Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Dieldrin”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,477 records · Page 82Linked to original sources
PubMed1984

Interference by DDT and cyclodiene types of insecticides with chloroplast-associated reactions.

The effects of DDT, some of its analogs, and selected cyclodiene insecticides on isolated spinach (Spinacea oleracea L.) thylakoids were identified, characterized, and compared to responses induced by selected herbicides. Except for endrin, the insecticides inhibited light-induced electron transport, altered chlorophyll fluorescence transients, and competitively displaced [14C]atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], a known photosystem II inhibitor, from the membranes. The insecticides appeared to act at, or near B, the secondary electron acceptor of photo-system II. Binding of DDT and dieldrin was estimated at 900 and 2200 molecules, respectively, per photosynthetic unit (490 chlorophyll molecules). The insecticides also inhibited valinomycin-induced swelling of the thylakoid membrane. Whereas inhibition of electron transport can be attributed to interaction by the insecticides with a proteinaceous component of the thylakoid membrane, interference with the action of valinomycin may involve interaction with lipoidal constituents of the membrane.

Binding, Competitive↗
PubMed1983

Serum levels of polychlorinated biphenyls and some organochlorine insecticides in women with recent and former missed abortions.

Polychlorinated biphenyls and some organochlorine insecticides (DDT isomers and their metabolites, lindane (gamma-BHC), dieldrin, heptachlor epoxide) were assessed in the serum of 17 women with recent missed abortions, 7 women who experienced one or several missed abortions in their past, and 7 women with normal, second trimester pregnancy. Fifty-three percent of the cases of recent missed abortion had PCB serum levels higher than the mean plus two standard deviations of the control group. The mean PCB serum level in women with recent missed abortion and relatively high PCB serum levels was significantly different from that of the control group (103.04 versus 20.69 ppb, P less than 0.001). The mean PCB serum level of the former missed abortions group was also significantly different from that of the control group (82.00 versus 20.69 ppb, P less than 0.001). The quantity of the higher chlorinated biphenyl homologues (penta- and hexachlorobiphenyls) was increased in the high PCB level, missed abortion group and in the former missed abortion group, while the lower chlorinated biphenyl homologues were decreased in these groups in comparison with the control group. The percentage of total o,p'-DDT serum level, as related to total DDT, showed an increase in the high PCB level, recent missed abortion and in the former missed abortion groups, in comparison with the control group (36.18 and 48.98 versus 25.57, respectively). The fact that the former missed abortion group showed increased PCB serum levels similar to those found in the high PCB level, recent missed abortion group confirms the existence of an association between relatively high PCB serum levels and the occurrence of missed abortion. The possible role of PCBs in the occurrence of missed abortion is discussed.

Abortion, Missed↗
PubMed1975

Effects of aldrin-transdiol on neuromuscular facilitation and depression.

The effects of aldrin-transdiol, one of the active metabolites of the insecticide dieldrin, on evoked transmitter release, neuromuscular facilitation and neuromuscular depression have been studied in frog sartorius nerve-muscle preparations. Conventional techniques of intracellular recordings were used. Aldrin-transdiol caused a marked increase in end-plate potential amplitude under conditions of low quantal content, i.e., in Mg2+-blocked junctions. The increase in end-plate potential amplitude was less pronounced in curarized junctions, in which the transmitter release was not impaired. Concomitant with the increase in end-plate potential size there was a marked enhancement of facilitation during short trains of stimuli applied to the motor nerve. The decay of facilitation was, however, not seriously affected by aldrin-transdiol. These effects may be explained in terms of the known 'calcium hypothesis' by assuring that aldrin-transdiol increases the amount of calcium which enters the nerve terminal during the nerve impulse. The increase in end-plate potential amplitude and in facilitation by aldrin-transdiol was transient. At later stages of poisoning, end-plate potential and facilitation decreased below control level and neuromuscular depression was significantly enhanced. This latter effect may be the result of a direct inhibitory effect of aldrin-transdiol on transmitter mobilization. As far as the fall in end-plate potential amplitude is concerned the known suppressive action of aldrin-transdiol on the chemical sensitivity of the postsynaptic membrane and on the nerve action potential probably plays a part as well. Finally, neuromuscular transmission was completely blocked by aldrin-transdiol.

