Potential of different species for use in removal of DDT from the contaminated soils

Dichlorodiphenyltrichloroethane (DDT) and its main metabolites, p,p'-DDD and p,p'-DDE (DDTs in this study included DDT, DDD and DDE), are frequently detected in agricultural soils even though its usage in agriculture was banned in 1980s or earlier. In this study, eleven plants including eight maize (Zea mays) cultivars and three forage species (alfalfa, ryegrass and teosinte) widely cultivated in China were grown in the soils spiked with DDTs to investigate their potential for removal of DDT from the contaminated soils. The plants varied largely in their ability to accumulate and translocate DDTs, with the bioconcentration factor (BCF; DDT concentration ratio of the plant tissues to the soils) ranging from 0.014 to 0.25 and the translocation factor (TF; DDT concentration ratio of the shoots to the roots) varying from 0.35 (Zea mays cv Chaotian-23) to 0.76 (Zea mays spp. mexicana). The amount of DDT phytoextraction ranged from 3.89mug (ryegrass) to 27.0mug (teosinte) and accounted for <0.1% of the total initial DDTs spiked in the soils. After 70d, the removal rates reached 47.1-70.3% of the total initial DDTs spiked in the soils with plants while that was only 15.4% in the soils without plant. Moreover, the higher removal rates of DDTs occurred at the first 20d of experiment, and then the removal rate decreased with time. The highest amount of DDTs phytoextracted was observed in teosinte, followed by Zea mays spp. mexicana, but the highest removal rate of DDTs was found in maize (Zea mays cv Jinhai-6). Even though phytoextraction is not the main removal process for DDTs, the plant species especially Zea mays cv Jinhai-6 showed high potential for removing DDTs from the contaminated soils.     

Preliminary evidence that copper inhibits the degradation of DDT to DDE in pip and stonefruit orchard soils in the Auckland region,New Zealand

Orchards (n=13) were sampled as part of a larger survey investigating agrichemical residues (pesticides and trace elements) in cropping soils in the Auckland region, New Zealand. SigmaDDT concentrations in orchard soils ranged from <0.03 to 24.41 mg kg(-1). DDT (o,p'- and p,p'-) comprised at least 40% of the SigmaDDT residues in 67% of orchards in which DDT residues were detected. There was a highly significant negative correlation (-0.924, P<0.001) between copper concentration (21-490 mg kg-1) and the ratio of DDE:DDT (0.4-5.2) in pip and stonefruit orchard soils. In further investigations involving five pip and stone fruit orchard sites and one grazing paddock it was found that soil respiration and the ratio of soil microbial carbon to soil carbon (%Cmic/Org-C) in orchard soils decreased with increasing copper concentration. These findings are consistent with the conclusion that elevated soil copper concentrations in pip and stone fruit orchard soils in the Auckland region may have reduced the ability of the indigenous soil microbial community to degrade DDT to DDE     

DDT污染土壤的植物修复技术

本文报道用植草方法研究为DDT及其主要降解产物污染土壤的植物修复技术。在污染物的浓度为 0 .2 15mg/kg的土壤中 ,种植 10种草 3个月后DDT及其主要降解产物的总含量分别降低 19.6 %— 73.0 %。种植不同品种的草对土壤中污染物有不同的去除能力 ,其中以种植丹麦产的Taya草 (Per .ryegrass)与美国产的Titan草 (Tallfescue)为最强。用种植草的方法修复受DDT及其主要降解产物污染的土壤是一项可行的技术。在去除土壤中DDT的作用上 ,草的吸收是轻微的 ,只占原施药量的 0 .13%— 1.0 8% ,土壤中污染物消失的主要因素是土壤中生物降解作用的结果。     

Adsorption and absorption of dichlorodiphenyltrichloroethane (DDT) and metabolites (DDD and DDE) by rice roots

A three-step sequential extraction procedure was applied to measure the concentrations of dichlorodiphenyltrichloroethane (DDT) on rice root surface and in root tissues collected from two sites in Tianjin. Bulk and rhizosphere soils were also analyzed. The measured DDXs in the rhizosphere soils were significantly higher than those in the bulk soils. On average, p,p'-DDT, p,p'-DDD, and p,p'-DDE in the soil accounted for 38%, 47% and 15% of the total. For total DDXs, approximately one third remained on the outer surface of the roots. The partition of DDXs between rhizosphere soil and root surface depend on contaminant affinity to soil organic matter, soil organic matter content and root specific area. A case specific equation was developed to quantitatively describe the partition of DDXs between soil and root surface.     

