Bioavailability Of DDT Research Articles

Influence of Dietary Lipid Type on the Bioavailability of DDT and Its Metabolites in Soil: Mechanisms and Health Implications

The impact of dietary lipid type on DDTr (DDT and its metabolites) relative bioavailability (RBA) in soil was investigated using an in vivo mouse model and in vitro assays. Three different lipids were long chain triglycerides (LCT), medium chain triglycerides (MCT), and short chain triglycerides (SCT). DDTr-RBA markedly (p < 0.05) increased from 51.3 ± 10.8% (control) to 94.6 ± 15.9% (10% w/w LCT) and 112 ± 20.8% (20% LCT) in LCT amended treatments. A significant increase in DDTr-RBA (92.2 ± 9.84%, p < 0.05) was also observed when mice were administered diets containing 20% MCT; however, no influence on DDTr-RBA was observed for SCT amended diets. Mechanism exploration showed that LCT and MCT enhanced DDTr solubilization by a factor of 7.31-9.59 compared to controls as a consequence of micelle formation which promoted DDTr mobilization from soil. LCT significantly enhanced DDTr intestinal absorption via increasing synthesis and secretion of apolipoprotein B 48 (32.2 ± 2.08 mg/L), compared to MCT (22.1 ± 1.32 mg/L) and SCT (15.5 ± 2.03 mg/L) treated Caco-2 cells. Mouse gut microflora analysis highlighted that LCT and MCT may increase intestinal permeability by regulating abundance of Lactobacillus, which may influence the absorption of DDTr.

The Influence of Food on the In Vivo Bioavailability of DDT and Its Metabolites in Soil.

Incidental soil ingestion is considered to be an important route of exposure to hydrophobic organic contaminants (HOCs), such as dichlorodiphenyl-trichloroethane (DDT). Contaminant ingestion often occurs during food consumption; however, knowledge on the influence of food on DDT bioavailability remains limited. In this study, the relative bioavailability (RBA) of soil DDTr (i.e., DDT and metabolites) was determined using an in vivo mouse model in the presence of eight kinds of food including rice, egg, pork, pear, soybean, bread, spinach, and milk powder. The values of DDTr-RBA ranged from 19.8 ± 10.9 to 114 ± 25.1%. DDTr-RBA was positively correlated with fat (r = 0.71) and negatively correlated with fiber (r = 0.63) content in food. A mechanistic study showed that fat enhanced micellarization and promoted the formation of chylomicron, which facilitated the dissolution and transport of DDTr in the intestinal tract. Bioaccessibility of DDTr was determined using a physiologically based in vitro method. The addition of lipase significantly improved the ability of the method to predict DDTr-RBA, indicating that the "fasted state" in vitro method required optimization for food scenarios. To the best of our knowledge, this is the first study to explore the mechanistic influence of food on DDTr-RBA and provide important knowledge on dietary approaches for reducing exposure to HOCs.

The fate of DDT in soils treated with hydroxypropyl-β-cyclodextrin (HPβCD)

ABSTRACTPoint Pelee National Park (PPNP) is highly contaminated with dichlorodiphenyltrichloroethane (DDT) due to the historical use of this persistent organochlorine pesticide. Hydroxypropyl-β-cyclodextrin (HPβCD) has previously been investigated for its role in the remediation of polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). In the present study, HPβCD's ability to promote DDT microbial degradation, enhance DDT phytoextraction by two native grasses (Schizachyrium scoparium and Panicum virgatum), and increase DDT bioavailability to redworms (Eisenia fetida) was investigated. Using a range of HPβCD concentrations (2.5% to 10%), it was determined that it did not promote DDT microbial degradation in PPNP soils, however, it was able enhance the DDT phytoextraction ability of S. scoparium plants due to the increased water solubility of DDT. Although HPβCD application to PPNP soil did not increase DDT bioavailability to redworms, its enhanced solubility allowed it to move through the soil column, and hence groundwater contamination is a possibility. Due to this important issue, in situ use of HPβCD to remediate DDT contamination is not recommended unless measures are in place to mitigate movement into groundwater.

