Degradation Of DDT Research Articles

Determination of co-metabolism for 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT) degradation with enzymes from Trametes versicolor U97

Trametes versicolor U97 isolated from nature degraded 73% of the 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT) in a malt extract liquid medium after a 40-d incubation period. This paper presents a kinetic study of microbial growth using the Monod equation. T. versicolor U97 degraded DDT during an exponential growth phase, using glucose as a carbon source for growth. The growth of T. versicolor U97 was not affected by DDT. DDT was degraded by T. versicolor U97 only when the secondary metabolism coincided with the production of several enzymes. Furthermore, modeling of several inhibitors using the partial least squares function in Minitab 15, revealed lignin peroxidase (98.7 U/l) plays a role in the degradation of DDT. T. versicolor U97 produced several metabolites included a single-ring aromatic compound, 4-chlorobenzoic acid.

Study on the Isolation, Identification and Degradation Characterizaion of a DDT-Degrading Bacteria

A Gram positive bacterium strain 12-3 for degrading DDT effectively was isolated from the DDT contaminated site of the shipyard in Guangzhou by enrichment culture, which could utilize DDT as the sole carbon source for growth. This strain was identified as Pseudomonas species. Based on the phenotype, physiological and biochemical identification, and fatty acids identification. Testing theirs DDT degradation rate with HPLC, the results showed that in a shaky flask containing 20 mg/L DDT, this strain could degrade DDT with degradation efficiency of 51.6% in 8 days at 30°C, pH 8.0.

Elevated Concentrations of Pesticides and PCBs in Soils at the Southern Caspian Sea (Iran) are Related to Land Use

Soil contamination by organochlorine pesticides or PCBs is almost undocumented for Iran. Here we report a soil survey in Mazandaran and Guilan provinces that hold >30% of the agricultural areas of Iran where pesticide use is widespread. Concentration of DDTs, HCHs, cyclodienes, and PCBs were measured in 45 soil samples from different agricultural land uses and forest land. The average concentrations of ∑DDT (37 μg kg−1) and ∑HCH (21 μg kg−1) in agricultural soils are among the largest ever reported and exceed international soil screening standards. All residues were larger in agricultural than in forest soil. Within agricultural land, ∑DDT were largest for tea gardens, lindane was largest in rice fields, and cyclodiens largest in citrus orchards. The ratio of (DDD + DDE)/DDT is an index of the extent of DDT degradation in soil and was lower in tea gardens than in other soils (0.7 versus 2–5), indicating either ongoing DDT input or lower degradation rate in the tea gardens that are more acid than the other soils (pH 4.5 versus 6.5–7.0). The o,p′–DDT/p,p′–DDT ratio was about 3 in forest soils, suggesting that DDT is derived from dicofol application and not from technical DDT as in agricultural soils. The PCB 28, 180, and 138 showed the highest mean concentration compared with other PCB congeners in all land uses. This survey is the first of this kind for Iran and illustrates that concentrations of organochlorine pesticide in soil are relatively large.

Enhancement effect of two ecological earthworm species (Eisenia foetida and Amynthas robustus E. Perrier) on removal and degradation processes of soil DDT

Effects of two ecological earthworm species (epigeic Eisenia foetida and endogeic Amynthas robustus E. Perrier) with different densities (15 and 30 individuals per kg of soil) on the removal of soil 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) with two pollution levels (2 and 4 mg kg(-1)) were investigated. Concentrations of DDT and its metabolites, including 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (DDD), 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (DDE), and 1-chloro-2,2-bis(4-chlorophenyl)ethylene (DDMU), were monitored after 60, 180, and 360 days of incubation. The results obtained showed that both earthworm species can significantly enhance degradation of soil DDT to its metabolites. For E. foetida, the higher earthworm density showed significantly higher rate of DDT degradation than the lower one. Anaerobic reductive dechlorination was the main degradation pathway over 180 days of incubation, while the aerobic dechlorination process was promoted between 180 and 360 days of incubation. Some earthworm amended treatments showed significantly higher microbial biomass carbon and nitrogen than the control, which suggested that earthworms might enhance the microbial degradation of DDT. Both earthworm species would have the potential to be applied to enhance the remediation of agricultural lands polluted by DDT.

