Biodegradation capacity of tributyltin by two Chlorella species

Two microalgal species, Chlorella vulgaris and Chlorella sp., which showed high tributyltin (TBT) tolerant ability were investigated for their capabil ities in degrading TBT at sublethal concentration. The distribution of TBT and its degraded products dibutyltin (DBT) and monobutyltin (MBT) in the in cubation medium, extracellular surface and intracellular fraction were moni tored during an exposure period of 14 days. Results showed that biosorption of TBT by the algal cell wall was the major mechanism in reducing 40% of t he initial TBT from the medium in the first 2 days. The half-life of TBT in cubated with C. vulgaris was 60 h while that of Chlorella sp. was 80 h. The occurrence of DBT at Day 1 in the culture medium provided direct evidence to the biodegradation of TBT by both Chlorella species. At the end of the e xperimental period, 27 and 41% of the original TBT were recovered as DBT an d MBT in cultures of C. vulgaris, respectively. In contrast, DBT appeared t o be the only degradation product of Chlorella sp. and only 26% of the orig inal TBT was transformed to DBT. Despite the same genus, TBT was debutylate d to a greater extent to MBT by C. vulgaris, while DBT was the end degradat ion product by Chlorella sp. The capability of such debutylating process th erefore accounted for the higher tolerant ability of C. vulgaris than Chlor ella sp. (C) 1999 Elsevier Science Ltd. All rights reserved.