Aldrin↗
PubMed1996

Stable expression of insect GABA receptors in insect cell lines. Promoters for efficient expression of Drosophila and mosquito Rdl GABA receptors in stably transformed mosquito cell lines.

We are interested in establishing stably transformed insect cell lines efficiently expressing the insect gamma-aminobutyric acid (GABA) receptor subunit gene Resistance to dieldrin or Rdl. In order to facilitate this we utilized a system based on stable transformation of Aedes albopictus mosquito cell lines using the dihydrofolate reductase (dhfr) gene as a selected marker. Here we report the production of stable mosquito cell lines carrying high copy numbers of Rdl genes from both Drosophila and Aedes aegypti mosquitoes and the subsequent high efficiency expression of functional GABA gated chlorine ion channels. We also used this system to compare the activity of a range of immediate early baculovirus promoters in mosquito cell culture and demonstrate that IE1 promoter constructs work efficiently across insect species. Results are discussed in relation to the potential use of these constructs in the generic transformation of non-Drosophilid insects.

Aedes↗
PubMed1979

Comparison of the compositions of Aroclor 1242 and Aroclor 1016.

The complete polychlorinated biphenyl compositions of two American products, Aroclor 1242 and its more modern replacement, Aroclor 1016, have been determined by gas-liquid chromatography (GLC) on twelve liquid phases of differing selectivities. Attempts were made to determine the degree of contamination of these Aroclors with chlorinated naphthalenes, using GLC with multiple ion-monitoring mass spectrometry. Chlorinated dibenzofurans, indetectable in Aroclor 1016, were tentatively identified by negative chemical-ionization mass spectrometry and their retention times relative to dieldrin on two GLC liquid phases. Quantitation of the dibenzofurans was initially accomplished using an electron-capture detector, and confirmed by negative chemical-ionization mass spectrometry. Aroclor 1242 contained less than 0.05 mol.% chloronaphthalenes, while Aroclor 1016 contained less than 0.06 mol.% of these compounds. Aroclor 1242 had approximately 150 ppb of chlorinated dibenzofurans, of which 43% was the toxic 2,3,7,8-tetrachloro isomer.

Aroclors↗
PubMed1988

Selective, on-column extraction of organochlorine pesticide residues from milk.

A rapid procedure has been developed that allows a single-step, selective extraction of organochlorine pesticide (OCP) residues from milk on solid-matrix disposable columns by means of acetonitrile-saturated light petroleum. Recovery experiments were carried out on homogenized milk (3.6% fat content) spiked with an ethanolic solution of nine OCPs, viz., HCB, alpha-HCH, beta-HCH, gamma-HCH, heptachlor epoxide, dieldrin, endrin, p,p'-DDE and p,p'-DDT, at levels ranging from 0.002 mg/kg for alpha-HCH to 0.008 mg/kg for p,p'-DDT. Average recoveries of four replicates were 77% for HCB and almost quantitative (94-113%) for the other pesticides, with relative standard deviations from 2.9 to 7.3%. Coextracted fatty material amounted to about 5 mg/ml of milk before the clean-up. The described procedure also showed a satisfactory performance with milk powder. The extraction procedure requires about 60 min. The main advantages are that emulsions do not occur, several samples can be run in parallel by a single operator, reusable glassware is not needed and simple operations are required.

Animals↗
PubMed1984

Interactions of lindane, toxaphene and cyclodienes with brain-specific t-butylbicyclophosphorothionate receptor.

Three major classes of chlorinated hydrocarbon insecticides, i.e., the lindane/hexachlorocyclohexane, toxaphene and aldrin/dieldrin types, are potent, competitive, and stereospecific inhibitors of t-butylbicyclophosphorothionate (TBPS) binding to brain-specific sites, thereby indicating an action at the gamma-aminobutyric acid (GABA)-regulated chloride channel. The most inhibitory and toxic of four isomers of hexachlorocyclohexane is lindane and of greater than 188 components of toxaphene is 2,2,5-endo, 6-exo,8,9,9,10-octachlorobornane. 12-Ketoendrin (IC50 = 36 nM) is twice as active as the most potent previously known inhibitor of TBPS binding and it is also the most inhibitory and toxic of 22 cyclodienes examined. Within each of these three series of polychlorocycloalkanes the mammalian toxicity is closely related to the potency for inhibition of TBPS binding. A modified receptor assay incorporating liver microsomes and reduced nicotinamide-adenine dinucleotide phosphate compensates in part for oxidative detoxification and bioactivation. Specific TBPS binding is reduced in a dose-dependent manner in dieldrin-poisoned rats. DDT, mirex and kepone are not inhibitors of TBPS binding, even at 10 microM.

