Solid phase extraction with silicon dioxide microsphere adsorbents in combination with gas chromatography-electron capture detection for the determination of DDT and its metabolites in water samples

The goal of the present study was to investigate the feasibility of silicon dioxide (SiO(2)) microspheres without special modification to enrich dichlorodiphenyltrichloroethane (DDT) and its main metabolites, p,p'-dichlorodiphenyl-2,2-dichloroethylene (p,p'-DDD) and p,p'-dichlorodiphenyldichloroethylene (DDE) in combination with gas chromatography-electron-capture detection. The experimental results indicated that an excellent linear relationship between the recoveries and the concentrations of DDT and its main metabolites was obtained in the range of 0.2-30 ng mL(-1) and the correlation coefficients were in the range of 99.96-99.99%. The detection limits based on the ratio of signal to the baseline noise (S/N = 3) were 2.2, 2.9, 3.8 and 4.1 ng L(-1) for p,p'-DDD, p,p'-DDT, o,p'-DDT, and p,p'-DDE, respectively. The precisions of the proposed method were all below 10% (n = 6). Four real water samples were utilized for validation of the proposed method, and satisfactory spiked recoveries in the range of 72.4-112.9% were achieved. These results demonstrated that the developed method was a simple, sensitive, and robust analytical method for the monitoring of pollutants in the environment.

Competitive sorption of persistent organic pollutants onto microplastics in the marine environment

Plastics are known to sorb persistent organic pollutants from seawater. However, studies to quantify sorption rates have only considered the affinity of chemicals in isolation, unlike the conditions in the environment where contaminants are present as complex mixtures. Here we examine whether phenanthrene and 4,4'-DDT, in a mixture, compete for sorption sites onto PVC with no added additives (unplasticised PVC or uPVC) and Ultra-High Molecular Weight polyethylene. Interactions were investigated by exposing particles of uPVC and UHMW PE to mixtures of 3H and 14C radiolabelled Phe and DDT. Changes in sorption capacity were modelled by applying a Freundlich binding sorption isotherms. An Extended Langmuir Model and an Interaction Factor Model were also applied to predict equilibrium concentrations of pollutants onto plastic. This study showed that in a bi-solute system, DDT exhibited no significantly different sorption behaviour than in single solute systems. However, DDT did appear to interfere with the sorption of Phe onto plastic, indicating an antagonistic effect.

Low concentrations of o,p'-DDT inhibit gene expression and prostaglandin synthesis by estrogen receptor-independent mechanism in rat ovarian cells

o,p'-DDT is an infamous xenoestrogen as well as a ubiquitous and persistent pollutant. Biomonitoring studies show that women have been internally exposed to o,p'-DDT at range of 0.3-500 ng/g (8.46×10(-10) M-1.41×10(-6) M) in blood and other tissues. However, very limited studies have investigated the biological effects and mechanism(s) of o,p'-DDT at levels equal to or lower than current exposure levels in human. In this study, using primary cultures of rat ovarian granulosa cells, we determined that very low doses of o,p'-DDT (10(-12)-10(-8) M) suppressed the expression of ovarian genes and production of prostaglandin E2 (PGE2). In vivo experiments consistently demonstrated that o,p'-DDT at 0.5-1 mg/kg inhibited the gene expression and PGE2 levels in rat ovary. The surprising results from the receptor inhibitors studies showed that these inhibitory effects were exerted independently of either classical estrogen receptors (ERs) or G protein-coupled receptor 30 (GPR30). Instead, o,p'-DDT altered gene expression or hormone action via inhibiting the activation of protein kinase A (PKA), rather than protein kinase C (PKC). We further revealed that o,p'-DDT directly interfered with the PKA catalytic subunit. Our novel findings support the hypothesis that exposure to low concentrations of o,p'-DDT alters gene expression and hormone synthesis through signaling mediators beyond receptor binding, and imply that the current exposure levels of o,p'-DDT observed in the population likely poses a health risk to female reproduction.

Enhanced solubilization and desorption of organochlorine pesticides (OCPs) from soil by oil-swollen micelles formed with a nonionic surfactant