Comparisons of field and laboratory estimates of risk of DDTs from contaminated sediments to humans that consume fish in Palos Verdes, California, USA

Calculating risk from seafood exposure to persistent organic pollutants continues to be problematic as estimates of exposure from diet require extensive monitoring of fish species and limited assessments of bioavailability from sediments where the contaminants tend to reside. Previous studies in our laboratory utilized a laboratory-based isotope dilution method (IDM) to estimate the bioavailability of DDT [1,1,1-trichloro-2, 2-bis(p-chloro-phenyl)ethane] and its metabolites from sediment to biota from a superfund site on the shelf of the Palos Verdes (PVS) Peninsula in California (USA). Using a biota-sediment accumulation factor (BSAF) derived from IDM and biomagnification factors (BMF) calculated from previous studies as well as seafood-consumption data specific to anglers in the PVS area, we estimated cancer and non-cancer risks for anglers and nursing infants representing sensitive groups. Predicted cancer risks from consumption of White croaker (Genyonemus lineatus) to the 50th and 95th percentile to all shore mode anglers were, respectively, 2×10−7 and 7×10−7, which were similar to field studies using fish concentrations of all DDT isomers and their environmental degradates (ΣDDT) from collected animals. The calculated non-cancer hazard quotient values for the 50th and 95th percentile shore mode anglers consuming White croaker from this study (0.008 and 0.023, respectively) were also of similar magnitude as those obtained from studies based on samples obtained solely from fish. For nursing infants, similar results were also observed. These results indicate that estimates of bioavailability using IDM from sediment could be used accurately to determine risk to ΣDDT in humans from fish consumption.

CHANGES ON THE BIOAVAILABILITY OF DDT IN SOIL BY ADDITION OF LIGNITE AND COAL SOLUBILIZING BACTERIA

DDT is an organochlorine insecticide that is persistent and exhibits residuality in the environment. This study assessed the effect of the application of lignite [low rank coal (LRC)] and coal solubilizing bacteria (CSB), on the bioavailability of DDT in soil with low organic matter content. In doing this, three trials were designed; in the first trial, soil samples were treated with CSB and LRC for 30 days and, afterwards, they were immersed in a DDT solution at water solubility limit and, lastly, the remaining DDT in the aqueous solution was determined. In the second trial, soil samples previously contaminated with DDT were treated with LRC and CSB. After 30 days of this interaction, the soil samples were immersed in water and the remaining DDT in solution was subsequently determined. The third trial was similar to the latter, but the interaction lasted for six months. In the first experiment, treatments with LRC and LRC + CSB, showed 8.16 and 3.4 % of remaining DDT respectively, thus indicating the retention of the compound in the soil. In the second trial, the treatment with CSB greatly reduced the bioavailable DDT (0.007 ppm), compared to the control (0.014 ppm); this is possible since these bacteria use DDT as a carbon source. In the third trial, the highest reduction in the bioavailability of DDT took place in LRC and LRC + CSB treatments; this trial also detected DDD produced from DDT transformation, which showed the same behavior; the interaction timeframe favors adsorption and copolymerization of pollutants to humified organic matter (HOM) in soil. Use of LRC as a source of HOM represents a promising strategy for the treatment of soils with low organic matter content affected by persistent organic pollutants such as DDT.

