In most cases, a significant fraction of the microbial popu¬ 
lation was resistant to inorganic tin and is, therefore, poten¬ 
tially capable of metabolizing tin to more toxic compounds. A 
much smaller fraction of the population was resistant to the 
organotin compound, dimethyltin chloride, attesting to the anti¬ 
bacterial properties of organic tin compounds. The data are con¬ 
sistent with the hypothesis that aquatic microorganisms can 
protect themselves against toxic tin compounds by transforming 
tin to organotins which, although toxic in themselves, are vola¬ 
tile and leave the immediate vicinity of the cell which formed 
them. 
Sediment from Spaniard Bar did not contain higher numbers of 
tin-resistant organisms than sediments from Buoy Rock, although 
a higher percentage of the population was resistant to tin at 
Spaniard Bar than at Buoy Rock. Sediment samples taken at the 
Chestertown sewage treatment plant contained a high percentage 
of organisms resistant to inorganic tin. There is little indi¬ 
cation of a higher level of tin-resistant microflora at Spaniard 
Bar than at Buoy Rock. The data available do not suggest that 
the freshwater sites contain higher numbers of tin-resistant or¬ 
ganisms than the estuarine sites. 
Data for production of volatile tin compounds are summarized 
in Table .24. The method used was effective in detecting organic 
tin compounds produced in bioflasks, as indicated by values ob¬ 
served from sterile medium which contained dimethyltin chloride. 
Variation among replicates indicates that the method is qualita¬ 
tive. Flasks which received inoculum containing the metabolic 
poison sodium azide yielded no volatile tin, indicating that 
volatile tin detected was the result of biological activity. 
Results from bioflasks and Hungate tubes demonstrate that each 
site contains microorganisms capable of converting inorganic tin 
to volatile organotin(s). The species of organotin produced were 
not identified. 
Tin in Water and Sediments 
The lower limit of sensitivity for tin analysis was 2 ppb. 
A recovery value of 77.8 percent was obtained when sediment from 
Tilghman Island was spiked with SnCl/j. When salt water or 
Nelson's liquid medium was spiked with SnCl^, recoveries of 
94-96 percent were obtained. 
Sediment samples contained more tin than water samples 
(Table 25), as expected. Sediment from Baltimore Harbor, known 
as a polluted site, contained over 200 ppm tin (>0.02 percent on 
a wet weight basis). In contrast, sediments from the Tilghman 
Island site contained less that 1 ppm (<0.0001 percent on a wet 
weight basis). All sediments associated with the Chester River, 
including sediments from the three freshwater sites, yielded more 
tin than sediments from the Tilghman Island site (Table 25). 
95 