The effect of oil-swollen micelles formed with nonionic surfactant polyoxyethylene sorbitan monooleate (Tween 80), cosurfactant 1-pentanol, and linseed oil on the solubilization and desorption of organochlorine pesticides (OCPs) including DDT and γ-HCH from both loam soil and clay soil were investigated. Results showed that the solubilizing capacities of oil-swollen micelles were dependent on the critical micelle concentration (CMC) of Tween 80. Once the concentrations of oil-swollen micelles exceeded the CMC of Tween 80, the oil-swollen micelles exhibited much higher solubilizing capacity than empty Tween 80 micelles for the two OCPs. Desorption tests revealed that oil-swollen micelles could successfully enhance desorption of OCPs from both loam soil and clay soil. However, compared with the efficiencies achieved by empty Tween 80 micelles, oil-swollen micelles exhibited their superiority to desorb OCPs only in loam soil-water system while was less effective in clay soil-water system. Distribution of Tween 80, 1-pentanol and linseed oil in soil-water system revealed that the difference in the sorption behavior of linseed oil onto the two soils is responsible for the different effects of oil-swollen micelles on the desorption of OCPs in loam soil and clay soil systems. Therefore, oil-swollen micelles formed with nonionic surfactant Tween 80 are better candidates over empty micelle counterparts to desorb OCPs from soil with relatively lower sorption capacity for oil fraction, which may consequently enhance the availability of OCPs in soil environment during remediation processes of contaminated soil.

PCBs and OCPs on a east-to-west transect: the importance of major currents and net volatilization for PCBs in the Atlantic Ocean

Air-water exchange gradients of selected polychlorinated biphenyl (PCB) congeners across a large section of the tropical Atlantic suggested net volatilization of PCBs to the atmosphere. Only for the higher chlorinated PCB 153 and hexachlorobenzene (HCB) were gradients near equilibrium detected. The use of passive samplers also enabled the detection of dichlorodiphenyltrichloroethane (DDT) and its transformation products across the tropical Atlantic, indicating net deposition. There were clear differences between the southern and northern hemisphere apparent in terms of atmospheric concentrations: Once the ship moved from the southern into the northern hemisphere air, concentrations of HCB and other organochlorine pesticides increased several-fold. For large swaths of the tropical Atlantic Ocean, neither PCB nor organochlorine pesticide dissolved concentrations varied much longitudinally, probably due to efficient mixing by ocean currents. In selected samples, dissolved concentrations reflected the influence of river plumes and major ocean currents far away from the continents. Dissolved concentrations of PCBs 28, 52, 101, 118, and HCB increased in the Amazon plume and the Gulf Stream. While the Amazon plume flushed only a few kg of PCBs and HCB, the Gulf Stream is potentially delivering tons of PCBs into the North Atlantic annually.

Use of solid phase microextraction to estimate toxicity: relating fiber concentrations to toxicity--part I

Use of solid-phase microextraction (SPME) fibers as a dose metric for toxicity testing was evaluated for hydrophobic pesticides to the midge Chironomus dilutus and the amphipod Hyalella azteca. Test compounds included p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), p,p'-dichlorodiphenyldichloroethane (p,p'-DDD), p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE), permethrin, bifenthrin, tefluthrin, and chlorpyrifos. Acute water toxicity tests were determined for 4- and 10-d exposures in both species. Median lethal and sublethal concentrations were expressed both on a water concentration (LC50 and EC50) and on an equilibrium SPME fiber concentration (LC50(fiber) and EC50(fiber)) basis. A significant log dose-response relationship was found between log fiber concentration and organism mortality. It has been shown in the literature that equilibrium SPME fiber concentrations reflect the bioavailable concentrations of hydrophobic contaminants, so these fiber concentrations should be a useful metric for assessing toxic effects from the bioavailable contaminant providing a framework to expand the use of SPME fibers beyond estimation of bioaccumulation.

Use of solid phase microextraction to estimate toxicity: relating fiber concentrations to body residues--part II

In the companion paper, solid phase microextraction (SPME) fiber concentrations were used as a dose metric to evaluate the toxicity of hydrophobic pesticides, and concentration-response relationships were found for the hydrophobic pesticides tested in the two test species. The present study extends the use of fiber concentrations to organism body residues to specifically address biotransformation and provide the link to toxic response. Test compounds included the organochlorines p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), p,p'-dichlorodiphenyldichloroethane (p,p'-DDD), and p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE); two pyrethroids, permethrin and bifenthrin; and an organophosphate, chlorpyrifos. Toxicity, body residues, and biotransformation of the target compounds were determined for the midge Chironomus dilutus and the amphipod Hyalella azteca. Significant regression relationships were found without regard to chemical, extent of biotransformation, or whether the chemical reached steady state in the organisms. The equilibrium SPME fiber concentrations correlated with the parent compound concentration in the biota; however, the regressions were duration specific. Furthermore, the SPME fiber-based toxicity values yielded species-specific regressions with the parent compound-based toxicity values linking the use of SPME fiber as a dose metric with tissue residues to estimate toxic response.

