Concentrations Of Organochlorine Residues Research Articles

Occurrence and seasonal variation of organochlorine pesticides in selected vegetable farmlands in Lagos State, Nigeria.

Pest infestation in crop production have increased farmers' interest in pesticides use with short and long term consequences. This study investigated the occurrence and seasonal variations of organochlorine pesticide residues in vegetable farms in selected areas of Lagos State. Non carcinogenic and carcinogenic risk assessment was also evaluated. Soil samples were collected during the wet and dry seasons at soil depth of 0-30 cm. Gas chromatography coupled with an Agilent mass spectrometer was used to analyse organochlorine residues (alpha-lindane,lindane, delta.-lindane, aldrin, heptachlor epoxide, alpha.-endosulfan, p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE), endrin, endosulfan, m,p'-dichlorodiphenyldichloroethane (m,p'-DDD), endosulfan sulfate, o,p'-dichlorodiphenyltrichloroethane (o,p'-DDT) and endrin ketone) in soil. Heptachlor epoxide showed maximum concentration of 43.03 mg/kg in Station 19 in Western zone during the dry season while m,p'-DDD and endosulfan had minimum value of 0.004 mg/kg in Station 2 and Station 5 respectively during the wet season in the Far eastern zone. The concentrations of organochlorine residues were intermediate in the Eastern zone in both seasons. There was significant (p < 0.05) increase in dry season concentrations when compared to wet season. The risk assessment indicated Hazard Quotient (HQ) > 1 for non-cancer risk and cancer risk > 10-6. Thus a need for stringent monitoring programs for pesticides.

Seasonal Emergence and Historical Contaminant Exposure of Cave Myotis (Myotis velifer) in Central Texas and Current Status of the Population

We examined the emergence patterns of Myotis velifer in central Texas in 2000 and assessed exposure to pesticide residues. We collected and analyzed guano from three caves for pesticide residues. In addition, bat carcasses were sampled from an active colony of cave myotis (Myotis velifer) in Shell Mountain. Organochlorine residue concentrations were highest in guano from the Egypt and Tippit Caves, whereas organophosphate concentrations were highest in Shell Mountain guano. Residue concentrations of organochlorines and metals in guano and carcasses collected from the three caves are considered low and probably of no biological concern. The study was one of very few to demonstrate the presence of OPs, including 18 different detectable compounds in the two most recent samples of bat guano. Comparisons between spring and fall guano samples from Shell Mountain suggest that HCB (hexachlorobenzene), total chlordanes, dieldrin, endrin, endosulfan II, p,p’-DDE (Dichloro-2,2-bis(p-chlorophenyl) ethylene), and o,p’-DDT (Dichlorodiphenyltrichloroethane) accumulated while bats were absent from the caves at Fort Hood. Lindane appeared to be the only chemical that increased while the bats were present at the site. Organochlorine concentrations in carcasses were generally lowest in lactating females and higher in nursing juveniles. The pattern of emergence coincides with the peak of agricultural activities, therefore, bats forage at a time when the insect pests are most abundant, but also potential to exposure to agricultural chemicals is highest. The current status of the population, however, remains stable in spite of the history of exposure.

Organochlorine compounds in bovine milk from the state of Mato Grosso do Sul – Brazil

Organochlorines are highly hydrophobic, synthetic organic pollutants that accumulate in the environment and in food webs. The primary route of human exposure to organochlorines is through food-mainly fat-rich food of animal origin such as meat, fish, and dairy products. Here we determined the presence and concentration of organochlorine residues in pasteurized milk from Mato Grosso do Sul, Brazil, to monitor consumer exposure to these contaminants. Organochlorine pesticides in milk samples were analyzed using solid phase extraction in octadecyl silica-prepacked columns and identified by gas chromatography using an electron capture detector. Of the 100 composite samples analyzed, more than 90% contained residues of organochlorine pesticides: aldrin was present in 44% of the samples, followed by ∑DDT (36%), mirex (34%), endosulfan (32%), chlordane (17%), dicofol (14%), heptachlor (11%) and dieldrin (11%). Compared to the values established by law, the concentration of the compounds in some samples was above the reference values. Given the importance that milk and its products have in the human diet, it is essential to know whether the levels of pesticide residues are kept well below the recommended levels to minimize the risk to human health.

