New analytical methods are available for detecting novel xenobiotic compounds in freshwater systems. Pharmaceuticals are suspected of having effects on freshwater biota at very low concentrations, although the nature of these effects remains unclear. Previous data from the Llobregat River revealed a positive statistical relationship between the biomass of benthic macroinvertebrates and the presence of certain non-steroidal anti-inflammatory drugs (NSAIDs) and beta-blockers. Here, experiments were conducted with the midge Chironomus riparius and the freshwater snail Physella (Costatella) acuta in sediments and water, respectively. The sediments and water were treated with the pharmaceuticals propranolol and indomethacin, with the aims of assaying the effects of these compounds on the organisms and testing the statistical relationships observed in field. The variables measured were survival; C. riparius biomass; and the carbon/nitrogen ratio, lipid content and fertility of freshwater snails. Indomethacin in treated sediments induced an increase in C. riparius biomass, whereas propranolol inhibited growth, albeit at marginal statistical significance. By contrast, indomethacin in water had no effect on any of the parameters measured in P. acuta.
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