Degradation of organotin compounds in organic and mineral forest soils

Broad industrial application of organotin compounds (OTC) leads to their release into the environment. OTC are deposited from the atmosphere into forest ecosystems and may accumulate in soils. Here, we studied the degradation of methyltin and butyltin compounds in a forest floor, a mineral, and a wetland soil with incubation experiments at 20degreesC in the dark. OTC degraded slowly in soils with half-lives estimated from 0.5 to 15 years. The first order degradation rate constants of OTC in soils ranged from 0.05 to 1.54 yr(-1). The degradation rates in soils were generally in the order mono- greater than or equal to di- > tri-substituted OTC. Stepwise dealkylation was observed in all cases of di-substituted OTC, but only in some cases of tri-substituted OTC. Decomposition rates of OTC in the forest floor were higher than in wetland and mineral soils. Tetramethyltin in the gas phase was not detected, suggesting little tin methylation in the wetland soils. Slow degradation of OTC in soils might lead to long-term storage of atmospherically deposited OTC in soils.