Concentrations of DDTs and enantiomeric fractions of chiral DDTs in agricultural soils from Zhejiang Province, China, and correlations with total organic carbon and pH

Dichlorodiphenyltrichloroethanes (DDTs) are persistent organic pollutants that were widely used in China, especially eastern China, as insecticides. This work investigated the concentration, dissipation, and volatilization of DDTs and enantiomeric fractions (EFs) of o,p'-DDD and o,p'-DDT in agricultural soils collected in 2006 from 58 sites in Zhejiang province. Correlations between DDT residues and soil properties were assessed to determine the effect of soil properties on the environmental attenuation of DDTs. High concentrations and detection frequencies were found for DDTs in agricultural soils in the region even though large-scale use of DDTs was banned over 20 years ago. The amount of DDTs was about 485 tons in the upper 20 cm of the soil column of cropland in the province in 2010, with a dissipation half-life of ~9 years. The mass flux of DDTs was 43 ng m(-2) h(-1), which corresponds to emissions of 7.6 tons with an emission factor of 1.6% in 2006. The low p,p'-DDT/p,p'-DDE ratios and high o,p'-DDT/p,p'-DDT ratios suggest that there were no recent inputs of DDTs but fresh application of dicofol, which contains DDT (o,p'-DDT in particular) impurities. The significant positive correlation between concentrations of DDTs and total organic carbon content (TOC) indicates the distribution of DDTs fit a typical "secondary distribution" pattern. DEVrac of o,p'-DDD, which is defined as the absolute value of EFs subtracted from 0.5, was significantly related with most of the physicochemical and microbial soil properties. The most significant correlation is that between DEVrac of o,p'-DDD and soil pH (p < 0.001), indicating that the soil pH plays a key role in enantioselective residues of DDTs.

Phytoremediation of trichloroethylene and dichlorodiphenyltrichloroethane-polluted water using transgenic Sesbania grandiflora and Arabidopsis thaliana plants harboring rabbit cytochrome p450 2E1

Sesbania grandiflora (L.) pers (Fabaceae) and Arabidopsis thaliana (L.) (Brassicaceae) were genetically engineered to constitutively express the rabbit cytochrome p450 2E1 enzyme aiming at increasing their activity toward trichloroethylene (TCE) and dichlorodiphenyltrichloroethane (DDT) removal Successful generation of Sesbania and Arabidopsis transgenic plants was verified using p450 2E1 specific PCR and confirmed by western blot analysis. Gas chromatography (GC) analysis revealed that small cuttings of Sesbania and third generation (F3) Arabidopsis transgenic plants exposed to TCE and DDT in small hydroponics' vessels accumulated more TCE and DDT compared to plants transformed with the empty vector. Furthermore, both transgenic plants were more effective in breaking down TCE and DDT with a 2-fold increase in TCE metabolism. Two independent Arabidopsis lines showed that DDT was metabolized about 4-fold higher than that detected in non transformed plants. Similarly, S. grandiflora cuttings removed 51 to 90% of the added DDT compared with only 3% removal in controls transformed with the null vector. Notably, stability of rabbit cytochrome p450 2E1 was confirmed using third generation Arabidopsis plants that displayed higher potential for the removal of two important pollutants, TCE and DDT compared with the controls.

Assessment of DDT relative bioavailability and bioaccessibility in historically contaminated soils using an in vivo mouse model and fed and unfed batch in vitro assays

In this study, DDTr (DDTr = DDT + DDD + DDE) relative bioavailability in historically contaminated soils (n = 7) was assessed using an in vivo mouse model. Soils or reference materials were administered to mice daily over a 7 day exposure period with bioavailability determined using DDTr accumulation in adipose, kidney, or liver tissues. Depending on the target tissue used for its calculation, some variability in DDTr relative bioavailability was observed; however, it did not exceed 25% (range 2-25%). When DDTr bioaccessibility was determined using organic physiologically based extraction test (Org-PBET), unified BARGE method (UBM), and fed organic estimation human simulation test (FOREhST) in vitro assays, bioaccessibility was less than 4% irrespective of the assay utilized and the concentration of DDTr in the contaminated soil. Pearson correlations demonstrate a poor relationship between DDTr relative bioavailability and DDTr bioaccessibility (0.47, 0.38, and 0.28, respectively), illustrating the limitations of the static in vitro methods for predicting the dynamic processes of the mammalian digestive system for this hydrophobic organic contaminant.

