Mixture toxicity in the Erft River: assessment of ecological risks and toxicity drivers

Abstract

Background: A vast number of chemical substances are released into the aquatic environment, leading to complex chemical mixtures in surface waters. Current water quality assessments, however, are based on the risk assessment of single substances. To consider potential mixture effects in water quality assessments, the North Rhine Westphalian State Agency for Nature, Environment and Consumer Protection (LANUV), Germany started a project assessing mixture toxicity in surface waters. This article summarises the mixture evaluation of chemical data collected by the Erftverband during a water sampling campaign in the Erft River in 2016/2017. Altogether, 153 substances were included in the analysis, of which 98 were detected. Two different approaches based on the concept of concentration addition were used to analyse the data. The results were compared to findings based on datasets from LANUV surveillance monitoring according to the EU Water Framework Directive. Results: Acute and chronic mixture risk calculations indicated risks for 32% and up to 90% of the samples, respectively. The greatest acute toxic pressure was identified for the aquatic flora due to continuous exposure to varying pesticides, whereas the greatest chronic mixture risk was identified for fish as result of a ubiquitous presence of the pharmaceuticals diclofenac and ibuprofen. Overall, only a limited number of substances significantly contributed to the calculated mixture risks. However, these substances varied seasonally and regionally. When mixture risks were calculated based on different datasets, the monitoring design markedly affected the outcome of the mixture risk assessment. Data gaps of both ecotoxicological and exposure data lead to high uncertainties in the mixture risk assessment. Conclusions: Ecotoxicological effects on aquatic organisms caused by chemical mixtures can be expected along the Erft River throughout the year. Both mixture risk assessment approaches can be used for a conservative assessment of mixture risks and characterise the aquatic pollution in the river more realistically than single substance assessments. For the integration of mixture risk evaluations into the assessment and management of the chemical water quality, a two-staged assessment combining both approaches is suggested. To improve future risk assessments, the accessibility and exchange of high-quality ecotoxicological data should be enhanced.

Risk Assessment of Pesticide Mixtures in Australian Rivers Discharging to the Great Barrier Reef

“…The GBRCLMP routinely detects complex mixtures of pesticides in the rivers that discharge to the GBR. , This is in line with the findings of other Australian environmental monitoring programs and similar programs in other countries. − The total risk of these pesticide mixtures to the riverine environment is systematically underestimated if the assessment is limited to a compound-by-compound approach. − Even pesticides detected below their individual environmental threshold values (ETVs) still contribute to the adverse effects of a mixture …”

“…Averaged across all the monitored rivers, approximately 90% of the risk was caused by five pesticides, diuron (45.7%), imidacloprid (26.1%), atrazine (14.5%), metalochlor (3.5%), and hexazinone (2.3%) (Figure a). Mixture risks driven by only a few compounds of each sample have been similarly illustrated in rivers in Southern Sweden and the Erft River in Germany …”

“…This comparatively low number, compared to the average of 25 pesticides detected in samples from, for example, the U.S.A. 28 or the average of 8 pesticides present in Swedish samples 57 might be explained by the comparatively small number of pesticides (50) included in the GBRCLMP analysis suite, while similar studies in Sweden, 57,58 Switzerland, 59 Germany, 30 China, 26 Kenya, 29 and the U.S.A. 28 included more than a hundred pesticides. Indeed, there is a positive relationship between the number of pesticides analyzed and the number of pesticides actually found.…”

“…Due to the small difference between the CA and IA estimates of risk, in order to align with OECD recommendations 32 and to facilitate comparison with other studies, 29,30,54,57 all subsequent mixture risk analyses were therefore based on the results of the CA-based assessment only.…”

“…Mixture risks driven by only a few compounds of each sample have been similarly illustrated in rivers in Southern Sweden 56 and the Erft River in Germany. 30 Figure 3a shows the contribution of all pesticides that contribute at least 0.05% to the total risk, ranked in order of their average relative RQ SUM for the 1451 samples that exceed an acceptable risk (RQ SUM > 1) (see SI for a full list of the pesticide rankings, normalized contribution to the pesticide mixture risk, their compound class, and mode of action in the target organisms). Sixteen compounds contributed 99% of the pesticide mixture risk across the monitored rivers, all of which are herbicides, with the exception of imidacloprid.…”