MAP), and 3,4-methylenedioxymethamphet-amine (MDMA)), a key precursor chemical (pseudoephedrine(PSE)) and two common synthetic by-products N-formylmethylam-phetamine (FMA, encountered in the Leuckardt and other prepara-tions of methamphetamine) and 1-benzyl-3-methylnaphthalene(BMN, encountered in the conversion of pseudoephedrine intomethamphetamine using the Nagai method). The target compoundsrepresent the chemicals associated with the most common methodsfor clandestine drug manufacture of MAP and MDMA in Australia.Basic information including IUPAC nomenclature, molecular for-mula, molecular weight, chemical structure of the target com-pounds are briefly summarized in Table 1.
2.2. Soils
Three contrasting soils were used in this study: an alkaline san-dy loam collected from the Mawson Lakes (ML) campus of the Uni-versity of South Australia; slightly acidic sandy loam from SturtGorge (SG); and a slightly acidic loam from the Waite Campus(WC) of The University of Adelaide, South Australia. The soils werefrom an urban area (ML), native bush land (SG), and agriculturalland (WC). Samples of surface soils (0–15 cm) were collected fromeach site, stored in polyethylene buckets, and brought to the labo-ratory. The soils were then screened to remove any plant parts orother artifacts, passed through 2 mm sieve, and then placed inrefrigerator operated at 4 �C.
The basic physico-chemical properties of the soils are summa-rized in Table 2. The physico-chemical properties of the soils weremeasured following the standard analytical procedures. The threesoils varied in terms of pH, organic carbon, clay content, and soiltexture. The pH (in 1:2.5 H2O) of the soils ranged between 5.64and 5.98 (slightly acidic) for WC and SG soils, respectively to8.91 (alkaline) for ML soil. The cation exchange capacity of the soilsranged between 6.30 and 19.24 cmol(p+) kg�1 soil. The organic car-bon content (on dry weight of soil basis) varied between 1.11%(ML) and 2.88% (SG). The soils contained a moderate level of clay(15–20%). The ML and SG soils were sandy loam while WC soilwas loam in texture.
2.3. Experimental approach
The degradation of the compounds was studied both undernon-sterile and sterile conditions. The moisture level of each soilwas adjusted to 50% of maximum water holding capacity (MWHC)and then pre-incubated at 25 �C in a constant temperature room
for 1 week. The soils were incubated in the dark to avoid photodeg-radation. Sub-samples of the pre-incubated soils (5 g) wereweighed into individual amber colored glass vials fitted with Tef-lon lined solid screw caps. For sterile degradation studies the soilsin individual vials were autoclaved at 121 �C for 20 min on threeconsecutive days (Megharaj et al., 1997). The sterile conditionswere maintained throughout the study period and affirmed period-ically by a microbiological plating technique.
The soils were spiked with 100 lg g�1 of each target compoundin separate vials. The stock solutions (2 g L�1) for MAP, MDMA, andPSE were prepared in water; while FMA and BMN stock solutions(20 g L�1) were prepared in acetone and hexane, respectively. Inthe case of the soils for sterile degradation, the stock solutionswere passed through sterile 0.45 lm filters and the soils spikedaseptically within a laminar airflow cabinet. The spiked soils werehomogenized by vortexing at very low speed for 10 s. Such level ofvortexing has no destructive effect on microbial activity as mea-sured by dehydrogenase enzyme assay. The dehydrogenase is anintracellular enzyme linked to the respiratory activity of microor-ganisms and thus is an indication of microbial activity in soil (Meg-haraj et al., 2000). Dehydrogenase activity in soils was measuredfollowing the method of Casida et al. (1964). The lids of the vialscontaining FMA or BMN spiked soils were kept open for 15–20 min to allow the solvents to evaporate. Three types of controlsoils were also maintained for both non-sterile and sterile condi-tions, one for each of the background solvents of the respectivestock solutions without added compound. The vials for non-steriledegradation study were aerated aseptically within a laminar air-flow every week. The moisture contents of the soils (both in non-sterile and sterile) were maintained by aseptic addition of sterileMilli-Q water. All the experimental treatments were conductedin duplicate. The concentrations of each compound were moni-tored at intervals for up to 1 year.