Bio-monitoring of Persistent Organochlorines in Human Milk and Blood Samples from Sub-Himalayan Region of India

In the present study, concentrations of organochlorine pesticide residues viz. Dichlorodiphenyltrichloroethane and its metabolites (DDTs) and Hexachlorocyclohexane isomers (HCHs) in human breast milk and human blood samples, collected from several high altitude regions of Garhwal Himalaya in Uttarakhand, India viz. Devprayag, Chamoli, Uttarkashi, Joshimath, Bhatwari and Gangnani (altitude ranging from 472 to 1,982m above sea level) were determined. Mean concentrations of HCH and DDT in human milk samples ranged from 4.53 to 34.32mg/kg and 6.09 to 12.98mg/kg, respectively. While the human blood showed mean values ranging from 6.64 to 281.7μg/L and 12.37 to 104.10μg/L for HCH and DDT, respectively. The study showed much higher concentrations of organochlorine residue contamination in the Garhwal region as compared to other parts of India. Risk assessments for infants were also calculated and were found within WHO limits.

Assessment of organochlorine pesticide residues in Atlantic Rain Forest fragments, Rio de Janeiro, Brazil

A superficial water quality survey in a watershed of the Paraíba do Sul River, the main water supply for the most populated cities of southeastern Brazil, was held in order to assess the impact of the expansion of agricultural activity in the near border of the Atlantic Rain Forest. The aim of this study was to investigate the presence of priority organochlorine pollutants in soils and superficial waters of Atlantic rainforest fragments in Teresópolis, Rio de Janeiro State. Soil sample preparations were compared by using ultrasound, microwave assisted extraction and Soxhlet extraction. Recoveries of matrix spiked samples ranged from 70 to 130%. Analysis of a certified soil material showed recoveries ranging from 71 to 234%. Although low concentrations of organochlorine residues were found in water and soil samples, this area is of environmental importance and concern, thus demanding a monitoring program of its compartments.

EFFECT OF HEAT TREATMENT ON THE NUTRITIVE VALUE AND RESIDUES OF SOME SYNTHETIC PESTICIDES IN FRESH BOLTI FISH

Fresh Bolti fish (Tilpia nilotica) collected randomly from 9 different markets in Ismailia Governorate for evaluation the effect of grilled fish by the method used in grillrooms and houses on the concentration of pesticide residues found and the nutritive value. Results revealed that decrease in the estimated parameters i.e. moisture, crude protein, fat and ash by grilling, this decrease were 6.07, 2.63, 4.07 and 1.56%, respectively. On the contrary, carbohydrates behaved another behavior that there was an obvious increase ranged from 1.98% to 2.92%. Fresh and grilled fish were analyzed to detect 12 organochlorine (OC) and 7 synthetic pyrethroid (SP) pesticides with a mean level on a lipid basis. Gas Liquid Chromatography equipped with Electron Capture Detector GC-ECD was used to detect the contamination in the samples. The results showed that p,p'-DDE isomer was dominated over the other isomers in all analyzed fish samples, followed by a-isomer of hexachlorocyclohexane. The concentrations of OC residues were higher than SP pesticides in all fish muscles. Also, the fresh fish muscle recorded higher concentrations of the evaluated pesticides than the grilled one.

Relations between and among contaminant concentrations and biomarkers in black bass (Micropterus spp.) and common carp (Cyprinus carpio) from large U.S. rivers, 1995–2004

Environmental contaminant and biomarker monitoring data from major U.S. river basins were summarized for black bass (Micropterus spp.) and common carp (Cyprinus carpio) sampled over a nine year period. Cumulative frequency distributions revealed taxon differences for many organochlorine residue concentrations, elemental contaminant concentrations, and biomarkers, but few gender differences were evident for chemical concentrations. Concentrations of dacthal, pentachloroanisole, p,p'-DDE, endosulfan sulfate, barium, cadmium, copper, manganese, lead, selenium, vanadium, and zinc were greater in carp than bass, but concentrations of mercury and magnesium were greater in bass. Gender differences were evident in bass for mercury and in carp for zinc, but the differences were small compared to taxon differences. Greater vitellogenin concentrations, 17beta-estradiol concentrations, 17beta-estradiol/11-ketotestosterone ratios, and percent oocyte atresia in female carp compared to female bass may be related to the sequential spawning of carp. Regression analyses indicated that as much as 78% of biomarker variation was explained by chemical contaminant concentrations. Sites grouped consistently by river basin in the chemical contaminant principal components analysis (PCA) models and were driven by mercury, magnesium, barium, mirex, and oxychlordane. PCA models for the biomarkers did not group the sites by basin for either bass or carp. Statistical analyses and data interpretation were limited by the study design. The implications of these limitations are discussed. Recommendations to be considered during the planning of future monitoring studies include the exclusion of gender- and species-specific sampling for certain chemical contaminants considering analytical methods with appropriate sensitivities; and allowing for the addition of new chemical and biological variables as methods and information needs evolve.

