Agricultural soil as a potential source of input of organochlorine pesticides into a nearby pond

A study was conducted in the southeastern region of Buenos Aires province, Argentina, to assess an agricultural soil as a potential source of organochlorine (OC) pesticides for the aquatic biota of a nearby pond. We analyzed gamma-HCH (lindane), still in use, and the following banned compounds: DDT, DDE, DDD heptachlor, heptachlor epoxide, aldrin, dieldrin and endrin in soil, bulrush, grass shrimp and fish using gas chromatography with electron capture detection (GC-ECD). Among the OC pesticides, lindane was most dominant in the soil (32.6 ng/g dry wt in the upper and 173.9 ng/g dry wt in the lower horizon) and bulrush (1.9 pg/g lipid). Macrophyte also accumulated high levels of heptachlor epoxide (1.5 pg/g lipid). Heptachlor, although present in the soil, was below the detection limit in all aquatic biota studied. Its primary degradation product, heptachlor epoxide, was found in both soil and biota samples. DDT was found at low levels in the surface soil (6.8 ng/g dry wt), but at higher concentrations in fish (3.6 pg/g lipid), although levels were still below permissible levels for human consumption. Since most of the compounds were found in both soil and aquatic biota, our study suggests that agricultural soil could be an important source for OC pesticides in the nearby pond.     

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     

Residues of organochlorine pesticides in Alabama soils

A survey was made of 36 Alabama agricultural soils to assess residues of formerly used organochlorine pesticides. Compounds determined comprised alpha- and gamma-hexachlorocyclohexane, heptachlor, heptachlor-exo-epoxide, trans- and cis-chlordane, trans-nonachlor, dieldrin, toxaphene, DDT and DDE. Concentrations varied by several orders of magnitude among farms and appeared to be log-normally distributed. Highest concentrations (ng g(-1) dry soil, arithmetic means) were found for toxaphene (285+/-390) and DDTs (p,p'-DDE, 22.7+/-21.4; p,p'-DDT, 24.6+/-30.5; o,p'-DDT, 4.00+/-5.86; p,p'-DDD, 2.40+/-2.41) which were once heavily used in the southern USA. Pesticide residues were not proportional to soil organic carbon content indicating that residue concentrations were a reflection of pesticide application history and dissipation rates rather than air-soil equilibrium. Mean ratios of DDT/DDE in six regions of the state ranged from 0.39 to 1.5, and compound ratios for chlordanes and toxaphene were different from those in the technical mixtures.     

A column test for leaching of organochlorines from soil by amphiphilic nonionic nanopolymers

Amphiphilic nonionic cross-linked nanopolymers (NPs) were synthesized to examine removal of five organochlorines (OCs), namely lindane, heptachlor, aldrin, dieldrin, endrin, and DDT, from a range of Thai agricultural soils. The synthesized NP particles had polarity characteristics similar to those of nonionic surfactant micelles and were largely in the size range of 55-155 nm. This work aimed to determine the optimal conditions for leaching of OC contaminated soil with NPs and also to investigate the role and influence of soil properties on this leaching. An investigation of the concentrations of aqueous dispersions of these particles found that a concentration of 10 g L(-1). was found most effective in leaching the OCs from a column of spiked soil. The optimal contact time that allowed a NP dispersion and spiked soil to reach equilibrium was 48 h. The results indicated influencing factors for OC removal and soil remediation were properties both of the soil and the compounds themselves. Soil organic carbon (SOC) content and soil texture played an important role on the sorption as well as compound hydrophobicity expressed as log K(OW) values. The removal efficiency was found to be in the range of 85.2-92.8 % for all soil samples and in the order of DDT < aldrin < heptachlor < dieldrin < endrin < lindane regardless of soil type. This order is inversely related to the log K(OC) values of these compounds. For OC compounds with a similar molecular structure, removal efficiency was related to molecular weight (MW).     

