2Part Major Organic Pollutants The next eight chapters will be devoted to the ecotoxicology of groups of com- pounds that have caused concern on account of their real or perceived environmental effects and have been studied both in the laboratory and in the eld. These are pre- dominantly compounds produced by humans. However, a few of them, for example, methyl mercury, methyl arsenic, and polycyclic aromatic hydrocarbons (PAHs), are also naturally occurring. In this latter case, there can be difculty in distinguishing between human and natural sources of harmful chemicals. The compounds featured in Part 2 have been arranged into groups according to their chemical structures. In many cases, members of the same group show the same principal mechanism of toxic action. The chlorinated cyclodienes act upon gamma aminobutyric acid (GABA) receptors, the organophosphorous and carba- mate insecticides are anticholinesterases, the pyrethroids act upon sodium channels, the anticoagulant rodenticides are vitamin K antagonists, and some of the PAHs are genotoxic. From an ecotoxicological point of view, there are advantages when groups of compounds can be identied that share the same mechanism of action. Here, it becomes possible to relate the toxicity of a mixture of similar compounds to a single event—for example, acetylcholinesterase inhibition or vitamin K antagonism—and so biomarker assays can be developed, which monitor the effects of combinations of chemicals (see Chapter 13). Unfortunately, processes are not always so simple. The members of groups such as polychlorinated biphenyls (PCBs) and PAHs, for example, do not all operate through the same principal mechanism of action. Also, some individual pollutants such as p,pb-DDT or tributyl tin work through more than one mode of action. Thus, it is often not possible to measure the combined effects of members of one group of pollutants with a single mechanistic biomarker assay. The situation © 2009 by Taylor & Francis Group, LLC 100 Organic Pollutants: An Ecotoxicological Perspective, Second Edition becomes complex when dealing with mixtures of different types of pollutants oper- ating through contrasting mechanisms of action, a problem that will be addressed in Part 3 of this text. © 2009 by Taylor & Francis Group, LLC 101 5 The Organochlorine Insecticides 5.1 BACKGROUND The organochlorine insecticides (henceforward OCs) can be divided into three main groups, each of which will be discussed separately in the sections that follow. These are (1) DDT and related compounds, (2) the cyclodiene insecticides, and (3) isomers of hexachlorocyclohexane (HCH; Brooks 1974; Figure 5.1). The rst OC to become widely used was dichlorodiphenyl trichloroethane (DDT). Although rst synthesized by Zeidler in 1874, its insecticidal properties were not discovered until 1939 by Paul Mueller of the Swiss company J.R. Geigy AG. DDT production commenced during the Second World War, in the course of which it was mainly used for the control of insects that are vectors of diseases, including malarial mosquitoes and the ectoparasites that transmit typhus (e.g., lice and eas). DDT was used to control malaria and typhus both in military personnel and in the civilian population. After the war, it came to be used widely to control agricultural and for- est pests. Following the introduction of DDT, related compounds rhothane (DDD) and methoxychlor were also marketed as insecticides, but they were only used to a very limited extent. Restrictions began to be placed on the use of DDT in the late 1960s, with the discovery of its persistence in the environment and with the growing evidence of its ability to cause harmful side effects. Cl Cl Cl Cl Cl Cl Cl H Aldrin H Cl C H CCl 3 p,p´-DDT Cl ClC H CHCl 2 p,p´-DDD Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl O O Cl H Dieldrin H Cl H Endrin γ-HCH (lindane) H FIGURE 5.1 Organochlorine insecticides. © 2009 by Taylor & Francis Group, LLC 102 Organic