Organochlorine Residues in Fish and Water Samples from Lake Victoria, Uganda

Nile tilapia and Nile perch samples from Lake Victoria were analyzed for lindane (gamma-1,2,3,4,5,6-hexachlorocyclohexane), aldrin (1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro-1,4:5,8-dimethanonaphthalene), alpha-endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3- benzo(e) dioxathiepin-3-oxide), dieldrin (1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-octahydro-1,4,5,8-dimethanonaphthalene), DDE (p,p'-1,1-dichloro-2,2-bis-(4-chlorophenyl)ethylene), and DDT (p,p'-1,1,1-trichloro-2,2-bis-(4-chlorophenyl)ethane). No significant difference (alpha = 0.05) in the residue levels between fish types for lindane, alpha-endosulfan, p,p'-DDE, p,p'-DDT, and dieldrin was observed. The aldrin levels in Nile perch (Lates niloticus) were significantly higher than the levels in Nile tilapia (Oreochromis niloticus). No difference was observed in the distribution of residues in the different parts of Nile tilapia, although a difference for p,p'-DDE was observed in the Nile perch. No significant difference was observed in the average fat content of the tissue of Nile perch and Nile tilapia; however, the distribution of fat was significantly different in the different parts of the fish, with the abdominal portion having the highest amount of fat. There was no correlation observed in this study between fat content and organochlorine concentration. Lower p,p'-DDT residues levels compared with the p,p'-DDE levels observed in this study indicate that DDT is no longer in use. The levels of organochlorine pesticide residues found in fish samples in this study were below the FAO, U.S. FDA, Australian, and German extraneous residue limits and maximum residue limits. The concentration of organochlorine residues in surface water within the Napoleon Gulf of Lake Victoria was below detection limit (0.1 microg L(-1)).

Integrating life-history and reproductive success data to examine potential relationships with organochlorine compounds for bottlenose dolphins ( Tursiops truncatus) in Sarasota Bay, Florida

Research initiated in 1970 has identified a long-term, year-round resident community of about 140 bottlenose dolphins ( Tursiops truncatus) in Sarasota Bay, Florida, providing unparalleled opportunities to investigate relationships between organochlorine contaminant residues and life-history and reproductive parameters. Many individual dolphins are identifiable and of known age, sex, and maternal lineage (≤4 generations). Observational monitoring provides data on dolphin spatial and temporal occurrence, births and fates of calves, and birth-order. Capture–release operations conducted for veterinary examinations provide biological data and samples for life-history and contaminant residue measurement. Organochlorine concentrations in blubber and blood (plasma) can be examined relative to age, sex, lipid content, and birth-order. Reproductive success is evaluated through tracking of individual female lifetime calving success. For the current study, 47 blubber samples collected during June 2000 and 2001 were analyzed for PCB concentrations of 22 congeners relative to life-history factors and reproductive success. Prior to sexual maturity, males and females exhibited similar concentrations of about 15–50 ppm. Classical patterns of accumulation with age were identified in males, but not in females. Subsequently, males accumulated higher concentrations of PCBs through their lives (>100 ppm), whereas females begin to depurate with their first calf, reaching a balance between contaminant intake and lactational loss (<15 ppm). In primiparous females, PCB concentrations in blubber and plasma and the rates of first-born calf mortality were both high. First-born calves had higher concentrations than subsequent calves of similar age (>25 vs.<25 ppm). Maternal burdens were lower early in lactation and increased as calves approached nutritional independence. Empirical data were generally consistent with a published theoretical risk assessment and supported the need for incorporation of threats from indirect anthropogenic impacts such as environmental pollutants into species management plans. Long-term observational monitoring and periodic biological sampling provide a powerful, non-lethal approach to understanding relationships between organochlorine residue concentrations in tissues and reproductive parameters for coastal dolphins.