Levels and seasonal variations of organochlorine pesticides in urban and rural background air of southern Ghana

Urban, suburban and rural background air samples were collected in southern Ghana in 2008 employing polyurethane foam disc passive air samplers (PAS). PAS were analysed for organochlorine pesticides (OCPs), namely hexachlorocyclohexanes (α-, β-, γ- and δ-hexachlorocyclohexane), dichlorodiphenyltrichloroethane including metabolites (o,p'- and p,p'-DDT, DDE and DDD), hexachlorobenzene, pentachlorobenzene, aldrin, dieldrin, endrins (endrin, endrin aldehyde and endrin ketone), isodrin, heptachlors (heptachlor, heptachlor epoxide A and heptachlor epoxide B), chlordanes (α-, β-chlordane, oxychlordane and trans-nonachlor), endosulfans (α- and β-endosulfan and endosulfan sulphate), methoxychlor and mirex using a gas chromatograph coupled to a mass spectrometer. The levels of OCPs ranged for the individual pesticides from below limit of quantification to 750 pg m(-3) (for α-endosulfan), and current agricultural application seemed to be the main primary source of most abundant pesticides. Re-volatilization of previously used pesticides from contaminated soils could not be ruled out either as potential secondary source of contamination, especially in warm and dry seasons and periods of intensive agricultural activities. Higher atmospheric concentrations were observed in November and December during the dry season compared to lower concentrations observed in June, July and August when the country experiences heavy rains. The highest seasonal variation was observed for currently used pesticides as α-endosulfan. A p,p'-DDT/p,p'-DDE ratio suggested recent inputs of fresh technical DDT.     

Organochlorine pesticides (DDTs and HCHs) in soils from the outskirts of Beijing, China

Concentrations of HCH (hexachlorocyclohexane) and DDT (Dichlorodiphenyltrichloroethane) were determined in shallow subsurface (5-30 cm depth) and deep soil layers (150-180 cm depth) from the outskirts of Beijing, China. Concentrations of total HCHs (including alpha, beta, gamma, delta-isomers) and total DDTs (including p,p'-DDT, p,p'-DDE, p,p'-DDD, o,p'-DDT) in shallow subsurface soils ranged from 1.36 to 56.61 ng/g dw (median 5.25 ng/g), and from 0.77 to 2178 ng/g (median 38.66 ng/g), respectively, and those in the deeper layers were approximately an order of magnitude less. The spatial distribution of HCHs and DDTs reflected the known historical usage of these pesticides. No correlation between the concentrations of pesticides and soil organic matter content or clay content can be found. The factors affecting residue levels and compositions of DDT and HCH were discussed. The contour maps of beta/gamma ratios and DDT/DDE ratios for both the shallow subsurface and deep layer soils were drawn.     

DDT residues in Lebanese soils

The present study was conducted to evaluate the levels of residual DDT in Lebanese soils. A total of 113 surface soil samples were collected for analysis from three major agricultural regions in the country: Mount Lebanon, Beqa'a valley and the coastal plain. The values of residual DDT in soils ranged between 0 and 1190 ng g(-1). The majority of the analyzed soil samples were free or contained very low concentrations of DDE. Only two surface soil samples, which were collected from urban areas with high human activities, contained relatively high concentrations of residual DDT. The levels of residual DDT in all of the analyzed soil samples were within the permissible limits for agricultural soils.     

Levels of organochlorine pesticide residues in marine-, surface-, ground- and drinking waters from the Eastern Cape Province of South Africa

Persistent organochlorine pesticides (OCPs) such as DDT and its metabolites (DDDs and DDEs). chlordane, hexachlorobenzene (HCB), heptachlor and endosulfan were determined in drinking-, ground-, surface- and marine waters from the Eastern Cape Province of South Africa. Percentage recoveries of the OCPs from spiked river water ranged from 71.03 +/- 8.15% (dieldrin) to 101.25 +/- 2.17% (alpha-BHC). The levels of OCPs ranged from 5.5 ng/L (2,4-DDD) to 160 ng/L (HCB) in the water samples. Some endocrine disrupting OCPs such as DDT, DDE, heptachlor, endosulfan and chlordane were detected.     

