API DR79-1984 Development of a Diluting Concentration method for Testing the Acute Toxicity of Chemically Dispersed Oil@ and the Results of Comparative studies (Reprinted in 1993)
"Introduction For several years the accepted method of testing the comparative toxicity of pollutants for a range of freshwater and marine species has been the 96-hr LC50 method (APHA@ 1975). These tests were usually conducted in closed (""static"") systems without feeding or replenishment of toxicants. The 4-day period was such that feeding was not needed (in most cases) and many of the toxicants did not evaporate substantially. As more chemical analyses were conducted@ investigators began to recognize that significant amounts of many toxicants sorbed to the walls of vessels@ evaporated@ and were taken up by the organisms. In tests with petroleum@ there were also problems with droplets moving to the surface (forming slicks) and numerous alterations related to different specific components. The inconsistencies were such that only water-soluble (or accommodated) fractions of oil could be linearly diluted. Decreases in component concentrations in as little as 24 hr could be as high as 90%. It was clearly necessary to utilize flowing exposures in tests with oils@ where the dominant hydrocarbons were still those that dissolved in seawater. Tests conducted with flowing exposures of soluble hydrocarbons have@ not suprisingly@ shown that organisms are affected at lower concentrations than those produced in static tests (Vanderhorst et al.@ 1976). Some of the flowing exposures have been conducted for several days or even weeks (Anderson et al.@ 1980). Many sublethal studies were also conducted for weeks or months and indicated that quite low concentrations affected the organisms (Caldwell et al.@ 1977). It became apparent that there was a need to develop a system for comparing the long-term tests with short-term (96-hr) bioassays. The most logical means of making such comparisons would be to consider time of exposure as a variable 2 equal in importance to concentration of exposure. If this hypothesis were valid@ then a 2-day exposure to 10 parts per million (ppm) of a water-soluble extract should produce the same effect as a 5-day exposure to 4 ppm@ or a 10-day exposure at 2 ppm@ etc. The relationship has been found to be consistent for exposure periods between about 8 hours and 8 days. Anderson et al. (1980) have shown that three species of crustaceans (2 shrimp and a mysid) exhibited mortality in a flowing exposure to an extract of Prudhoe Bay crude oil which was a function of the product of concentration and time. The product was referred to as the ""toxicity index"" (in ppm-days). When 50% mortality occurred in a tank@ the time in days was merely multiplied by the mean exposure concentration@ which was measured by infrared. Spectrophotometry (IR) at 1 or 2 day intervals. All 50% mortality data could be plotted on log-log paper with time versus concentration@ and a curve of -1.2 slope was produced. The slopes did not vary with the species@ but the most sensitive species (a mysid) produced a curve which indicated greater sensitivity than the two shrimp species. Since the toxicity index has proven to be a valid approach for estimating the toxicity of soluble hydrocarbons@ we proposed to apply the same methodology to studies on chemically dispersed oil. In addition to toxicity measurements for oil dispersions@ it was necessary to consider thephysical form of the exposure materials."
API DR79-1984 history
1984API DR79-1984 Development of a Diluting Concentration method for Testing the Acute Toxicity of Chemically Dispersed Oil@ and the Results of Comparative studies (Reprinted in 1993)