Animals↗
PubMed1988

Comparison of two techniques for quantifying environmental contaminants in human serum.

Peak area matching and linear regression were used to quantify eight chlorinated pesticides and polychlorinated biphenyls (as Aroclor 1260) in human serum. There are no statistically significant differences in data obtained by these two quantifying techniques which were indicated by the paired t-test. For chlorinated pesticides, p = 0.053-0.62, and for polychlorinated biphenyls (as Aroclor 1260), p = 0.64. Analyte residues for the chlorinated pesticides ranged from 0.5 ppb for hexachlorobenzene (HCB) to 186 ppb for dichlorodiphenyldichloroethylene (DDE). Analyte residues for the polychlorinated biphenyls (as Aroclor 1260) ranged from 5-114 ppb. The absolute mean percent difference between the two quantifying techniques ranged from 0.06% for DDE to 8.06% for dieldrin (HEOD) among the chlorinated pesticides. The absolute mean percent difference between the two quantifying techniques for the polychlorinated biphenyls (as Aroclor 1260) was 3.4%. Peak area matching and linear regression were found to be comparable for quantifying these environmental residues in serum when the following conditions apply: 1) the concentration of the chlorinated pesticides is greater than or equal to 0.5 ppb (e.g., HCB, hexachlorocyclohexane (HCCH), oxychlordane (OC), heptachlor epoxide (HE), transnonachlor (TN), HEOD, and dichlorodiphenyltrichloroethane (DDT); 2) the concentration of the chlorinated pesticide is greater than or equal to 3 ppb (e.g., DDE); and 3) the total concentration of polychlorinated biphenyls (e.g., as Aroclor 1260) is greater than or equal to 5 ppb.

Environmental Monitoring↗
PubMed1995

Drosophila GABA-gated chloride channel: modified [3H]EBOB binding site associated with Ala-->Ser or Gly mutants of Rdl subunit.

The non-competitive blocker site of the GABA-gated chloride ion channel in normal susceptible strains of Drosophila melanogaster and simulans binds 4-n-[3H]propyl-4'-ethynylbicycloorthobenzoate ([3H]EBOB) at specific sites with KdS of 1.6-1.9 nM and BmaxS of 171-181 fmol/mg protein. This specific binding of [3H]EBOB is strongly inhibited by: a large number and variety of insecticidal channel blockers at 20 nM (lindane, alpha-endosulfan, dieldrin, 12-ketoendrin, fipronil, and a representative bicycloorthobenzoate and dithiane) or 200 nM (picrotoxinin); the insecticidal channel activators avermectin and moxidectin at 20 nM; muscimol at 30 microM and GABA at 300 microM. Cyclodiene resistance in D. melanogaster has been attributed to a mutation resulting in an Ala302-->Ser replacement in the Rdl GABA receptor subunit and in D. simulans to an homologous Ala-->Ser or Gly replacement. These mutations are shown here to greatly reduce [3H]EBOB binding, i.e. lower affinity and apparent number of binding sites. The Ala-->Ser replacement with both melanogaster and simulans almost always reduces the potency in inhibiting [3H]EBOB binding of each of eight channel blockers and of muscimol and GABA. The Ala-->Gly replacement in D. simulans is generally less effective than the Ala-->Ser modification in reducing sensitivity to the channel blockers and to muscimol and GABA. The channel activators avermectin and moxidectin usually retain their inhibitory potency in the Rdl subunit mutants. Thus, it appears that replacement of Ala by Ser generally modifies the non-competitive blocker site and its coupling to the GABA-recognition site with less effect on the channel activator site. In contrast, the Ala-->Gly replacement has less impact in protecting the chloride channel from the action of insecticidal blockers. Each of the resistant strains has the same level of resistance to the lethal action of the five channel blockers examined but none to avermectins and muscimol.

Alanine↗
PubMed1983

Bacterial mutagenicity investigation of epoxides: drugs, drug metabolites, steroids and pesticides.