Simultaneous determination of organochlorine pesticides and bisphenol A in edible marine biota by GC-MS

A study to assess the level of organochlorine pesticides (OCPs) and bisphenol A (BPA) in edible marine biota collected from coastal waters of Malaysia was conducted using GC-MS and SPE extraction. An analytical method was developed and validated to measure the level of 15 OCPs and BPA simultaneously from five selected marine species. It was observed that some samples had low levels of p,p'-DDE, p,p'-DDT and p,p'- DDD ranging from 0.50 ng g(-1) to 22.49 ng g(-1) dry weight (d.w) but significantly elevated level of endosulfan I was detected in a stingray sample at 2880 ng g(-1) d.w. BPA was detected in 31 out of 57 samples with concentration ranging from below quantification level (LOQ: 3 ng g(-1)) to 729 ng g(-1) d.w. The presence of OCPs is most likely from past use although there is also indication of illegal use in recent times. The study also reveals that BPA is more widely distributed in coastal species caught off the coast of the most developed state. The potential health risk from dietary intakes of OCPs and BPA from the analysed fish species was negligible.

Assessment of exposure to DDT and metabolites after indoor residual spraying through the analysis of thatch material from rural African dwellings

INTRODUCTION

We report on the analysis of 4,4'-dichlorodiphenyltrichloroethane (4,4'-DDT) and its metabolites in thatch and branch samples constituting the wall materials of dwellings from South African subtropical areas. This approach was used to assess the exposure to DDT in the residents of the dwellings after indoor residual spraying (IRS) following recommended sanitation practices against malaria vectors.

DISCUSSION

Examination of the distributions of DDT compounds (2,4'-DDT, 4,4'-DDT and its metabolites) in 43 dwellings from the area of Manhiça (Mozambique) has shown median concentrations of 19, 130, and 23 ng/g for 2,4'-DDT, 4,4'-DDT, and 4,4'-DDE, respectively, in 2007 when IRS implementation was extensive. The concentrations of these compounds at the onset of the IRS campaign (n = 48) were 5.5, 47, and 2.2 ng/g, respectively. The differences were statistically significant and showed an increase in the concentration of this insecticide and its metabolites. Calculation of 4,4'-DDT in the indoor air resulting from the observed concentrations in the wall materials led to the characteristic values of environments polluted with this insecticide.

Dechlorination of p,p'-DDTs coupled with sulfate reduction by novel sulfate-reducing bacterium Clostridium sp. BXM

A novel non-dsrAB (without dissimilatory sulfite reductase genes) sulfate-reducing bacterium (SRB) Clostridium sp. BXM was isolated from a paddy soil. Incubation experiments were then performed to investigate the formation of reduced sulfur compounds (RSC) by Clostridium sp. BXM, and RSC-induced dechlorination of p,p'-DDT in culture medium and soil solution. The RSCs produced were 5.8 mM and 4.5 mM in 28 mM sulfate amended medium and soil solution respectively after 28-day cultivation. The p,p'-DDT dechlorination ratios were 74% and 45.8% for 5.8mM and 4.5 mM RSCs respectively at 6h. The metabolites of p,p'-DDT found in the two reaction systems were identified as p,p'-DDD and p,p'-DDE. The dechlorination pathways of p,p'-DDT to p,p'-DDD and p,p'-DDE were proposed, based on mass balance and dechlorination time-courses. The results indicated that RSC-induced natural dechlorination may play an important role in the fate of organochlorines.

Risk posed by chlorinated organic compounds in Abu Qir Bay, East Alexandria, Egypt

INTRODUCTION

In Egypt, the picture of threats to humans and the environment from the exposure to organic pollutants is still incomplete. Thus the objectives of this study were to assess the occurrence and distribution of polychlorinated biphenyls (PCBs), organochlorine pesticides, and chlorpyrifos in sediments and mussels of Abu Qir Bay and their risks for environment and human health.

MATERIALS AND METHODS

Twenty-three different compounds organochlorines were determined in 20 surfacial sediment and 10 mussel samples by gas chromatography-electron capture detector. A Screening Level Ecological Risk Assessment (SLERA) and a Human Health Risk Assessment (HHRA) were performed with the data.

RESULTS AND DISCUSSION

ΣDDT (DDT, DDE, DDD) (average concentration 27 µg/kg dw) dominated the detected organic pollutants in the sediments, followed by CHLs (chlordane, heptachlor, heptachloro epoxide), hexachlorocyclohexane, chlorpyrifos, endosulfane, dieldrine, Σ6 PCBs, aldrine, hexachlorobenzene, pentachlorobenzene, methoxychlor, and mirex. In general, concentrations of Σ6 PCBs in mussels were higher than their corresponding sediment concentrations reflecting their relatively high bioavailability and bioaccumulative potential. However, concentrations of the organochlorine pesticides in mussels were lower than their corresponding sediment samples. Nevertheless, the SLERA on the bay sediments revealed that adverse ecological effects to benthic species are expected to occur whereas the HHRA showed that adverse health effects are not expected to occur from the consumption of the mussels.

