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PubMed1964

THE USE OF GAS CHROMATOGRAPHY FOR THE QUANTITATIVE DETERMINATION OF MICRO-AMOUNTS OF INSECTICIDE PICKED UP BY MOSQUITOS.

The test method recommended by the WHO Expert Committee on Insecticides for determining the susceptibility or resistance of adult mosquitos to insecticides has been evaluated quantitatively by the use of gas chromatography to measure the amount of dieldrin picked up by adult Culex quinquefasciatus Say (= C. pipiens fatigans Wiedemann). A strain homozygous for dieldrin-resistance was used to determine the pick-up as a function of time and concentration of dieldrin. The results of experiments using electron-capture detection with gas chromatography suggest that the pick-up is a linear function of the concentration on the paper and also of the time of exposure, even of the 24-hour exposure to the 4.0% dieldrin paper.

Animals↗
PubMed2000

Detection of an estrogen receptor in two nematode species and inhibition of binding and development by environmental chemicals.

The presence of estrogen receptors or binding proteins was demonstrated in the free-living nematode species Panagrellus redivivus and Caenorhabditis elegans by radioimmunoassay. Twenty-five nanomolar concentrations of toxaphene, dieldrin, and dieldrin plus nonylphenol significantly inhibited estrogen binding to the receptor in P. redivivus. Binding was inhibited but not significantly by 25 nM nonylphenol, toxaphene plus dieldrin, or toxaphene plus nonylphenol. The current research supports the hypothesis that dieldrin, nonylphenol, and toxaphene may mimic estrogen, altering the normal pathways of estrogen metabolism. Based on observations of secondary sex structures, estrogenic chemicals had no effect on sex ratios or growth in Panagrellus redivivus, but caused a reduction of fecundity in this nematode.

Animals↗
PubMed1979

Pesticide and PCB residues in the upper Snake River ecosystem, Southeastern Idaho, following the collapse of the Teton dam 1976.

The Teton Dam in Southeastern Idaho collapsed on June 5, 1976. The resulting flood damaged a large area and caused the release of toxicants into the Snake River. A pesticide recovery team in a helicopter worked the flooded area for three weeks and collected 1,104 containers, about 35% of which contained toxicants. It was estimated that less than 60% of the lost pesticide containers were recovered. This paper addresses the results of a one-time sampling effort designed to determine the magnitude of the chemical contamination. Over 300 samples of fish, plankton, waterfowl, sediments, water, stream drift, aquatic plants, and soil were taken. Pesticide residues were measured as microgram/kg (ppb) wet weight, whole animal basis. Rainbow trout had as much as 1432 micrograms/kg total DDT plus analogs, 66 micrograms/kg dieldrin, and 1010 micrograms/kg PCBs. Utah suckers had up to 1420 micrograms/kg total DDT plus analogs, 32 micrograms/kg dieldrin, and 1800 micrograms/kg PCB. Rocky Mountain whitefish had as much as 2650 micrograms/kg total DDT and analogs, 30 micrograms/kg dieldrin and 1400 micrograms/kg PCBs. These PCB and DDT levels were high, approaching the 2,000 micrograms/kg FDA proposed tolerance, but were below the 5,000 micrograms/kg present tolerance. Dieldrin levels were low and organophosphates were undetectable. An undeveloped area (the Fort Hall Bottoms) showed higher levels of contaminants than did an industrialized area (the lower Portneuf River). This apparent discrepancy remains unexplained. Very little pre-flood data on a whole fish basis were available for comparison (Johnson et al 1977). However, it does not appear that any human health hazard due to pesticide levels exists in this portion of the Snake River.

Animals↗
PubMed1976

Organochlorine insecticide residues in ducklings and their dilution by growth.

Residues of DDT, DDD, DDE, and dieldrin in 7 species of ducklings from Alberta, Canada, were measured. Levels of DDT and metabolites ranged from 0 to 36.48 ppm in fat of 96% of the birds and from 0 to 0.97 ppm im muscle from 67% of the birds. Residue levels of dieldrin ranged from 0 to 2.62 ppm in fat and from 0 to 0.11 ppm in muscle of 43 and 19% of the birds, respectively. Growth dilution was considered to be the most significant factor in reducing the insecticide residue levels in the ducklings. DDT (total DDT, DDE, and DDD) residue levels were decreased with increased weight of pintail (A. acuta), baldpate (Mareca americana), and gadwall (A. strepera) ducklings. Dieldrin used in grasshopper control did not contribute to residue levels in the ducklings. Contamination by DDT was considered to have originated from outside the habitat. No dieldrin or DDT residues were found in ducklings' food sources analysed.

