DDT-contaminated Soil Research Articles

Olivibacter jilunii sp. nov., isolated from DDT-contaminated soil

Bacterial strain 14-2A(T), isolated from a long-term DDT-contaminated soil in China, was characterized by using a polyphasic approach to clarify its taxonomic position. Strain 14-2A(T) was found to be Gram-negative, aerobic, non-spore-forming, non-motile, non-flagellated and rod-shaped. The new isolate was able to grow at 4-42 °C, pH 6.0-9.0 and with 0-5 % NaCl. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the isolate belongs to the family Sphingobacteriaceae. The 16S rRNA gene sequence of strain 14-2A(T) showed the highest similarity with Olivibacter oleidegradans TBF2/20.2(T) (99.4 %), followed by Pseudosphingobacterium domesticum DC-186(T) (93.8 %), Olivibacter ginsengisoli Gsoil 060(T) (93.6 %), Olivibacter terrae Jip13(T) (93.1 %), Olivibacter soli Gsoil 034(T) (92.8 %) and Olivibacter sitiensis AW-6(T) (89.6 %). The DNA-DNA hybridization value between strains 14-2A(T) and O. oleidegradans TBF2/20.2(T) was 34.45±2.11 %. Strain 14-2A(T) contained phosphatidylethanolamine, phosphatidylmonomethylethanolamine, aminophospholipid and phosphatidylinositol mannoside as the major polar lipids. The DNA G+C content was 41.2 mol%. MK-7 is the major isoprenoid quinone. Summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), iso-C15 : 0 and iso-C17 : 0 3-OH are the major fatty acids. The phenotypic and chemotaxonomic data confirmed the affiliation of strain 14-2A(T) to the genus Olivibacter. On the basis of the phylogenetic and phenotypic characteristics, and chemotaxonomic data, strain 14-2A(T) is considered to represent a novel species of the genus Olivibacter, for which the name Olivibacter jilunii sp. nov. is proposed; the type strain is 14-2A(T) ( = KCTC 23098(T) = CCTCC AB 2010105(T)).

Studies on Remediation of DDT-Contaminated Soil and Dechlorination of DDT

A practical and efficient disposal method for 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)-contained soil is reported. The treatment process was a combination technique: first to extract DDT in the soil, and then to hydrogenate the extract containing DDT. 4, 4'-DDT was effectively extracted in the soil and hydrodechlorinated in this treatment process. Additionally, solvent media and extracting time for DDT removal were investigated. An efficient heterogeneous catalytic method was also developed by comparing the rates of dechlorination of DDT over two different catalysts in organic-aqueous heterogeneous system. Compared to Raney Ni, Pd/C is a more efficient catalyst in disposing DDT. (C) 2012 Selection and/or peer-review under responsibility of Basel Convention Coordinating Centre for Asia and the Pacific and National Center of Solid Waste Management, Ministry of Environmental Protection of China.

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.

Pseudoxanthomonas jiangsuensis sp. Nov., a DDT-Degrading Bacterium Isolated from a Long-Term DDT-Polluted Soil