2.4. Extraction procedure
Two extraction procedures were used to extract the compoundsfrom the soil samples. For MAP, MDMA, and PSE the incubated soilswere extracted with 40 mL of chloroform: acetonitrile: methanol:acetic acid (80:10:9:1) in two steps (20 mL each). The soils werevortexed and extracted twice on an electric shaker for the periodof 1 h and 15 min, respectively, and each extraction was followedby ultrasonic vibration for 5 min at 30 �C. For each of the extractionsteps the vials were centrifuged and the aliquots were filteredthrough 0.22 lm Teflon filters. The aliquots were combined, evap-orated under nitrogen stream, and re-dissolved with HPLC grademethanol for direct HPLC analysis. For BMN three extraction stepswere employed. To begin with, 10 mL of acetone was used fol-lowed by subsequent extractions with 10 mL of ethyl acetate. Ineach of the extraction steps the vials were vortexed for 1 min. fol-lowed by ultrasonic vibration for 15 min at 30 �C. The aliquotswere filtered, combined, evaporated under nitrogen stream, andre-dissolved with chromatographic grade ethyl acetate for directGC analysis. All analyses included appropriate positive and nega-tive control samples.
0
20
40
60
80
100
120
0 100 200 300 400
Con
cent
ratio
n (m
g-kg
-1)
Period ( Day)
MAPMawson Lakes
Sturt Gorge
Waite Campus
0
20
40
60
80
100
120
0 50 100 150
Con
cent
ratio
n (m
g-kg
-1)
Period (Day)
MDMAMawson Lakes
Sturt Gorge
Waite Campus
0
20
40
60
80
100
120
0 50 100 150
Con
cent
ratio
n (m
g-kg
-1)
Period (Day)
PSEMawson Lakes
Sturt Gorge
Waite Campus
0
20
40
60
80
100
120
0 100 200 300 400C
once
ntra
tion
(mg-
kg-1
)
Period (Day)
FMAMawson Lakes
Sturt Gorge
Waite Campus
0
20
40
60
80
100
120
0 100 200 300 400
Con
cent
ratio
n (m
g-kg
-1)
Period (Day)
BMNMawson Lakes
Sturt Gorge
Waite Campus
Fig. 1. Non-sterile degradation of target compounds in three experimental soils.
R. Pal et al. / Chemosphere 85 (2011) 1002–1009 1005
2.5. Determination of target compounds
The determinations of MAP, MDMA, PSE and FMA were per-formed using HPLC (Agilent 1100 series) equipped with an auto-sampler, binary pump system, a mass selective detector (Agilent1100), and Chemstation software for data integration. Chromato-graphic separation of the target compounds were made using aZORBAX Eclipse XDB-C18 150 � 4.6 mm, 5 lm column operatedat 25 �C. The mobile phase consisted of two combinations of sol-vent A (20% methanol + 0.1% acetic acid + 10 mM ammonium ace-tate) and solvent B (90% methanol + 0.1% acetic acid + 10 mMammonium acetate) maintaining the flow-rate of 0.8 mL min�1.The timetable for the changes of the solvents of the mobile phasefor the total run time (26 min) was 0–8 min (100% A), 8–12 min(90% A + 10% B), 12–25 min (100% B), and 25–26 min (100% A).The detector was operated in Electrospray ionization (ESI) modewith positive polarity. The scan parameters were fixed at the massrange of 100 (low) to 350 (high), Fragmentor 120, Gain EMV 3.0,Threshold 0.0, and step size 0.10. The nebulizer pressure in thespray chamber was 35 psig and drying gas 12.0 L min�1. Proprano-lol was used as the internal standard during the analysis.
The determination of BMN was performed by GC (Agilent6890 N system) equipped with an auto-sampler, a mass selectivedetector (Agilent 5973), and Chemstation software for data inte-
gration. The GC inlet was operated in splitless mode at 250 �Cand helium was the carrier gas with constant flow mode. The inletpressure was 96.46 kPa, purge flow 49 mL min�1, purge time0.75 min, and total flow 52.8 mL min�1. The separation wasachieved on a DB-5 column (30 m � 0.25 mm � 0.50 lm). The ini-tial flow in column was 1 mL min�1. The oven temperature wasstarted at 90 �C for 2.50 min and ramped at 45 �C min�1 to300 �C, and held for 9.00 min. The mass spectra were collectedafter a 4 min solvent delay over the mass range of 50–550 m/z.Phenanthrene was used as the internal standard during theanalysis.
The detection limit of the analytical methods ranged between0.05 ± 0.003 ng (MAP) and 0.11 ± 0.006 ng (FMA), and the limitsof quantification were 127 ± 6.93 ng g�1 (MAP) to 704 ± 44.0 ng g�1
(BMN) when n = 3. The average recoveries of the analytical proce-dures were 51 ± 1.66 (PSE) to 86 ± 1.95% (FMA) when n = 3.