Pollutants: An Ecotoxicological Perspective, Second Edition The cyclodiene insecticides aldrin, dieldrin, endrin, heptachlor, endosulfan, and others were introduced in the early 1950s. They were used to control a variety of pests, parasites, and, in developing countries, certain vectors of disease such as the tsetse y. However, some of them (e.g., dieldrin) combined high toxicity to verte- brates with marked persistence and were soon found to have serious side effects in the eld, notably in Western European countries where they were extensively used. During the 1960s, severe restrictions were placed on cyclodienes so that few uses remained by the 1980s. HCH, sometimes misleadingly termed benzene hexachloride (BHC), exists in a number of different isomeric forms of which the gamma isomer has valuable insec- ticidal properties. These were discovered during the 1940s, and HCH came to be widely used as an insecticide to control crop pests and certain ectoparasites of farm animals after the Second World War. Crude technical BHC, a mixture of isomers, was the rst form of HCH to be marketed. In time, it was largely replaced by a rened product called lindane, containing 99% or more of the insecticidal gamma isomer. Those OCs that came to be widely marketed were stable solids that act as neuro- toxins. Some OCs, or their stable metabolites, proved to have very long biological half-lives and marked persistence in the living environment. Where persistence was combined with high toxicity, as in the case of dieldrin and heptachlor epoxide (stable metabolite of heptachlor), there were sometimes serious environmental side effects. Because of these undesirable properties, no fewer than eight out of twelve chemi- cals or chemical groups identied by the United Nations Environment Programme (UNEP) as persistent organic pollutants (POPs or, more informally, “the dirty dozen”) are OCs. These are aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, and toxaphene. The intention is that high priority should be given by national and international environmental regulatory bodies to the eventual removal of POPs from the environment. 5.2 DDT [1,1,1,-TRICHLORO-2,2-BIS (P-CHLOROPHENYL) ETHANE] 5.2.1 C HEMICAL PROPERTIES The principal insecticidal ingredient of technical DDT is p,pb-DDT (Table 5.1 and Figure 5.1). The composition of a typical sample of technical DDT is given in Table 5.2. The composition of the technical insecticide varies somewhat between batches. However, the ppb isomer usually accounts for 70% or more of the total weight. The o,pb isomer is the other major constituent, accounting for some 20% of the technical product. o,pb-DDT is more readily degradable and less toxic to insects and verte- brates than the p,pb isomer. The presence of small quantities of p,pb-DDD deserves mention. Technical DDD has been marketed as an insecticide on its own (rhothane) and the p,pb isomer is a reductive metabolite of p,pb-DDT. p,pb-DDT is a stable white crystalline solid with a melting point of 108°C. It has very low solubility in water and is highly lipophilic (log K ow = 6.36); thus, there is a high potential for bioconcentration and bioaccumulation. It has a low vapor pressure, © 2009 by Taylor & Francis Group, LLC The Organochlorine Insecticides 103 and is consequently relatively slow to sublimate when applied to surfaces (e.g., leaves, walls, or surface waters). p,pb-DDT is not very chemically reactive. However, one important chemical reac- tion is dehydrochlorination to form p,pb-DDE, which takes place in the presence of KOH, NaOH, and other strong alkalis. Dehydrochlorination is also a very important biotransformation and will be discussed further in Section 5.2.2. p,pb-DDT under- goes reductive dechlorination by reduced iron porphrins. In the presence of strong radiation, it undergoes slow photochemical decomposition. TABLE 5.1 Chemical Properties of Organochlorine Insecticides Chemical Description Water Sol. (mg/L) log K