A Gram-negative, strictly aerobic, rod-shaped bacterium, designated strain wax(T), was isolated from DDT-contaminated soil in Yangzhou, China. Growth of strain wax(T) was observed at 10-45°C (optimum 30°C) and pH 5.0-10.0 (optimum pH 7.0-8.0). The predominant fatty acids were iso C(15:0) (32.21%) and anteiso C(15:0) (22.2%). The strain contained large amounts of the polar lipids diphosphatidylglycerol, phosphatidylethanolamine, and phosphatidylglycerol, but small amounts of an unknown amino-group-containing polar lipid and phospholipids were also present. The major quinone was ubiquinone-8 (Q-8) and the G + C content of the genomic DNA was 67.12 ± 0.8 mol.%. The phylogenetic tree shows that strain wax(T) clustered within the genus Pseudoxanthomonas. Isolate wax(T) showed moderate 16S rRNA gene sequence similarities to Pseudoxanthomonas broegbernensis B1616/1(T) (98.3%), P. suwonensis 4M1(T) (98.2%), P. daejeonensis TR6-08(T) (98%), P. koreensis TR7-09(T) (97.7%), P. kaohsiungensis J36(T) (97.5%), P. mexicana AMX 26B(T) (97.2%), and P. japonensis 12-3(T) (97%). The level of DNA-DNA relatedness between strain wax(T) and Pseudoxanthomonas type strains were low, e.g., P. koreensis TR7-09(T) (25.9%), P. broegbernensis B1616/1(T) (36.4%), P. suwonensis 4M1(T) (27.7%), P. daejeonensis TR6-08(T) (40%), P. kaohsiungensis J36(T) (20.4%), P. mexicana AMX 26B(T) (29.0%), P. japonensis 12-3(T) (33.3%). On the basis of the phenotypic, chemotaxonomic data and molecular properties, strain wax(T) represents a novel species within the genus Pseudoxanthomonas, for which the name Pseudoxanthomonas jiangsuensis sp. nov. is proposed. The type strain is wax(T) (=DSM 22398(T) = CGMCC 1.10137(T)).

Remediation of DDT‐contaminated soil using optimized mixtures of surfactants and a mixing system

AbstractSoil contaminated with persistent pesticides, such as DDT, poses a serious risk to humans and to wildlife. A surfactant‐aided soil‐washing technique was studied as an alternative method for remediation of DDT‐contaminated soil. An ex situ soil washing method was investigated using nonionic and anionic surfactants due to the clayey structure of the contaminated soil. A mixture of 1 percent nonionic surfactant (Brij 35) and 1 percent anionic surfactant (SDBS) removed more than 50 percent of DDT from soil in a flow‐through system, whereas individual surfactants or other combinations of the surfactants had a lower removal efficiency. The soil‐washing technique was improved using a mixing system. The mixture of surfactants was optimized in the mixing system, and the combination of 2 percent Brij 35 and 0.1 percent SDBS was found to be optimum, removing 70 to 80 percent of DDT. Prewashing of the soil with tap water decreased the adsorption of surfactants to soil particles by 30 to 40 percent, and postwashing recovered 90 percent of the surfactants. © 2010 Wiley Periodicals, Inc.

Co-metabolism of DDT by the newly isolated bacterium, Pseudoxanthomonas sp. wax

Microbial degradation of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) is the most promising way to clean up DDT residues found in the environment. In this paper, a bacterium designated as wax, which was capable of co-metabolizing DDT with other carbon sources, was isolated from a long-term DDT-contaminated soil sample by an enrichment culture technique. The new isolate was identified as a member of the Pseudoxanthomonas sp., based on its morphological, physiological and biochemical properties, as well as by 16S rRNA gene analysis. In the presence of 100 mg l-1 glucose, the wax strain could degrade over 95% of the total DDT, at a concentration of 20 mg l-1, in 72 hours, and could degrade over 60% of the total DDT, at a concentration of 100 mg l-1, in 144 hours. The wax strain had the highest degradation efficiency among all of the documented DDT-degrading bacteria. The wax strain could efficiently degrade DDT at temperatures ranging from 20 to 37ºC, and with initial pH values ranging from 7 to 9. The bacterium could also simultaneously co-metabolize 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD), 2,2-bis(p-chlorophenyl)-1,1-dichlorethylene (DDE), and other organochlorine compounds. The wax strain could also completely remove 20 mg kg-1 of DDT from both sterile and non-sterile soils in 20 days. This study demonstrates the significant potential use of Pseudoxanthomonas sp. wax for the bioremediation of DDT in the environment.

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.