Comparing different methods for assessing contaminant bioavailability during sediment remediation

Sediment contamination by persistent organic pollutants from historical episodes is widespread and remediation is often needed to clean up severely contaminated sites. Measuring contaminant bioavailability in a before-and-after manner lends to improved assessment of remediation effectiveness. However, a number of bioavailability measurement methods have been developed, posing a challenge in method selection for practitioners. In this study, three different bioavailability measurement methods, i.e., solid phase microextraction (SPME), Tenax desorption, and isotope dilution method (IDM), were compared in evaluating changes in bioavailability of DDT and its degradates in sediment following simulated remediation treatments. When compared to the unamended sediments, all three methods predicted essentially the same degrees of changes in bioavailability after amendment with activated carbon, charcoal or sand. After normalizing over the unamended control, measurements by different methods were linearly correlated with each other, with slopes close to 1. The same observation was further made with a Superfund site marine sediment. This finding suggests that different methods may be used in evaluating remediation efficiency. However, Tenax desorption or IDM consistently offered better sensitivity than SPME in detecting bioavailability changes. Results from this study highlight the value of considering bioavailability when evaluating remediation effectiveness and provide guidance on the selection of bioavailability measurement methods in such assessments.

Predicting the Relative Bioavailability of DDT and Its Metabolites in Historically Contaminated Soils Using a Tenax-Improved Physiologically Based Extraction Test (TI-PBET)

Due to their static nature, physiologically based in vitro assays often fail to provide sufficient sorption capacity for hydrophobic organic contaminants (HOCs). The addition of a sorption sink to in vitro intestinal solution has the potential to mimic dynamic intestinal uptake for HOCs, thereby increasing their desorption from soil. However, the effectiveness of sorption sinks for improving in vitro assays needs to be compared with in vivo data. In this study, Tenax was added as a sorption sink into the physiologically based extraction test (PBET), while DDT and its metabolites (DDTr) were investigated as typical HOCs. Tenax added at 0.01-0.2 g to the PBET intestinal solution sorbed ∼100% of DDTr in 6.3-19 min, indicating its ability as an effective sorption sink. DDTr bioaccessibility in six contaminated soils using Tenax-improved PBET (TI-PBET; 27-56%) was 3.4-22 fold greater than results using the PBET (1.2-15%). In vivo DDTr relative bioavailability (RBA) was measured using a mouse adipose model with values of 17.9-65.4%. The inclusion of Tenax into PBET improved the in vivo-in vitro correlation from r(2) = 0.36 (slope = 2.1 for PBET) to r(2) = 0.62 (slope = 1.2 for TI-PBET), illustrating that the inclusion of Tenax as a sorption sink improved the in vitro prediction of DDTr RBA in contaminated soils.

Atomic elucidation of the cyclodextrin effects on DDT solubility and biodegradation.

DDT (1,1,1-trichloro-2.2-bis(p-chlorophenyl)ethane), one of the most abused insecticides, is a highly hazardous component for both human health and environmental applications. The biodegradation of DDT into non-toxic, environmentally benign components is strongly limited by the poor bioavailability of DDT. In this work, we combined experiments and molecular simulations to examine the effect of three cyclodextrins (α-, β-, and γ-CD) on their structure-specific interactions with DDT, specifically in relation to DDT solubility and biodegradability. It was found that all three CDs were able to bind to DDT with their inner hydrophobic cavity and different binding affinities and orientations, demonstrating their ability to improve DDT solubility. Different from the strong binding between DDT and β-/γ-CDs via a fully DDT bury mode, α-CD had a relatively weak binding with DDT via a partial DDT bury mode, which allowed DDT to be readily disassociated from α-CD at the lipid membrane interface, followed by DDT permeation into and across the cell membrane. The different binding modes between DDT and CDs explain why only α-CD can promote the bioavailability and biodegradation of DDT by simultaneously increasing its aqueous solubility and membrane interaction. This work provides structural-based binding information for the further modification and optimization of these three CDs to enhance their solubility and biodegradability of DDT.

In situ bioavailability of DDT and Hg in sediments of the Toce River (Lake Maggiore basin, Northern Italy): accumulation in benthic invertebrates and passive samplers.

