Factors affecting the toxic effect of tin on estuarine microorganisms

Inorganic tin (SnCl(4).H(2)O) is toxic to microbial populations obtained from estuarine sediments plated on nutrient medium solidified with either agar or purified agar. The use of gelatin as a gelling agent decreased the apparent toxicity of tin, and toxicity was markedly reduced in medium solidified with silica gel. There was no evidence that toxic agar-tin complexes were involved. Cd, Cu, Pb, Ni, and Zn exhibited similar toxicity patterns; therefore, toxicity levels determined in the laboratory should be extrapolated to the environment with caution. The addition of cysteine to the medium had no effect on tin toxicity. Serine or 3-hydroxyflavone enhanced toxicity, while humic acids or gelatin inhibited toxicity. Replacement of SO(4) with NO(3) did not alter tin toxicity, but replacement of Cl with NO(3) decreased tin toxicity. Thus, the toxic effect(s) of tin depend as much on the chemical speciation of the metal as on the total concentration of the metal in the medium.