A Comparison of Organochlorine Contaminant Levels, on a Lipid Basis, in Sea Lamprey Larvae from Mad River, Lake Huron Basin and Michipicoten River, Lake Superior Basin (1960-1976)

Abstract Organochlorine concentrations, on a lipid basis, were determined for formalin-preserved sea lamprey larvae, collected between 1960 and 1976 in the Mad River, Lake Huron basin, and compared with previously published data from Michipicoten River, Lake Superior basin. Although the ages of the lamprey specimens between the two lake basins were different, their lipid content, expressed as a percentage of dry body weight, was comparable. Despite the fact that the samples came from areas separated by about 550 km and with different land use (heavily forested area with mining activities but little agriculture for Lake Superior versus poultry farming, agricultural, urban and military uses for Lake Huron), no statistically significant differences were found for most organochlorine residue concentrations (Σaldrin, ΣCB, Σchlordane, ΣDDT, Σendosulfan and ΣPCB) between the two lake basins. The exception was ΣHCH, which was significantly lower in Lake Huron due to the absence of a high-level period observed in 1970 to 1975 in Lake Superior samples. Additionally, no differences were found between the relative concentrations of the various DDT metabolites between the two basins, but significantly higher relative concentrations of higher chlorinated PCBs (hexa to decachloro congeners) were found in Lake Huron samples. This study demonstrates the usefulness of formalin-preserved museum material to conduct retrospective contaminant analyses. However, given that certain amounts of contaminants were also found in the preservative solution, consideration of these levels is important to properly interpret the results.

The Distribution of Organochlorine Pesticides in Marine Samples along the Indian Ocean Coast of Kenya

The concentrations of organochlorine residues of lindane, aldrin, ∝- endosulfan, dieldrin, endrin, p,p′-DDE, p,p′-DDD and p,p′-DDT in samples of seawater, sediment, fish and seaweed from different locations along the coast of Kenya are discussed in relation to the geographical location of the sampling sites and potential sources of residue over a period of two years. All sediment samples were found to contain very low levels of organic carbon except those sampled from Sabaki River that had high (4.7%) organic carbon due to greater primary activity. Most of the pesticides residues (112 samples analysed in 1997 and 258 analysed in 1998/99) were detected in fish, water, sediments and seaweed. The concentration of some residues was higher during the wet season than the dry season in 1997, but no marked seasonal variation was observed in 1998/99. Lindane, aldrin, p,p′-DDT and p,p′-DDE were the most frequently observed residues in all samples while ∝-endosulfan, dieldrin, p,p′-DDD and endrin were either present in low concentrations or absent in most samples. Water samples had the lowest concentrations of residues (range 0.503 - 9.025 ng g−1). Sediments had the second highest levels of pesticides residues with a range of 0.584 - 59.00 ng g−1 while fish lipid content had the highest levels of residues in 1989/99 with p,p′-DDT concentration of 1011 ng g−1 and 418 ng g−1 p,p′-DDD in Siganus rivulatus.

Organochlorine pesticides and hexachlorobenzene along the central coast of New South Wales: multi-scale distributions using the territorial damselfish Parma microlepis as an indicator

Concentrations of 10 organochlorine pesticides and hexachlorobenzene (HCB) were determined in the territorial damselfish Parma microlepis at three urban locations and three reference locations centred on the Sydney region. Dieldrin, HCB and DDE were the most frequently detected organochlorines, occurring in 70–100% of samples collected. Alpha and gamma chlordane were also reasonably common and occurred in more than 30% of the samples. Each organochlorine compound investigated had a distinct spatial pattern of distribution. Related chemicals such as alpha and gamma chlordane, and DDT, DDE and DDD tended to have similar patterns of distribution. There were clear differences in patterns of distribution in organochlorines between urban and reference locations shown using non-parametric multivariate techniques. Relative variability of samples from urban locations was higher than at reference locations in 1993, but there was no consistent pattern of differences in the dispersions of samples among urban and reference locations in 1994. Age and condition indices ( K) showed no association with total concentrations of organochlorine residues in fish. Significant, but weak associations were found between organochlorine residues and size, gonad somatic and liver somatic indices.

