Organic chemicals jeopardize the health of freshwater ecosystems on the continental scale

Abstract

Organic chemicals can contribute to local and regional losses of freshwater biodiversity and ecosystem services. However, their overall relevance regarding larger spatial scales remains unknown. Here, we present, to our knowledge, the first risk assessment of organic chemicals on the continental scale comprising 4,000 European monitoring sites. Organic chemicals were likely to exert acute lethal and chronic long-term effects on sensitive fish, invertebrate, or algae species in 14% and 42% of the sites, respectively. Of the 223 chemicals monitored, pesticides, tributyltin, polycyclic aromatic hydrocarbons, and brominated flame retardants were the major contributors to the chemical risk. Their presence was related to agricultural and urban areas in the upstream catchment. The risk of potential acute lethal and chronic long-term effects increased with the number of ecotoxicologically relevant chemicals analyzed at each site. As most monitoring programs considered in this study only included a subset of these chemicals, our assessment likely underestimates the actual risk. Increasing chemical risk was associated with deterioration in the quality status of fish and invertebrate communities. Our results clearly indicate that chemical pollution is a large-scale environmental problem and requires far-reaching, holistic mitigation measures to preserve and restore ecosystem health.

Keywords: ecological data; effect thresholds; river basins; streams; toxicity.

Fig. 1.

Chemical risk (by percentage range) in European river basins. The map displays the fraction of sites where the maximum chemical concentration exceeds the acute risk threshold (A) and the mean chemical concentration exceeds the chronic risk threshold (B) for any organism group. The color code shows the level of chemical risk, from low chemical risk (blue) to high chemical risk (red). River basins with up to six sites are displayed in gray (SI Appendix, Table S5), whereas river basins without data are displayed in white. The numbers denote the median of the acute-risk chemicals analyzed at the monitoring sites of each river basin. Direct comparisons between river systems are potentially biased by the ecotoxicologically relevant compounds analyzed and the limit of quantification of the compounds (SI Appendix, Fig. S2 and Table S2).

Fig. 2.

Proportion of sites acutely affected by different chemical groups. The chemical groups analyzed were insecticides (Ins), fungicides (Fung), organotin compounds (OrgTins), herbicides (Herb), polycyclic aromatic hydrocarbons (PAH), brominated flame retardants (BFR), and other compounds (chemical groups with five or fewer sites acutely affected which comprised polychlorinated biphenyls, halogenated alkanes, and phenols). The groups of organisms considered were fish (represented by P. promelas), invertebrates (represented by D. magna), and algae (represented by P. subcapitata). Acutely affected sites were all sites with maximum concentrations exceeding 1/10 of the LC₅₀.

Fig. 3.

Box-and-whisker plots of the chemical risk for different land use categories. The two categories used comprised anthropogenically influenced areas (AI) and natural vegetation (NV) for the acute risk threshold (ART) and chronic risk threshold (CRT). The categories analyzed were significantly different for both thresholds (P < 0.05).

Fig. 4.

Mean chemical risk of the river basins to exceed the risk thresholds as a function of the number of acute-risk chemicals (ARCs) analyzed. ARCs are chemicals for which the maximum concentration exceeds 1/10 of the lethal effect concentration at any site. Dots correspond to the acute risk threshold (ART), and triangles are for the chronic risk threshold (CRT). The total number of sites for each ARC interval is given in parentheses on the x axis. For the relationship between the number of acute-risk chemicals analyzed and the chemical risk, a cubic smoothing spline (all, df = 3) was fitted to the data to visualize the significant increasing trend (all, P < 0.05, n = 30; ART, dashed line: Kendall τ = 0.53; CRT, solid line: Kendall τ = 0.74).

Fig. 5.

Proportion of sites in high and good ecological status for fish, invertebrates, and diatoms. Sites were classified as acutely affected by chemicals (>ART), chronically affected by chemicals (CRT-ART) and not affected by chemicals (Methods for details; SI Appendix, Table S7 for the number of sites).