Use of field data to support European water framework directive quality standards for dissolved metals

Quality standards (QS) for dissolved metals in freshwaters have been proposed under the European Water Framework Directive (WFD) and are based mainly upon laboratory ecotoxicity data. Uncertainties remain about laboratory-to-field extrapolation to establish QS that are neither over nor underprotective. Freshwater benthic macroinvertebrates are a group of organisms of known sensitivity to heavy metals. We analyzed a dataset from England and Wales of dissolved metal concentrations (cadmium, chromium, copper, iron, nickel, lead, and zinc) and associated benthic invertebrate community metrics, using piecewise regression, quantile regression, and information on metal concentrations consistent with good quality status. Analysis of these field data suggests that dissolved metal QS proposed under the WFD are similar to metal concentrations in rivers associated with unimpaired benthic invertebrate assemblages in England and Wales. The only exceptions to this are QS for iron and zinc, where use of relatively large assessment factors leads to standards that are substantially below concentrations associated with impaired invertebrate assemblages in the field.