No abstract

The accumulation and depuration of bis(tributyltin) oxide (TBTO), a widely used active ingredient in antifouling paints, and its acute and chronic toxicity to sheepshead minnows (Cyprinodon variegatus) were determined. Equilibrium between the concentration of carbon-14-labeled-TBTO in seawater and in fish tissues was not reached after 58 days of exposure. The maximum observed bioconcentration factor in whole fish was ×2600. The maximum observed bioconcentration factors for the muscle, viscera, and remains were ×1810, ×4580, and ×2120, respectively. Sheepshead minnows depurated 52 percent of the 14C-TBTO within 7 days and 74 percent after 28 days. The 21-day median lethal concentration (LC50) for sheepshead minnows exposed to TBTO was 0.96 ppb. The only statistically significant effect observed in the life-cycle test was mortality of the F0 fish in the mean measured TBTO concentration of 4.8 ppb. There was an obvious concentration-response relationship in mortality of the F1 fish, although, no statistically significant differences in mortality were detected between the control and the TBTO-exposed treatments. The surviving F1 fish exhibited no signs of abnormal development, nor was growth decreased as a result of F0 exposure to TBTO concentrations <-1.0 ppb. Tissue samples from the life-cycle test, analyzed for total tin, confirmed the bioconcentration of TBTO, showed the accumulation to be concentration dependent, and indicated that the fish were actively metabolizing TBTO into its lower and less toxic alkyl moieties.

Chronic (full life-cycle) toxicity tests have been performed with freshwater fishes during the past decade to obtain data for the establishment of water quality criteria. More recently, chronic tests have been performed with a saltwater fish, the sheepshead minnow. Examination of the results of chronic tests has lead to the development of shorter, early life-stage tests for both fresh and saltwater species to estimate specific application factors (the ratio of chronic: acute toxicity). The criteria for toxic effect utilized in the early life-stage tests are hatching success, juvenile mortality, and juvenile growth. We found that the growth of sheepshead minnows during early life-stage tests was not a statistically sensitive indicator of effect in 16 of 18 (89 percent) tests surveyed. In only one test was growth found to be a more sensitive indicator of toxic effect than was juvenile mortality, and thus necessary for establishing the estimated maximum acceptable toxicant concentration. Since in all the early life-stage tests reviewed, 95 percent of all mortality had occurred by Day 14 after hatching, we suggest that early life-stage tests with sheepshead minnows be shortened to 14 days after hatching and growth be eliminated as an indicator of toxic effect. This would substantially reduce the time and effort expended, and ultimately the cost, in arriving at reasonable specific application factors for sheepshead minnows when the chemical being tested does not exhibit cumulative toxicity and has a single mode of action.

This symposium marks the tenth time that we have gathered as a group of professional scientists who share common goals and ideas concerning the protection of our nation's aquatic resources. This tenth symposium seems like a fitting time to reflect on our origins, our successes, and our plans for the future. To that end, several people who have been instrumental in shaping the science of aquatic toxicology and hazard (risk) assessment were invited to present their views on the growth of this science and their ideas about its future. This paper is, then, a collection of those viewpoints, which are set down in writing so that others may benefit from the experience of the authors and so that newcomers to this field may benefit by knowing about the roots of aquatic toxicology and hazard assessment. The fact that the science has persisted and grown over the past ten years is a tribute to all those who have contributed their time, energy, and intellect.

Entire life-cycle toxicity tests are practical with sheepshead minnows, Cyprinodon variegatus. This is the only estuarine fish that has been utilized successfully in life-cycle toxicity tests, using methods formulated only since 1973. Salinity, temperature, and spawning requirements were determined, and initial life-cycle toxicity tests with endrin were conducted at the U.S. Environmental Protection Agency Gulf Breeze (Florida) Laboratory. Subsequent tests with heptachlor, carbofuran, methoxychlor, and malathion were conducted at Gulf Breeze or at EG&G, Bionomics. All studies confirmed the feasibility of using this estuarine fish for determining maximum acceptable toxicant concentrations and application factors. Results of our tests also corroborate data on application factors obtained in studies completed elsewhere with freshwater fishes and the same pesticides.