Assessing spatial distribution,sources, and human health risk of organochlorine pesticide residues in the soils of arid and semiarid areas of northwest China

Thirty-two topsoil samples were collected to analyze the residue levels of organochlorine pesticides (OCPs) in topsoil of arid and semiarid areas of northwest China in 2011. Results showed that DDTs were the dominant contaminants with a mean concentration of 12.52 ng/g. The spatial distribution characteristics indicated that α-hexachlorocyclohexanes (HCHs) were mainly used in rural sites, whereas hexachlorobenzene (HCB) and endosulfan were detected mostly in urban areas. DDTs, heptachlor, and chlordane were found almost equally in both urban and rural areas. Source identification revealed that the current levels of HCHs in soils were attributable to the residues from their historical use and fresh usage of lindane (γ-HCH). DDTs were mainly from historical use and fresh usage of dicofol, and HCB was emitted from the chemical industry. It was also found that the current soil levels of heptachlor were mainly from its historical usage, endosulfan from fresh input, and chlordane from long-range atmospheric transport, respectively. The noncarcinogenic health risk assessment with a model was also conducted using USEPA standards for adults and children. Results indicated that health risk under nondietary exposure to OCPs decreased in the sequence of ΣDDT?>?ΣHCH?>?HCB?>?Σheptachlor?>?Σendosulfan?>?Σchlordane. According to the reference dose from the USEPA, the health risk under nondietary exposure to OCPs in the soil samples was at a relatively safe level.     

A column test for leaching of organochlorines from soil by amphiphilic nonionic nanopolymers

Amphiphilic nonionic cross-linked nanopolymers (NPs) were synthesized to examine removal of five organochlorines (OCs), namely lindane, heptachlor, aldrin, dieldrin, endrin, and DDT, from a range of Thai agricultural soils. The synthesized NP particles had polarity characteristics similar to those of nonionic surfactant micelles and were largely in the size range of 55–155 nm. This work aimed to determine the optimal conditions for leaching of OC contaminated soil with NPs and also to investigate the role and influence of soil properties on this leaching. An investigation of the concentrations of aqueous dispersions of these particles found that a concentration of 10 g L^?1. was found most effective in leaching the OCs from a column of spiked soil. The optimal contact time that allowed a NP dispersion and spiked soil to reach equilibrium was 48 h. The results indicated influencing factors for OC removal and soil remediation were properties both of the soil and the compounds themselves. Soil organic carbon (SOC) content and soil texture played an important role on the sorption as well as compound hydrophobicity expressed as log K_OW values. The removal efficiency was found to be in the range of 85.2–92.8 % for all soil samples and in the order of DDT < aldrin < heptachlor < dieldrin < endrin < lindane regardless of soil type. This order is inversely related to the log K_OC values of these compounds. For OC compounds with a similar molecular structure, removal efficiency was related to molecular weight (MW).     

Organochlorine pesticide residue and PCBs in harbour porpoise (Phocoena phocoena) incidentally caught in Scandinavian waters