Alberta↗
PubMed1984

Susceptibility of ticks to acaricides in Zambia.

The susceptibility of some Zambian ticks to dieldrin, dioxathion, dimethoate and chlorfenvinphos was determined on two- to three-week-old larvae of Amblyomma variegatum, Boophilus decoloratus, B. microplus, Rhipicephalus appendiculatus, R. e. evertsi and a member of the R. pravus group. Some strains of B. decoloratus and R. appendiculatus were resistant to dieldrin, dioxathion and dimethoate and some R. e. evertsi were resistant to dieldrin and dioxathion. A single strain of an R. pravus group tick was resistant to dioxathion and one out of four strains of A. variegatum was resistant to dieldrin.

Animals↗
PubMed1998

Characterization and comparative pharmacological studies of a functional gamma-aminobutyric acid (GABA) receptor cloned from the tobacco budworm, Heliothis virescens (Noctuidae:Lepidoptera).

This paper reports the functional expression and pharmacological characterization of a full length complementary deoxyribonucleic acid (cDNA) (pIVY12) cloned from a Heliothis virescens fertilized egg cDNA library that encodes for a gamma-aminobutyric acid (GABA) receptor subunit (HVRDL-Ser 285). Two electrode voltage clamp recordings of Xenopus oocytes expressing the HVRDL GABA-gated chloride channel revealed robust chloride ion conductance in response to GABA and the GABAA receptor agonist, muscimol. Baclofen, a GABAB agonist had no effect. Phenobarbital showed a positive dose-dependent allosteric modulatory effect, whereas the benzodiazepine, flunitrazepam, had no effect. Chloride conductance was depressed by the novel insecticide, fipronil ((+/-)-5-amino-1-(2,6 dichloro-alpha, alpha, alpha-trifluoro-p-tolyl)-4-trifluoromethyl-sulfinylpyrazole-3-carb onitrile) and the GABAA antagonist, picrotoxinin. The HVRDL GABA receptor was insensitive to blockage by dieldrin and the GABAA antagonist, bicuculline. The comparative actions of fipronil, picrotoxinin and dieldrin were examined on oocytes expressing the H. virescens wild-type (HVRDL-Ser 285), the site-directed mutant (HVRDL-Ala 285), the Drosophila melanogaster Rdl wild-type (DMRDL-Ala 302) and the Rdl dieldrin resistant (DMRDL-Ser 302) homo-oligomeric GABA receptors. HVRDL-Ala 285 was 15-fold more sensitive to blockage by fipronil than HVRDL-Ser 285. DMRDL-Ala 302 and DMRDL-Ser-302 showed a similar level of sensitivity to blockage by fipronil. HVRDL-Ser 285 and DMRDL-Ser 302 exhibited a similar level of insensitivity to picrotoxinin. HVRDL-Ala 285 and DMRDL-Ala 302 showed a similar range of picrotoxinin sensitivity. DMRDL-Ala 302 and HVRDL-Ala 285 showed some sensitivity to blockage by dieldrin. Fipronil sensitivity was significantly altered by the serine to alanine mutation at position 285 in the M2 region of the HVRDL subunit, whereas no difference was observed between the DMRDL-Ser 302 and DMRDL-Ala 302 receptors.

Amino Acid Sequence↗
PubMed1985

Persistence of aldrin in flooded soil under the cover of rice.

The persistence of aldrin in soil and its translocation into rice plants and grains were tested under two different field conditions. Treatment T1, which consisted of aldrin application at the rate of 1.5 kg active ingredient/ha at nursery sowing, did not leave aldrin residues in rice plants 40 days after application (10 days after transplanting). Dieldrin was present in plants to the extent of 0.04 ppm at this stage but completely disappeared (below detectable limit) within 70 days (30 days after transplanting). Treatment T2 involved aldrin application 10 days after transplanting in flooded soil at the same rate and left 0.518 ppm residues in soil just after application. These residues dissipated to their half in 90 days. At this stage its conversion to dieldrin was also observed. Remaining residues dwindled to below the detectable limit in 270 days. Plant samples analyzed from this treatment at 7 and 30 days contained 0.079 and 0.169 ppm aldrin and 0.025 and 0.08 ppm dieldrin, respectively. Rice grains also had aldrin and dieldrin residues (each at 0.001 ppm level) at harvest time but these were below the Maximum Tolerance Limits. Both the treatments were found safe from the toxic residue point of view.