Organochlorine pesticides in soil profiles from Tianjin, China

Soil cores were collected from soils at five sites in Tianjin area for the determination of hexachlorocyclohexane isomers (HCHs, including alpha-HCH, beta-HCH, gamma-HCH and delta-HCH), dichlorodiphenyltrichloroethane and metabolites (DDXs, including p,p'-DDT, p,p'-DDE and p,p'-DDD) and total organic carbon (TOC). The levels and vertical distributions of HCHs and DDXs are studied. Results show that the application of pesticides in the past years was the major contributor of HCHs and DDXs accumulation in the sampling areas. Significant positive correlations were seen between the residual and application amounts of HCHs and DDXs. Wastewater irrigation did not bring a significant contribution of HCHs or DDXs into the soils. HCHs and DDXs concentrations peak at the surface and decline in soil profile with depth, while fluctuations were observed in the plow layers of some cultivated soils caused by frequent cultivation activities and batch irrigation. Positive correlations were observed between the contents of TOC and HCHs and DDTs. Although the amounts of HCHs application in all sampling sites are larger than DDXs, at surface and near surface layers of most sampling sites, the concentrations of summation operatorHCHs are lower than summation operatorDDXs. The composition of DDXs in the applied pesticides and sampled soils indicates that there is no recent DDT input at the sample areas.     

Level and distribution of DDT in surface soils from Tianjin, China

One hundred and eighty eight surface soil samples were collected from the Tianjin area to study the contamination of DDT and its metabolites. Measurements were taken for p,p'-DDE, p,p'-DDD, p,p'-DDT, o,p'-DDE, o,p'-DDD and o,p'-DDT for all samples. The results indicated that p,p'-DDT and p,p'-DDE were the predominant contaminant compounds in the surface soil samples, with mean concentrations of 27.5 and 18.8 ng g(-1) respectively. No significant differences in DDT concentrations were found between the soils from wastewater treated irrigated areas and other areas, suggesting that wastewater irrigation is not an important source of DDT in the area. However, the spatial distribution of soil DDTs levels in the area did correlate well with early direct application rates of pesticides. In addition, both pH level and organic carbon content are also known factors affecting the level of DDT and its metabolites. Although it was assumed that the use of these chemicals was banned in the early 1980s, the current concentration levels appear to be too high to be mere residuals after 20 years degradation.     

Impact of repeated application on the binding and persistence of [14C]-DDT and [14C]-HCH in a tropical soil

An Indian sandy loam soil was initially treated with 1 kg a.i. ha(-1) of either [(14)C]-p,p'-DDT or [(14)C]-gamma-HCH during winter. DDT concentration after 30 days declined to 75.3%, which included 2.1% soil-bound residues. After 150 days, DDT levels further decreased to 42.4% with a concomitant increase in bound residues amounting to 5.9%. Identical treatment with HCH caused the residue levels to be reduced to 67.4 and 23.6%, after 30 and 150 days, respectively. During this period, the soil-bound residues of HCH increased from 5.2 to 12.8%. Repeat application to pre-treated soils in summer and subsequent field exposure for 30 days reduced the concentration of DDT to 52.1% and that of HCH to 42.4% of the total concentration following the second treatment. In parallel control experiments, which received only a single treatment, DDT levels declined to 61.3%, while HCH slumped to 45.3%, indicating a slower dissipation rate than in the corresponding repeated treatments. In repeat experiments, the soil-bound residues of DDT and HCH showed only a 1.07 to 1.08-fold increase in 30 days, as compared to three to ten-times increase in the control experiments. The results amply demonstrate that pre-treatment of tropical soils with DDT or HCH enhances their rate of dissipation and significantly reduce the formation of their soil-bound residues.     

