Biogeochemistry of organotin compounds and tin in a forested catchment in Germany

Organotin compounds (OTC) are highly toxic pollutants that have been shown to affect many aquatic ecosystems. Little is known about the input and fate of OTC in terrestrial ecosystems. Here, soil pools, concentrations and fluxes in bulk precipitation, throughfall, fog, litterfall and runoff of OTC and Sntotal were investigated in a forested ecosystem (Picea abies, Karst.) in NE Bavaria, Germany. The concentrations of OTC and Sntotal were generally in the order fog>throughfall>bulk precipitation. Average concentrations of OTCtotal ranged from 57 ng Sn l−1 in fog to 5.8 ng Sn l−1 in bulk precipitation. Concentrations of Sntotal were in the same order but between 490 ng Sn l−1 in fog and 140 ng Sn l−1 in bulk precipitation, on average.
Average OTCtotal concentrations in litterfall were 12.9 ng Sn g−1 and those of Sntotal in litterfall 38 ng Sn g−1. All OTC concentrations in runoff were lower than in bulk precipitation, while those of Sntotal were similar to the concentrations in bulk precipitation. Monobutyltin was the dominating OTC in bulk precipitation, throughfall, fog and litterfall, but was seldom detected in the runoff. The annual total deposition of OTCtotal (calculated as throughfall+litterfall) was 172 mg Sn ha−1 year−1, with 45 mg Sn ha−1 year−1 represented by litterfall. The annual runoff from the catchment of OTCtotal amounted to 25 mg Sn ha−1 year−1. The total deposition of Sntotal was 4.9 g Sn ha−1 year−1, of which 0.2 g Sn ha−1 year−1 was litterfall. The annual runoff of Sntotal was 2.4 g Sn ha−1 year−1. The mass balance showed a high retention of OTC and Sntotal in the catchment. The forest soils act as a strong sink for OTC and Sntotal. Only small amounts of deposited OTC are released to runoff. The ratio of soil pools to annual accumulation for total OTC (46 years) indicates that OTC inputs have been occurring already for many decades or have been substantially higher in the past than today.