TOXICITY OF SCRAP TIRE LEACHATES IN ESTUARINE SALINITIES - ARE TIRES ACCEPTABLE FOR ARTIFICIAL REEFS

Shredded scrap tires were leached in a modified toxicity characteristi c leaching procedure (TCLP) extraction method in synthetic saltwater s olutions for three sequential 7-d periods. Test salinities were 5, 15, and 25 parts per thousand. Acute toxicity tests were conducted with l arval sheepshead minnows Cyprinodon variegatus and daggerblade grass s hrimp Palaemonetes pugio. Mortality decreased following multiple seque ntial leaching periods. Toxicity decreased with increasing salinity. T he fish were more sensitive than the grass shrimp. Dilution series tox icity bioassays were performed with fish and grass shrimp at 5 parts p er thousand salinity and at 15 parts per thousand with fish only. The 96-h LC50s (lethal concentration for half of the test animals) for fis h were 10% leachate at 5 parts per thousand and 26% at 15 parts per th ousand. The 96-h LC50 for grass shrimp at 5 parts per thousand was 63% . The 96-h lowest observed effect concentrations (LOEC) for fish survi val were 12.5% at 5 parts per thousand and 25% at 15 parts per thousan d. The 96-h LOEC for grass shrimp survival was 50% at 5 parts per thou sand. Growth LOEC values were 12.5% at both salinities for fish and 50 % for grass shrimp at 5 parts per thousand. Chemical analyses revealed no specific components as the cause of observed toxicity. Antagonism between sea salt and toxic chemicals is hypothesized to cause differen tial toxicity at varying salinities, as opposed to differential solubi lity of the toxicants. Extrapolation of laboratory results indicates t hat proposed tire reefs should not pose a serious threat to water qual ity in Chesapeake Bay. No observed effects concentrations (NOEC) were an order of magnitude or greater above field concentrations calculated from simplified methods. Toxic substances appear to leach from the su rface of the tires not from the tire matrix. The use of tires in highe r salinity environments appears to pose little direct toxicological ri sk to resident organisms. However, because unknown toxic chemicals wer e present in leachates at all test salinities, no assessment can be ma de regarding persistence, fate, transport, or possible bioaccumulative effects.