Aldrin↗
PubMed2006

Determination of oxidative metabolism in Collembolan Proisotoma minuta (Tullberg).

An oxidative metabolism of Collembolan Proisotoma minuta was determined with a model compound of aldrin and dieldrin in this paper. The seven-day LD(50) values for aldrin, dieldrin, and piperonyl butoxide in salt solution were 0.496, 0.367, and 8.346 mg L(-1), respectively. When P. minuta were exposed to aldrin, dieldrin was the sole metabolite. The conversion of aldrin to dieldrin was known to be catalyzed by P450 monooxygenases system. It has been shown that the synergist piperonyl butoxide inhibited the metabolism of aldrin in P. minuta.

Aldrin↗
PubMed1982

Macrophage induction of T-suppressor cells in pesticide-exposed and protozoan-infected mice.

The use of infectious pathogens has allowed the detection of the development of synergism between pathogens and ubiquitous environmental chemical contaminants. This synergism has been demonstrated to result in a state of immunosuppression which either did not occur in the independent and singular presence of the chemical or pathogen and/or was greater than additive when both were combined. The immunosuppression was distinct with regard to the organochloride used and, therefore, is not a ubiquitous characteristic of all organohalides. The production of a macrophage soluble factor which appeared to induce T-suppressor cells was demonstrated in hepatic Kupffer cells from mice administered 5 ppm of dieldrin for 10 weeks and then infected with Leishmania tropical promastigotes. The factor was not generated in mice administered dieldrin and infected with malaria nor in mice administered only dieldrin nor in mice only infected with Leishmania. Additional studies revealed a profound impairment in macrophage antigen processing with macrophages obtained from mice administered dieldrin. The use of pathogen models may allow the immunosuppressive potential of environmental chemical contaminants to be expressed in a more sensitive manner.

Animals↗
PubMed1959

Insecticide resistance in anophelines in eastern Saudi Arabia.

In 1953, the fifth year of a malaria control programme with DDT in Eastern Saudi Arabia, the resting of Anopheles stephensi on recently sprayed surfaces suggested the development of resistance in this species to DDT, and this suspicion has been confirmed by tests carried out from 1955 to 1958.DDT was replaced by dieldrin in 1955 and malaria rates, which had been rising, were again reduced. No dieldrin-resistance has been found in local. A. stephensi strains, and no A. stephensi have been collected from treated villages since the wide use of dieldrin.A. pulcherrimus, A. coustani var. tenebrosus, A. fluviatilis and A. sergenti have proved susceptible to DDT, but the first two have developed resistance to dieldrin. A. pulcherrimus was rarely collected before and during the use of DDT but has become increasingly frequent since the introduction of dieldrin. Its possible role in transmitting malaria in the area is discussed.Egg measurements and ratios on several series of eggs obtained from locally collected A. stephensi fall within the limits of the range set for A. stephensi mysorensis, not previously recorded outside India.

Animals↗
PubMed1993

Insecticide susceptibility status of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti in Panaji, Goa.

Adult and larval insecticidal tests conducted in Panaji, Goa, revealed that adults of An. stephensi were resistant to DDT (4.0%), dieldrin (0.4%) and malathion (5.0%). The larvae of An. stephensi were also resistant to DDT (2.5 mg/l) and malathion (3.125 mg/l). Cx. quinquefasciatus adults were resistant to DDT, dieldrin, malathion and fenitrothion (1.0%), and larvae were highly resistant to DDT but showed low resistance to malathion and fenitrothion (0.125 mg/I). Adults of Ae. aegypti were resistant to DDT and dieldrin and the larvae showed resistance to DDT but good susceptibility to fenitrothion and complete susceptibility to malathion. The triple resistance of An. stephensi to DDT, dieldrin and malathion is intriguing as malathion has never been used in the health sector in Goa. A very limited use of malathion was done in the agricultural sector in Chandor area, which is 50 km away from the study area.