Although it has been observed that many epoxides are ultimate mutagens, surprisingly little is known about epoxides to which man may be extensively exposed, e.g., physiological compounds, drugs, drug metabolites and pesticides. We have now investigated 35 such and related epoxides for mutagenicity, using reversion of his- Salmonella typhimurium TA98 and TA100 as biological end-point. None of the tested steroids (12 compounds), vitamin K epoxides (3 compounds) and pesticides (dieldrin, endrin, HEOM (1,2,3,4,9,9-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8, 8a-octahydro-1,4-methanonaphthalene), heptachlor epoxide) showed any mutagenic activity. Negative results were also obtained with the antibiotics oleandomycin, anti-capsin and asperlin, the cardiotonic drug resibufogenin, the widely used parasympatholytic drugs butylscopolamine and scopolamine, the sedatives valtratum, didovaltratum and acevaltratum, the tranquilizer oxanamide as well as with the drug metabolites carbamazepine 10,11-oxide and diethylstilbestrol alpha,beta-oxide. Three barbiturate epoxides, formed by metabolism of allobarbital, alphenal and secobarbital, caused weak but reproducible mutagenic effects at high concentrations. The cytostatic agent ethoglucide was the only drug having substantial mutagenic activity. Its mutagenic potency was similar to those of the control epoxides styrene 7,8-oxide, p-bromostyrene 7,8-oxide and m-bromostyrene 7,8-oxide, but much lower than those of benzo[a]pyrene 4,5-oxide, benzo[e]pyrene 4,5-oxide and 7,12-dimethylbenz[a]anthracene 5,6-oxide. Some epoxides were also tested in other Salmonella typhimurium strains or in the presence of rat-liver S9 mix. Positive results were only obtained with compounds that had already been detected as mutagens in the direct test with strain TA100.

Animals↗
PubMed1988

Action of polychlorocycloalkane insecticides on binding of [35S]t-butylbicyclophosphorothionate to Torpedo electric organ membranes and stereospecificity of the binding site.

Binding of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) to Torpedo electric organ membranes was characterized. A dose- and pH-dependent binding (100.8 pmol/mg protein) was detected with a single affinity (Kd of 0.9 microM) in the presence of 150 mM KCl at pH 6.8. Other anions such as Br- and I- also increased binding affinity, but to a lower degree than Cl-, which increased the affinity by two- to threefold. In presence of 150 mM KCl, [35S]TBPS binding was inhibited noncompetitively by Zn2+ and by 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) (IC50 of 9 microM). The gamma-isomer of hexachlorocyclohexane (BHC) was much more potent in inhibiting this [35S]TBPS binding and the inhibition was competitive (Ki = 40 nM). Like binding of [35S]TBPS to the gamma-aminobutyric acid (GABA) receptor, its binding to Torpedo membranes was inhibited by pentobarbital, mephobarbital, and hexobarbital (IC50 of 85, 225, and 300 microM), respectively), but not by phenobarbital. Binding was not inhibited by diazepam, GABA, bicuculline, or avermectin B1a, ligands that bind to the GABAA receptor. [35S]TBPS binding was inhibited by BHC isomers with the following decreasing order of potency alpha = gamma greater than sigma greater than beta, and by cyclodiene insecticides. Endrin was more potent than dieldrin, but endosulfan I and II had similar effects. The data suggest that the binding site for polychlorocycloalkane insecticides on this protein is much less stereoselective than that of the Cl- channel of the GABAA receptor. Also, even though this Torpedo protein has higher affinity for insecticides, such as gamma-BHC, than does the GABAA receptor, it is the latter whose specificity correlates best with polychlorocycloalkane toxicity. Nevertheless, because of its high affinity for gamma-BHC such a protein in muscles or brain may be an important target for the action of this insecticide.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1996

Organochlorine compounds in blubber, liver and brain in neonatal grey seal pups.

