Tri-n-butyltin (TBT) is used as an antifouling agent in ship bottom paints. The pollution caused by TBT is widespread in coastal areas. At concentrations of 1 µg/L or less, TBT can be toxic to many marine organisms, including algae. Some types of microalgae can tolerate a TBT concentration of 25 µg/L and degrade TBT to dibutyltin (DBT), butyltin (MBT) and inorganic tin. This pathway focuses on the microalgal biodegradation of TBT. The steps labeled as A, B, C are possibly catalyzed by enzyme action. beta-Hydroxylation is predominant during the degradation of TBT, however other types of hydroxylation are possible (Lee RF, Valkirs AO, Seligman PF Importance of Microalgae in the Biodegradation of Tributyltin in Estuarine Waters Environ Sci Technol 23: 1515-1518, 1989).