Aedes↗
PubMed1997

Organochlorine pesticides and polychlorinated biphenyls in foodstuffs from Asian and oceanic countries.

Public concern about the adverse environmental and human health impacts of organochlorine contaminants led to strict regulations on their use in developed nations two decades ago. Nevertheless, DDT and several other organochlorine insecticides are still being used for agriculture and public health programs in developing countries in Asia and the South Pacific. As a consequence, humans in this region are exposed to greater dietary levels of organochlorines. In this review, published information on organochlorine concentrations in foodstuffs from South and Southeast Asia and Oceanic countries has been compiled. Foodstuffs that contribute to human exposures and dietary intakes of organochlorines were examined, and the data compared with those reported from more developed nations. Among various developing countries in Asia, considerable information on organochlorines in foodstuffs has been available from India since the late 1960s. DDT and HCH were the major insecticides in Indian foodstuffs. Concentrations of these insecticides have declined more than two orders of magnitude in farm products, such as food grains and vegetables, in two decades. Milk and milk products are the major sources of dietary exposure to DDT and HCH in India. The residues of these insecticides in dairy products were close to or above the MRLs of the FAO/WHO. Dietary intake of DDT and HCH by Indians was > 100 fold that in more developed nations. Sporadic incidences of greater concentrations (> 1 microgram/g) of aldrin, dieldrin, and heptachlor have been measured in Indian vegetables. Untreated surface waters could be a potential source of DDT and HCH exposure. In most Southeast Asian countries DDT was the common contaminant in animal origin foodstuffs. The higher percentage of p,p'-DDT in meat and fish from Southeast Asian countries, except Japan and Korea, indicated the recent use of DDt in vector control operations. Dietary intakes of DDt and HCH in Southeast Asia were an order of magnitude less than those of Indians but 5- to 10 fold greater than in more developed nations. In addition to DDT, aldrin and dieldrin were prominent in meat collected from Thailand and Malaysia. Aquatic food products from more industrialized countries, such as Japan, South Korea, Hong Kong, and Taiwan, contained significant levels of PCBs. In South Pacific countries, particularly in Australia and New Zealand, chlordanes and PCBs were the most prevalent organochlorines in foodstuffs. Food contamination by DDT, HCH, aldrin, and dieldrin was less than in developing countries in Asia but greater than in the U.S. and Japan. Intake of PCBs in Australia was greater than in the U.S. Meat and fish were the major sources of organochlorine exposure by Australians. Human dietary intake of organochlorines has been declining more slowly in developing countries in Asia. Current intakes were at least 5- to 100 fold greater than those in more developed nations, suggesting a greater risk from organochlorine exposure. Factors such as malnutrition, common among rural poor in developing nations, can increase these risks. Of greatest concern is the magnitude of exposure to organochlorines to which infants and children are subjected through human and dairy milk. The estimated intake of DDT by infants was at least 100 fold greater than the ADI of the FAO/WHO. In addition to DDT, excessive exposures to HCH and dieldrin may cause potential health effects in infants because they are more vulnerable to toxic effects. The design and implementation of appropriate epidemiological studies and their integration with monitoring of human, food, and environmental samples would be a major step in assessing the risks of organochlorine residues in foods and controlling or eliminating them. With the continued globalization of trade in food products, and the concomitant risk that food contaminated through point-source pollution may be widely distributed, identification of sources and their control should be matters of

Asia↗
PubMed2001

Acute exposure to organochlorine pesticides does not affect striatal dopamine in mice.

The purpose of this study was to evaluate the possible association between the risk of developing Parkinson's disease (PD) and exposure to organochlorine pesticides in the mouse model. Animals were treated with a single subcutaneous injection of either dieldrin (40 and 80 mg/kg) or 2,4-dichlorophenoxyacetic acid (100 and 200 mg/kg, 2,4-D) and levels of dopamine (DA) and DA metabolites were measured in the striatum at the 7-day time point. Dieldrin exposure did not affect the striatal concentrations of DA, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). Administration of 2,4-D did not produce any changes with the exception of a slight (15%), but statistically significant decrease in DOPAC using the higher dose of the pesticide. No neurochemical signs of dopaminergic injury were found following the combined treatment with either dieldrin or 2,4-D plus diethyldithiocarbamate (DDC), a compound known to potentiate the effects of the dopaminergic toxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Furthermore, neither dieldrin nor 2,4-D caused additional damage in animals previously lesioned with MPTP. Data failed to support the hypothesis that acute exposure to organochlorine compounds or synergistic interactions involving these pesticides may cause significant damage to dopaminergic terminals and therefore contribute to nigrostriatal degeneration in PD.

