Pharmaceuticals in agricultural surface waters: Detection, distribution, exposure and risk

Recent studies have shown different classes of pharmaceuticals to be present at low concentrations in a range of environmental matrices. Pharmaceuticals are produced with the intent of eliciting a biological effect but the ecotoxicological and human risks associated with their environmental presence are poorly understood. Currently a paucity of data exists pertaining to what pharmaceuticals are present and their prevalence under conditions of use in Canada, knowledge that is critical to the risk characterization process.;A broad range of pharmaceuticals was detected in the surface waters, the most pervasive of which included monensin, lincomycin and carbamazepine. Concentrations were in the ng/L range with concentration fluctuations generally, but not exclusively, inversely proportional to flow rate. Water quality parameters such as nitrate, phosphate and organic carbon were found to be poor predictors for pharmaceutical input. Pharmaceuticals with a high frequency of detection were stable to both hydrolysis and biodegradation and showed a propensity to sorb and desorb from sediments. Evidence is provided in support of the hypothesis that increased surface water concentrations during low flow events are, in part, a reflection of desorption from sediment bound residue.;Probabilistic exposure profiles for the more prevalent pharmaceuticals provided a means to estimate centiles of exposure concentrations to aquatic organisms in the Grand River Watershed. Potency distributions characterizing the estimated total potency of pharmaceuticals detected in surface waters demonstrated a very low acute risk to the aquatic macrophyte, Lemna gibba, as well as to fish, Daphnia and green algae. These exposure profiles will be useful for characterizing chronic risks once pertinent chronic effects data are available. Toxicity trends of surface water extracts highlighted the need to include chemical mixtures as part of the risk assessment process.;The occurrence and temporal trends for pharmaceuticals in surface waters receiving predominately agricultural inputs within a watershed in southern Ontario was examined. Correlations between water quality parameters indicative of agricultural input, and pharmaceutical concentration were measured. In addition, the toxicological significance of environmental concentrations and mixtures was examined.