OW Vapor Pressure mm Hg (at 25nC) p,pb-DDT Solid <0.1 6.36 1.9 × 10 −7 (20°C) m.p. 108°C p,pb-DDD Solid <0.1 m.p. 109°C Aldrin Solid <0.1 6.5 × 10 −5 m.p. 104°C Dieldrin Solid 0.2 5.48 3.2 × 10 −6 m.p. 178°C Heptachlor Solid 0.056 5.44 4 × 10 −4 m.p. 93°C Endrin Solid 0.2 5.34 2 × 10 −7 m.p. 226–230°C Endosulfan Solid 0.06–0.15 1 × 10 −5 m.p. 79–100°C Gamma HCH Solid 7 3.78 9.4 × 10 -6 m.p. 112°C Note: m.p. = melting point. TABLE 5.2 Composition of a Typical Sample of Technical DDT Compound Percentage of Technical Product p,pb-DDT 72 o,pb-DDT 20 p,pb-DDD 3 o,ob-DDT 0.5 Other 4.5 © 2009 by Taylor & Francis Group, LLC 104 Organic Pollutants: An Ecotoxicological Perspective, Second Edition 5.2.2 METABOLISM OF DDT p,pb-DDT is rather stable biochemically as well as chemically. Thus, it is markedly persistent in many species on account of its slow biotransformation. Metabolism of p,pb-DDT is complex, and there is still some controversy about its specics. The most important metabolic pathways are shown in Figure 5.2. A major route of biotransformation in animals is dehydrochlorination to the stable lipophilic and highly persistent metabolite p,pb-DDE. p,pb-DDE is far more persis- tent in animals than is p,pb-DDT. Therefore, dehydrochlorination does not promote excretion, although it usually results in detoxication because the metabolite is less acutely toxic than the parent compound. However, as will be seen, p,pb-DDE causes certain sublethal effects. Such metabolic conversion of parent compounds to persis- tent lipophilic metabolites also occurs with other OCs (see Section 5.3.2), and they may be regarded as a malfunction of detoxication systems that originally evolved to promote the elimination of naturally occurring lipophilic xenobiotics through the rapid excretion of their water-soluble metabolites and conjugates (Chapter 1). The dehydrochlorination of p,pb-DDT is catalyzed by a form of glutathione-S-transferase, and involves the formation of a glutathione conjugate as an intermediate. Under anaerobic conditions, p,pb-DDT is converted to p,pb-DDD by reductive dechlorination, a biotransformation that occurs postmortem in vertebrate tissues such as liver and muscle and in certain anaerobic microorganisms (Walker and Jefferies 1978). Reductive dechlorination is carried out by reduced iron porphyrins. It is carried out by cytochrome P450 of vertebrate liver microsomes when supplied with NADPH in the absence of oxygen (Walker 1969; Walker and Jefferies 1978). Reductive dechlorination by hepatic microsomal cytochrome P450 can account for the relatively rapid conversion of p,pb-DDT to p,pb-DDD in avian liver immediately after death, and mirrors the reductive dechlorination of other organochlorine sub- strates (e.g., CCl 4 and halothane) under anaerobic conditions. It is uncertain to what extent, if at all, the reductive dechlorination of DDT occurs in vivo in vertebrates (Walker 1974). Cl ClC H CCl 3 p,p´-DDT Reductive dechlorination DDT dehydrochlorinase ? Route MO Cl ClC H CCl 2 p,p´-DDE Cl ClC H COOH p,p´-DDA (excreted as peptide conjugates) Cl ClC OH CCl 3 Kelthane Cl ClC H CHCl 2 p,p´-DDD FIGURE 5.2 Metabolism of p,pb-DDT. © 2009 by Taylor & Francis Group, LLC The Organochlorine Insecticides 105 A major, albeit slow, route of detoxication in animals is conversion to the water- soluble acid p,pb-DDA, which is excreted unchanged, or as a conjugate. In one study, the major urinary metabolites of p,pb-DDT in two rodent species were p,pb-DDA- glycine, p,pb-DDA-alanine, and p,pb-DDA-glucuronic acid (Gingell 1976). The route by which p,pb-DDA is formed remains uncertain. Early studies suggested that con- version might be via p,pb-DDD, but the later observation that this is a postmortem process has cast some doubt on these ndings. Some or all of the p,pb-DDD found in livers in these studies would have been generated postmortem because analysis was carried out after a period of storage. Another possibility is that this