The present study focuses on the distribution and accumulation of persistent organochlorine compounds in different tissues and organs of grey seal (Halichoerus grypus) pups. Thus, levels of drins (aldrin, dieldrin, endrin), chlordanes (heptachlor, heptachlorepoxide, oxychlordane, transnonachlor), DDTs (p,p'-DDE, o,p'-DDD, p,p'-DDD, o,p'-DDT, p,p'-DDT) and 22 PCB congeners were determined in samples of brain, fat, and liver of 0-10 days old grey seal pups from the species' main breeding site in Norway. Whereas 10 different compounds were detected in the blubber, 8 compounds were detected in the liver. The concentrations of the two major classes of OCs (PCBs and DDTs) in liver were both about 75% of that in blubber. In cerebral tissue, only two PCB congeners were detected, and sigma PCB was only about 1% of that measured in the blubber. The distribution pattern of PCB-congeners in liver and brain differed significantly from that in blood and blubber tissue, indicating that the physico-chemical properties of the individual congeners and the lipid composition of the tissue are decisive for the tissue-specific pattern of congener distribution. A significant increase of the sigma DDT/sigma PCB-ratio as a function of blubber thickness indicates that DDT compounds are more readily accumulated in older pups.

Adipose Tissue↗
PubMed1984

Behaviour of persistent organochlorine micropollutants during primary sedimentation of waste water.

The removal of polychlorinated biphenyls and the organochlorine insecticides gamma-HCH, aldrin, dieldrin and endrin during primary sedimentation of raw sewage has been studied using a pilot plant facility. A matrix of sixteen experiments was performed, where the pilot plant was operated at four different hydraulic loadings with four different influent suspended solids loadings. Significant removals of micropollutants into the primary sludge were observed, although no particular relationship with the removal of suspended solids was evident. It is concluded that a proportion of the organic microcontaminants present in raw sewage were associated with non-settleable solids and were also in the dissolved form. The significance of the behaviour of organochlorine micropollutants in waste water treatment processes and the hydrological cycle are discussed in the context of water re-use operations.

Insecticides↗
PubMed1986

Levels of some organochlorine residues in blood of patients with arteriosclerotic disease.

This study aims to elucidate if any association exists between the development of arteriosclerotic disease and contamination of the internal human environment with certain organochlorine compounds (OCCs). For this purpose the levels of DDT isomers and their metabolites, and of lindane, dieldrin, heptachlor epoxide, and polychlorinated biphenyls (PCBs) were determined in blood serum of 11 patients suffering from slight to moderate (group A), and 24 patients with moderate to severe (group B), arteriosclerotic lesions. The control group consisted of 27 patients with no obvious manifestations of arteriosclerosis. The main findings of the study in comparison with the control group were: Mean OCC residue levels in blood were slightly higher in group A and markedly so in group B; The variability and the extent of departure from normality of distributions of organochlorine insecticides (OCIs) decreased, whereas those of PCBs increased, in arteriosclerotic patients (more markedly in group B); The degree of correlation between blood serum levels of various OCCs was elevated in group A and low in group B. It remains to be ascertained whether changes in the body burden of OCCs are primary, resulting from increased exposure to and absorption of these compounds which thus contribute to the development of arteriosclerosis, or are of secondary origin, due to inhibition of xenobiotic metabolism caused by interference of the arteriosclerotic process with the functions of drug metabolizing enzymes of liver microsomes.

Arteriosclerosis↗
PubMed1987

Changes in pattern of organochlorine residues in blood of general Israeli population, 1975-1986.

This study reviews data on the changes with time of the blood levels of some organochlorine compounds (OCCs) in the general Israeli population. All the studied OCC residues, except for p,p'-DDD, were significantly lower in 1985-1986 than in 1975. A decline in blood residues of organochlorine pesticides was observed mainly in the second half of the 1970s, whereas a fall in the polychlorinated biphenyl residue levels took place in the first half of the 1980s. During the latter period, unexplained increases in p,p'-DDD, dieldrin and heptachlor epoxide residue levels were seen. A significant decrease in the blood levels of OCCs quickly metabolized in the body (p,p'-DDT, tetrachlorobiphenyls) indicated a considerable reduction of environmental exposures. The clear decline in OCC contamination of the environment and, in particular, of the human body during the reviewed period (1975-1986) resulted from the restrictions imposed in Israel on the use of OCCs. Nevertheless this does not mean that this problem has been solved. Some health implications of low-level life-long OCC exposure are discussed, and further environmental and biological monitoring and control measures are recommended.

Adult↗
PubMed1990

Geographical distribution of contaminants and productivity measures of herring gulls in the Great Lakes: Lake Erie and connecting channels 1978/79.

