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EXTOXNET PIP -DDT Page 4 of 6 levels were declining further, but DDT or metabolites were still seen in a very high proportion of the samples (73). Levels of DDT or metabolites may occur in fatty tissues (e.g. fat cells, the brain, etc.) at levels of up to several hundred times that seen in the blood (73). DDT or metabolites may also be elminated via motherOs milk by lactating women (73). ECOLOGICAL EFFECTS . Effects on Birds: DDT may be slightly toxic to practically non-toxic to birds. Reported dietary LD50s range from greater than 2,240 mg/kg in mallard, 841 mg/kg in Japanese quail and 1,334 mg/kg in pheasant(81). Other reported dietary LD50s in such species as bobwhite quail, California quail, red-winged blackbird, cardinal, house sparrow, blue jay, sandhill crane and clapper rail also indicate slight toxicity both in acute 5-day trials and over longer periods of up to 100 days (82). In birds, exposure to DDT occurs mainly through the food web through predation on aquatic and/or terrestrial species having body burdens of DDT, such as fish, earthworms and other birds (82). There has been much concern over chronic exposure of bird species to DDT and effects on reproduction, especially eggshell thinning and embryo deaths (82). The mechanisms of eggshell thinning are not fully understood. It is thought that this may occur from the major metabolite, DDE, and that predator species of birds are the most sensitive to these effects (82). Laboratory studies on bird reproduction have demonstrated the potential of DDT and DDE to cause subtle effects on courtship behavior, delays in pairing and egg laying and decreases in egg weight in ring doves and Bengalese finches (82). The implications of these for long-term survival and reproduction of wild bird species is unclear. There is evidence that synergism may be possible between DDTOs metabolites and organophosphate(cholinesterase-inhibiting) pesticides to produce greater toxicity to the nervous system and higher mortality(82). Aroclor(polychlorinated biphenyls, or PCBs) may result in additive effects on eggshell thinning (82). . Effects on Aquatic Species: DDT is very highly toxic to many aquatic invertebrate species. Reported 96-hour LC50s in various aquatic invertebrates (e.g., stoneflies, midges, crayfish, sow bugs) range from 0.18 ug/L to 7.0 ug/L, and 48-hour LC50s are 4.7 ug/L for daphnids and 15 ug/L for sea shrimp (55). Other reported 96-hour LC50s for various aquatic invertebrate species are from 1.8 ug/L to 54 ug/L (82). Early developmental stages are more susceptible than adults to DDTOs effects (82). The reversibility of some effects, as well as the development of some resistance, may be possible in some aquatic invertebrates (55). DDT is very highly toxic to fish species as well. Reported 96-hour LC50s are less than 10 ug/L in coho salmon (4.0 ug/L), rainbow trout(8.7 ug/L),northern pike (2.7 ug/L), black bullhead (4.8 ug/L), bluegill sunfish (8.6 ug/L), largemouth bass (1.5 ug/L), and walleye (2.9 ug/L) (55). The reported 96-hour LC50s in fathead minnow and channel catfish are 21.5 ug/L and 12.2 ug/L respectively(55). Other reported 96-hour LC50s in largemouth bass and guppy were 1.5 ug/L and 56 ug/L respectively (82). Observed toxicity in coho and chinook salmon was greater in smaller fish than in larger(82). It is reported that DDT levels of 1 ng/L in Lake Michigan were sufficient to affect the hatching of coho salmon eggs (3). DDT may be moderately toxic to some amphibian species and larval stages are probably more susceptible than adults(81, 82). In addition to acute toxic effects,DDT may bioaccumulate significantly in fish and other aquatic species, leading to long-term exposure. This occurs mainly through uptake from sediment and water into aquatic flora and fauna, and also fish (82). Fish uptake of DDT from the water will be size-dependent with smaller fish taking up relatively more than larger fish(82). A half-time for elimination of DDT from rainbow trout was estimated to be 160 days (82). The reported bioconcentration factor for DDT is 1,000 to 1,000,000 in various aquatic species (83), and bioaccumulation may occur in some species at very low environmental concentrations (55). Bioaccumulation may also result in exposure to species which prey on fish or other aquatic organisms (e.g., birds of prey). . Effects on Other Animals (Nontarget species): Earthworms are not susceptible to acute effects of DDT and its metabolites at levels higher than those likely to be found in the environment, but they may serve as an exposure source to species that feed on them (82). DDT is non-toxic to bees; the reported topical LD50 for DDT in honeybees is 27 ug/bee (82). Laboratory studies indicate that bats may be affected by DDT released from stored body fat during long migratory periods (82). ENVIRONMENTAL FATE http://extoxnet.orst.edu/pips/ddt.htm 3/7/2007