DDT-Contaminated Soil Treatment with Persulfate and Hydrogen Peroxide Utilizing Different Activation Aids and the Chemicals Combination with Biosurfactant

AbstractThe efficacy of DDT-contaminated soil treatment with hydrogen peroxide and persulfate utilizing different activation aids and the chemicals combination with biosurfactant was evaluated. The addition of a supplementary activator was able to improve the degradation of total DDT with both the hydrogen peroxide and persulfate oxidation processes indicating a lack of available activator. Ferrous iron added gradually was effectively utilized in the oxidation system with gradual addition of hydrogen peroxide, while chelated metal iron addition promoted the oxidation with more stable persulfate. The treatment with solid carriers of hydrogen peroxide, either calcium peroxide or magnesium peroxide, can be an effective alternative to the liquid one resulting in a higher degradation level of the contaminant. Strong alkalization with elevated dosages of NaOH sustained the persulfate oxidation of DDT. The addition of biosurfactant, rhamnolipid-alginate complex obtained by biosynthesis of strain Pseudomonas sp. PS-17, and EDTA improved the degradation of DDT by both persulfate and hydrogen peroxide oxidation processes indicating that the combined application of chemical oxidants and biosurfactant at natural soil pH has prospects as an effective option for contaminated soil remediation.

Steviaside Containing Plant as Deconstractive (Degradative) Agent for Persistent Organic Pollutants

Steviaside containing plant extracts have been used for degradation of persistent chloroorganic pesticides. Reactions between DDT and Steviaside or sum of extractive substances isolated from ground up part of plant Stevia were studied to give of less toxic DDE. Herein researches on studying interaction sum of polysaccharides of Stevia with DDT in various ratios resulted also. The GC-MS and GLC methods were used for analyzing degradation degree of pesticides and to determine obtained compounds. Treat HCCH by water extract of Stevia basically formed tetrachlorocyclo-hexadiene (HCH) with 86.9% yield and in particularly formed of tri-, tetrachlorobenzenes. The HCH formed in 79.7% on treat pesticide by 80% Steviaside. Degradation of HCCH and DDT by water extract of Stevia in a presence of Ana-basine in a ratio of 2:1:1 occur to degrade of HCCH up to 70-80%, and DDT on 25% - 30%.

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

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. 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. 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. 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. 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. 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.

Bioremediation of DDT contaminated soil using brown-rot fungi

The ability of brown-rot fungi (BRF) to eliminate DDT in artificially and historically contaminated soil was investigated to determine whether the BRF would be suitable for the bioremediation of DDT in soil. Gloeophyllum trabeum, Fomitopsis pinicola and Daedalea dickinsii showed an ability to eliminate DDT in artificially contaminated sterilized (SL) and un-sterilized (USL) soils. The addition of Fe 2+ to the soil system enhanced the ability of some BRF to eliminate DDT. In the contaminated SL soil, the DDT was eliminated by approximately 41%, 9% and 15% by G. trabeum, F. pinicola and D. dickinsii, respectively. Compared with the controls, in the USL soil approximately 43%, 29% and 32% of DDT was eliminated and approximately 20%, 9% and 26% of DDD (1,1-dichloro-2,2-bis (4-chlorophenyl) ethane) was detected as a metabolic product with G. trabeum, F. pinicola and D. dickinsii, respectively. Of the BRF, G. trabeum demonstrated the greatest ability to eliminate DDT both in the SL and USL soils. G. trabeum was applied to a historically contaminated soil which had a DDT concentration more than three times the artificially contaminated soil. G. trabeum remediated about 64% of the initial DDT with the addition of Fe 2+. There were no significant differences in the results with or without the addition of Fe 2+, indicating that G. trabeum can be used directly for the degradation of DDT in soil without any other additional treatment. This study identified that G. trabeum is the most promising BRF for use in the bioremediation of DDT contaminated soil.