DDT and mercury (Hg) contamination in the Toce River (Northern Italy) was caused by a factory producing technical DDT and using a mercury-cell chlor-alkali plant. In this study, DDT and Hg contamination and bioavailability were assessed by using different approaches: (1) direct evaluation of sediment contamination, (2) assessment of bioaccumulation in native benthic invertebrates belonging to different taxonomic/functional groups, and (3) evaluation of the in situ bioavailability of DDT and Hg using passive samplers. Sampling sites were selected upstream and downstream the industrial plant along the river axis. Benthic invertebrates (Gammaridae, Heptageniidae, and Diptera) and sediments were collected in three seasons and analyzed for DDT and Hg content and the results were used to calculate the biota sediment accumulation factor (BSAF). Polyethylene passive samplers (PEs) for DDT and diffusive gradients in thin films (DGTs) for Hg were deployed in sediments to estimate the concentration of the toxicants in pore water. Analysis for (DDx) were performed using GC-MS. Accuracy was within ±30% of the certified values and precision was >20% relative standard deviation (RSD). Total mercury concentrations were determined using an automated Hg mercury analyzer. Precision was >5% and accuracy was within ±10% of certified values. The results of all the approaches (analysis of sediment, biota, and passive samplers) showed an increasing contamination from upstream to downstream sites. BSAF values revealed the bioavailability of both contaminants in the study sites, with values up to 49 for DDx and up to 3.1 for Hg. No correlation was found between values in sediments and the organisms. Concentrations calculated using passive samplers were correlated with values in benthic invertebrates, while no correlation was found with concentrations in sediments. Thus, direct analysis of toxicant in sediments does not provide a measurement of bioavailability. On the contrary, analysis of bioaccumulation in benthic organisms provides the most realistic picture of the site-specific bioavailability of DDx and Hg, but this approach is time-consuming and not always feasible. On the other hand, the in situ deployment of passive samplers proved to be a powerful tool, providing a good surrogate measure of bioaccumulation.

Bioavailability assessments following biochar and activated carbon amendment in DDT-contaminated soil

The effects of 2.8% w/w granulated activated carbon (GAC) and two types of biochar (Burt's and BlueLeaf) on DDT bioavailability in soil (39 μg/g) were investigated using invertebrates (Eisenia fetida), plants (Cucurbita pepo spp. pepo) and a polyoxymethylene (POM) passive sampler method. Biochar significantly reduced DDT accumulation in E. fetida (49%) and showed no detrimental effects to invertebrate health. In contrast, addition of GAC caused significant toxic effects (invertebrate avoidance and decreased weight) and did not significantly reduce the accumulation of DDT into invertebrate tissue. None of the carbon amendments reduced plant uptake of DDT. Bioaccumulation of 4,4'DDT and 4,4'-DDE in plants (C. pepo spp. pepo) and invertebrates (E. fetida) was assessed using bioaccumulation factors (BAFs) and compared to predicted bioavailability using the freely-dissolved porewater obtained from a polyoxymethylene (POM) equilibrium biomimetic method. The bioavailable fraction predicted by the POM samplers correlated well with measured invertebrate uptake (<50% variability), but was different from plant root uptake by 134%. A literature review of C. pepo BAFs across DDT soil contamination levels and the inclusion of field data from a 2.5 μg/g DDT-contaminated site found that these plants exhibit a concentration threshold effect at [DDT](soil) > 10 μg/g. The results of these studies illustrate the importance of including plants in bioavailability studies as the use of carbon materials for in situ contaminant sorption moves from predominantly sediment to soil remediation technologies.

Influence of Hydroxypropyl-β-cyclodextrin on the Extraction and Biodegradation of p,p′-DDT, o,p′-DDT, p,p′-DDD, and p,p′-DDE in Soils

