Tin and Tin-Resistant Microorganisms in Chesapeake Bay

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Abstract
Sediment and water samples from nine stations in Chesapeake Bay were examined for tin content and for microbial populations resistant to inorganic tin (75 mg of Sn liter−1 as SnCl4·5H2O) or to the organotin compound dimethyltin chloride [15 mg of Sn liter−1 as (CH3)2SnCl2]. Tin concentrations in sediments were higher (3.0 to 7.9 mg kg−1) at sites impacted by human activity than at open water sites (0.8 to 0.9 mg kg−1), and they were very high (239.6 mg kg−1) in Baltimore Harbor, which is impacted by both shipping and heavy industry. Inorganic tin (75 mg Sn liter−1) in agar medium significantly decreased viable counts, but its toxicity was markedly reduced in liquid medium; it was not toxic in medium solidified with silica gel. Addition of SnCl4·5H2O to these media produced a tin precipitate which was not involved in the metal9s toxicity. The data suggest that a soluble tin-agar complex which is toxic to cells is formed in agar medium. Thus, the toxicity of tin depends more on the chemical species than on the metal concentration in the medium. All sites in Chesapeake Bay contained organisms resistant to tin. The microbial flora was more sensitive to (CH3)2SnCl2 than to SnCl4·5H2O. The elevated level of tin-resistant microorganisms in some aeas not containing unusually high tin concentrations suggests that factors other than tin may participate in the selection for a tin-tolerant microbial flora.