Ectomycorrhizas impede phytoremediation of polycyclic aromatic hydrocarbons (PAHs) both within and beyond the rhizosphere

Exploitation of mycorrhizas to enhance phytoremediation of organic pollutants has received attention recently due to their positive effects on establishment of plants in polluted soils. Some evidence exist that ectomycorrhizas enhance the degradation of pollutants of low recalcitrance, while less easily degradable polyaromatic molecules have been degraded only by some of these fungi in vitro. Natural polyaromatic (humic) substances are degraded more slowly in soil where ectomycorrhizal fungi are present, thus phytoremediation of recalcitrant pollutants may not benefit from the presence of these fungi. Using a soil spiked with three polycyclic aromatic hydrocarbons (PAHs) and an industrially polluted soil (1 g kg(-1) of summation operator12 PAHs), we show that the ectomycorrhizal fungus Suillus bovinus, forming hydrophobic mycelium in soil that would easily enter into contact with hydrophobic pollutants, impedes rather than promotes PAH degradation. This result is likely to be a nutrient depletion effect caused by fungal scavenging of mineral nutrients.     

热解吸对土壤中POPs农药的去除及土壤理化性质的影响

为探索土壤热解吸修复技术对POPs污染土壤的修复效果及修复后土壤可耕作性,选择北京某农药厂旧址的POPs农药污染土壤,研究了不同温度下热解吸处理后土壤中滴滴涕(DDTs)和六六六(HCHs)各组分的去除率以及土壤理化性质的变化。结果表明,热解吸修复技术可有效去除土壤中POPs农药,其中,p,p’-DDE与α-HCH组分去除率受热解吸温度的影响比其他组分更为明显。∑HCH与∑DDT在310℃、340℃时分别达到97%、99%的去除率,且此时土壤中的污染物含量低于我国《展览会用地土壤环境质量评价标准》,此后去除率受温度的影响不明显。热解吸温度对修复后土壤的理化性质有一定的影响,不同温度影响的程度各不相同,其中,有机质含量与全氮含量分别由0.78%、0.0352%降至0.14%、0.0107%;pH波动幅度较小,由7.80变至8.25;阳离子交换量变化存在波动,但呈整体下降趋势,由7.87 mg/kg降至5.00mg/kg;土壤中速效磷显著增加,由7.59 mg/kg升至21.8 mg/kg。而在最优温度条件下,土壤理化性质受热解吸温度的影响较小。由此可以说明,热解吸技术可以用于POPs污染土壤的修复,选择适当的热解吸温度对土壤的可耕作性影响有限,因而是一种潜在的绿色修复技术。     

Effects of long-term contamination of DDT on soil microflora with special reference to soil algae and algal transformation of DDT

DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) and its principle metabolites, DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene) and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane) are widespread environmental contaminants but little information is available concerning their effects on non-target microflora (especially microalgae and cyanobacteria) and their activities in long-term contaminated soils. For this reason a long-term DDT-contaminated soil was screened for DDT residues and toxicity to microorganisms (bacteria, fungi, algae), microbial biomass and dehydrogenase activity. Also, five pure cultures isolated from various sites (two unicellular green algae and three dinitrogen-fixing cyanobacteria) were tested for their ability to metabolise DDT. Viable counts of bacteria and algae declined with increasing DDT contamination while fungal counts, microbial biomass and dehydrogenase activity increased in medium-level contaminated soil (27 mg DDT residues kg(-1) soil). All the tested parameters were greatly inhibited in high-level contaminated soil (34 mg DDT residues kg(-1) soil). Species composition of algae and cyanobacteria was altered in contaminated soils and sensitive species were eliminated in the medium and high contaminated soils suggesting that these organisms could be useful as bioindicators of pollution. Microbial biomass and dehydrogenase activity may not serve as good bioindicators of pollution since these parameters were potentially influenced by the increase in fungal (probably DDT resistant) counts. All the tested algal species metabolised DDT to DDE and DDD; however, transformation to DDD was more significant in the case of dinitrogen-fixing cyanobacteria.     

