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

Abstract

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 Sn total were investigated in a forested ecosystem ( Picea abies, Karst.) in NE Bavaria, Germany. The concentrations of OTC and Sn total were generally in the order fog>throughfall>bulk precipitation. Average concentrations of OTC total ranged from 57 ng Sn l −1 in fog to 5.8 ng Sn l −1 in bulk precipitation. Concentrations of Sn total 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 OTC total concentrations in litterfall were 12.9 ng Sn g −1 and those of Sn total in litterfall 38 ng Sn g −1. All OTC concentrations in runoff were lower than in bulk precipitation, while those of Sn total 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 OTC total (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 OTC total amounted to 25 mg Sn ha −1 year −1. The total deposition of Sn total 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 Sn total was 2.4 g Sn ha −1 year −1. The mass balance showed a high retention of OTC and Sn total in the catchment. The forest soils act as a strong sink for OTC and Sn total. 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.