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Background, aim, and scope Characterization factors for ecotoxicity in the Life Cycle Impact Assessment (LCIA) are used to convert emissions into ecotoxicological impacts. Deriving them involves a fate and an effect analysis step. The fate factor quantifies the change in environmental concentration per unit of emission, while the effect factor quantifies the change in impact on the ecosystem per unit of environmental concentration. This paper calculates freshwater ecotoxicological effect factors for 397 pesticides belonging to 11 pesticide-specific toxic modes of action (TMoA), such as acetylcholinesterase inhibition and photosynthesis inhibition. Moreover, uncertainties in the effect factors due to uncertain background concentrations and due to limited toxicity data are quantified. Methods To calculate median ecotoxicological effect factors (EEFs), toxic pressure assessments were made, based on the species sensitivity distribution-and the multisubstance potentially affected fraction-concept. The EEF quantifies an estimate of the fraction of species that is probably affected due to a marginal change in concentration of a pesticide. EEFs were divided into a TMoA-specific and a chemical-specific part, which were calculated on the basis of physicochemical properties, emissions, and toxicity data. Propagation of parameter uncertainty in the EEFs and the TMoA-and chemical-specific parts was quantified by Monte Carlo simulation and results were reported as 90% confidence intervals. Results Median EEFs range from 2·10 −3 to 7·10 6 l/g. Uncertainty in the TMoA-specific part is dominated by uncertainty in the TMoA-specific spread in species sensitivity and by uncertainty in the effective toxicity of a TMoA. Uncertainty in the chemical-specific part of the EEFs depends on the number of species for which toxicity data are available to calculate average toxicity (n s ) and ranges from a median uncertainty of 2.6 orders of magnitude for n s =2 to one order of magnitude for n s ≥4. The TMoA-specific effect factor for systemic fungicides shows the largest uncertainty range. For seven TMoAs, uncertainty ranges of the TMoA-specific effect factor are less than two orders of magnitude. For the other four TMoAs, the EEF uncertainty range is between two and eight orders of magnitude. For the chemical-specific part of the EEFs, we found that variation in uncertainty readily decreases for pesticides for which toxicity data are available for at least three species. Discussion The same parameters that contributed most to uncertainty were found for pesticides as were found before for high-production-volume chemicals. However, uncertainty in concentrations of pesticides was lower. TMoA-specific factors obtained with the applied nonlinear method differ up to nine orders of magnitude from the factor of 0.5, which is used in the linear method. With the applied method, a distinction in EEFs can be made among different TMoAs. Conclusions Ecotoxicological effect factors are presented, including overviews of their uncertainty ranges and the main ...

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Although risk assessments on a per-chemical basis are required during the registration procedure of pesticides, cumulative risks from the use of all pesticides on the variety of crops in a catchment area of a river are not assessed. The present study aimed to rank pesticides used in outdoor agricultural practice within the catchment of the rivers Rhine, Meuse, and Scheldt according to their potential toxic impact on the North Sea coastal ecosystem. Toxic pressure calculations (based on steady-state concentrations calculated with a multimedia fate model) and species-sensitivity distribution-based risk estimations were performed for pesticide emissions in the years 1998 (189 pesticides) and 2004 (133 pesticides). A ranking was established according to the relative contribution of single pesticides and crop types to the overall toxic pressure. Calculations were performed probabilistically to deal with parameter uncertainties. Only a few pesticides and crop types dominate overall toxic pressure because of emissions in both years, and the uncertainty appears to be caused largely by uncertainties in interspecies variances of aquatic toxicities. For 1998, these pesticides were fentin-acetate, with a median relative contribution (RCx) to the toxic pressure of multiple chemicals on an ecosystem of 0.43. For 2004, the pesticides that contributed most were pencycuron and paraquat-dichloride, with a median RCx, of 4.4 x 10(-2) and 3.9 x 10(-2), respectively. Pesticides applied to potato cropland and fruit trees contributed most to the overall toxic pressure.