4.4.2 Degradation by Biota 



Within the water column, the primary means of degradation of organotin 

 compounds is likely to be planktonic algae or other microorganisms. Thain 

 (1987) and Lee et al. (1987) have found that degradation of TBT did not 

 occur in natural water where filtration had been used to remove all 

 organisms. In the presence of light, diatoms appear to be a significant 

 agent for the degradation of TBT (Lee, 1987) . In Atlantic coastal waters, 

 the chain forming diatom Skeletonema costatum has been identified as the 

 most common TBT debutylating agent. Thain et al. (1987) found that 

 microalgae were able to degrade 1/2 of available TBT in 6 days at 20°C 

 but at 5°C the same degradation took 60 days. The species of algal 

 cells present, as well as ambient temperature and light intensity, all 

 appear to affect the rate of TBT degradation. In the absence of light, 

 bacteria become the principal organism for the degradation of TBT in 

 natural waters. Because of the number of variables involved, a high 

 diversity in half life periods are reported in the literature, ranging 

 from a half life of several months to 3.5 days. The lowest estimate was 

 developed at the Marine Ecosystem Research laboratory (MERL) using 14 C 

 labeled tributyltin introduced into the enclosed ecosystem containing 

 natural water, plankton, sediment and benthic organisms from Narragansett 

 Bay (Hinga et al., 1987). They found a first order removal rate constant 

 of 0.20/day or a half life of 3.5 days. 



It is not known at this time if dissolved organotins form complexes with 

 the lipids and detritus in the microlayer and thus become biologically 

 more available to filter feeders or deposit feeders or whether the 

 presence of such high concentrations may be biologically significant from 

 a toxicity perspective. The neuston (floating and swimming) comprises 

 organisms who inhabit the surface microlayer. These organisms include 

 microbial populations, and the eggs and larvae of invertebrates and of 

 fish. The chemistry of the surface microlayer is extremely complex and 

 poorly understood (see Brinckman et al., 1982 and 1987). Light impinging 

 on the surface film may hasten the debutylation of tributyltin in the 

 microlayer. Lee et al. (1986) , found that under sunlight conditions that 

 the half-lives of TBTR in the Elizabeth and James Rivers in June were 6 

 and 10 days respectively. They also found that for the Skidaway River 

 during a year-long study that the half -lives varied from 4 to 13 days for 

 individual data sets and that degradation was always higher in the light 

 relative to dark treatments. The population of bacterio-neuston may also 

 debutylate TBT into the less toxic and less bioavailable moieties, or they 

 may serve principally as a food chain link passing the TBT to protozoans 

 and subsequently to larval fish which are the most sensitive life stage 

 for many species (Gucinski, 1986) . Researchers at NBS have found that 

 bacterial biof ilm communities from paint panels did not degrade TBT but 

 bioconcentrate it up to greater than 350 mg/1 (Blair et al., 1987). 

 Similar work in progress with algal biof ilms has found that degradation 

 does occur (Brinckman, personnel communication) . 



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