The toxic effects of the antifouling agent tributyltin (TBT) on three microalgal species, Chlorella vulgaris, Chlorella pyrenoidosa and Dunaliella tertiolecta, were studied. Toxic effects of TBT on growth, reproduction and physiology of the microalgae were assessed. The 5-day EC50 on growth inhibition of C. vulgaris, C. pyrenoidosa and D. tertiolecta were 130 /μg I-1, 33 μg 1-l and 3 μg I-1 TBT, respectively. The results indicated that the vulnerability to TBT was highly species dependent. When comparing with other species of microalgae, C. vulgaris was a highly tolerant microalgal species, with EC50 value one or two order of magnitude higher. For this reason, the tolerant mechanism of microalgae was further investigated....[ Read more ]

The toxic effects of the antifouling agent tributyltin (TBT) on three microalgal species, Chlorella vulgaris, Chlorella pyrenoidosa and Dunaliella tertiolecta, were studied. Toxic effects of TBT on growth, reproduction and physiology of the microalgae were assessed. The 5-day EC50 on growth inhibition of C. vulgaris, C. pyrenoidosa and D. tertiolecta were 130 /μg I-1, 33 μg 1-l and 3 μg I-1 TBT, respectively. The results indicated that the vulnerability to TBT was highly species dependent. When comparing with other species of microalgae, C. vulgaris was a highly tolerant microalgal species, with EC50 value one or two order of magnitude higher. For this reason, the tolerant mechanism of microalgae was further investigated.

The biodegradation, biosorption and bioaccumulation of TBT in C. vulgaris and C. pyrenoidosa were studied. The results of gas chromatography with flame photometric detector analysis showed that C. vulgaris could eliminate 50 % of the initial 100 μg 1-l TBT from external medium in 60 hours. At the end of a 2-week experimental period, it was measured that 25 % and 39 % of the original amount of TBT were degraded to dibutyltin (DBT) and monobutyltin (MBT), respectively. In contrast to C. vulgaris, DBT appeared to be the only degradation product for C. pyrenoidosu within the testing period, with 30 % of the original amount of TBT transformed into DBT. The results demonstrated that the higher tolerant ability of C. vulgaris may due to its capability in degrading TBT into less toxic metabolite.

The biochemical study on the enzyme system involving in degradation process showed that the in vivo cytochtome P-450 content in C. vulgaris was significantly increased after 4-day exposure to sublethal concentration of TBT. A maximum of 80-fold increase in cytochrome P-450 was recorded. Meanwhile, the activity of NADPH-cytochrome c reductase was concurrently increased as cytochrome P-450 when the algal cells were exposed to sublethal concentration. NADPH-cytochrome c reductase, rather than cytochrome b5, was the potential primary electron donor for the mixed function oxygenase (MFO) reaction. Inhibition studies using piperonyl-butoxide, cinnamic acid and carbon monoxide greatly reduced the algal in vivo biotransformation of TBT by 74 %, 61 % and 60 %, respectively. All these results suggested that debutylation of TBT in C. vulgaris was mediated by a cytochrome P-450 dependent oxygenase system.