Distribution of silver in mussels and oysters along the French coasts: data from the national monitoring program.

Distribution and behavior of many trace elements in the aquatic environment has been well characterized, but little is known about silver (Ag) concentrations in coastal waters, even though this element ranks among the most toxic to marine invertebrates (Calabrese et al., 1977 ; Fisher and Hook, 1997 ; Webb and Wood, 1998). Studies conducted by Flegal et al. (1995), River-Duarte et al. (1999), and Ndung'u et al. (2001), provided the first valuable data on Ag distribution in the oceanic environment, indicating that this element is found in very low concentrations in the dissolved phase. However, although silver concentrations in coastal waters do not reach the nanomolar range (Smith and Flegal, 1993 ; Squire et al., 2002), formation of a stable chloro complex enhances bioavailability and toxicity to biota (Luoma et al., 1995). Experimental studies have shown that Ag is toxic to some living organisms at environmentally realistic levels (Bryan and Langston, 1992). Silver found in the aquatic environment mainly originates in effluents from sewage treatment plants (Rozan and Hunter, 2001). Silver can therefore be used as a tracer of wastewater discharges in coastal waters (Martin et al., 1988 ; Sañudo-Wilhelmy and Flegal, 1992), for instance through the use of sentinel organisms, which concentrate bioavailable contaminants in their tissues (Stephenson and Leonard, 1994 ; Jiann and Presley, 1997 ; Riedel et al., 1998 ; Muñoz-Barbosa et al., 2000).