During Norwegian and Danish harbour porpoise projects 1987-1991, subcutaneous blubber samples of 34 male harbour porpoises (Phocoena phocoena) were collected. Animals from three geographical locations, ranging from 56 degrees N, 12 degrees E to 71 degrees N, 26 degrees E, were chosen in order to study the organochlorine (OC) contamination in this species inhabiting the northeastern part of the North Atlantic Ocean, the northern North Sea and Kattegat, at the locations of Tufjord, Vestlandet and Gilleleje, respectively. Analytical standards used consisted of the industrial chemicals PCBs (22 individual PCB congeners and 6 industrial mixtures which contained 104 PCB congeners or group of congeners) and HCB, and the organochlorine pesticides DDT, HCH, the cyclodienes endrin, dieldrin and the chlordane metabolites oxychlordane and trans-nonachlor, and heptachlor epoxide. A total of 16 PCB congeners or groups of congeners, all the DDT metabolites except o,p'-DDD, and all the pesticides were detected in all animals. The concentrations of sigmaPCB (sum of concentrations of 47 detected PCB congeners) and sigmaDDT (sum of concentrations of all DDT detected compounds) ranged from 3.7-65.3 and 3.2-45.0 microg g(-1) lipid weight, respectively. The range of mean concentrations of dieldrin, endrin and trans-nonachlor was 1-3 microg g(-1), while mean concentrations of HCHs, heptachlor epoxide, and HCB were <1 microg g(-1). No significant variation in PCB congener pattern was apparent between geographical areas. The major PCB congeners nos 147/123, 153, 138/163/164, 182/187 and 180 at Gilleleje, Vestlandet and Tufjord represented 53%, 45% and 44% of sigmaPCB, respectively. A significant difference was found between the number of PCB congeners in blubber of newborn and older porpoises. This might indicate the presence of a blood/placenta barrier and/or selective mammary transport of PCBs with specific structures. A significant OC accumulation with age was apparent, with the exception of HCB and HCHs. Geographical differences in the levels of OCs were apparent for all compounds except for dieldrin and heptachlor epoxide. Significantly higher levels of chlordane metabolites (trans-nonachlor and oxychlordane) and endrin were found in the group of animals from the northern location Tufjord, while sigmaDDT, p,p'-DDTs, HCHs and PCBs were highest in the group of animals from the southern location Gilleleje. Highest levels of the o,p'-substituted DDTs were found in specimens from the middle location Vestlandet. These findings indicate little or no regular migration of harbour porpoise between these three locations. No correlations were found between OC concentrations and blubber thickness. Although mean values of sigmaDDT and sigmaPCB were in the lower end of previously reported levels in harbour porpoise from adjacent waters in the eastern part of the North Atlantic Ocean and along the coasts of North America, these levels are relatively high. The organochlorine concentrations in harbour porpoises in the present study were 2-3 times higher than corresponding OC levels detected in harbour seals (Phoca vitulina) from the same areas.     

Distribution of organochlorine pesticides in soils from South Korea

Soil samples were collected from rice growing and industrial areas in South Korea and analysed for organochlorine pesticide content using gas chromatography with electron capture detection. The soils were monitored for the presence of 18 organochlorine pesticides. The main pesticides found were gamma- and delta-hexachlorocyclohexane, heptachlor epoxide and dieldrin. The range of concentrations, for each compound, was respectively, 0.17-0.94, 0.77-2.97, 1.38-48.0 and 0.32-0.49 ng/g soil. The highest values were found in soil obtained from rice fields indicating that, although the use of organochlorine pesticides has been discontinued since 1980, substantial concentrations of residues particularly the oxidised form of heptachlor remain in the soil.     

Levels of Organochlorine Pesticide Residues in Marine-, Surface-, Ground- and Drinking Waters from the Eastern Cape Province of South Africa

Abstract

Persistent organochlorine pesticides (OCPs) such as DDT and its metabolites (DDDs and DDEs), chlordane, hexachlorobenzene (HCB), heptachlor and endosulfan were determined in drinking-, ground-, surface- and marine waters from the Eastern Cape Province of South Africa. Percentage recoveries of the OCPs from spiked river water ranged from 71.03 ± 8.15% (dieldrin) to 101.25 ± 2.17% (α-BHC). The levels of OCPs ranged from 5.5 ng/L (2,4-DDD) to 160 ng/L (HCB) in the water samples. Some endocrine disrupting OCPs such as DDT, DDE, heptachlor, endosulfan and chlordane were detected.     