Occurrence of selected organochlorine pesticide residues in surface sediments from the Velke Kozmalovce, Ruzin, and Zemplinska Sirava water reservoirs, Slovakia

Surface sediment samples from three water reservoirs of Slovakia were analyzed for selected organochlorine pesticides (OCPs). Concentrations of total dichlorodiphenyltrichloroethanes (ΣDDTs) in the sediments from Velke Kozmalovce, Ruzin, and Zemplinska Sirava ranged from 12 to 24 ng g-1, 5 to 28 ng g-1, and 1 to 20 ng g-1, respectively, with the exception of one sediment sample from Zemplinska Sirava, having anomalously high concentration of ΣDDTs (526 ng g-1). Concentrations of hexachlorobenzene (HCB) in the sediments from these water reservoirs were generally lower and ranged from 0.3 to 9 ng g-1. Other organochlorine pesticides such as mirex, lindane and heptachlor were not detected in the surface sediments. Ratios of DDT/(DDE + DDD) were lower than 1.0 in majority of the sediment samples indicating that the degradation of the parent DDT occurred significantly and DDT in the sediments from the studied water reservoirs was derived mainly from the weathered agricultural soils. Moreover, ratios of DDD/DDE indicated that the parent DDT was degraded under aerobic conditions before depositing into the sediments of these water reservoirs.

Fishpond sediment-borne DDTs and HCHs in the Pearl River Delta: Characteristics, environmental risk and fate following the use of the sediment as plant growth media

Investigation was made to characterize the fishpond sediment-borne DDTs and HCHs in a dyke-pond integrated agriculture–aquaculture system. Microcosm experiment was conducted to track the fate of DDTs and HCHs following the use of the sediment as plant growth media. The ratios of DDT/DDE+DDD, o,p′-DDT/p,p′-DDT and DDD/DDE were over 4, over 2 and nearly 2, respectively. These suggest that fresh DDT inputs from dicofol application are likely and anaerobic decomposition was the major pathway of DDT degradation. The sediments had higher percentage of δ-HCH and lower percentage of γ-HCH, compared to technical HCH. The levels of both DDTs and HCHs were higher in the sediments, as compared to those in the estuarine sediments and fishpond sediments in non-traditional dyke-pond system. The sediment-borne DDTs and HCHs posed an environmental threat to the local ecosystem. Upon its use as plant growth media, the majority of DDTs was retained in the soil while <1/3 of the original soil-borne DDTs were lost; no leaching loss was recorded and plant uptake was negligible. Only <20% of the original soil-borne HCHs were retained in the soil while leaching loss accounted for 1.24%; nearly 79% of the original soil-borne HCHs disappeared as a result of HCHs degradation and possibly volatilization.

Reductive Degradation of p,p′-DDT cy Fe(II) in Nontronite NAu-2

AbstractClay minerals are abundant in soils and sediments and often contain Fe. Some varieties, such as nontronites, contain as much as 40 wt.% Fe2O3 within their molecular structure. Several studies have shown that various Fe-reducing micro-organisms can use ferric iron in Fe-bearing clay minerals as their terminal electron acceptor, thereby reducing it to ferrous iron. Laboratory experiments have also demonstrated that chemically or bacterially reduced clays can promote the reductive degradation of various organics, including chlorinated pesticides and nitroaromatics. Therefore, Fe-bearing clays may play a crucial role in the natural attenuation of various redox-sensitive contaminants in soils and sediments. Although the organochlorinated pesticide p,p′-DDT is one of the most abundant and recalcitrant sources of contamination in many parts of the world, the impact of reduced Fe-bearing clays on its degradation has never been documented. The purpose of the present study was to evaluate the extent of degradation of p,p′-DDT during the bacterial reduction of Fe(III) in an Fe-rich clay. Microcosm experiments were conducted under anaerobic conditions using nontronite (sample NAu-2) spiked with p,p′-DDT and the metal-reducing bacteria Shewanella oneidensis MR-1. Similar experiments were conducted using a sand sample to better ascertain the true impact of the clay vs. the bacteria on the degradation of DDT. Samples were analyzed for DDT and degradation products after 0, 3, and 6 weeks of incubation at 30°C. Results revealed a progressive decrease in p,p′-DDT and increase in p,p′-DDD concentrations in the clay experiments compared to sand and abiotic controls, indicating that Fe-bearing clays may substantially contribute toward the reductive degradation of DDT in soils and sediments. These new findings further demonstrate the impact that clay materials can have on the natural attenuation of pollutants in natural and artificial systems and open new avenues for the passive treatment of contaminated land.

