TOXICITY OF TRIBUTYLTIN CHLORIDE TO ANAEROBIC NITROGEN TRANSFORMATIONS IN SEDIMENT AND POREWATER

The influence of tributyltin chloride (TBTCl) on N transformations in anoxic sediment cultures, during approximately 14-d incubations, was studied using acetylene inhibition and acetylene reduction techniques as measures of microbially mediated denitrification and dinitrogen fixation, respectively. The accumulation of N2O, CO2 and C2H4 with time was modeled with a best-fit polynomial to detect statistically significant differences between treatments and with a three-segment continuous line model to assess lag times, rates of accumulation and rates of subsequent loss of these gases from the headspace. In sediment cultures, the presence of up to 100 mg L-1 of TBT had a barely detectable influence on these transformations. However, the analogous processes in porewater, prepared by centrifuging sediment slurry at 3 000 x g for 30 min, were appreciably modified by the presence of > 1 mg L-1 of this toxicant. Although the two media were different in terms of their denitrifying potential and their fermenting capacity, dose-related responses in the porewater were evident for both processes. Apparently the presence of particulate matter in the sediment slurry appreciably attenuated the inhibitory effects of the toxicant. Moreover, a portion of the denitrifiers in cultures of porewater developed a resistance to 100 mg L-1 of TBT in the medium and reduced added nitrate stoichiometrically. When transferred to autoclaved medium containing the same level of toxicant, aliquots of the resistant culture stoichiometrically reduced the added nitrate after a shorter lag time. The resistance was not the result of metabolic detoxification as indicated by the recovery of 74% of toxicant in an unchanged form, after 15 d incubation, using analytical methods which would have detected a 1% conversion of TBT to either Bu2Sn2+ or to BuSn3+. When added, at 10 mg L-1, to autoclaved porewater, an appreciable portion of the toxicant became associated with residual particulate matter (the fraction removed by centrifugation at 10 000 x g but not by 3 000 x g) with only approximately 9% remaining in the supernatant fluid. When 0.5 mL of TBT-resistant culture was added to the identical matrix and incubated, the TBT in the supernatant phase was reduced below the limit of detection and only 40% was recovered in the particulate/microbial cell fraction. Thus, both particulate materials and microbial growth immobilized TBT serving to limit its concentration in the surrounding water.