Trends in organochlorine residue concentrations and burdens in grey seals ( Halichoerus grypus) from Sable Is., NS, Canada, between 1974 and 1994

In blubber from maternal grey seals ( Halichoerus grypus) from Sable Is., NS, ΣDDT ( p,p′-DDE and p,p′-DDT) concentrations declined from 12 μg/g lipid in 1974 to 0.5 μg/g in 1994. Pup blubber ΣDDT concentrations were about 60% of those of their mothers, and declined at similar rates. In maternal seals, p,p′-DDE increased from 56% ΣDDT in 1974 to 89% in 1994. Polychlorinated biphenyl concentrations did not change between 1976 and 1988, but then declined; the relative proportion of chlorobiphenyl (CB) 101 increased, and those of CBs 170 and 187 decreased between 1985 and 1991. Concentrations of α-hexachlorocyclohexane and trans-nonachlor declined after 1988, and of oxychlordane after 1992; concentrations of hexachlorobenzene were constant between 1984 and 1994.

Histological alterations in fish from Sydney reefs: possible biomarkers for environmental effects?

This study examines the utility of histopathology in the damselfish, Parma microlepis, as a biomarker for the effects of organochlorine pesticides and hexachlorobenzene (HCB). Linkages between organochlorine residue concentrations and contaminant-associated histological effects in fish were examined using field collections and a manipulative field experiment. The distribution of 11 frequently identified organochlorines were measured in wild fish at different spatial scales, spanning 270 km of coastline centred around the Sydney region. Histopathology was used to investigate possible effects on liver, gills and gonad tissues in these fish. Pearson correlations and correlative multivariate statistical techniques were used to explore possible associations between concentrations of organochlorines in fish collected from the field and histological alterations in tissues. Only 6% of correlations between organochlorine residues and histological alterations in fish from field collections, were significant. A weak correlation was found between the occurrence of lamellar fusion in gills and the concentration of aldrin and dieldrin in a manipulative field experiment. A hypothetical model is suggested to explain these results.

Relationships between environmental organochlorine contaminant residues, plasma corticosterone concentrations, and intermediary metabolic enzyme activities in Great Lakes herring gull embryos.

Experiments were conducted to survey and detect differences in plasma corticosterone concentrations and intermediary metabolic enzyme activities in herring gull (Larus argentatus) embryos environmentally exposed to organochlorine contaminants in ovo. Unincubated fertile herring gull eggs were collected from an Atlantic coast control site and various Great Lakes sites in 1997 and artificially incubated in the laboratory. Liver and/or kidney tissues from approximately half of the late-stage embryos were analyzed for the activities of various intermediary metabolic enzymes known to be regulated, at least in part, by corticosteroids. Basal plasma corticosterone concentrations were determined for the remaining embryos. Yolk sacs were collected from each embryo and a subset was analyzed for organochlorine contaminants. Regression analysis of individual yolk sac organochlorine residue concentrations, or 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs), with individual basal plasma corticosterone concentrations indicated statistically significant inverse relationships for polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDDs/PCDFs), total polychlorinated biphenyls (PCBs), non-ortho PCBs, and TEQs. Similarly, inverse relationships were observed for the activities of two intermediary metabolic enzymes (phosphoenolpyruvate carboxykinase and malic enzyme) when regressed against PCDDs/PCDFs. Overall, these data suggest that current levels of organochlorine contamination may be affecting the hypothalamo-pituitary-adrenal axis and associated intermediary metabolic pathways in environmentally exposed herring gull embryos in the Great Lakes.

Relationships between Environmental Organochlorine Contaminant Residues, Plasma Corticosterone Concentrations, and Intermediary Metabolic Enzyme Activities in Great Lakes Herring Gull Embryos

Experiments were conducted to survey and detect differences in plasma corticosterone concentrations and intermediary metabolic enzyme activities in herring gull (Larus argentatus) embryos environmentally exposed to organochlorine contaminants in ovo. Unincubated fertile herring gull eggs were collected from an Atlantic coast control site and various Great Lakes sites in 1997 and artificially incubated in the laboratory. Liver and/or kidney tissues from approximately half of the late-stage embryos were analyzed for the activities of various intermediary metabolic enzymes known to be regulated, at least in part, by corticosteroids. Basal plasma corticosterone concentrations were determined for the remaining embryos. Yolk sacs were collected from each embryo and a subset was analyzed for organochlorine contaminants. Regression analysis of individual yolk sac organochlorine residue concentrations, or 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs), with individual basal plasma corticosterone concentrations indicated statistically significant inverse relationships for polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDDs/PCDFs), total polychlorinated biphenyls (PCBs), non-ortho PCBs, and TEQs. Similarly, inverse relationships were observed for the activities of two intermediary metabolic enzymes (phosphoenolpyruvate carboxykinase and malic enzyme) when regressed against PCDDs/PCDFs. Overall, these data suggest that current levels of organochlorine contamination may be affecting the hypothalamo-pituitary-adrenal axis and associated intermediary metabolic pathways in environmentally exposed herring gull embryos in the Great Lakes.