Application of mushroom waste medium from Pleurotus ostreatus for bioremediation of DDT-contaminated soil

The ability of spent mushroom waste (SMW) from Pleurotus ostreatus to degrade 1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane (DDT) was investigated. DDT was degraded by 48% during a 28 d incubation and 5.1% of the DDT was mineralized during a 56 d incubation by SMW from P. ostreatus. The degradation potential in artificial DDT-contaminated soil was also investigated. The SMW from P. ostreatus degraded the DDT by 40% and 80% during a 28 d incubation in sterilized (SL) and un-sterilized (USL) soils, respectively. [U- 14C]DDT was mineralized by 5.1% and 8.0% during a 56 d incubation in SL and USL soils, respectively. These results indicate that SMW from P. ostreatus is a medium which can be potentially used for bioremediation in DDT-contaminated environments.

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.

Co-metabolism of DDT by the newly isolated bacterium, Pseudoxanthomonas sp. wax.

Microbial degradation of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) is the most promising way to clean up DDT residues found in the environment. In this paper, a bacterium designated as wax, which was capable of co-metabolizing DDT with other carbon sources, was isolated from a long-term DDT-contaminated soil sample by an enrichment culture technique. The new isolate was identified as a member of the Pseudoxanthomonas sp., based on its morphological, physiological and biochemical properties, as well as by 16S rRNA gene analysis. In the presence of 100 mg l-1 glucose, the wax strain could degrade over 95% of the total DDT, at a concentration of 20 mg l-1, in 72 hours, and could degrade over 60% of the total DDT, at a concentration of 100 mg l-1, in 144 hours. The wax strain had the highest degradation efficiency among all of the documented DDT-degrading bacteria. The wax strain could efficiently degrade DDT at temperatures ranging from 20 to 37°C, and with initial pH values ranging from 7 to 9. The bacterium could also simultaneously co-metabolize 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD), 2,2-bis(p-chlorophenyl)-1,1-dichlorethylene (DDE), and other organochlorine compounds. The wax strain could also completely remove 20 mg kg-1 of DDT from both sterile and non-sterile soils in 20 days. This study demonstrates the significant potential use of Pseudoxanthomonas sp. wax for the bioremediation of DDT in the environment.

Biodegradation Kinetics of DDT in Soil under Different Environmental Conditions by Laccase Extract from White Rot Fungi

Biodegradation of 2,2-bis( p-chlorophenyl)-1,1,1-trichloroethane (DDT) in soil by laccase extract from white rot fungi under different experimental conditions was investigated. DDTs, which stands for the sum of p,p′-DDE, o,p′-DDT, p,p′-DDD and p,p′-DDT in soil was degraded efficiently, and the residue decreased rapidly during the first 15 days and then slowly during the period of 16-25 days. The biodegradation of DDTs in soil fitted the pseudo-first-order kinetics. For 5, 10, 15 and 25 days of incubation with laccase, the residue of DDTs in soil under different atmospheres was decreased by 20%-33%, 34%-52%, 41%-61% and 41%-69% respectively, under different flooding conditions that was decreased by 12%-17%, 17%-30%, 30%-45% and 35%-52% respectively, and for different soils that was decreased by 25%-34%, 39%-53%, 44%-58% and 47%-62% respectively. The half-life of DDTs in soil ranged from 15.07 to 32.95 days under O 2, air or N 2 atmospheres, 23.07 to 40.71 days under different flooding conditions, and 18.78 to 28.88 days for different soils. Laccase is an efficient and safe agent for bioremediation of DDT-contaminated soil.