Effect of Aeromonas hydrophila on Reductive Dechlorination of DDTs by Zero-Valent Iron

This study presents a reductive transformation method that combines zerovalent iron (ZVI) and Aeromonas hydrophila HS01 with iron oxide reduction property to degrade DDT (1,1-trichloro-2,2-bis(4-chlorophenyl)ethane) under anoxic conditions. The results suggest that HS01 has weak capability in terms of reducing DDT to DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane) and nearly failed to reduce DDD or its transformed intermediates. The coexistence of ZVI and HS01 results in a slight enhancement of DDT degradation compared with the ZVI system alone. The reduction of intermediates by ZVI, however, can be obviously accelerated in the presence of HS01, and the addition of anthraquinone-2,6-disulfonic disodium salt (AQDS) can accelerate the transformation rates further, especially for intermediate reduction. The analysis of the amount and electrochemical properties of Fe(III)/Fe(II) indicates that the presence of HS01 with or without AQDS is beneficial to the reduction of Fe(III) to Fe(II), resulting in the removal of passivating ferric precipitates on the ZVI surface. A mechanism and pathway that clarify the roles of ZVI, HS01, and AQDS in the ZVI + HS01 + AQDS system for DDT transformation are proposed. The quick removal of surface ferric precipitates is thought to be the reason for the enhancement of the transformation of DDT and its intermediates.

Characterization of a bacterial strain capable of degrading DDT congeners and its use in bioremediation of contaminated soil

A bacterial strain DDT-6 (D6) capable of utilizing dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethane (DDD), and dichlorodiphenyldichloroethylene (DDE) (DDTs) as its sole carbon and energy source was isolated and identified as Sphingobacterium sp. The degradation of DDTs by strain D6 in mineral salt medium and in field soil was investigated. The half-lives of the degradation of DDTs increased with increasing concentration ranging from 1 to 50mgL−1. Favorable degradation conditions for DDTs by strain D6 were found to be pH 7.0 and 30°C. The degradation of DDTs by strain D6 was found to be statistically significantly enhanced (p≤0.05) by the addition of glucose. Based on the metabolites detected, a pathway was proposed for DDT degradation in which it undergoes dechlorination, hydrogenation, dioxygenation, decarboxylation, hydroxylation, and phenyl ring-cleavage reactions to complete the mineralization process. The addition of strain D6 into the contaminated soils was found to statistically significantly enhance (p≤0.05) the degradation of DDTs. The results indicate that the isolate D6 can be used successfully for the removal or detoxification of residues of DDTs in contaminated soil.

Involvement of Fenton reaction in DDT degradation by brown-rot fungi

In this study, the ability of the brown-rot fungi (BRF) Fomitopsis pinicola and Daedalea dickinsii to degrade DDT (1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane) was investigated. F. pinicola and D. dickinsii degraded approximately 63% and 47% of total DDT in potato dextrose broth (PDB) medium, respectively. Degradation of DDT by D. dickinsii resulted in several metabolic products; DDD (1,1-dichloro-2,2-bis (4-chlorophenyl) ethane), DDE (1,1-dichloro-2,2-bis (4-chlorophenyl) ethylene), and DDMU (1-chloro-2,2-bis (4-chlorophenyl) ethylene), whereas degradation by F. pinicola produced only one metabolic product, DDD. Investigation was done to find out whether the Fenton reaction was involved in the degradation process. More DDT was degraded in medium lacking FeSO 4 than in that containing FeSO 4, suggesting that these fungi lack the benzoquinone-driven Fenton reaction cycle system. In addition, F. pinicola and D. dickinsii produced only very low levels of hydroxyl radicals (1.2 and 5.1 μM, respectively), which provides further evidence that these fungi lack the Fenton reaction cycle system. The addition of mannitol as a hydroxyl radical scavenger did not inhibit DDT degradation. Hydroxyl radical production increased when the medium was supplemented with Fe 2+. Higher levels of hydroxyl radicals enhanced DDT degradation by D. dickinsii, but not by F. pinicola. These results indicate that F. pinicola and D. dickinsii have different mechanisms for degrading DDT from that reported for the BRF Gloeophyllum trabeum, in which the Fenton reaction is an important factor in DDT degradation.