The effect of temperature and solar radiations on volatilisation, mineralisation and degradation of [14C]-DDT in soil

The influence of temperature and solar radiations on the rapid dissipation of DDT from tropical soils was studied by quantifying volatilisation, mineralisation, binding and degradation of ((14)C)-p,p'-DDT in a sandy loam soil. The bulk of the DDT loss occurred by volatilisation, which increased fivefold when the temperature changed from 15 to 45 degrees C. Degradation of DDT to DDE was also faster at higher temperatures. Mineralisation of DDT, though minimal, increased with temperature and time. Higher temperatures also enhanced binding of DDT to soil. Flooding the treated soil further increased volatilisation and degradation, although mineralisation was greatly reduced. Exposure of flooded and unflooded soils treated with DDT to sunlight in quartz, glass and dark tubes for 42 days during summer resulted in significant volatile losses. Volatilisation in the quartz tubes was nearly twice as great as that in the dark tubes The volatilised organics from the quartz tubes contained larger amounts of p,p'-DDE than the glass and dark tubes. Higher rates of volatilisation and degradation were found in flooded soils. Also significant quantities of p,p'-DDD were detected in addition to DDE. The data clearly show that volatilisation is the major mechanism for the rapid dissipation of DDT from Indian soils.     

Oxalate and root exudates enhance the desorption of p,p'-DDT from soils

The abiotic desorption of p,p'-DDT from seven Chinese soils spiked with p,p'-DDT and the effects of oxalate at 0.001-0.1M and the root exudates of maize, wheat, and ryegrass were evaluated using batch experiments. Soil organic carbon played a predominant role in the retention of DDT. Oxalate significantly increased the desorption of p,p'-DDT, with the largest increments ranging from 11% to 54% for different soils. Oxalate addition also resulted in the increased release of dissolved organic carbon and inorganic ions from soils. Root exudates had similar effects to those of oxalate. Root exudates significantly increased DDT desorption from the soils, and the general trend was similar among the plant species studied for all the soils (p > 0.05). Low molecular weight dissolved organic carbon amendments caused partial dissolution of the soil structure, such as the organo-mineral linkages, resulting in the release of organic carbon and metal ions and thus the subsequent enhanced desorption of DDT from the soils. The enhancing effects of oxalate and root exudates on DDT desorption were influenced by the contents of soil organic carbon and dissolved organic carbon in soils.     

Pesticide residues in Nile tilapia (Oreochromis niloticus) and Nile perch (Lates niloticus) from Southern Lake Victoria, Tanzania

Nile tilapia (Oreochromis niloticus) and Nile perch (Lates niloticus) samples were collected from fish landing stations in nine riparian districts on the Tanzanian side of Lake Victoria and screened for residues of 64 organochlorine, organophosphorus, carbamate, and pyrethroid pesticides. The residue levels in the fish fillet were up to 0.003, 0.03 and 0.2 mg/kg fresh weight (0.7, 3.8 and 42 mg/kg lipid weight) of fenitrothion, DDT and endosulfan, respectively. Mean levels within sites were up to 0.002, 0.02 and 0.1 mg/kg fresh weight (0.5, 0.5 and 16 mg/kg lipid weight), respectively. The detection of higher levels of p,p'-DDT than the degradation products (p,p'-DDD and p,p'-DDE), and higher levels of endosulfan isomers (alpha and beta) than the sulphate, in fish samples, implied recent exposure of fish to DDT and endosulfan, respectively. Generally, most of the fish samples had residue levels above the average method detection limits (MDLs), but were within the calculated ADI.     

Dissipation and leaching of (14)C-monocrotophos in Soil Columns under subtropical climate

Dissipation and leaching behavior of 14C-monocrotophos was studied for 365 days under field conditions using PVC cylinders. The first set (24 cylinders) was spiked with 1.0 microCi 14C-labeled monocrotophos along with 1.06 mg unlabeled monocrotophos to give a concentration of 2 mg kg -1 in the soil up to 15 cm depth. The second set (24 cylinders) received 14C-labeled monocrotophos along with other non-labeled insecticides viz., dimethoate @ 300 g a.i ha-1, deltamethrin @ 12.5 g a.i ha-1, endosulfan @ 750 g a.i ha-1, cypermethrin @ 60 g a.i ha-1, and triazophos @ 600 g a.i ha-1 at an interval of 15 days each as recommended for the cotton crop. 14C-monocrotophos dissipated faster, up to 45% in first 90 days in columns treated with only monocrotophos compared to 25% in columns that received monocrotophos along with other insecticides. However, both the columns showed similar residues 180 days onward. After 180 days of treatment, 46% radiolabeled residues were observed, which reduced up to 39.6% after 365 days. Leaching of 14C-monocrotophos to 15-30 cm soil layer was observed in both the experimental setups. In the 15-30 cm soil layer of both soil columns, up to 0.19 mg 14C-monocrotophos kg-1d. wt. soil was detected after 270 days.     