CONCLUSIONS

With the help of a SLERA, it was possible to indicate which class of chlorinated organic compounds is of highest concern to assess and to improve the environmental quality of the bay. Monitoring of organochlorines and chlorpyrifos would be needed to control the future trend of pollution.

Toxicity, dioxin-like activities, and endocrine effects of DDT metabolites--DDA, DDMU, DDMS, and DDCN

BACKGROUND, AIM, AND SCOPE

2,2-bis(chlorophenyl)-1,1,1-trichloroethane (DDT) metabolites, other than those routinely measured [i.e., 2,2-bis(chlorophenyl)-1,1-dichloroethylene (DDE) and 2,2-bis(chlorophenyl)-1,1-dichloroethane (DDD)], have recently been detected in elevated concentrations not only in the surface water of Teltow Canal, Berlin, but also in sediment samples from Elbe tributaries (e.g., Mulde and Havel/Spree). This was paralleled by recent reports that multiple other metabolites could emerge from the degradation of parent DDT by naturally occurring organisms or by interaction with some heavy metals. Nevertheless, only very few data on the biological activities of these metabolites are available to date. The objective of this communication is to evaluate, for the first time, the cytotoxicity, dioxin-like activity, and estrogenicity of the least-studied DDT metabolites.

METHODS

Four DDT metabolites, p,p'-2,2-bis(chlorophenyl)-1-chloroethylene (DDMU), p,p'-2,2-bis(chlorophenyl)-1-chloroethane (DDMS), p,p'-2,2-bis(4-ch1oropheny1)acetonitrile (DDCN), and p,p'-2,2-bis(chlorophenyl)acetic acid (DDA), were selected based on their presence in environmental samples in Germany such as in sediments from the Mulde River and Teltow Canal. O,p'-DDT was used as reference in all assays. Cytotoxicity was measured by neutral red retention with the permanent cell line RTG-2 of rainbow trout (Oncorhynchus mykiss). Dioxin-like activity was determined using the 7-ethoxyresorufin-O-deetylase assay. The estrogenic potential was tested in a dot blot/RNAse protection-assay with primary hepatocytes from male rainbow trout (O. mykiss) and in a yeast estrogen screen (YES) assay.

RESULTS

All DDT metabolites tested revealed a clear dose-response relationship for cytotoxicity in RTG-2 cells, but no dioxin-like activities with RTL-W1 cells. The dot blot/RNAse protection-assay demonstrated that the highest non-toxic concentrations of these DDT metabolites (50 μM) had vitellogenin-induction potentials comparable to the positive control (1 nM 17β-estradiol). The estrogenic activities could be ranked as o,p'-DDT > p,p'-DDMS > p,p'-DDMU > p,p'-DDCN. In contrast, p,p'-DDA showed a moderate anti-estrogenic effect. In the YES assay, besides the reference o,p'-DDT, p,p'-DDMS and p,p'-DDMU displayed dose-dependent estrogenic potentials, whereas p,p'-DDCN and p,p'-DDA did not show any estrogenic potential.

DISCUSSION

The reference toxicant o,p'-DDT displayed a similar spectrum of estrogenic activities similar to 17β-estradiol, however, with a lower potency. Both p,p'-DDMS and p,p'-DDMU were also shown to have dose-dependent estrogenic potentials, which were much lower than the reference o,p'-DDT, in both the vitellogenin and YES bioassays. Interestingly, p,p'-DDA did not show estrogenic activity but rather displayed a tendency towards anti-estrogenic activity by inhibiting the estrogenic effect of 17β-estradiol. The results also showed that the p,p'-metabolites DDMU, DDMS, DDCN, and DDA do not show any dioxin-like activities in RTL-W1 cells, thus resembling the major DDT metabolites DDD and DDE.

CONCLUSIONS

All the DDT metabolites tested did not exhibit dioxin-like activities in RTL-W1 cells, but show cytotoxic and estrogenic activities. Based on the results of the in vitro assays used in our study and on the reported concentrations of DDT metabolites in contaminated sediments, such substances could, in the future, pose interference with the normal reproductive and endocrine functions in various organisms exposed to these chemicals. Consequently, there is an urgent need to examine more comprehensively the risk of environmental concentrations of the investigated DDT metabolites using in vivo studies. However, this should be paralleled also by periodic evaluation and monitoring of the current levels of the DDT metabolites in environmental matrices.

