Tributyltin oxide

Tributyltin oxide (TBTO) is an organotin compound chiefly used as a biocide (fungicide and molluscicide), especially a wood preservative. Its chemical formula is [(C4H9)3Sn]2O. It is a colorless viscous liquid. It is poorly soluble in water (20 ppm) but highly soluble in organic solvents. It is a potent skin irritant. 
Tributyltin compounds had been used as marine anti-biofouling agents. Concerns over toxicity of these compounds have led to a worldwide ban by the International Maritime Organization. It is now considered a severe marine pollutant and a Substance of Very High Concern by the EU.