Degradation and sorption of imidacloprid in dissimilar surface and subsurface soils

Degradation and sorption/desorption are important processes affecting the leaching of pesticides through soil. This research characterized the degradation and sorption of imidacloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine) in Drummer (silty clay loam) and Exeter (sandy loam) surface soils and their corresponding subsurface soils using sequential extraction methods over 400 days. By the end of the incubation, approximately 55% of imidacloprid applied at a rate of 1.0 mg kg(-1) degraded in the Exeter sandy loam surface and subsurface soils, compared to 40% of applied imidacloprid within 300 days in Drummer surface and subsurface soils. At the 0.1 mg kg(-1) application rate, dissipation was slower for all four soils. Water-extractable imidacloprid in Exeter surface soil decreased from 98% of applied at day 1 to >70% of the imidacloprid remaining after 400 d, as compared to 55% in the Drummer surface soil at day 1 and 12% at day 400. These data suggest that imidacloprid was bioavailable to degrading soil microorganisms and sorption/desorption was not the limiting factor for biodegradation. In subsurface soils > 40% of (14)C-benzoic acid was mineralized over 21 days, demonstrating an active microbial community. In contrast, cumulative (14)CO(2) was less than 1.5% of applied (14)C-imidacloprid in all soils over 400 d. Qualitative differences in the microbial communities appear to limit the degradation of imidacloprid in the subsurface soils.     

Biodegradation of endosulfan by Mortieralla sp. strain W8 in soil: Influence of different substrates on biodegradation

To examine the bioremediation potential of Mortierella sp. strain W8 in endosulfan contaminated soil, the fungus was inoculated into sterilized and unsterilized soil spiked with endosulfan. Wheat bran and cane molasses were used as substrates to understand the influence of different organic materials on the degradation of endosulfan in soil. Strain W8 degraded α- and β-endosulfan in both sterilized and unsterilized soil. In unsterilized soil with wheat bran+W8, α- and β- endosulfan were degraded by approximately 80% and 50%, respectively after 28 d incubation against the initial endosulfan concentration (3 mg kg(-1) dw). The corresponding values for α- and β-endosulfan degradation with wheat bran only were 50% and 3%. Endosulfan diol metabolite was detected after 14 d incubation in wheat bran+W8 whereas it was not found with wheat bran only. Production of endosulfan sulfate, the main metabolite of endosulfan, was suppressed with wheat bran+W8 treatment compared with wheat bran only. It was demonstrated that wheat bran is a more suitable substrate for strain W8 than cane molasses. Wheat bran+W8 is a superior fungus and substrate mix for bioremediation in soil contaminated with endosulfan.     

Influence of arsenic co-contamination on DDT breakdown and microbial activity

The impacts of arsenic co-contamination on the natural breakdown of 1,1,l1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) in soil are investigated in a study of 12 former cattle dip sites located in northeastern NSW, Australia. This study examines the relationship between the intrinsic breakdown of DDT to 1,1 -dichloro-2,2-bis(4-chlorophenyl)ethane (DDD) and 1,l-dichloro-2,2-bis(4-chlorophenyl)ethylene (DDE), and the impacts of arsenic co-contamination on this breakdown. Between-site analysis demonstrated that arsenic at 2000 mg/kg gave a 50% reduction in the concentration of DDD compared to background arsenic of 5 mg/kg.Within-site analysis also showed the ratio of DDT:DDD increased in soils as arsenic concentrations increased. This within-site trend was also apparent with the DDT:DDE ratio, suggesting inhibition of DDT breakdown by arsenic co-contamination. Microbial activity was inhibited as residues of total DDTs and arsenic increased. Hence arsenic co-contamination and high concentrations of DDT in soil may result in an increased persistence of DDT in the environment studied.     