The distribution and size of colonies, residue levels of DDE, DDT, HCB, dieldrin, mirex and PCBs in eggs, productivity and eggshell thickness were determined for herring gulls at 14 sites in Lake Erie and connecting channels. The centre of distribution for breeding herring gulls was the Western Basin where approximately 90% of the 6200 nests in the study area were located. Seven of 22 colonies showed an average annual population increase of 48.3%. Most of the increase in breeding herring gulls on Lake Erie is directly associated with sites that have undergone habitat modification by man. Levels of PCBs and DDE ranged from 35 to 140 ppm (wet weight) and from 2.8 to 9.4 ppm, respectively; all other residues were less than 0.49 ppm. Most organochlorine residue levels were highest in eggs from colonies in or near the Niagara or Detroit Rivers. Mirex residues were greatest in the Niagara River and decreased significantly to the west. PCB residues were greatest in the Detroit River and decreased significantly to the east. The lowest levels generally came from colonies in the Sandusky Basin and near Pelee Island in western Lake Erie. Discriminant function analysis of six organochlorine contaminants correctly classified 90% or more of the eggs from up to four colonies in one or more years. Levels of PCBs and HCB appeared to have the greatest discriminating power. Herring gull productivity at all colonies (1-1.7 young gulls/pair) was normal and showed no significant geographical variation. Eggshell thickness was greatest in colonies in the Sandusky Basin and least in colonies in the Detroit River and extreme west end of the lake; mean eggshell thickness was 0.350 +/- 0.02 mm (6.7% thinning), which was weakly, but significantly correlated to DDE concentration. The variation in contaminants in herring gull eggs on a Basin basis (i.e., Western, Eastern, Sandusky, etc.) paralleled those known for sediments, water and fish. Thus, we suggest that in addition to its role as an indicator of lake-wide contamination of the Great Lakes, the herring gull, under some circumstances, may function as an indicator of "regional" contamination. This is an important distinction as it improves the geographical specificity of the herring gull as an indicator species on the Great Lakes, where it is a non-migratory species.

Animals↗
PubMed1991

Residues of chlorinated biphenyl congeners and pesticides in brain and liver of the oystercatcher (Haematopus ostralegis) in relation to age, sex and biotransformation capacity.

Polychlorinated biphenyl concentrations in brain and liver oystercatchers, Haematopus ostralegis, increased similarly in males and females until sexual maturation. The concentrations were higher in adult males than in subadults, but for females the concentrations were lower in adults than in subadults. Absolute PCB, dieldrin and DDE concentrations were higher in liver than in brain. Compared with these compounds, alpha-HCH was relatively enriched in brain. No significant relation between pesticide concentrations and age or sex could be established. Despite differences in absolute PCB concentrations, the PCB patterns were very similar between all categories of birds and between brain and liver of the same animals. Only in the brain of juvenile males were some congeners present in relatively higher concentrations than in the brain of subadults and adults. Oystercatchers are able to metabolize CB congeners with vicinal H-atoms in the meta and para positions irrespective of the number of ortho-chlorines present. However, their ability to metabolize congeners with vicinal H-atoms in the ortho and meta positions is limited.

Aging↗
PubMed1993

Impact of organochlorine pesticide residues and PCBs on otters (Lutra lutra): a study from western Britain.

A study of otter (Lutra lutra) populations and levels of organochlorine (OC) pesticide residues and PCBs in otter droppings (spraints) was made on eight stretches of river in three catchments in Wales and West Midland England. Population and contaminant levels were compared against target values. The otter populations (as measured by an index) remained stable on one stretch over 11 years, while they increased rapidly to equilibrium on four other stretches. The three lower stretches of rivers showed more erratic trends and on only one stretch did the index exceed, occasionally, the target value. Marking intensity at spraint sites was also lower at the three lowland sites. Concentrations of dieldrin, DDE and PCBs were significantly greater in spraint samples from the three lowland stretches. Over 50% of samples from the three lowland stretches had OC concentrations above the maximum allowable concentration, whereas most samples from the upland stretches had concentrations below the 'no effects level'. It is suggested that the colonization, by otters, of their former lowland range is inhibited by OC contamination of their food chain but, if contaminant levels can be reduced, spread will occur rapidly.

Animals↗