Volatile organotin compounds (butylmethyltin) in three European estuaries (Gironde, Rhine, Scheldt)

The occurrence of volatile organometallicspecies of tin was evidenced and investigatedin three major European estuaries, such as theGironde (F), the Rhine (NL) and the Scheldt(B/NL), along with the salinity gradient andfor all seasons. The most ubiquitous species,observed in surface water, were found to bemethylated forms of butyl-tin derivatives(Bu_nSnMe_4-n, n = 0–3), withconcentrations significantly higher in theScheldt (ca. 75–2000 fmol l^–1) than in theRhine (ca. 5–125 fmol l^–1) and the Gironde(ca. 5–90 fmol l^–1). Additionally,estuarine anoxic sediments were found tocontain large amount of such volatile tinspecies.The presence of volatile organic tin compoundsis then supposed to result from naturalmethylation processes of both inorganic metaland anthropogenic derivatives accumulated inthe sediments (i.e. tributyltin released fromship antifouling paintings and waste waterdischarges). These results suggest thatmicrobial mediated and/or chemical methylationmechanisms are likely to produce volatileorganotin species in anoxic estuarineenvironments. The production of volatileorganotin species is also mainly dependent onthe direct anthropogenic load of butyltincompounds within the estuary and on theresidence time of such compounds in the system.Estuarine profiles along with the salinitygradient demonstrate that all investigatedestuaries are continuous sources of volatiletin species, although these estuaries presentdifferent anthropogenic organotin discharges.In consequence, significant export of volatiletin species to the adjacent coastal waters werefound. Finally, the evaluation of the seasonalfluxes of volatile tin species to theatmosphere establishes that volatilisation is amajor sink for such compound in estuaries withlong water residence time (i.e. Scheldt, Gironde).