3. Results and discussion
3.1. Degradation patterns
Figs. 1 and 2 show the changes in the concentrations of thecompounds throughout the incubation period for all the three soils
0
20
40
60
80
100
120
Con
cent
ratio
n (m
g-kg
-1)
Period (Day)
MDMAMawson Lakes
Sturt Gorge
Waite Campus
0
20
40
60
80
100
120
Con
cent
ratio
n (m
g-kg
-1)
Period (Day)
PSE Mawson Lakes
Sturt Gorge
Waite Campus
0
20
40
60
80
100
120
0 20 40 60 80 0 20 40 60 80
0 50 100 150 200
Con
cent
ratio
n (m
g-kg
-1)
Period (Day)
FMAMawson Lakes
Sturt Gorge
Waite Campus
Fig. 2. Sterile degradation of target compounds in three experimental soils.
Table 3Regression equation, rate constant (k), and half-life (t½) values for the degradation of target compounds under non-sterile and sterile conditions.
Soil Compound Non-sterile Sterile
Regression equation t½ (d) Regression equation t½ (d)
Mawson Lakes MAP y = �0.0011x + 1.9563 274Sturt Gorge y = �0.0023x + 2.0450 131Waite campus y = �0.0006x + 1.9489 502Mawson Lakes MDMA y = �0.0051x + 2.9735 59.0 y = �0.0036x + 1.9753 83.6Sturt Gorge y = �0.0195x + 2.7630 15.4 y = �0.0040x + 1.9471 75.3Waite campus y = �0.0113x + 2.9967 26.6 y = �0.0028x + 1.9751 108Mawson Lakes PSE y = �0.0814x + 3.1800 3.70 y = �0.0021x + 1.9921 143Sturt Gorge y = �0.0100x + 2.9782 30.1 y = �0.0006x + 1.9816 502Waite campus y = �0.0553x + 3.1646 5.44 y = �0.0008x + 1.9861 376Mawson Lakes FMA y = �0.0086x + 3.2364 35.0 y = �0.0010x + 1.9426 301Sturt Gorge y = �0.0069x + 3.1672 43.6 y = �0.0016x + 1.9290 188Waite campus y = �0.0052x + 3.1817 57.9 y = �0.0014x + 1.9324 215Mawson Lakes BMN y = �0.00003x + 1.9542 10 034Sturt Gorge y = �0.0020x + 2.0461 151Waite campus y = �0.0005x + 2.0108 602
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
MAP MDMA PSE FMA BMN MDMA PSE FMA
SterileNon-sterile
Deg
rada
tion
rate
con
stan
t (k-1
)
Experimental condition
ML
SG
WC
Fig. 3. A plot for the rate constant (k�1) values to compare the degradationpotential of the target compounds under different experimental conditions.
1006 R. Pal et al. / Chemosphere 85 (2011) 1002–1009
both under non-sterile and sterile conditions. The results showedMAP and BMN to be quite persistent even under non-sterile condi-tions; therefore Fig. 2 does not include graphs for these two com-pounds. In non-sterile soils, loss (in percent) of MAP over a periodof 1 year were recorded at 68.4 ± 1.27, 89.6 ± 0.59, and 45.8 ± 1.24for ML, SG, and WC soils, respectively, while that for the BMN were15.3 ± 1.41, 84.1 ± 0.64, and 32.8 ± 1.41, respectively. The results ofthe present study corroborates well with our previous report onthe biotic–abiotic degradation of methylamphetamine sulfate inSouth Australian agricultural soils (Janusz et al., 2003). In the pre-vious study, the degradation of methylamphetamine sulfate(spiked at 500 lg g�1 soil) was investigated over a period of6 weeks in soils from Tailem Bend (pH 6.95, electrical conductivity86 lS cm�2, organic carbon 2.60%, and clay, 13.0%). Although someinitial degradation of the compound was shown in both the non-sterile and sterile soils over 12 d, the concentration level remainednearly constant after this period and two-thirds of the initial con-centration was still recorded after 6 weeks. Although there is a dif-ference in basic physico-chemical properties of the soils, spiking
0
20
40
60
80
100
ML SG WC ML SG WC ML SG WC
Total Abiotic Biotic
Perc
ent d
egra
datio
n
Nature of degradation
MDMA
Day 7
Day 15
Day 60
0
20
40
60
80
100
ML SG WC ML SG WC ML SG WC
Total Abiotic Biotic
Perc
ent d
egra
datio
n
Nature of degradation
PSEDay 7
Day 15
Fig. 4. A plot for the comparative role of biotic and abiotic factors on degradation ofparent drug and precursor compound at different periods of incubation.
