The chronic toxicity of silver to the sea urchin (Arbacia punctulata) was determined in 30 per thousand salinity seawater during a three-part study: A fertilization test (1-h sperm exposure), a 48-h embryo test, and a 30-d adult test. Combined data from the three tests resulted in a lowest-observed-effect concentration of 19 microg/L, a no-observed-effect concentration of 8.6 microg/L, and a maximum acceptable toxicant concentration of 13 microg/L, based on measured concentrations of dissolved silver. The 96-h median effective concentration was 40 microg/L, and the acute to chronic toxicity ratio was 3.1. During the tests, measured concentrations of free ionic silver (Ag+) were only 0.0027 to 0.0046% of dissolved silver concentrations, as predicted by ion-speciation theory. Some measured Ag+ concentrations were lower than predicted, indicating the presence of other ligands in the seawater test media. These strong sulfide ligands were exuded by the exposed sea urchins into the seawater (where Ag-sulfide complexes formed) in amounts that increased in direct proportion to the silver concentration during the toxicity test. This suggests a toxicity-defense mechanism that functioned by modifying the chemistry of the surrounding external medium.
Tests were conducted with mysids (Americamysis bahia) and silversides (Menidia beryllina) to evaluate the influence of salinity and organic carbon on the chronic toxicity of silver. During 7- and 28-d tests conducted at 10, 20, and 30% per hundred salinity, higher concentrations of dissolved silver generally were required to cause a chronic effect as the salinity of the seawater was increased. The 28-d mysid and silverside 20%-effective concentration values (expressed as dissolved silver) ranged from 3.9 to 60 and from 38 to 170 microg/L, respectively, over the salinity range. This pattern was not observed when the same test results were evaluated against the concentrations of free ionic silver (measured directly during toxicity tests), as predicted by the free-ion activity model. Increasing the concentration of dissolved organic carbon from 1 mg/L to the apparent maximum achievable concentration of 6 mg/L in seawater caused a slight decrease in chronic toxicity to silversides but had no effect on the chronic toxicity to mysids. The possible additive toxicity of silver in both food and water also was investigated. Even at the maximum achievable foodborne concentration, the chronic toxicity of silver added to the water was not affected when silver was also added to the food, based on the most sensitive endpoint (growth). However, although fecundity was unaffected at all five tested concentrations during the test with silver in water only, it was significantly reduced at the two highest waterborne silver concentrations (12 and 24 microg/L) during the test with silver dosed into food and water.
: Large quantities of trap and skeet clay targets are used in shooting activities around the United States. For example, the number of targets used since 1970 has averaged approximately 560 million a year. A number of acute and chronic tests were performed to determine the toxicity of Remington Arms Company Blue Rock(®) trap and skeet target fragments upon selected freshwater and marine organisms. These studies were undertaken in support of an environmental impact study of trap and skeet shooting activities at a major gun club in the northeast United States. Targets were composed of approximately 67% dolomitic limestone, 32% petroleum pitch and 1% fluorescent aqueous paint (painted targets only). The majority of samples were painted, new targets obtained from the manufacturer and painted and aged targets collected around a shooting range. Additional tests were conducted using non-painted, new targets and leachates prepared from both painted, new and aged targets. Targets were crushed to small fragments and were either directly added to the test vessels at extremely high concentrations ranging from 670 to 600 000 mgl(-1) or used in leachate tests. In direct tests all target materials were essentially non-toxic to marine and freshwater organisms, except for the non-painted new targets which exhibited minimal acute toxicity to Daphnia magna (48 h EC 50=2200 mgl(-1)). In leachate tests, the leachate was not-toxic to mysid shrimp, the only organism tested. Additional samples of crushed targets were analysed for the presence of selected priority pollutants (EP toxicity test) and polycyclic aromatic hydrocarbons (PAHs). The targets did not exhibit the characteristics of toxicity as determined by the EP toxicity test but did contain substantial amounts of PAHs. However, results from new and aged targets suggest that PAH are tightly bound in the petroleum pitch and limestone matrix and are unlikely to be readily available in the environment. The potential impact of targets on the environment is further discussed.
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