process, similar to dehydrochlorination, takes place via glutathione conjugation. After conjugation and consequent loss of HCl, the DDE moiety, which remains bound to glutathione, may undergo hydrolysis, leading eventually to deconjugation and formation of p,pb-DDA. A mechanism of this type has been proposed for the conversion of dichloromethane to HCHO (Schwarzenbach et al. 1993, p. 514; Chapter 2, Figure2.15 of this book). One other biotransformation deserving mention is the oxidation of p,pb-DDT to kelthane, a molecule that has been used as an acaricide. This biotransformation occurs in certain DDT-resistant arthropods, but does not appear to be important in vertebrates. Unchanged p,pb-DDT tends to be lost only very slowly by land vertebrates. There can, however, be a certain amount of excretion by females into milk or across the pla- centa into the developing embryo (mammals) or into eggs (birds, reptiles, and insects). 5.2.3 ENVIRONMENTAL FATE OF DDT In discussing the environmental fate of technical DDT, the main issue is the per- sistence of p,pb-DDT and its stable metabolites, although it should be born in mind that certain other compounds—notably, o,pb-DDT and p,pb-DDD—also occur in the technical material and are released into the environment when it is used. The o,pb isomer of DDT is neither very persistent nor very acutely toxic; it does, however, have estrogenic properties (see Section 5.2.4). A factor favoring more rapid metabo- lism of the o,pb isomer compared to the p,pb isomer is the presence, on one of the benzene rings, of an unchlorinated para position, which is available for oxidative attack. p,pb-DDD, the other major impurity of technical DDT, is the main component of technical DDD, which has been used as an insecticide in its own right (rhothane). p,pb-DDD is also generated in the environment as a metabolite of p,pb-DDT. In prac- tice, the most abundant and widespread residues of DDT found in the environment have been p,pb-DDE, p,pb-DDT, and p,pb-DDD. When DDT was widely used, it was released into the environment in a number of different ways. The spraying of crops, and the spraying of water surfaces and land to control insect vectors of diseases, were major sources of environmental contamina- tion. Waterways were sometimes contaminated with efuents from factories where DDT was used. Sheep-dips containing DDT were discharged into water courses. Thus, it is not surprising that DDT residues became so widespread in the years after the war. It should also be remembered that, because of their stability, DDT residues can be circulated by air masses and ocean currents to reach remote parts of the globe. Very low levels have been detected even in Antarctic snow! © 2009 by Taylor & Francis Group, LLC 106 Organic Pollutants: An Ecotoxicological Perspective, Second Edition Some data on the half-lives of these three compounds are given in Table 5.3. All of them are highly persistent in soils, with half-lives running to years once they become adsorbed by soil colloids (especially organic matter—see Chapter 3). The degree of persistence varies considerably between soils, depending on soil type and temperature. The longest half-lives have been found in temperate soils with high levels of organic matter. (See, for example, Cooke and Stringer 1982.) Of particular signicance is the very long half-lives for p,pb-DDE in terrestrial animals, approach- ing 1 year in some species, and greatly exceeding the comparable values for the other two compounds. This appears to be the main reason for the existence of much higher levels of p,pb-DDE than of the other two compounds in food chains even when technical DDT was widely used. Following the wide-ranging bans on the use of DDT in the 1960s and 1970s, p,pb-DDT residues have fallen to very low levels in biota, although signicant residues of p,pb-DDE are still found, for example, in terrestrial food chains such as earthworms n thrushes n sparrow hawks in Britain (Newton 1986) and in aquatic food chains. A nationwide investigation of OC residues in bird tissues and bird eggs was con- ducted in Great Britain in the early 1960s, a period during which DDT was widely used (Moore and Walker 1964). The most abundant residue was p,pb-DDE; levels of p,pb-DDT and p,pb-DDD were considerably lower. Levels in depot fat were some 10–30-fold higher than in tissues such as liver or muscle. The magnitude of residues was related to position in the food chain, with low levels in omnivores and herbivores and the highest levels in predators at the top of both terrestrial and aquatic food chains (see Walker et al. 1996, Chapter 4). Similar results were obtained with both bird tissues and eggs. The highest p,pb-DDE levels (9–12 ppm) were found in the eggs of sparrowhawks, which are bird eaters, and in herons (Ardea cinerea), which are sh eaters. Thus, when considering the fate of technical DDT in food chains generally, p,pb-DDE was found to be more stable and persistent (i.e., refractory) than TABLE 5.3 Half-Lives of p,pb-DDT and Related Compounds Compound Material/ Organism t 50 (Years) Compound Material/ Organism t 50 (Days) p,pb-DDT Soil 2.8 p,pb-DDT Feral pigeon (Columba livia) 28 p,pb-DDD Soil 10+ (British soils) p,pb-DDD Feral pigeon 24 p,pb-DDE Feral pigeon 250 p,pb-DDT Bengalese nch (Lonchura striata) 10 p,pb-DDT Hens (Gallus domesticus) 36–56 (in fat) p,pb-DDT Rat 57–107 p,pb-DDT Rhesus monkey 32 and 1520 Source: Data from Edwards (1973) and Moriarty (1975). © 2009 by Taylor & Francis Group, LLC The Organochlorine Insecticides 107 either p,pb-DDT or p,pb-DDD and underwent strong biomagnication with transfer along food chains. Studies on the marine ecosystem of the Farne Islands in 1962–1964 showed that p,pb-DDE reached concentrations over 1000-fold higher in sh-eating birds at the top of the food chain than those present in macrophytes at the bottom of the food chain (Figure 5.3). Fish-eating shag (Phalocrocorax aristotelis) contained residues some 50-fold higher than those in its main prey species, the sand eel (Ammodytes lanceolatus). The sand eel was evidently the principal source of p,pb-DDE for the shag, so there had apparently been very efcient bioaccumulation over a consider- able period (Robinson et al. 1967a). However, as explained in Chapter 4, it should be borne in mind that the biomagnication of highly lipophilic chemicals along the entire aquatic food chain is a consequence not only of bioaccumulation through the different stages of the food chain, but also of bioconcentration of chemicals present in ambient water. For example, aquatic invertebrates of lower trophic levels acquire much of their residue burden of lipophilic compounds such as p,pb-DDE by direct uptake from ambient water (see Chapter 4). In a study of marine food chains in the Pacic Ocean during the 1980s, biocon- centration factors of the order of 10,000-fold for total DDT residues (very largely p,pb-DDE) were reported when comparing levels in zooplankton with those in ambi- ent water (Tanabe and Tatsukawa 1992). Striking levels of biomagnication were evident in the higher levels of the food chain. Thus, in comparison with residues in zooplankton, mycotophid (Diaphus suborbitalis) and squid (Todarodes pacicus) contained residues some tenfold greater, and striped dolphin (Stenella coerolea alba), several 100-fold greater. Total DDT residues of <50 mg/kg wet weight of blubber were reported for the striped dolphin. In a later study conducted in the Mediterranean in 0.001 1 23 Trophic Levels 45 12345 Concentration of Organochlorine Compound (ppm) 0.01 0.1 1.0 10.0 HEOD (dieldrin) DDE FIGURE 5.3 Organochlorine insecticides in the Farne Island ecosystem. From Walker et al. (2000). Trophic levels: (1) serrated wrack, oar weed; (2) sea urchin, mussel, limpet; (3) lobster, shore crab, herring, sand eel; (4) cod, whiting, shag, eider duck, herring gull; (5) cormorant, gannet, grey seal. © 2009 by Taylor & Francis Group, LLC 108 Organic Pollutants: An Ecotoxicological Perspective, Second Edition 1990, total DDT residues of <230 mg/kg were reported for this species (Kannan et al. 1993; O’Shea and Aguilar 2001), producing further evidence of the continuing high level of pollution in this inland sea. In a study conducted in 1995, total DDT residues (very largely p,pb-DDE) were determined in marine organisms from the Barents Sea, near Svalbard in the Arctic (Borga, Gabrielsen, and Skaare 2001). Again, marked biomagnication was evident in residues, expressed as micrograms per gram in lipid with movement up the food chain, as indicated in the following table. Whole samples of sh and excised livers of birds were submitted for analysis. Trophic level Organisms Biomagnification Factors for Total DDT (cf. trophic levels 2/3) 2/3 Crustaceans 1 4 Cod (Gadus morhua) r 2 Guillemots (Uria lomvia and Cepphus grylle) r 47 Kittiwake (Rissa tridactyla) r 82 5 Glaucous gull (Larus hyperboreus) r 2300 Once again, sh-eating species—the two guillemots and the kittiwake—in trophic level 4 show considerable biomagnication of residue in comparison with the inverte- brates of levels 2 and 3. Most strikingly, though, the ultimate predator in trophic level 5, the glaucous gull, shows a biomagnication factor of 2300! It is suggested that this may be related to the fact that these predators feed upon fauna associated with ice. The mean value for total DDT levels in the livers of glaucous gulls, expressed as micrograms per gram in lipid, was 42. In a later study of organochlorine residues in arctic seabirds (Borga et al. 2007), p,pb-DDE remained a dominant residue in birds occupying positions in higher trophic levels, these species including little auk (Alle alle) as well as the two species of guillemot and kittiwake mentioned here. The dif- ferential biomagnication of organochlorine residues was examined in these species and related to factors such as diet, habitat, and metabolic capacity. Finally, an investigation of total DDT levels in seal (Phoca sibirica) from Lake Baikal, Russia (the largest lake in the world), during the 1990s showed substantial levels with evidence of strong biomagnication in this aquatic food chain (Lebedev et al. 1998). p,pb-DDE can also undergo bioaccumulation in terrestrial food chains. Studies with earthworms and slugs indicate that there can be a bioconcentration of total DDT residues (p,pb-DDT + p,pb-DDE + p,pb-DDD) relative to soil levels of one- to fourfold by earthworms, and above this by slugs (Bailey et al. 1974; Edwards 1973). When DDT was still widely used in orchards in Britain, blackbirds (Turdus merula) and song thrushes (Turdus philomelis) that had been found dead contained very high levels of DDT residues in comparison with those in the earthworms they ate. Some results from a study on one orchard sprayed with DDT are given in Table 5.4. Interpretation of eld data involving such small numbers of individual specimens needs to be done with caution. However, the principal source of DDT residues for the two Turdus species appears to have been earthworms and other invertebrates (including slugs and snails). The birds found dead were probably poisoned by DDT © 2009 by Taylor & Francis Group, LLC [...]... Birds LC50 LC50 LC50 LC50 (96 h) LD50 (acute oral) LD50 (acute oral) LD50 (acute oral) LD50 (acute oral) 0. 45 2.4 μg/L (48 or 96 h) 28 μg/L (48 or 96 h) 0.4–1800 μg/L (48 or 96 h) 1 .5 5. 6 μg/L 100– 250 0 mg/kg 880–1240 mg/kg 400–3400 mg/kg >50 0 mg/kg Source: Data from ETC 9, ETC 83, and Edson et al (1966) © 2009 by Taylor & Francis Group, LLC 112 5. 