R. Pal et al. / Chemosphere 85 (2011) 1002–1009 1007
level of the compound, and the overall incubation period, a closesimilarity in the degradation behavior between the two studies isnoticeable. MAP is fairly stable in soils and little affected by thephysico-chemical and biological soil processes. The relatively smalldecrease in the concentration of BMN especially in ML and WCsoils over 1 year incubation period under non-sterile conditionmight be ascribed to its molecular nature (i.e., benzyl group inthe a-position of naphthalene may cause steric hindrance) makingit less susceptible to biotic and abiotic soil processes. However, inSG soil BMN recorded a fairly steady degradation pattern over1 year period. The significantly higher degradation in SG soil com-pared to ML and WC soils might be ascribed to the soil microbio-logical processes. The soil microbes in SG soil might have beenadapted between the initial to mid phase of the incubation periodand thereafter became efficient in utilizing BMN as one of the car-bon source. Therefore, the persistence pattern of BMN seems to beclosely related to the basic soil characters in addition to its ownmolecular properties. Recent studies by Abouseoud et al. (2010)demonstrate the marked effect of alkaline pH or high salinity onthe naphthalene solubility of a biosurfactant. These findings sug-gest that the high pH of ML soil compared to the SG and WC soilsand extremely high electrical conductivity of WC soil followed byML soil might be the dominating factor for the high persistencyof BMN in ML and WC soils. Thus, no specific comment can bemade on degradation behavior of BMN before any thorough studyemploying a series of soils varying in their physico-chemicalproperties.
Under non-sterile conditions, FMA was also found to be relativelystable for about 4 months in all the soils irrespective of experimentalconditions. Thereafter the concentration falls to practically zero after9 months in ML and SG soils, and to practically zero after 12 months inWC soil. This delay could be related to adaptation of the microbes sothat they acquire ability to decompose a synthetic compound overtime. The result for FMA might be attributed to the presence of ter-tiary amine group in the molecule, which has been reported to inhibitbiodegradation (Hiromatsu et al., 2000). On the other hand, FMA con-centration under sterile conditions declined moderately over1 month and showed nearly a stable pattern in all the three soils afterthis period until 6 months incubation.
The results for MDMA showed a steady decline over the4 month incubation period in non-sterile soils recording residualconcentrations up to the levels of 17.9 ± 0.93, 0.21 ± 0.03, and2.27 ± 0.17% for ML, SG, and WC soils, respectively.
PSE concentrations declined rapidly in non-sterile ML and WCsoils to 0.69 ± 0.06 and 3.18 ± 0.11% of their original concentrationswithin 4 weeks, while the concentration in SG soil declined to4.81 ± 0.13% after 4 months.
3.2. Degradation potential
The regression equations, regression coefficient (r2), rate con-stant (k�1), and half-life (t½) values to describe the degradation ofMAP, MDMA, PSE, FMA, and BMN in both non-sterile and sterile con-ditions are presented in Table 3. It should however be noted that theregression equations for MAP and BMN in sterile soils were not cal-culated due to non-measurable changes in concentration over the1 year incubation period as mentioned earlier. The experimentaldata were fitted to simple regression equations considering first or-der reaction, where y is concentration and x is time. The half-life val-ues were calculated from the best fit lines of the logarithm ofresidual concentrations vs. time elapsed in the incubation period.The results show that the degradation behavior of the target com-pounds, when compared in terms of the half-life values, generallyfollowed the descending order of MAP � BMN > MDMA � FMA > PSEin non-sterile soils. Using the regression equation, the half-life (d)values for the non-sterile soils were predicted and these ranged from
131 (SG) to 502 (WC) for MAP, 15.4 (SG) to 59.0 (ML) for MDMA, 3.70(ML) to 30.1 (SG) for PSE, 35.0 (ML) to 57.9 (WC) for FMA, and 151(SG) to 10034 (ML) for BMN. However, the half-lives (d) for the ster-ile soils ranged from 75.3 (SG) to 108 (WC) for MDMA, 143 (ML) to502 (SG) for PSE, and 188 (SG) to 301 (ML) for FMA. The results thusshowed that BMN was quite stable in ML soil and almost completelystable in WC soils. The high persistency of BMN in ML and WC soilsmight be ascribed to their relatively high pH and salinity as dis-cussed earlier. It can also be noted that MAP remained fairly stablein WC soil.
