Risk assessment of triclosan released from sewage treatment plants in European rivers using a combination of risk quotient methodology and Monte Carlo simulation.

Ιn this study a probabilistic risk assessment was applied to investigate the environmental risks for the European aquatic environment associated with triclosan (TCS) occurrence in treated wastewater. The concentrations of TCS in effluents of European Sewage Treatment Plants (STPs) were recorded through literature review, while toxicity data was collected for three groups of aquatic organisms (algae, Daphnia magna and fish). The ratio of Measured Environmental Concentration (MEC) and Predicted No Effect Concentration (PNEC), expressed as a Risk Quotient (RQ), was calculated for risk characterization, while Monte Carlo simulation was applied to quantify the associated uncertainty. TCS monitoring data was available for 349 STPs located in 15 out of the 50 European countries. Its mean concentrations in STPs effluents ranged between 2.2ngL-1 and 47,800ngL-1 . Higher TCS concentrations were observed in primarily treated wastewater; whereas no differences among countries or among secondary and tertiary effluents on the basis of the whole set of collected data were found. The 95th percentile of RQ for TCS was higher than 1 (in algae) for rivers with dilution factors (DFs) equal to or lower than 100, when the maximum concentration values were used, whereas the 95th percentile of RQ exceeded 1 for rivers with DFs up to 10, in cases where the calculations were based on mean concentration values. The probability that RQ exceeds 1 in rivers (for algae) ranged from 0.2% (DF=1000) to 45% (DF=2), when calculations are based on mean concentration values. The corresponding probabilities in rivers with DFs equal to 2 for Daphnia magna and fish were 0.7% and 0.4%, respectively. We propose that TCS monitoring should be intensified, especially on smaller rivers, to verify the findings of this study for possible environmental risks.