Dieldrin sublethal effects

FIGURE 5.6 Dieldrin intoxication in hnmans and its relationship to blood levels. The hatched area represents the sublethal effects seen at 15-30% of lethal threshold concentration in blood (after Jager 1970). 

Moriarty, F.M. (1968). The toxicity and sublethal effects of p-p -DDT and dieldrin to Aglais urticae and Chorthippus brunneus. Annals of Applied Biology 62, 371-393. 

Experimental animals exposed to sublethal doses of cyclodienes show a similar picture, with changes in EEG patterns, disorientation, loss of muscular coordination and vomiting, as well as convulsions, the latter becoming more severe with increasing doses (Hayes and Laws 1991). It is clear from these wide-ranging studies that a number of neurotoxic effects can be caused by cyclodienes at levels well below those that are lethal. In the human studies described here, subclinical symptoms were frequently reported when dieldrin blood levels were in the range 50-100 pg/L, an order of magnitude below those associated with lethal intoxication. 

One negative effect of pesticide use is how they stimulate suppressed species. For example, DDT and several other pesticides may accelerate the development of suppressed species (just as they did with the spider mites) and increase the frequency with which new generations are born. Sublethal doses of dieldrin and parathion do not decrease the Colorado beetle s egg production - they increase it by 33-65% in a way we do not yet understand [3]. Data from 1976 showed that using carbofurans increased the Colorado beetle population in several U.S. states [20]. Trichlorfon also stimulates the Colorado beetle s development at specific dose levels. 

Researchers were also able to establish the link between declines of other predatory species such as the European sparrowhawk and the use of organo-chlorine pesticides other than DDT. For instance, the cyclodiene insecticides aldrin, dieldrin, and he-ptachlor used as seed treatments caused massive mortality of both seed-eating species and their predators. All of the insecticides had the following points in common they were highly soluble in fats and refractory to metabolism. The impacts on the predatory species typically take place in periods of food stress when fat soluble residues are released from fat stores and returned into general circulation. In a food-stressed individual, the brain remains as the most lipid rich tissue and this is where contaminants move to. Toxicity results when threshold values in brain tissue are exceeded. At sublethal levels, documented effects of cyclodiene insecticides in birds have included changes in their reproductive, social, and avoidance behaviors. 

Under the present system (EPA, 1996b), the two numbers in the criterion are calculated from the final acute value, the final chronic value, and the final plant value. The three values for dieldrin in freshwater and salt water are shown in Table VII. The criterion maximum concentration is equated to half the final acute value. Division by 2 in this case to some extent corrects for the fact that much of the acute toxicity information is based on observations of lethal effects, whereas the real concern is protection of organisms fi om sublethal stresses. The criterion continuous concentration is the smaller of the final chronic value and the final plant value. 

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