Impact of iron concentration and ph on zero‐valent iron dechlorination of DDT for brownfields

AbstractSoil contamination with persistent pesticides such as dichloro‐diphenyl‐trichloroethane (DDT) is a major issue at many brownfield sites. A technology that can be used to treat DDT‐contaminated soil using surfactants is to enhance the migration of the contaminants from the soil phase to the liquid phase, followed by the dechlorinating of the mobilized DDT in the liquid phase using zero‐valent iron (ZVI). The DDT degradation using ZVI occurs under anaerobic conditions via reductive reactions. The effect of the iron concentration on the dechlorination rate is assessed in the range of 1 to 40 percent (weight to volume) for remediation of a DDT‐contaminated site in Ontario, Canada. The optimum percentage of iron is found to be 20 percent at which the dechlorination rates of DDT and 1,1‐dichloro‐2,2‐bis(p‐chlorophenyl)ethane (DDD) were 4.5 and 0.6 mg/L/day, respectively. While mixing of the reaction solution is shown to be important in providing the iron surface available for the dechlorination reaction throughout the reaction solution, there is no significant difference between batch and fed‐batch mode of adding iron to the dechlorination process. Low pH values (pH = 3) increased the dechlorination rates of DDT and DDD to 6.03 and 0.75 mg/L/day, respectively at a 20 percent iron concentration, indicating increased dechlorination rates in acidic conditions. © 2010 Wiley Periodicals, Inc.

DDT degradation potential of cattle manure compost

The purpose of this study was to investigate the ability of cattle manure compost (CMC) to degrade 1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane (DDT). DDT was degraded during composting and 1,1-dichloro-2,2-bis (4-chlorophenyl) ethane (DDD) was detected as a metabolic product. Degradation of DDT at 60 °C was the most effective of all the stages of composting. Fourteen strains of fungi were isolated and identified from CMC, and most of them were closely related to Mucor circinelloides and Galactomyces geotrichum. These fungi demonstrated a high ability to degrade DDT both at 30 and 60 °C in potato dextrose broth (PDB) medium. DDD and 4,4-dichlorobenzophenone (DBP) were detected as metabolic products. Degradation of DDT-contaminated soil was also investigated. Composting materials in the mesophilic stage exhibited the highest ability to degrade DDT in un-sterilized (USL) contaminated soil during a 28 d incubation period. The isolated fungi possessed the ability to degrade DDT in sterilized (SL) and un-sterilized (USL) soils. These results indicated that CMC contains fungi that can be potentially used for bioremediation in DDT-contaminated environments.

Effects of Soil Oxygen Conditions and Soil pH on Remediation of DDT-contaminated Soil by Laccase from White Rot Fungi

High residues of DDT in agricultural soils are of concern because they present serious threats to food security and human health. This article focuses on remediation of DDT-contaminated soil using laccase under different soil oxygen and soil pH conditions. The laboratory experiment results showed significant effects of soil oxygen conditions and soil pH on remediation of DDT-contaminated soil by laccase at the end of a 25-d incubation period. This study found the positive correlation between the concentration of oxygen in soil and the degradation of DDT by laccase. The residue of DDTs in soil under the atmosphere of oxygen decreased by 28.1% compared with the atmosphere of nitrogen at the end of the incubation with laccase. A similar pattern was observed in the remediation of DDT-contaminated soil by laccase under different flooding conditions, the higher the concentrations of oxygen in soil, the lower the residues of four DDT components and DDTs in soils. The residue of DDTs in the nonflooding soil declined by 16.7% compared to the flooded soil at the end of the incubation. The residues of DDTs in soils treated with laccase were lower in the pH range 2.5–4.5.