Dichlorodiphenyltrichloroethane (DDT) is one of the persistent organic pollutants (POPs) that are highly toxic to the environment. Effective evalu- ation on the bioavailability of DDTs in soils is essen- tial for risk assessment and soil remediation. The aims of this study were to verify the feasibility of the hydroxypropyl-β-cyclodextrin (HPCD) extraction method for predicting the bioavailability of DDT, dichlorodiphenyldichloroethane (DDD), and dichlorodiphenyldichloroethylene (DDE) in soils, and to examine the effect of HPCD on their biodeg- radation in different soils. Four soils were aged with a mixture of p,p'-DDT, o,p'-DDT, p,p'-DDD and p,p'- DDE (0.25 μ gg −1 for each compound) for 20 and 100 days, respectively. For each of the DDTs, a sig- nificant positive correlation between HPCD- extractable fraction and biodegradable fraction in each soil was observed. It was demonstrated that the amounts of HPCD-extractable p,p'-DDT and o,p'- DDT were not significantly different from the amounts that were degradable as assessed from their degradation by Enterobacter sp. LY402 (p>0.05). Such 1:1 relationship between extraction and degra- dation was not obtained in the cases of p,p'-DDD and p,p'-DDE, as the amounts of degradable p,p'-DDD and p,p'-DDE were lower than the amounts that were extractable with HPCD. Additionally, the biodegra- dation of p,p'-DDT, o,p'-DDT, p,p'-DDD, and p,p'- DDE was inhibited in the presence of HPCD, which could be due to the binding of the compounds to HPCD, making them less available to access the bac- teria for degradation. This study provides the possi- bility of using the HPCD extraction method to predict the bioavailability of p,p'-DDTand o,p'-DDTin soils. But when HPCD was used as an additive in the bioremediation of DDT-contaminated soils, it might have a negative effect on biodegradation.

Utilizing thin-film solid-phase extraction to assess the effect of organic carbon amendments on the bioavailability of DDT and dieldrin to earthworms

Improved approaches are needed to assess bioavailability of hydrophobic organic compounds in contaminated soils. Performance of thin-film solid-phase extraction (TF-SPE) using vials coated with ethylene vinyl acetate was compared to earthworm bioassay (Lumbricus terrestris). A DDT and dieldrin contaminated soil was amended with four organic carbon materials to assess the change in bioavailability. Addition of organic carbon significantly lowered bioavailability for all compounds except for 4,4′-DDT. Equilibrium concentrations of compounds in the polymer were correlated with uptake by earthworms after 48d exposure (R2 = 0.97; p < 0.001), indicating TF-SPE provided an accurate uptake simulation. Bioavailability of residues in soil was compared with a spiked soil aged for 90d in laboratory. Dieldrin and DDX were respectively 18% and 11% less bioavailable in contaminated soil relative to spiked soil despite >40yr of aging. Results show that TF-SPE can be useful in examining potential risks associated with contaminated soils and to test effectiveness of remediation efforts.

Effect of Seaweeds on Degradation of DDT in Soils

Seaweed was investigated as an amendment to enhance remediation of 1,1,1-trichloro-2,2-bis (p-chlorophenyl) ethane (DDT)-contaminated soil. Under anaerobic conditions, the addition of seaweeds increased DDT degradation between 61 % and 88 % of the original concentration after 14 days of incubation whereas only 33 % of DDT was degraded in unamended soil. DDT was degraded to metabolites such as 1,1-dichloro-2,2-bis (p-chlorophenyl) ethane (DDD), 1,1-dichloro-2,2-bis (p-chlorophenyl) ethylene (DDE), and 1-chloro-2,2-bis (p-chlorophenyl) ethylene (DDMU). Seaweed-amended soils converted 35–56 % of DDT to DDD while the unamended soil formed only 15 % DDD. Seaweed amendments modified soil conditions which include soils’ dissolved organic carbon (DOC), ionic strength, redox potential, and pH. These significant physicochemical changes influenced the increase in DDT bioavailability and transformation in seaweed-amended soils compared to the unamended soils. Multiple linear regression analysis also suggested that factors such as DOC, calcium, redox potential, and pH are involved against DDT degradation (p = 0.02).