RECOMMENDATIONS AND PERSPECTIVES

Our results clearly point out the need to integrate the potential ecotoxicological risks associated with the "neglected" p,p'-DDT metabolites. For instance, these DDT metabolites should be integrated into sediment risk assessment initiatives in contaminated areas. One major challenge would be the identification of baseline data for such risk assessment. Further studies are also warranted to determine possible additive, synergistic, or antagonistic effects that may interfere with the fundamental cytotoxicity and endocrine activities of these metabolites. For a more conclusive assessment of the spectrum of DDT metabolites, additional bioassays are needed to identify potential anti-estrogenic, androgenic, and/or anti-androgenic effects.

Topsoil dichlorodiphenyltrichloroethane and polychlorinated biphenyl concentrations and sources along an urban-rural gradient in the Yellow River Delta

The Yellow River Delta (YRD) is a typical agricultural and petrochemical industrial area of China. To assess the current status of soil dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCB) residues, topsoil samples (0-15 cm) (n = 82) were collected in Bincheng District, at the geographic center of the YRD. The total concentrations of six DDT homologues were within 3.3-3819 microg/kg, with a mean concentration of 191 microg/kg, showing significant increase along urban-rural gradient. Soil concentrations of seven indicator PCBs in the area ranged from non-detectable to 87.0 microg/kg, dominated by heavily chlorinated PCBs (PCB-101 and -118). Soil PCBs concentrations were significantly greater in urban than suburban and rural areas. Principal component and multiple linear regression analysis suggest that 86.4% of soil DDTs originate from past DDT usage, and 13.6% originate from dicofol application. Soil PCBs most likely originate from the petrochemical industry (77.1%), municipal solid waste disposal (16.5%), local commercial PCB homologues usage (5.2%), and long-range atmospheric deposition (1.2%). In general, soil DDTs pollution was classified as low level, and mean PCBs concentrations were below the severe contamination classification range. Because PCB-118 is a dioxin-like congener, monitoring and remediation is advised to assess and reduce negative environmental and human health effects from soil DDTs and dioxin-like congeners in the study area.

Study of DDT and its derivatives DDD, DDE adsorption and degradation over Fe-SBA-15 at low temperature

Mesoporous SBA-15 with different Fe2O3 loading were synthesized by an in-situ coating progress for removals of dichlorodiphenyltrichloroethane (DDT) and its derivatives, i.e., 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethane (DDD) and 1,1-dichloro-2,2-bis-(4-chloro -phenyl) ethane (DDE). The results from XRD (X-ray diffractometer), TEM (transmission electron microscopy) indicated that the iron could be well dispersed on SBA-15 within 6 wt.% Fe2O3 loading. Nitrogen adsorption-desorption tests indicated that the synthesized materials were characterized by ordered meso-structure, high surface area and large pore volume. DDTs were removed from aqueous media in 12-hr treatment and high removal efficiency of DDTs was achieved at over 94%. DDTs could be completely degraded at 350 degrees C under the existence of SBA-15 with 4 wt.% Fe2O3 loading. The final degradation products of DDT were dichlorobenzophenone (DCB) and bis-(4-chloro-phenyl) methane (DDM), suggesting a complete dechlorination from trichloromethyl.

Microemulsion-enhanced remediation of soils contaminated with organochlorine pesticides

Soil contaminated by organic pollutants, especially chlorinated aromatic compounds such as DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane), is an environmental concern because of the strong sorption of organochlorine pesticide onto the soil matrix and persistence in the environment. The remediation of organochlorine pesticide contaminated soils through microemulsion is an innovative technology to expedite this process. The remediation efficiency was evaluated by batch experiments through studying the desorption of DDT and hexachlorocyclohexane (y-HCH) and sorption of microemulsion composed of Triton X-100, 1-pentanol and linseed oil in the soil-surfactant-water suspension system. The reduction of desorption efficiency caused by the sorption loss of microemulsion components onto the soil could be corrected by the appropriate adjustment of C/S (Cosurfactant/Surfactant) and O/S (Oil/Surfactant) ratio. The C/S and O/S ratios of 1:2 and 3:20 were suitable to desorb DDT and gamma-HCH from the studied soils because of the lower sorption of Triton X-100 onto the soil. Inorganic salts added in microemulsion increased the pesticides desorption efficiency of pesticides and calcium chloride has a stronger ability to enhance the desorption of DDT than sodium chloride. From the remediation perspective, the balance of surfactant or cosurfactant sorbed to soil and desorption efficiency should be taken into consideration to enhance the remediation of soils contaminated by organochlorine pesticides.