Identification and quantification of polychlorinated biphenyls and some endocrine disrupting pesticides in human adipose tissue from Finland

Organochlorine pesticides and polychlorinated biphenyls (PCBs) were analysed in extracts of human adipose tissue. The samples consisted of abdominal, mammary, and perirenal fat tissue of 27 Finnish adult males and females. Lipids were separated from the low-molecular compounds by preparative gel permeation chromatography (GPC) and the extracts were further cleaned-up using Florisil chromatography. The compounds were analysed in the extracts by gas chromatography (GC) using electron capture detection and by GC-mass spectrometry in the selected ion monitoring mode. Of the 23 analysed pesticide residues only seven could be detected in the extracts. All the extracts contained the DDT metabolite 4,4'-DDE, hexachlorobenzene, and PCBs. Other compounds found in the extracts were 4,4'-DDT, 4,4'-DDD, pentachlorobenzene, and beta- and gamma-hexachlorocyclohexane (HCH). The antiandrogenic 4,4'-DDE was the most abundant pesticide with concentration levels ranging from 3.5 to 3229 ng/g lipids (ppb). The mean concentration of DDE was 567 ppb, of pesticides in all 1008 ppb and of PCBs 504 ppb. Several of the identified compounds have been shown to exhibit endocrine disrupting effects. Statistical analysis showed a positive age correlation of DDE in females and hexachlorobenzene in males. No statistically significant differences were found for concentrations of individual compounds between sexes.     

Residues of organochlorine pesticides,polychlorinated biphenyls and heavy metals in the eggs of predatory birds from Doñana National Park (Spain), 1980–1983

Abstract

Organochlorine pesticides and heavy metal residues were determined in 54 eggs of five species of predatory birds collected at Doñana National Park (Spain) during the nesting season between 1980 and 1983. The species analyzed were the imperial eagle (Aquila heliaca), the red kite (Milvus milvus), the black kite (Milvus migrans), the hobby (Falco subbuteo) and the booted eagle (Hieraetus pennatus). DDE, DDT and PCBs were detected in all samples. α‐HCH, α‐HCH, aldrin, dieldrin, heptachlor, heptachlor epoxide, TDE and dichlorobenzophenone were also detected but less frequently. The DDE content of eggs decreased in the period between 1972/1976 and 1980/1983, but the PCBs contents were stable. The declines are attributed to the restrictions on the use of DDT in most countries. Mercury, lead, cadmium, copper and zinc were detected in all samples. The levels of organochlorine pesticides, PCBs and heavy metals in these Falconiforme eggs are generally below the levels known to cause direct effects on survival or reproduction of birds.     

A preliminary investigation of persistent organic pollutants in ambient air in Hong Kong

Air samples were collected for characterisation of PCDD/Fs and other persistent organic pollutants (POPs) such as aldrin, alpha-HCH, beta-HCH, delta-HCH, gamma-HCH, o,p'-DDT, p,p'-DDT, o,p'-DDE, p,p'-DDE, o,p'-DDD, p,p'-DDD, dieldrin, endrin, endosulfan I and II, heptachlor, heptachlor epoxide and hexachlorobenzene during the winter of 2000/2001 at the weather station of the Hong Kong Observatory at Tai Mo Shan (TMS), which is the highest point (approximately 957 m) in Hong Kong, besides the routine monitoring of PCDD/Fs and 200 other toxic air pollutants (TAPs) at two urban TAPs stations at Tsuen Wan and Central & Western. Concentrations of the pollutants detected at TMS station were evaluated and compared to those recorded at the urban stations. Though pesticides including alpha-HCH, hexachlorobenzene, DDT, DDE, heptachlor, and endosulfan I were detected, these pesticides were found at relatively low concentrations of about 0.02-0.23 ng/m3 and should not have any significant health effects. Concentrations of some of the monitored POPs were found to be higher whilst most of the monitored TAPs were at comparable levels to those measured at the urban stations during the same period. According to the Stockholm Convention on POPs (May 2001), the 12 chemicals labelled by the United Nations as the most dangerous are: aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, toxaphene, hexachlorobenzene, PCBs and dibenzo-p-dioxins/dibenzofurans (PCDDs)/(PCDFs). Given that there has not been any large scale use of organo-chlorine pesticides recorded since the decline of local farming activities in recent years, the results of the present study again show that pesticides and POPs such as PCDDs/PCDFs are ubiquitous environmental contaminants present in the atmosphere of Hong Kong. The findings also indicate that organo-chlorine pesticides and PCDDs/PCDFs are among the most prevalent chlorinated semi-volatile pollutants present in Hong Kong. Results obtained in the present study suggest that selected pesticides may be used as tracers for transport of pollutants for regional air quality study.     

