Aldrin species differences

As mentioned earlier (Figure 5.5), aldrin and heptachlor are rapidly metabolized to their respective epoxides (i.e., dieldrin and heptachlor epoxide) by most vertebrate species. These two stable toxic compounds are the most important residues of the three insecticides found in terrestrial or aquatic food chains. In soils and sediments, aldrin and heptachlor are epoxidized relatively slowly and, in contrast to the situation in biota, may reach significant levels (note, however, the difference between aldrin and dieldrin half-lives in soil shown in Table 5.8). The important point is that, after entering the food chain, they are quickly converted to their epoxides, which become the dominant residues. 

As a consequence, our research group has been involved in the assessment of the residue levels in both marine and freshwater ecosystems, as well as in the determination of persistence, toxic effects to fish and the transport of these compounds in different soils in the country. A comparative review of the pesticides, phosphates and polychlorinated biphenyls residues detected in water, sediments and biota from fresh water ecosystems and their effect on fish species has been presented. It gives comparative levels of a number of pesticides studied that include aldrin, dieldrin, a-endosulfan, endrin, DDT, DDE, DDD, PCBs and lindane for the period between 1998 and 2004. The previously detected residue levels in marine samples ranged from 0.503 to 9.025 pg/1 in seawater, 0.584 to 59.0 pg /kg in sediments and BDL to 101 Ipg /kg in biota. The residue levels in freshwater ecosystem ranged between BDL and 0.44 pg/1 in water, BDL and 65.48 pg/kg in sediments, BDL and 10.07 pg/kg in weeds, and BDL and 481.18 pg/kg in fish samples. 

Dick and Scott (1992) measured skin permeability of several lipophilic (aldrin, carbaryl, and fluaziflop-butyl) and hydrophilic (water, maimitol, and paraquat) compounds in pig ear skin, rat dorsal skin, and hiunan abdominal skin. Although different concentrations and vehicles make a comparison of the compounds difficult, all the data can be used for interspecies comparison because the vehicle and penetrant concentration were the same for all species studied. There is a discrepancy between values shown in Figure 4 and Table 1 that appears to be an error in the typesetting of Table 1 (see discussion in Appendix B). The quahtative conclusion that pig ear skin and rat dorsal skin are both more permeable than human abdominal skin is not affected by this error. 

It is well known that farmers use different types of insecticides to protect crops from insects. The more widely used insecticides are organophosphates, carbamates and organochlorides. Of these, organophosphates and carbamates are less persistent in the environment compared to the organochlorides (for example aldrin, dieldrin and DDT). Though the latter are definitely effective but they tend to bioaccumulate in many plant and animal species and incorporate into the food chain. Some of the insecticides are also responsible for the population decline" of beneficial insects and animals, such as honeybees, lacewings, mites, bald eagles etc. 

Chlorinated pesticides differ substantially in their toxicity to aquatic plants. Endrin is among the most toxic, inhibiting growth and carbon uptake at concentrations as low as 0.1-1.0 [xg (Menzel etal., 1970). Equally low levels of dieldrin and aldrin may reduce growth, whereas DDT and DDE generally have little inhibitory effect below 1.0 /xg (Luard, 1973 Powers etal, 1975). Development of tolerance to DDT and its derivatives is frequent, and there are several species that are apparently unaffected by DDT levels > 1000 jug L (Luard, 1973). Chlordane generally elicits toxic responses at concentrations < 50 ju.g L and is therefore more toxic than either heptachlor or toxaphene. However, this order is subject to considerable variability, due to the development of resistance, effects of other species-related variables, and differences in environmental conditions. Lindane and its isomers are generally the least toxic of the pesticides and probably pose little threat to aquatic plants in natural waters the majority of species tolerate concentrations > 1000 /xg L (Luard, 1973). 

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