Assessing bioavailability of DDT and metabolites in marine sediments using solid‐phase microextraction with performance reference compounds

Solid-phase microextraction (SPME) has often been used to estimate the freely dissolved concentration (Cfree ) of organic contaminants in sediments. A significant limitation in the application of SPME for Cfree measurement is the requirement for attaining equilibrium partition, which is often difficult for strongly hydrophobic compounds such as DDT. A method was developed using SPME with stable isotope-labeled analogues as performance reference compounds (PRCs) to measure Cfree of DDT and metabolites (DDTs) in marine sediments. Six (13) C-labeled or deuterated PRCs were impregnated into polydimethylsiloxane (PDMS) fiber before use. Desorption of PRCs from PDMS fibers and absorption of DDTs from sediment were isotropic in a range of sediments evaluated ex situ under well-mixed conditions. When applied to a historically contaminated marine sediment from a Superfund site, the PRC-SPME method yielded Cfree values identical to those found by using a conventional equilibrium SPME approach (Eq-SPME), whereas the time for mixing was reduced from 9 d to only 9 h. The PRC-SPME method was further evaluated against bioaccumulation of DDTs by Neanthes arenaceodentata in the contaminated sediment with or without amendment of activated carbon or sand. Strong correlations were consistently found between the derived equilibrium concentrations on the fiber and lipid-normalized tissue residues for DDTs in the worms. Results from the present study clearly demonstrated the feasibility of coupling PRCs with SPME sampling to greatly shorten sampling time, thus affording much improved flexibility in the use of SPME for bioavailability evaluation.

Tenax TA extraction to assess the bioavailability of DDTs in cotton field soils

The rapid-desorbing fraction plays an important role in the bioavailability of organic pollutants in soil. In the present study, DDT's desorption from the cotton field soils was investigated by Tenax extraction. The results of the Tenax consecutive extraction (400 h) indicated that the rate constants were in the order of 10 −1, 10 −2, and 10 −4 h −1 for the rapid, slow and very-slow desorption, respectively. The rapid-desorbing fraction was about 0.3 times the total soil DDTs, and about 2 times the Tenax 6 h-extracted fraction (single-point extraction). The rapid-desorbing fraction correlated well with the 6 h-extracted fraction ( p < 0.05), implying the feasibility of measuring the rapid-desorbing fraction with Tenax 6 h-extration. The strong correlation with the carrot accumulation suggested that Tenax 6 h-extrated fraction could serve as a good predictor of DDT's bioavailability to carrot roots. Risk assessment demonstrated that when based on the rapid-desorbing concentration and 6 h-extracted concentration, about 60.7% and 17.9% of the soil samples were moderately polluted, however, up to 78.5% were moderately polluted when based on the total soil DDTs concentration. The risk assessment might be more representative when based on Tenax extraction because of the strong correlation with the carrot accumulation. Our results provided implications for site risk assessment and cleanup strategies.

The usefulness of total concentrations and pore water concentrations of pesticides in soil as metrics for the assessment of ecotoxicological effects ‐ Scientific Opinion of the Panel on Plant Protection Products and their Residues (PPR)

The usefulness of total concentrations and pore water concentrations of pesticides in soil as metrics for the assessment of ecotoxicological effects ‐ Scientific Opinion of the Panel on Plant Protection Products and their Residues (PPR)

Bioavailable DDT residues in sediments: Laboratory assessment of ageing effects using semi-permeable membrane devices

We describe the reduction in bioavailability of DDT in contaminated soil after it was incubated as sediment for 365 d. Bioavailability was assessed using semi-permeable membranes. Contaminated soils from three cattle dip sites, one spiked paired uncontaminated site, and one spiked OECD standard soil were studied. Sandy soil with residues of 1880 mg/kg ∑DDT incurred since 1962, initially had 4.6% of ∑DDT available, reducing to 0.6% following 365 d. Clay soil (1108 mg ∑DDT/kg) had 4.1% initially available, reducing to 0.3% after 365 d. Freshly spiked soils had a greater amount of DDT initially available (10.9%), but this reduced to 1.5% by the end of the incubation. Of the DDT congeners, both o, p′-DDD and p, p′-DDD were most bioavailable in the soils, but also had the most significant decrease following incubation.