The phytoremediation potential of bioenergy crop Ricinus communis for DDTs and cadmium co-contaminated soil

Cadmium (Cd) and dichlorodiphenyltrichloroethane (DDT) or its metabolite residues are frequently detected in agricultural soils and food, posing a threat to human health. The objective of this study was to compare the ability of 23 genotypes of Ricinus communis in mobilizing and uptake of Cd and DDTs (p,p'-DDT, o,p'-DDT, p,p'-DDD and p,p'-DDE) in the co-contaminated soil. The plant genotypes varied largely in the uptake and accumulation of DDTs and Cd, with mean concentrations of 0.37, 0.43 and 70.51 for DDTs, and 1.22, 2.27 and 37.63 mg kg(-1) dw for Cd in leaf, stem and root, respectively. The total uptake of DDTs and Cd varied from 83.1 to 267.8 and 66.0 to 155.1 μg per pot, respectively. These results indicate that R. communis has great potential for removing DDTs and Cd from contaminated soils attributed to its fast growth, high biomass, strong absorption and accumulation for both DDTs and Cd.

[Effect of surfactant on sorption behaviors of DDT on Jiaozhou Bay sediment]

A batch sorption study was carried out to investigate the sorption behaviors of DDT onto JiaoZhou Bay sediment in the presence of an anionic surfactant sodium dodecylbenzene sulfonate (SDBS), and a cationic surfactant, cetyltrimethylammonium bromide (CTAB) with low concentrations. The results indicated that the sorption process followed the pseudo-second-order model and the sorption systems could be well described by the Freundlich type. Within the investigated concentrations of CTAB and SDBS, both SDBS and CTAB increased the sorption of DDT to sediment. The sorption rate and capacity increased with increasing SDBS and CTAB concentrations, and CTAB showed a significant impact. Take p ,p'-DDT as an example, the sorption rate constant increased from 1.232 x 10(-2) g x (microg x min)(-1) to 4.193 x 10(-2) g x (microg x min)(-1) and the Freundlich coefficient increased from 2.866 (microg x g(-1)) (L x microg(-1))(1/n) to 7.932 (microg x g(-1)) (L x microg(-1))(1/n) when the SDBS concentration was 10 mg x L(-1). The influence of temperature on sorption of DDT in the presence of SDBS was also studied. Within the temperature range of 283-308 K, lower temperature had a positive effect on the sorption. The thermodynamic parameters showed that the sorption was spontaneous and exothermic, and the randomness was increased during the process. Furthermore, the presence of SDBS caused lower deltaG0, deltaH0 and deltaS0 values. This study provided theoretical foundation for migration, transformation and fate of DDT in Jiaozhou Bay sediment.

The sorption behavior of DDT onto sediment in the presence of surfactant cetyltrimethylammonium bromide

The sorption behavior of p,p'- and o,p'-dichlorodiphenyltrichloroethane (DDT) in the presence of a cationic surfactant cetyltrimethylammonium bromide (CTAB) on sediment was studied. Batch experiments were carried out to investigate the kinetics and thermodynamics of the process. The kinetic behavior of these three chemicals on sediment was described by pseudo-second-order kinetic equations, and the isotherms followed the Freundlich model well. The presence of CTAB was able to remarkably accelerate and enhance the sorption of DDT, whereas DDT showed no effect on the sorption of CTAB in our considered concentration ranges. The thermodynamic parameters, such as standard enthalpy change (ΔH0), standard entropy change (ΔS0) and standard Gibbs free energy change (ΔG0) showed that the sorption process of p,p'- and o,p'-DDT was physical, spontaneous and exothermic, and the randomness at the solid-liquid interface increased during the process. In the presence of CTAB, the sorption of DDT showed significantly negative ΔG0 and ΔH0 values.

[Accumulation and degradation of organochorine pesticides in shellfish culture environment in Xiamen sea area]

By using GC-ECD, the concentrations of organochlorine pesticides hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT) in the shellfish culture environment (sea water, sediments, and culture-shellfishes) in Xiamen sea area were analyzed, and the accumulation and degradation patterns of the HCH and DDT were preliminarily approached. In the sea area, there existed remarkable differences in the accumulation and degradation of HCH and DDT among different shellfish culture environments, being mostly associated with the habitation environment and physiological life habits of shellfish. The accumulated HCH isomers (Rx > 1) were mainly beta-HCH, delta-HCH, and gamma-HCH, whereas the degraded HCH isomers (Rx < 1) were mainly alpha-HCH. The ratio of alpha-HCH to gamma-HCH was less than or equal to 1.0, suggesting that the HCH was come from industrial HCH and lindane, most of the HCH had remained in the culture environment for a longer time, and a small amount of lindane was imported. The DDT in the sea water was aerobically degraded, its main degradation product was DDE, and the ratios of (DDD+DDE) to DDTs (p,p-DDE+p,p-DDD+o,p-DDT+p,p-DDT) was less than 0.5, whereas the DDT in sediments and shellfishes was anaerobically degraded, its main degradation product was DDD, and the ratios of (DDD+DDE) to DDTs was greater than 0.5, suggesting that there was a small amount of DDT newly imported in the sea water, and most DDT in sediments and shellfishes were already degraded and transformed into DDD and DDE. There were definite differences in the degradation rates of HCH isomers in the culture environment, suggesting the conformational change of HCH in its transformation processes in the shellfish culture ecosystem.

