Volatilization of organotin compounds from estuarine and coastal environments

The occurrence and speciation of volatile tin compounds (Sn) have been investigated in a contaminated area of the Arcachon Bay (SW France)and in the water column of the Scheldt (Belgium/Netherlands) and Gironde (SW France) estuaries. This paper describes the application of a multi-isotope analytical method, using gas chromatography and inductively coupled plasma-mass spectrometry. Analytes were collected by cryogenic trapping of the gaseous species. This trapping has allowed us to probe volatile tin compounds by detecting both Sn-118 and Sn-120 isotopes. Volatile organic tin compounds have been determined in both sediment and water. They could result from both natural methylation and hydridization processes of inorganic tin (RnR4-n'Sn; R = Me, R' = H, n = 0-4) and from anthropogenic butyltin derivatives released from ship antifouling paintings which have accumulated in sediments (RnR4-n'Sn; R = Bu, R' = H or Me, n = 0-3). The most ubiquitous species were found to be the methylated forms of butyltin derivatives (BunSnMe4-n, n = 0-3). These results suggest that biological and/or chemical methylation mechanisms are likely to occur in sediments and to lead to remobilization of tin species into the water column and subsequently to the atmosphere. Finally, sediment-water and water-atmosphere fluxes have been calculated to assess the potential impact of these processes on the fate of organotin compounds in coastal environments.