2 .5 Organic Pollutants: An Ecotoxicological Perspective, ... livia) Rat 96h LC50 330 μg/L 96h LC50 4–18 μg/L 96h LC50 1.2–9.9 μg/L 96h LC50 7 μg/L Acute oral LD50 37–87 mg/kg Acute oral LD50 45 50 mg/kg Acute oral LD50 40–162 mg/kg Acute oral LD50 67 mg/kg Acute oral LD50 4–43 mg/kg Sources: Environmental Health Criteria 38, 91, and 130 © 2009 by Taylor & Francis Group, LLC 124 Organic Pollutants: An Ecotoxicological Perspective, Second Edition and birds Heptachlor... wide-ranging review of two of the most important cyclodienes Moriarty, F (Ed.) (19 75) Organochlorine Insecticides: Persistent Organic Pollutants—A collection of focused chapters on ecotoxicological aspects of the organochlorine insecticides Shore, R.F and Rattner, B.A (2001) Ecotoxicology of Wild Mammals—A very detailed, well-structured, and well-referenced text in which organochlorine insecticides and... especially in insects where dehydrochlorination of p,p -DDT represents a detoxication mechanism despite the greater persistence of the metabolite compared to the parent compound TABLE 5. 5 Ecotoxicity of p,p -DDT and Related Compounds Compound Organism Test Median Lethal Dose or Concentration p,p -DDT p,p -DDE p,p -DDT p,p -DDT p,p -DDT p,p -DDE p,p -DDD p,p -DDT Marine invertebrates Marine invertebrate (brown... the 1961 population decline and subsequent recovery, together with an outline of pesticide usage (from Ratcliffe 1993) © 2009 by Taylor & Francis Group, LLC 126 Organic Pollutants: An Ecotoxicological Perspective, Second Edition % Tilled land 60% 4 FIGURE 5. 8 Changes in the status of sparrowhawks in relation to agricultural land use and organochlorine use The agricultural... Pigeon Dog Man 2 .5 yr 0.3 yr 0.8 yr 12– 15 d 47 d (mean) 28–32 d 369 d (mean) Sources: Soil data from Edwards (1973) Data for pigeon from Robinson et al (1967b) Other data from Environmental Health Criteria 91 © 2009 by Taylor & Francis Group, LLC 120 Organic Pollutants: An Ecotoxicological Perspective, Second Edition Table 5. 8 gives some examples of cyclodiene half-lives measured in (1) soils, and (2)... acute toxicity of p,p -DDT to both vertebrates and invertebrates is attributed mainly to its action upon axonal Na+ channels, which are voltage dependent (see Figure 5. 4; Eldefrawi and Eldefrawi 1990) The molecule binds reversibly to a site © 2009 by Taylor & Francis Group, LLC 110 Organic Pollutants: An Ecotoxicological Perspective, Second Edition FIGURE 5. 4 Sites of action of organochlorine insecticides:... 1976–82 1983–86 20 20 Number 20 Number 25 1963– 75 Number 25 0. 75 ppm 15 10 4.8 ppm 5 15 0 .55 ppm 10 5 0 0.1 1 10 100 ppm HEOD (log scale) 100 0.1 1 10 ppm HEOD (log scale) 0 0.1 1 100 ppm HEOD (log scale) 10 8 6 4 2 0 0.01 75 Area 1 1963–86 Number Number (a) 0.1 1 10 ppm HEOD (log scale) 100 Area 2 1963–86 50 25 0 0.01 0.1 1 10 ppm HEOD (log scale) 100 (b) FIGURE 5. 9 (a) Distribution of dieldrin (HEOD)... German cockroach, and the mosquito Anopheles arabiensis (Du et al 20 05) also confer very high levels of resistance to dieldrin An alanine-to-glycine substitution in another mosquito, Anopheles gambiae, has also been shown to confer resistance to dieldrin (Du et al 20 05) The levels of resistance of these strains to HCH and certain other cyclodienes are far less than those shown to dieldrin (Salgado... isomers, the alpha and beta forms are less toxic than the gamma form However, the beta form is more persistent than the gamma form, and unacceptably high residues have sometimes been reported in foods originating from countries where technical HCH is still used (Environmental Health Criteria 123) © 2009 by Taylor & Francis Group, LLC 132 5. 5 Organic Pollutants: An Ecotoxicological Perspective, Second . Product p,pb-DDT 72 o,pb-DDT 20 p,pb-DDD 3 o,ob-DDT 0 .5 Other 4 .5 © 2009 by Taylor & Francis Group, LLC 104 Organic Pollutants: An Ecotoxicological Perspective, Second Edition 5. 2.2 METABOLISM. herring, sand eel; (4) cod, whiting, shag, eider duck, herring gull; (5) cormorant, gannet, grey seal. © 2009 by Taylor & Francis Group, LLC 108 Organic Pollutants: An Ecotoxicological Perspective, . p,pb-DDT p,pb-DDE p,pb-DDD Total DDT Residues/Sample Soil Random 1.2–3 .5 0 .5 1.1 0.22–0.72 2.1 5. 3 Earthworm Random 1.1–6.8 1.4–4.2 0.46 5. 5 3.9–11 .5 Blackbird 2 birds found dead 0/6.8 130/180 58 /195