Journal Article↗
PubMed1978

Effects of chlorinated hydrocarbon on plasma alpha-lipoprotein cholesterol in rats.

Ten chlorinated hydrocarbons (tetradifon, Chlorobenzilate, Kepone, lindane, Kelthane, toxaphene, dieldrin, hexachlorobenzene, dienochlor, and Aroclor 1254; see below) were evaluated in rats to assess agents which might selectively elevate high-density lipoprotein cholesterol (C-HDL). Single, nontoxic doses of Aroclor, dieldrin, and Kepone elevated C-HDL at day 7 (31%, 26%, and 24%, respectively, p less than 0.05). The C-HDL elevations were maintained at days 21 and 60 (28% and 31%, p less than 0.01) in the Aroclor group, while C-HDL returned to baseline in the dieldrin and Kepone groups. Liver function tests were unchanged from control, suggesting that the changes in C-HDL were not the consequence of hepatotoxicity. The hepatic microsomal cytochrome P-450 content of animals receiving Aroclor, dieldrin, and Kepone was 67%, 56%, and 44% higher than control values (p less than 0.02), indicating probable hepatic enzyme induction. If HDL (an antiatherogenic lipoprotein) is also selectively elevated by chlorinated hydrocarbons in man, then analogues might potentially be developed as antiatherogenic pharmacologic agents. Alternatively, the implications of man's exposure to halogenated hydrocarbons may be better understood.

Cholesterol↗
PubMed1984

Pollutants in harp seals (Phoca groenlandica). I. Organochlorines.

Between 1976 and 1978, 248 harp seals were sampled from 5 locations in the Northwest Atlantic and Arctic for organochlorine (OC) residue analysis in tissue. Blood, kidney, brain, muscle and blubber samples were analysed for PCB, DDT, dieldrin, hexachlorobenzene (HCB), and heptachlor epoxide. Levels were generally greatest in blubber tissue. Overall, mean levels of DDT and PCB were greater than those of other OC. A barrier prevented OC compounds from accumulating in the brain to the level one might expect in lipid tissues. Positive correlations were found between 1: DDT and PCB, 2: DDT and dieldrin, and 3: PCB and deildrin. Male harp seals bioaccumulated DDT, PCB, heptachlor epoxide and dieldrin with age. As a group, adult males sampled in the Gulf of St. Lawrence carried the highest concentrations of all OC, except that chlordane did not appear to bioaccumulate and levels of hexachlorobenzene were minimal. Females generally ceased exhibiting significant bioaccumulation once breeding age was reached, due to transplacental and transmammary residue transfer of OC from mother to pup. There were some significant differences in OC levels between locations with DDT: Gulf greater than Front; PCB: Gulf greater than Front; dieldrin: Gulf greater than Front; heptachlor epoxide: Front greater than Gulf. No significant differences were found, however, when northern locations (Grise Fiord, Northwest Greenland, Pangnirtung) were compared to southern (Gulf, Front) on a group basis. The latter is not surprising in view of the harp seals extensive cyclical annual migration between the southern breeding grounds and the High Arctic.

Animals↗
PubMed1987

Residues of organochlorine pesticides in environmental samples from the Shatt al-Arab River, Iraq.