[Characteristics of organochlorine pesticide residues in agricultural soil of Chongming Island in Shanghai]

Thirty surface soil samples were collected to investigate the residue concentrations of organochlorine pesticides (OCPs) in agricultural soil of Chongming Island in July 2008. Those samples were extracted using accelerated solvent extraction (ASE) and determined by gas chromatography with an electron capture detector (GC-microECD). Results showed that the concentrations of OCPs (dry weight) ranged between 3.11-117.47 ng x g(-1), with mean value of 26.25 ng x g(-1). Two major contaminants of OCPs were DDTs and HCHs, the concentration of which varied from 0.14 ng x g(-1) to 77.89 ng x g(-1) and from 1.14 ng x g(-1) to 22.43 ng x g(-1), respectively. At the same times, hexachlorobenzene (0.23-11.63 ng x g(-1)), aldrin (0.03-0.75 ng x g(-1)), heptachlor epoxide (0.05-1.44 ng x g(-1)), dieldrin (0.05-5.33 ng x g(-1)), endrin (ND-14.66 ng x g(-1)) and mirex (0.03-10.58 ng x g(-1)) could also be detected. Most of DDTs had been degraded to DDD and DDE, with the major compounds of DDE (about 64.7%), and the recent existed DDT was the residue of early input. All of the four isomers of HCHs were detected, and the contents of alpha-HCH (about 48.1%) and beta-HCH (about 33.4%) were the maximum. The highest OCPs residues appeared in the soil of farm cultivation compared to greenhouse cultivation and ordinary open-air cultivation.

Curious about pesticide action

The safe and effective use of pesticides requires knowledge of their mode of action in pests and adverse effects in nontarget organisms coupled with an understanding of their metabolic activation and detoxification. The author and his laboratory colleagues were privileged to observe, participate in, and sometimes influence these developments for the past six decades. This review considers contributions of the Berkeley and Madison laboratories to understanding insecticides acting at voltage-gated sodium and GABA-gated chloride channels and the nicotinic receptor and at serine hydrolases and other targets as well as the action of insecticide synergists and selected herbicides and fungicides. Some of the discoveries gave new probes, radioligands, photoaffinity labeling reagents, and understanding of reactive intermediates that changed the course of pesticide investigations and related areas of science. The importance of coupling mode of action with metabolism and design with serendipity is illustrated with a wide variety of chemotypes.

Determination of n-octanol/water partition coefficient for DDT-related compounds by RP-HPLC with a novel dual-point retention time correction

n-Octanol/water partition coefficients (P) for DDTs and dicofol were determined by reversed-phase high performance liquid chromatography (RP-HPLC) on a C(18) column using methanol-water mixture as mobile phase. A dual-point retention time correction (DP-RTC) was proposed to rectify chromatographic retention time (t(R)) shift resulted from stationary phase aging. Based on this correction, the relationship between logP and logk(w), the logarithm of the retention factor extrapolated to pure water, was investigated for a set of 12 benzene homologues and DDT-related compounds with reliable experimental P as model compounds. A linear regression logP=(1.10±0.04) logk(w) - (0.60±0.17) was established with correlation coefficient R(2) of 0.988, cross-validated correlation coefficient R(cv)(2) of 0.983 and standard deviation (SD) of 0.156. This model was further validated using four verification compounds, naphthalene, biphenyl, 2,2-bis(4-chlorophenyl)-1,1-dichloroethane (p,p'-DDD) and 2,2-bis(4-chlorophenyl)-1,1-dichloroethene (p,p'-DDE) with similar structure to DDT. The RP-HPLC-determined P values showed good consistency with shake-flask (SFM) or slow-stirring (SSM) results, especially for highly hydrophobic compounds with logP in the range of 4-7. Then, the P values for five DDT-related compounds, 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1,1-trichloroethane (o,p'-DDT), 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1-dichloroethane (o,p'-DDD), 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1-dichloroethene (o,p'-DDE), and 2,2,2-trichloro-1,1-bis(4-chlorophenyl)ethanol (dicofol) and its main degradation product 4,4'-dichlorobenzophenone (p,p'-DBP) were evaluated by the improved RP-HPLC method for the first time. The excellent precision with SD less than 0.03 proved that the novel DP-RTC protocol can significantly increases the determination accuracy and reliability of P by RP-HPLC.