* 
example, at concentrations too low (15-30 ppb) to affect some 
fish, triphenyltin acetate and several tributyltin compounds af¬ 
fect snails, zooplankton, and small fish, while warm-blooded 
species show no toxicity. In contrast, some soil microorganisms 
are not affected by concentrations of tributyltin oxide at con¬ 
centrations up to 100 ppm (Thayer 1974) . 
In comparison with other metals such as mercury, lead, and 
cadmium, relatively little is known about biological transforma¬ 
tions of tin. But sufficient information is available that a 
biological cycle has been proposed (Ridley et al. 1977). 
b 
(a) CH 3 SnX 3 + e-+CH 3 —»-(CH 3 ) 2 SnX 2 + X" 
In the diagram, X indicates a counteranion. The free radical 
SnX 3 can be methylated in a series of biological reactions (re¬ 
action a) involving methylocobalamins (e.g., vitamin-B]_ 2 ) to 
yield mono-, di-, tri-, and tetramethyl tin (Ridley et al. 1977). 
A Pseudomonas species which is purportedly capable of methylating 
tin has been isolated from Chesapeake Bay (Huey et al. 1974). In 
the presence of ionic mercury, trimethyltin can react to yield 
the highly toxic methylmercury (Huey et al. 1974). Methyltins 
3 