Application of high resolution gas chromatography has confirmed relatively low residue levels of sumDDT, endrin and dieldrin in the Shatt al-Arab River. Thus, average concentration of these compounds in the edible portion of the cyprinid (Barbus xanthopetrus) were 21, 4 and 2 microg kg(-1) wet weight respectively. Mean values of sumDDT, endrin and dieldrin in surface sediments were 5, 40 and 20 microg kg(-1) dry weight respectively. Shrimps sampled from the Shatt al-Arab River were found to contain residues of o, p'-DDD only (average concentration was 2 microg kg(-1) wet weight). However, comparison of these samples with those from an area affected directly by a point source of organochlorine pesticides has shown that the cyprinid of the same age group contained significantly higher residue levels (average concentrations of sumDDT, endrin and dieldrin were 166, 20 and 7 microg kg(-1) wet weight respectively). Thus, it may be concluded that there was no direct input of organochlorine pesticides to the Shatt al-Arab River, and transportation via the natural processes, such as drainage, appeared to be the sole source. Based upon the observation that the original compound (p,p'-DDT) has not been detected in this river, it has also been concluded that there was no recent contribution of DDT here. Relatively higher residue levels of sumDDT, endrin and dieldrin were encountered in the muscles of the Indian shad captured from the Shatt al-Arab River (average concentrations were 163, 80 and 28 microg kg(-1) wet weight respectively). However, these elevated values were attributed to this fish being migratory and it being exposed to these pesticides elsewhere.

Journal Article↗
PubMed2004

The dechlorination of cyclodiene pesticides by methanogenic granular sludge.

Cyclodiene pesticides: aldrin, isodrin, dieldrin and endrin were dechlorinated by methanogenic granular sludge in spiked batch tests. Initial pesticides concentration was 7 or 9 mgl(-1). Two monodechlorinated analogues were formed during the conversions of aldrin and isodrin. Dieldrin was transformed into two monodechlorinated products as well as into aldrin and two monodechlorinated derivatives of aldrin. In respect of endrin three monodechlorinated and three didechlorinated products were found. The dechlorination of endrin was the most rapid, and was almost complete within 28 days. The dechlorinations of aldrin, isodrin and dieldrin were much slower: over a period of 3 months only 59%, 70% and 88% was transformed, respectively. The amounts of released chloride corresponded 0.54 +/- 0.23, 1.05 +/- 0.25, 1.10 +/- 0.12 of theoretical value for suggested reactions, for aldrin, isodrin and dieldrin respectively. For endrin it was much higher. These transformations did not occur in control samples containing autoclaved granules or in control blank samples without sludge. However, in aldrin spiked blanks, a conversion into a six-chlorinated analogue was found.

Anaerobiosis↗
PubMed2004

Soil-air exchange of organochlorine pesticides in the Southern United States.

Soil samples were collected from 30 farms in Alabama, Louisiana and Texas during 1999-2000 to determine residues of organochlorine pesticides (OCPs). One or more of the DDT compounds (p,p'-DDT, o,p'-DDT, p,p'-DDD, p,p'-DDE, o,p'-DDE) was above the quantitation limit (0.1 ng g(-1) dry weight) in every soil, and toxaphene was above the quantitation limit (3 ng g(-1)) in 26 soils. Chlordanes, dieldrin and hexachlorocyclohexane (HCH) isomers occurred less frequently (quantitation limits 0.1 ng g(-1) for dieldrin and 0.05 ng g(-1) for chlordanes and HCHs). OCPs were measured in air at 40 cm above the soil at selected farms to investigate soil-air partitioning. Concentrations of OCPs in air were positively and significantly (P<0.001-0.004) correlated to soil concentrations for toxaphene, p,p'-DDT, o,p'-DDT, p,p'-DDE, dieldrin, and trans-nonachlor. The regression was weaker (P=0.022) for cis-chlordane and not significant for trans-chlordane (P=0.43) nor gamma-HCH (P=0.80). Approach to soil-air equilibrium was assessed by calculating fugacities in the soil and air (f(s) and f(a)) for samples with quantifiable residues in both compartments. The fugacity fraction f(s)=0.5 at equilibrium and is <0.5 or >0.5 for net deposition and net volatilisation, respectively. Fugacity fractions varied greatly for different soil-air pairs, reflecting generally disequilibrium conditions. Mean fugacity fractions indicated near-equilibrium for some OCPs (p,p'-DDE, chlordanes, trans-nonachlor and dieldrin) and net volatilisation for others (p,p'-DDT, o,p'-DDT, toxaphene, gamma-HCH). Chiral analysis showed that enantioselective degradation of (+) or (-) o,p'-DDT in soil was accompanied by enrichment or depletion of the corresponding enantiomers in the overlying air, although there appeared to be some dilution by racemic o,p'-DDT from regional air transport.

Agriculture↗