Remediation of DDT-Contaminated Water and Soil by Using Pretreated Iron Byproducts from the Automotive Industry

The objective of this study was to quantify the effectiveness of different pretreated iron byproducts from the automotive industry to degrade DDT [(1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane] in aqueous solutions and soil slurry. Iron byproducts from automotive manufacturing were pretreated by three different methods (heating, solvent and 0.5N HCl acid washing) prior to experimentation. All pretreated irons were used at 5% (wt v− 1) to treat 0.014 mM (5 mgL− 1) of DDT in aqueous solution. Among the pretreated irons, acid pretreated iron results in the fastest destruction rates, with a pseudo first-order degradation rate of 0.364 d− 1. By lowering the pH of the DDT aqueous solution from 9 to 3, destruction kinetic rates increase more than 20%. In addition, when DDT-contaminated soil slurry (3.54 mg kg− 1) was incubated with 5% (wt v− 1) acid-pretreated iron, more than 90% destruction of DDT was observed within 8 weeks. Moreover, DDT destruction kinetics were enhanced when Fe(II), Fe(III) or Al(III) sulfate salts were added to the soil slurry, with the following order of destruction kinetics: Al(III) sulfate > Fe(III) sulfate > Fe(II) sulfate. These results provide proof-of concept that inexpensive iron byproducts of the automotive industry can be used to remediate DDT-contaminated water and soil.

Abandoned Mid-Canada Radar Line sites in the Western James region of Northern Ontario, Canada: A source of organochlorines for First Nations people?

The potential exists for human exposure to polychlorinated biphenyls (PCBs) and other contaminants originating from abandoned Mid-Canada Radar Line (MCRL) sites in sub-arctic Canada. We examined patterns of differences with respect to body burden of organochlorines (lipid-adjusted) between residents of the Ontario First Nations of Fort Albany (the site of MCRL Site 050) and Kashechewan (no radar base) and Hamilton (an industrial, southern Ontario community) to assess whether the presence of Site 050 influenced organochlorine body burden with respect to the people of Fort Albany. PCBs (Aroclor 1260 and ∑14 PCBs congeners [CBs]) and DDE in the plasma of Fort Albany and Kashechewan subjects were elevated relative to Hamilton participants. PCB and DDE-plasma levels in First Nation women were of comparable magnitude to those reported for Inuit women living in the west/central Northwest Territories. Significantly lower DDE/DDT ratios observed for Fort Albany indicates exposure to higher levels of DDT compared to Kashechewan. The probable source of DDT exposure for Fort Albany people is the DDT-contaminated soil surrounding buildings of Site 050.The results of the correspondence analysis (CA) indicated that people from Hamilton had relatively higher pesticides and lower CB body burdens, while people from Fort Albany and Kashechewan exhibited relatively higher CBs and lower pesticide levels (CA-1). The separation of Fort Albany and Kashechewan from Hamilton was also clear using questionnaire data (i.e., plotting dietary principal component [PC]-1 scores against PC-2); PC-1 was correlated with the consumption of a traditional diet. Separation of Kashechewan and Albany residents occurred because the people of Kashechewan ate more traditional meats and consumed shorebirds. Only one significant relationship was found between PC analysis and contaminant loadings; PC-1 versus CA-3 for Kashechewan.The presence of Site 050 on Anderson Island appears to have influenced organochlorine body burden of the people of Fort Albany. ANCOVA results revealed that it was not activity on Anderson Island that was important, but activity on Site 050 was the influential variable. When these results are considered with the DDE/DDT ratio data and the CB 187 results (Fort Albany and Kashechewan residents differed significantly), the findings are suggestive that Site 050 did influence organochlorine body burden of people from Fort Albany.

DDT Resistance and Transformation by Different Microbial Strains Isolated from DDT-Contaminated Soils and Compost Materials

