The usefulness of a sediment bioassay with the gastropod Nassarius reticulatus in tributyltin monitoring programs.

Despite the use of tributyltin (TBT) had been banned worldwide in 2008 there is still evidence of its deleterious presence in environment. We evaluate the usefulness of a 28days sediment bioassay with Nassarius reticulatus females to monitor TBT pollution, using imposex as endpoint. In addition, butyltins were determined in sediments and tissues, and, whenever posible, imposex was assessed in native N. reticulatus at the same sites where sediments were sampled. In the bioassay, a significant increase in imposex parameters was obtained with three sediments (Vi2, Vi3, and Vi4). No correlation was found between this and TBT concentrations in sediment although good correlations were obtained for TBT in tissues, putting in evidence TBT bioavailability in sediment. A significant decrease in imposex from 2008 to 2013 in native snails was only observed at sites that did not cause any effect in the bioassay. In contrast, imposex levels in 2013 were kept as high as 2008 in one of the sites where a significant imposex increase in the bioassay was observed. The bioassay proves thus to be a practical and ecological relevant tool, as: (i) it can be conducted in sites with no native populations of snails, (ii) it provides early identification of polluted sites, anticipating future imposex levels or early identification of recovering, and (iii) it yields information on the bioavailable fraction of the TBT in the sediment. Therefore, this tool can be of extreme usefulness under the scope of recent European legislative frameworks.