Résumé
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 multiisotope 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 118Sn and 120Sn 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 (R(n)R'4- (n)Sn; R = Me, R' H, n = 0-4) and from anthropogenic butyltin derivatives released from ship antifouling paintings which have accumulated in sediments (R(n)R'4-(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 (Bu(n)SnMe4- (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.