Bioremediation is a potential option to treat 1, 1, 1-trichloro-2, 2-bis (4-chlorophenyl) ethane (DDT) contaminated sites. In areas where suitable microbes are not present, the use of DDT resistant microbial inoculants may be necessary. It is vital that such inoculants do not produce recalcitrant breakdown products e.g. 1, 1-dichloro-2, 2-bis (4-chlorophenyl) ethylene (DDE). Therefore, this work aimed to screen DDT-contaminated soil and compost materials for the presence of DDT-resistant microbes for use as potential inoculants. Four compost amended soils, contaminated with different concentrations of DDT, were used to isolate DDT-resistant microbes in media containing 150 mg l−1 DDT at three temperatures (25, 37 and 55°C). In all soils, bacteria were more sensitive to DDT than actinomycetes and fungi. Bacteria isolated at 55°C from any source were the most DDT sensitive. However DDT-resistant bacterial strains showed more promise in degrading DDT than isolated fungal strains, as 1, 1-dichloro 2, 2-bis (4-chlorophenyl) ethane (DDD) was a major bacterial transformation product, while fungi tended to produce more DDE. Further studies on selected bacterial isolates found that the most promising bacterial strain (Bacillus sp. BHD-4) could remove 51% of DDT from liquid culture after 7 days growth. Of the amount transformed, 6% was found as DDD and 3% as DDE suggesting that further transformation of DDT and its metabolites occurred.

Remediation of Persistent Organic Pollutants Using a Novel Two-Phase Soil Washing Biosorption Process

A two-phase soil washing biosorption process was developed for the remediation of p,p′-DDT-contaminated soil. The process involved desorption of contaminants from soil using dilute primary alcohols (40% 1-propanol) followed by contaminant removal from cosolvent solutions using fungal biosorption. Bench scale remediation studies were preformed to simulate ex situ (recycling experiment) or in situ (soil column study) treatment strategies. Both systems were effective at cleaning the soil to below Australian regulatory p,p′-DDT levels. After 50–80 hours of soil washing, over 93% of p,p′-DDT was removed from the soil(990 mg kg-1 to <65 mg kg-1) using either of these methods.p,p′-DDT was removed from the cosolvent phase by sorption onto the fungal biomass. This resulted in only low levels of p,p′-DDT remaining in the cosolvent solution(<1.5 mg l-1). The application of both treatment strategies resulted in the rapid clean up of p,p′-DDT-contaminated soil and the potential to recycle cosolvent solutions. The ability to recycle cosolvent solutions provides a mechanism for cost reductions of the remediation strategy.

Development of a Two-Phase Cosolvent Washing-Fungal Biosorption Process for the Remediation of DDT-Contaminated Soil

A bench scale, two-phase soil washing-biosorption process was developed for the remediation of p,p′-DDT-contaminated soil (containing 990 and 7750 mg kg-1 of p,p′-DDT). Removal of p,p′-DDT from contaminated soil was achieved by washing the soil with low molecular weight primary alcohols (ethanol or 1-propanol). An improved efficiency of p,p′-DDT removal was observed with increasing C-chain length of the cosolvent and by increasing the cosolvent volume fraction. When 40 or 80% 1-propanol were used, greater than 93% of p,p′-DDT was desorbed from the respective soils. p,p′-DDT was partitioned from the cosolvent solutions using biomass of Cladosporium sp. strain AJR318,501 as the sorptivematrix. When studies were conducted using a cosolvent-recycling regime (with 80% 1-propanol) greater than 95% of p,p′-DDT was removed from Soil A (990 mg kg-1p,p′-DDT) and Soil B (7750 mg kg-1p,p′-DDT) with the majority of the desorbed organochlorine repartitioning onto the fungal biomass. Less than 2.4 μg mL-1p,p′-DDT was detected in the cosolvent wash solution of Soil A after 80 hr: potentially the cosolvent could be further reused to treat other soil. A higher concentration of p,p′-DDT was detected in the cosolvent wash solution of soil B after 120 hr (13.3 μg mL-1) indicating that the p,p′-DDT sorption sites on the fungal biomass were fully saturated.