Residues of organochlorinated pesticides in soils from the Czech Republic

National POPs inventories carried out currently in many countries as a part of the implementation of Stockholm Convention revealed the need for detailed information about a distribution of pollutants in various regions. Screening for the residues of selected organochlorinated pesticides (chlordane, heptachlor, dieldrin, aldrin, endrin, isodrin, endosulfan I, endosulfan II, methoxychlor, mirex) in soil and biotic samples from the Czech Republic was performed. Although these pesticides have never been used in large quantities in this region, results indicate that their residues still persist in the top layer soils more than 20 years after they have been banned. The fact that their soil concentrations in the mountains are generally higher than those in agricultural areas, and detection of the traces of pesticides that have never been used in this region suggest on their occurrence in soils due to the atmospheric redistribution rather than as a result of direct application.     

Modeling the dynamics of DDT in a remote tropical floodplain: indications of post-ban use?

Significant knowledge gaps exist regarding the fate and transport of persistent organic pollutants like dichlorodiphenyltrichloroethane (DDT) in tropical environments. In Brazil, indoor residual spraying with DDT to combat malaria and leishmaniasis began in the 1950s and was banned in 1998. Nonetheless, high concentrations of DDT and its metabolites were recently detected in human breast milk in the community of Lake Puruzinho in the Brazilian Amazon. In this work, we couple analysis of soils and sediments from 2005 to 2014 at Puruzinho with a novel dynamic floodplain model to investigate the movement and distribution of DDT and its transformation products (dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD)) and implications for human exposure. The model results are in good agreement with the accumulation pattern observed in the measurements, in which DDT, DDE, and DDD (collectively, DDX) accumulate primarily in upland soils and sediments. However, a significant increase was observed in DDX concentrations in soil samples from 2005 to 2014, coupled with a decrease of DDT/DDE ratios, which do not agree with model results assuming a post-ban regime. These observations strongly suggest recent use. We used the model to investigate possible re-emissions after the ban through two scenarios: one assuming DDT use for IRS and the other assuming use against termites and leishmaniasis. Median DDX concentrations and p,p′-DDT/p,p′-DDE ratios from both of these scenarios agreed with measurements in soils, suggesting that the soil parameterization in our model was appropriate. Measured DDX concentrations in sediments were between the two re-emission scenarios. Therefore, both soil and sediment comparisons suggest re-emissions indeed occurred between 2005 and 2014, but additional measurements would be needed to better understand the actual re-emission patterns. Monte Carlo analysis revealed model predictions for sediments were very sensitive to highly uncertain parameters associated with DDT degradation and partitioning. With this model as a tool for understanding inter-media cycling, additional research to refine these parameters would improve our understanding of DDX fate and transport in tropical sediments.     

Pesticide pollution remains severe after cleanup of a stockpile of obsolete pesticides at Vikuge, Tanzania

High levels of DDT residues and hexachlorocyclohexanes (HCHs) were found in soil, well water, and surface water around a collapsed pesticide storage shed at Vikuge Farm, Tanzania. Residues of DDT and HCHs were found at three soil depths down to 50 cm. Surface soil samples contained up to 28% total DDT and 6% total HCH residues. Water samples had concentrations of up to 30 microg L(-1) of organochlorine pesticides. Other compounds detected were aldrin, azinphos-methyl, carbosulfan, gamma-chlordane, chlorprofam, heptachlor, hexazinone, metamitron, metazachlor, pendimethalin, and thiabendazole. Although the visible remains of pesticides have been removed, the remaining soil is itself hazardous waste and poses a risk to the environment and the inhabitants of the surrounding villages. These findings show the necessity to follow up the environmental situation at former storage sites of obsolete stocks of pesticides, and that the environmental problems are not necessarily solved by removing the visible remains.     

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.