To examine the degradation potential of the target compoundsunder diverse experimental conditions, the results were expressedin terms of degradation rate constant (k�1: degradation of targetcompound per unit time). In Fig. 3, the rate constant values are com-pared for degradation of all the compounds in non-sterile and sterilesoils. The results were initially compared within soils under non-sterile condition. The highest k values for PSE (0.0814) and FMA(0.0086) were recorded in ML soil, while that for MAP (0.0023),MDMA (0.0195), and BMN (0.0020) were in SG soil. Alternatively,the lowest k values were recorded for MDMA (0.0051) and BMN(0.00003) in ML soil, PSE (0.0100) in SG soil, and MAP (0.0006) andFMA (0.0052) in WC soil. The results thus indicate that PSE andFMA has highest degradation potential in ML soil as indicated bythe respective k values, while that for MAP, MDMA, and BMN wasin SG soil. Interestingly, some matching pattern was also apparentbetween non-sterile and sterile conditions. In accord with thenon-sterile soils, MDMA and PSE recorded their maximum k valuesin SG and ML soil, respectively under sterile condition. On the basisof the above results the potential for degradation of target com-pounds among soils follow the descending order of SG > ML > WC.However, the results from all the three non-sterile soils showed
1008 R. Pal et al. / Chemosphere 85 (2011) 1002–1009
that parent drug (MAP and MDMA) and by-products (FMA andBMN) recorded much lower k values compared to the precursorchemical (PSE).
3.3. Role of biotic–abiotic soil processes in degradation
Biodegradation is considered to be one of the most importantfactors in risk assessment of many chemical substances due toinfluence on their removal after release into to the environment(Hiromatsu et al., 2000; Jaworska et al., 2003). In the present study,the aim was directed to determine the role of the biotic and/or abi-otic soil process in the degradation of the target compounds. Thepresent experiment was thus designed to eliminate any chancesof photodegradation of the target compounds. To accomplish this,soils were incubated in amber colored glass vials in the dark. Thus,the degradation of the compounds in sterile soils can be attributedto abiotic factors such as oxidation or hydrolysis. In addition, it isalso reasonable to assume that the higher degradation in non-ster-ile compared to sterile soils is indicative of the role of soilmicrobes.
To investigate the possible role of the biotic–abiotic soil pro-cesses in the degradation of target compounds, the percent degra-dation data for the two least stable compounds (e.g., MDMA andPSE) were compared at different periodic intervals (Fig. 4). Theabiotic losses of MDMA showed an increase over time irrespectiveof soils and its biotic degradation in SG and WC soils followed asimilar pattern. However, in ML soil a decrease in biotic degrada-tion of MDMA was evident after 7 d, while in SG soil the percentdegradation appeared virtually stable over time. The results thusrevealed that in SG and WC soils, a similar contribution of bioticand abiotic soil processes are maintained at least at the laterstages of incubation, while in ML soil the abiotic processes aremore dominant.
For PSE an increase over time is apparent for biotic losses espe-cially in ML and WC soils and abiotic losses in all the soils. How-ever, the magnitude of losses due to biotic soil processessignificantly exceeds losses due to abiotic processes for PSE.
Compared to MDMA therefore, abiotic degradation for PSE wasmore prominent. In contrast, biotic degradation in ML and WC soilswas higher for PSE than MDMA, while the reverse was apparent forSG soil. The higher biotic degradation of PSE might be ascribed tothe presence of OH substituent in the molecule, which has been re-ported to enhance the biodegradability of compounds regardless ofthe skeleton structure (Hiromatsu et al., 2000).
4. Conclusion
The present study clearly indicates that the environmentalbehavior of clandestine laboratory chemicals is a fairly complexprocess and depends on several factors. The overall degradationpattern of the test compounds depended mostly on the role of bio-tic and abiotic properties of individual soil. The nature of the testcompounds (e.g., chemical structure, nature of functional groups,etc.) was also a determining factor, as they have the potential tostrongly influence the degradation pattern (Hiromatsu et al.,2000). MAP and BMN recorded highest half life values followedby FMA, MDMA, and PSE in non-sterile soils and in most casesthe half life values were higher in ML and WC soils compared toSG soil.
Caution must be exercised in extrapolation of the results de-scribed herein to actual field conditions. Prior to any commentbeing made on the ‘‘real-life’’ degradation pattern of chemicals in-volved with illicit drug manufacture, the overall result of thisstudy suggest that there are number of factors to be consideredfor further research in particular: (i) the affect of different soil
physico-chemical properties on the degradation of these com-pounds, (ii) the influence of soil moisture regime (e.g., field capac-ity of soil, waterlogged condition, etc.), and (iii) degradation underanaerobic conditions. The results under diverse environmentalconditions may reflect the degradation pattern, metabolite profile,and distribution potential of these chemicals in soil. The results canthen be extrapolated to determine the potential hazard arisingfrom the release of these compounds into environment and anassessment be made on the environmental impact of clandestinedrug laboratories.
Acknowledgment
This work was supported by a National Drug Law EnforcementResearch Fund (NDLERF) Grant.
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