Sodium Application Enhances DDT Transformation in a Long-Term Contaminated Soil

Bioremediation is an economically attractive option to remediate soil contaminated with DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] and other organochlorine pesticides. However, lack of DDT bioavailability in soil presents one major obstacle to this technology particularly in soils that have been contaminated for long periods. In this work, sodium ion (Na+) was applied to a long-term DDT contaminated soil as Na+ is known to disperse clays, which would potentially release and/or expose physically protected DDT thereby enhancing DDT bioavailability. Sodium ion addition significantly increased dissolved organic carbon (DOC) levels, anaerobic bacterial numbers and the amount of DDT residues measured in soil solution. DDT transformation ranged from 95% (30—80 mg Na+ kg-1 soil) to 72% (no Na+ added) with the optimum level of DDT transformation occurring at 30 mg Na+ kg-1 soil. Higher Na+ levels repressed DDT transformation and this appeared to be related to lower DOC levels and flocculation of soils. The anaerobic incubation conditions employed (high water content) prevented DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene] production and DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane] was the major breakdown product formed. Overall it appeared that Na+ has potential as a cheap and safe alternative to surfactants as a method for increasing DDT transformation in contaminated soil.

Bioremediation of DDT‐contaminated soil: enhancement by seaweed addition

AbstractDDT [1,1,1‐trichloro‐2,2‐bis (p‐chlorophenyl) ethane] is a major environmental pollutant and economical methods to remove DDT from the environment are required. In this work we used seaweed (dried and ground) to enhance DDT transformation in waterlogged soils. Initial daily rates of DDT biodegradation increased in the following order relating to the percentage by weight of added seaweed to soil 0.5 &gt; 1 &gt; 0 &gt; 3 &gt; 5 &gt; 13 (w/w). The actual percentages of DDT biodegradation occurring within 6 weeks were 80, 64, 60, 50, 40 and 34 respectively. During soil incubation DDD [1,1,1‐trichloro‐2,2‐bis (p‐chlorophenyl) ethane] was the major metabolite found with small amounts of DDE [1,1,1‐trichloro‐2,2‐bis (p‐chlorophenyl) ethane] produced. The maximum amount of 4,4′‐dichlorobenzophenone (DBP) (2.5%) produced was found in soil amended with 0.5% (w/w) seaweed, indicating that further degradation of DDD occurred. High levels of dissolved organic carbon (DOC), between 309 and 509 mg kg−1 soil, were present in soil amended with 3–13% (w/w) seaweed immediately after seaweed addition. It is possible that the high levels of DOC in soils amended with larger amounts of seaweed significantly retarded DDT biodegradation, possibly due to binding of DDT to DOC and subsequently decreasing the bioavailability of DDT to soil microbes. Copyright © 2004 Society of Chemical Industry

Use of sequential ASE extraction to evaluate the bioavailability of DDT and its metabolites to wheat roots in soils with various organic carbon contents

An accelerated solvent extraction (ASE) procedure using water, n-hexane and a mixture of n-hexane and acetone as solvents in sequence was developed and tested to evaluate the bioavailability of DDT and its metabolites including p, p′-DDT, o, p′-DDT, p, p′-DDE, and p, p′-DDD (ΣDDTs) to wheat uptake from soils characterized by varied organic carbon contents. Results indicated that the extractability of ΣDDTs with water was enhanced considerably in the presence of water soluble organic carbon (WSOC), while the amount of ΣDDTs extracted with n-hexane was negatively correlated to the content of water insoluble organic carbon (WIOC). The interaction between ΣDDTs and WIOC also reduced the bioavailability of the pesticides to wheat roots during uptake. There was a good positive correlation between the amount of ΣDDTs extracted by n-hexane and the amount of ΣDDTs accumulated in wheat roots, suggesting some potential for the use of the n-hexane ASE-extracted fraction as an indicator of ΣDDTs’ bioavailability to plant uptake. As such, the three sequentially extracted fractions may be viewed as representing the mobile, bioavailable, and fixed pools of ΣDDTs in the soil.