Reproductive success and biochemical effects in tree swallows(Tachycineta bicolor)exposed to chlorinated hydrocarbon contaminants in wetlands of the great lakes and st. lawrence river basin, USA and Canada

AbstractReproduction and biochemical indicators (vitamin A, ethoxyresorufin‐O‐deethylase [EROD], highly carboxylated porphyrins) of contaminant effects, and concentrations of organochlorine residues were measured in tree swallows from wetlands within the watersheds of the Great Lakes and the St. Lawrence River, USA and Canada. To assess the vitamin A sources in the tree swallow diets, insects were collected, by ligature, from nestlings at four of these sites. Diet samples were analyzed for retinol and α‐ and β‐carotene. Marked differences were found in chlorinated hydrocarbon residues in eggs and nestlings among sites; however, we did not find any significant differences in hatching or fledging success. The maximum polychlorinated biphenyl (PCB) concentration found was 11.1 μg/g in eggs from Akwesasne Reserve, New York, USA, on the St. Lawrence River, whereas the highest p, p′‐DDE concentration of 2.57 μg/g was found in eggs from Mud Creek, Ontario, Canada, in the Lake Erie watershed. Concentrations of other organochlorine pesticides and chlorobenzenes were low and not variable among sites. Significant differences in hepatic EROD activity, retinol and retinyl palmitate, and uroporphyrin in nestling birds existed among sites. EthoxyresorufinO‐deethylase activity was highest and retinol and retinyl palmitate were lowest at Cornwall Island, Ontario, Canada, in the St. Lawrence River, whereas porphyrins were highest at Toronto and Hamilton harbors, Ontario, Canada, in Lake Ontario. EthoxyresorufinO‐deethylase induction was significantly and negatively correlated with nestling hepatic retinol concentrations, whereas uroporphyrin concentrations were positively correlated with PCB congener 118 in nestlings. In contrast, few differences occurred in vitamin A concentrations in diet samples among sites. Together, these findings suggest that depressed hepatic vitamin A and elevated highly carboxylated porphyrin concentrations are strongly associated with sites with the highest organochlorine exposure in tree swallows.

Hydrocarbon and organochlorine residue concentrations in sediments from Bay of Chetumal, Mexico.

Hydrocarbon and organochlorine residue concentrations in sediments from Bay of Chetumal, Mexico.

CYP1A concentrations, hepatic mono-oxygenase activities and organochlorine residue concentrations in beluga whales from NWT, Canada

CYP1A concentrations, hepatic mono-oxygenase activities and organochlorine residue concentrations in beluga whales from NWT, Canada

Trends in Organochlorine Residue Concentrations in Ringed Seal (&lt;i&gt;Phoca hispida&lt;/i&gt;) from Holman, Northwest Territories, 1972-91

Samples of blubber for organochlorine (OC) analysis were collected from ringed seals (Phoca hispida) taken during subsistence hunts at Holman, Northwest Territories, in 1972, 1981, 1989, and 1991. DDT-group residue burdens did not change appreciably between 1972 and 1981, but after 1981 concentrations of p,p'-DDE and p,p'-DDT began to fall. By 1991, p,p'-DDE concentrations were less than half, and p,p'-DDT concentrations about 20%, of their 1972 values. Concentrations of polychlorinated biphenyls (PCB) fell to about one-third of their 1972 values by 1981, and then stayed constant until 1991; small but significant changes in the relative proportions of individual congeners, probably resulting from metabolism, occurred between 1981 and 1991. Concentrations of hexachlorobenzene (HCB) fell by 40 to 50% between 1981 and 1991, but those of alpha and beta hexachlorocyclohexanes (HCH) did not change. Only minor changes were seen in the distribution of other OC pesticides (oxychlordane, cis- and trans-chlordane, cis- and trans-nonachlor, mirex, heptachlor epoxide and dieldrin). Female ringed seals consistently had lower blubber DDT-group and PCB concentrations than males. These temporal trends are consistent with changes in the production and use pattern of some OCs, and with their expected environmental behaviour as inferred from their physico-chemical properties.