In situ Remediation of DDT-contaminated Soil Using a Two-Phase Cosolvent Flushing-Fungal Biosorption Process

The effectiveness of cosolvent soil flushing and fungal biosorption for the remediation of p,p′-DDT-contaminated soil was evaluated usingpacked soil columns in order to simulate an in situ soil flushing technique. Greater than 95% of p,p′-DDT (940 mg kg-1) was desorbed from the soil by flushing with 40 or 80% 1-propanol. Increasing the cosolvent volume fraction increased the rate of p,p′-DDT removal from the soil, however, the extent of p,p′-DDT removal was not enhanced. A further enhancement in therate of p,p′-DDT removal was achieved by increasing the cosolventflow rate from 6 ml hr-1 to 12 ml hr-1 (pore water velocity from 18.9 to 37.8 cm hr-1). The desorbed p,p′-DDT was removed from cosolvent wash solutions by partitioning onto fungal biomass. Biosorption of p,p′-DDT resulted in low concentrations of the organochlorine (3.3 μg ml-1) remaining in thecosolvent effluent indicating that the cosolvent could be reused for further p,p′-DDT desorption. Using this technique, between 53 and 95 pore volumes were required to reduce p,p′-DDT concentrationsfrom 990 mg kg-1 to below Australian and New Zealand Environmentaland Conservation Council (ANZECC) guidelines (50 mg kg-1).

Aerobic degradation of dichlorodiphenyltrichloroethane (DDT) by Serratia marcescens DT-1P

Microbial degradation of 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)-residues is one of the mechanisms for the removal of this compound from the environment. A DDT-degrading consortium was isolated by long term enrichment of soil samples collected from DDT-contaminated fields. This consortium was acclimated by repeated passages through a mineral salt medium containing increasing concentrations of DDT. This acclimated consortium could degrade 25 ppm of DDT in 144 h. The consortium consisted of four bacteria. Of these, Serratia marcescens DT-1P was used for further studies. Various factors such as inoculum size, concentration of DDT, pH, temperature, presence of co-substrates, the type of carbon source used influenced the degradation of DDT in shake flasks. Complete degradation was observed up to 15 ppm DDT, followed by inhibitory effects at higher concentrations showing a total loss of degradative ability at 50 ppm DDT. Effective degradation of DDT was obtained with the inoculum pre-exposed to DDT for 72 h. Degradation was inhibited in the presence of auxiliary carbon sources such as citrate, rice straw hydrolysate. However, the presence of yeast extract, peptone, glycerol and tryptone soya broth (TSB) showed complete disappearance of DDT. Mesophilic temperatures (26–30 °C) and near neutral pH (6.0–8.0) were most favourable for degradation. This microbial culture holds the potential for use in bioremediation of DDT-contaminated soils, waste deposits and water bodies.

Bioremediation of DDT-Contaminated Soils: A Review

The insecticide 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)ethane (DDT) has been used extensively since the 1940s for control of agricultural pests, and is still used in many tropical countries for mosquito control. Despite a ban on DDT use in most industrialized countries since 1972, DDT and its related residues (DDTr) persist in the environment and pose animal and human health risks. Abiotic processes such as volatilization, adsorption, and photolysis contribute to the dissipation of DDTr in soils, often without substantial alteration of the chemical structure. In contrast, biodegradation has the potential to degrade DDTr significantly and reduce soil concentrations in a cost-effective manner. Many bacteria and some fungi transform DDT, forming products with varying recalcitrance to further degradation. DDT biodegradation is typically co-metabolic and includes dechlorination and ring cleavage mechanisms. Factors that influence DDTr biodegradation in soil include the composition and enzymatic activity of the soil microflora, DDTr bioavailability, the presence of soil organic matter as a co-metabolic substrate and (or) inducer, and prevailing soil conditions, including aeration, pH, and temperature. Understanding how these factors affect DDTr biodegradation permits rational design of treatments and amendments to stimulate biodegradation in soils. The DDTr-degrading organisms, processes and approaches that may be useful for bioremediation of DDTr-contaminated soils are discussed, including in situ amendments, ex situ bioreactors and sequential anaerobic and aerobic treatments.