Although many chemicals are in use, the environmental impacts of only a few have been established, usually on per-chemical basis. Uncertainty remains about the overall impact of chemicals. This paper estimates combined toxic pressure on coastal North Sea ecosystems from 343 high-production-volume chemicals used within the catchment of rivers Rhine, Meuse, and Scheldt. Multimedia fate modeling and species sensitivity distribution-based effects estimation are applied. Calculations start from production volumes and emission rates and use physicochemical substance properties and aquatic ecotoxicity data. Parameter uncertainty is addressed by Monte Carlo simulations. Results suggest that the procedure is technically feasible. Combined toxic pressure of all 343 chemicals in coastal North Seawater is 0.025 (2.5% of the species are exposed to concentration levels above EC50 values), with a wide confidence interval of nearly 0−1. This uncertainty appears to be largely due to uncertainties in interspecies variances of aquatic toxicities and, to a lesser extent, to uncertainties in emissions and degradation rates. Due to these uncertainties, the results support gross ranking of chemicals in categories:  negligible and possibly relevant contributions only. With 95% confidence, 283 of the 343 chemicals (83%) contribute negligibly (less than 0.1%) to overall toxic pressure, and only 60 (17%) need further consideration.

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Multimedia environmental fate models are commonly-applied tools for assessing the fate and distribution of contaminants in the environment. Owing to the large number of chemicals in use and the paucity of monitoring data, such models are often adopted as part of decision-support systems for chemical risk assessment. The purpose of this study was to evaluate the performance of three multimedia environmental fate models (spatially-and non-spatially-explicit) at a European scale. The assessment was conducted for four polycyclic aromatic hydrocarbons (PAHs) and hexachlorobenzene (HCB) and compared predicted and median observed concentrations using monitoring data collected for air, water, sediments and soils. Model performance in the air compartment was reasonable for all models included in the evaluation exercise as predicted concentrations were typically within a factor of 3 of the median observed concentrations. Furthermore, there was good correspondence between predictions and observations in regions that had elevated median observed concentrations for both spatiallyexplicit models. On the other hand, all three models consistently underestimated median observed concentrations in sediment and soil by 1-3 orders of magnitude. Although regions with elevated median observed concentrations in these environmental media were broadly identified by the spatially-explicit models, the magnitude of the discrepancy between predicted and median observed concentrations is of concern in the context of chemical risk assessment. These results were discussed in terms of factors influencing model performance such as the steady-state assumption, inaccuracies in emission estimates and the representativeness of monitoring data.

Ecotoxicological effect factors are part of the analysis of relative impacts by chemical contaminants on ecosystems. Uncertainty distributions, represented by the 90% confidence interval, belonging to ecotoxicological effect factors for freshwater ecosystems were determined. This study includes 869 high production volume chemicals, related to 7 nonspecific toxic modes of action (TMoAs). The ecotoxicological effect factors are divided into a TMoA-specific part and a chemical-specific part. The 90% confidence interval of the TMoA-specific part of the effect factor ranges from 23 orders of magnitude for acrylate toxicity to 2 orders of magnitude for nonpolar narcosis. The range in the TMoA-specific part of the effect factor is mainly caused by uncertainty in the spread in toxic sensitivity between species (sigma(j)). Average uncertainty in the chemical-specific part of the effect factors depends on the number of species tested and ranges on average from a factor of 5 for more than 3 species tested to a factor of about 1,000 for 2 species tested. Average uncertainty in the ecotoxicological effect factors ranges from a factor of 100 for more than 3 species tested to a factor of nearly 10,000 for 2 species tested. It is recommended that the ecotoxicological effect factor of a chemical is based on toxicity data of at least 4 species.

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