title: Pesticides drive risk of micropollutants in wastewater-impacted streams during low flow conditions.
abstract: Micropollutants enter surface waters through various pathways, of which wastewater treatment plants (WWTPs) are a major source. The large diversity of micropollutants and their many modes of toxic action pose a challenge for assessing environmental risks. In this study, we investigated the potential impact of WWTPs on receiving ecosystems by describing concentration patterns of micropollutants, predicting acute risks for aquatic organisms and validating these results with macroinvertebrate biomonitoring data. Grab samples were taken upstream, downstream and at the effluent of 24 Swiss WWTPs during low flow conditions across independent catchments with different land uses. Using liquid chromatography high resolution tandem mass spectrometry, a comprehensive target screening of almost 400 organic substances, focusing mainly on pesticides and pharmaceuticals, was conducted at two time points, and complemented with the analysis of a priority mixture of 57 substances over eight time points. Acute toxic pressure was predicted using the risk assessment approach of the multi-substance potentially affected fraction, first applying concentration addition for substances with the same toxic mode of action and subsequently response addition for the calculation of the risk of the total mixture. This toxic pressure was compared to macroinvertebrate sensitivity to pesticides (SPEAR index) upstream and downstream of the WWTPs. The concentrations were, as expected, especially for pharmaceuticals and other household chemicals higher downstream than upstream, with the detection frequency of plant protection products upstream correlating with the fraction of arable land in the catchments. While the concentration sums downstream were clearly dominated by pharmaceuticals or other household chemicals, the acute toxic pressure was mainly driven by pesticides, often caused by the episodic occurrence of these compounds even during low flow conditions. In general, five single substances explained much of the total risk, with diclofenac, diazinon and clothianidin as the main drivers. Despite the low predicted acute risk of 0%-2.1% for affected species, a significant positive correlation with macroinvertebrate sensitivity to pesticides was observed. However, more effect data for pharmaceuticals and a better quantification of episodic pesticide pollution events are needed for a more comprehensive risk assessment.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland; Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, 8092 Zürich, Switzerland.
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Munz
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Francis J
authors.initials: FJ
authors.lastname: Burdon
authors.affiliation: Mermayde, Groet, The Netherlands.
authors.forename: Dick
authors.initials: D
authors.lastname: de Zwart
authors.affiliation: Swiss Centre for Applied Ecotoxicology Eawag-EPFL, 8600 Dübendorf, Switzerland.
authors.forename: Marion
authors.initials: M
authors.lastname: Junghans
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Laura
authors.initials: L
authors.lastname: Melo
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Marta
authors.initials: M
authors.lastname: Reyes
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Urs
authors.initials: U
authors.lastname: Schönenberger
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Heinz P
authors.initials: HP
authors.lastname: Singer
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Barbara
authors.initials: B
authors.lastname: Spycher
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland; Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, 8092 Zürich, Switzerland. Electronic address: juliane.hollender@eawag.ch.
authors.forename: Juliane
authors.initials: J
authors.lastname: Hollender
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Stamm
mesh_terms: D004784:Environmental Monitoring; D010575:Pesticides; D062065:Wastewater / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D010575:Pesticides; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: Mixture toxicity; Multi-substance potentially affected fraction (msPAF); Pesticides; Pharmaceuticals; Risk assessment; Wastewater treatment plants