Removal of polycyclic aromatic hydrocarbons from manufactured gas plant-contaminated soils using sunflower oil: laboratory column experiments

Laboratory column experiments were performed to remove PAHs (polycyclic aromatic hydrocarbons) from two contaminated soils using sunflower oil. Two liters of sunflower oil was added to the top of the columns (33 cm x 21 cm) packed with 1 kg of PAH-contaminated soil. The sunflower oil was applied sequentially in two different ways, i.e. five additions of 400 ml or two additions of 1l. The influence of PAH concentration and the volume of sunflower oil on PAH removal were examined. A soil respiration experiment was carried out and organic carbon contents of the soils were measured to determine degradability of remaining sunflower oil in the soils. Results showed that the sunflower oil was effective in removing PAHs from the two soils, more PAHs were removed by adding sunflower oil in two steps than in five steps, probably because of the slower flow rate in the former method. More than 90% of total PAHs was removed from a heavily contaminated soil (with a total 13 PAH concentration of 4721 mg kg(-1)) using 4 l of sunflower oil. A similar removal efficiency was obtained for another contaminated soil (with a total 13 PAH concentration of 724 mg kg(-1)), while only 2l was needed to give a similar efficiency. Approximately 4-5% of the sunflower oil remained in the soils. Soil respiration curves showed that remaining sunflower oil was degraded by allowing air exchange and supplying with nutrients. Organic carbon content of the soil was restored to original level after 180 d incubation. These results indicated that the sunflower oil had a great capacity to remove PAHs from contaminated soils, and sunflower oil solubilization can be an alternative technique for remediation of PAH contaminated soils.     

The extractability and mineralisation of cypermethrin aged in four UK soils

Cypermethrin is a widely used insecticide that has caused concern due to its toxicity in the aquatic environment. As with all land applied pesticides, the most significant source of water pollution is from the soil, either due to leaching or washoff. The behaviour of cypermethrin in the soil controls the likelihood of future pollution incidents, with two of the most significant processes being the formation of bound residues and microbial degradation. The formation of bound residues and mineralisation was measured in four organically managed soils from the UK. The formation of bound residues was measured using three different extraction solutions, 0.01 M CaCl₂, 0.05 M HPCD and acetonitrile. Biodegradation was assessed by measurement of mineralisation of cypermethrin to CO₂. The formation of bound residues varied according to extraction method, soil type and length of ageing. In two of the four soils studied, acetonitrile extractability decreased from 100% initially to 12-14% following 100 d ageing. The extent of mineralisation increased after 10-21 d ageing, reaching 33% of remaining activity in one soil, however following 100 d ageing the extent of mineralisation was significantly reduced in three out of the four soils. As with the formation of bound residues, mineralisation was impacted by soil type and length of ageing.     

2,4-Dichlorophenoxyacetic acid (2,4-D) sorption and degradation dynamics in three agricultural soils

The fate and transport of 2,4-dichlorophenoxyacetic acid (2,4-D) in the subsurface is affected by a complex, time-dependent interplay between sorption and mineralization processes. 2,4-D is biodegradable in soils, while adsorption/desorption is influenced by both soil organic matter content and soil pH. In order to assess the dynamic interactions between sorption and mineralization, 2,4-D mineralization experiments were carried using three different soils (clay, loam and sand) assuming different contact times. Mineralization appeared to be the main process limiting 2,4-D availability, with each soil containing its own 2,4-D decomposers. For the clay and the loamy soils, 45 and 48% of the applied dose were mineralized after 10 days. By comparison, mineralization in the sandy soil proceeded initially much slower because of longer lag times. While 2,4-D residues immediately after application were readily available (>93% was extractable), the herbicide was present in a mostly unavailable state (<2% extractable) in all three soils after incubation for 60 days. We found that the total amount of bound residue decreased between 30 and 60 incubation days. Bioaccumulation may have led to reversible immobilization, with some residues later becoming more readily available again to extraction and/or mineralization.