Isolation and degradation ability of the DDT-degrading bacterial strain KK

A 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)-degrading bacterium was isolated from soil samples that had been enriched with DDT over a prolonged period of time; these samples were collected from the sewer sludge of a pesticide factory and from DDT-contaminated fields. This consortium was acclimated by repeated passage through a mineral salt medium containing increasing concentrations of DDT. We examined the effects of various factors such as the pH, temperature, concentration of DDT, and the presence of an additional carbon source on the degradation rate of DDT. Based on the analysis of the phenotype, physiological and biochemical characteristics, and 16S rDNA, the strain KK was identified to belong to the bacteria Alcaligenes. The results showed that at the end of 10 days, the rate of degradation of DDT by the strain KK was 66.5%. When the additional carbon source concentration, pH, concentration of DDT, and cultivation temperature is 0.5%, 6, 10 mg l−1, and 30°C, respectively, the biodegradation rate peaks. The results also suggested that (1) bacterial growth increases positively with an increase in the carbon source concentration; (2) the appropriate pH is between 8.0 and 10.0; and (3) the optimal temperature and DDT concentration are 30°C and 10 mg l−1, respectively.

An immobilized dehydrohalogenase based potentiometric biosensor for the detection of chlorinated pesticides

Among the organochlorine pesticides, DDT and HCH are the major cause for food and environmental contamination. To detect them effectively in water samples an immobilized dehydrohalogenase based potentiometric biosensor was developed. The chloride ion released as a result of dehalogenation by immobilized dehydrohalogenase during the degradation of DDT and HCH, respectively, was detected using an ion selective electrode. The voltage response had a direct linear relationship with the concentration of chloride (Cl−) released by DDT and HCH, respectively. The immobilization was advantageous in improving the enzyme property and could be used repeatedly without losing activity.

Organochlorine pesticides and polybrominated diphenyl ethers in irrigated soils of Beijing, China: Levels, inventory and fate

Limited information on the levels, inventory and fate of Organochlorine pesticides (OCPs) and Polybrominated diphenyl ethers (PBDEs) in the soils irrigated by sewage or wastewater is available. In this study, variation in concentrations, profiles and fate of OCPs and PBDEs were investigated using soil samples collected from a region irrigated by sewage, mixed water and clean water in the east of Beijing, China. No significant variation was observed among groups, except for penta-BDEs. The measured ΣOCPs and ΣPBDEs residues ranged from 6.4 to 171.2 ng g −1 (dw) and 501.9 to 3310.7 pg g −1 (dw), respectively. ΣDDTs and BDE-209 were the most abundant congeners accounting for about 76% of ΣOCPs and 93% of ΣPBDEs. Concentrations of hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethane (DDTs) and its major degradation products, and hexachlorobenzene (HCB) ranged from 1.2 to 11.4 ng g −1 (dw), 4.0 to 155.6 ng g −1 (dw) and 0.3 to 3.4 ng g −1 (dw), respectively. The major DDT degradation products were p, p′-DDT and p, p′-DDE. The major hexachlorocyclohexane (HCH) isomer in irrigated soils is β-HCH, reflecting its higher affinity to solids and resistance to degradation than other isomers. Both α-HCH/β-HCH and p, p′-DDT/ p, p′-DDE ratios were log-normally distributed and negatively correlated to log(ΣHCHs) and log(ΣDDTs), respectively, suggesting no significant recent application of OCPs. Individual BDE congeners, ΣPBDEs and ΣOCPs were significantly correlated with total organic carbon (TOC). Moreover, a good correlationship between ΣPBDEs and black carbon (BC) was obtained but not between ΣOCPs and BC. Sewage irrigation did not have obvious effect on their contaminant levels and inventory of OCPs and PBDEs.