Fungicides: An Overlooked Pesticide Class?

Abstract

Fungicides are indispensable to global food security and their use is forecasted to intensify. Fungicides can reach aquatic ecosystems and occur in surface water bodies in agricultural catchments throughout the entire growing season due to their frequent, prophylactic application. However, in comparison to herbicides and insecticides, the exposure to and effects of fungicides have received less attention. We provide an overview of the risk of fungicides to aquatic ecosystems covering fungicide exposure (i.e., environmental fate, exposure modeling, and mitigation measures) as well as direct and indirect effects of fungicides on microorganisms, macrophytes, invertebrates, and vertebrates. We show that fungicides occur widely in aquatic systems, that the accuracy of predicted environmental concentrations is debatable, and that fungicide exposure can be effectively mitigated. We additionally demonstrate that fungicides can be highly toxic to a broad range of organisms and can pose a risk to aquatic biota. Finally, we outline central research gaps that currently challenge our ability to predict fungicide exposure and effects, promising research avenues, and shortcomings of the current environmental risk assessment for fungicides.

Figure 1

Violin plots of physicochemical properties related to pesticide mobility and dissipation in aquatic systems for fungicides, herbicides, and insecticides currently registered for use in the EU (fungicides: n = 120/45/124/95/106, herbicides: n = 150/83/148/123/145, insecticides: n = 82/51/86/60/74, for A, B, C, D, and E, respectively; extracted from the Pesticide Properties DataBase). Black bars within violins represent medians. To facilitate readability, data points are randomly scattered along a hypothetical x-axis and are greyed out within the violins.

Figure 2

Violin plots of physicochemical properties related to pesticide mobility and dissipation in aquatic systems for major fungicide groups (only substances currently registered for use in the EU are shown; chloronitriles [i.e., chlorothalonil]: n = 1/1/1/1/1, demethylation inhibitors: n = 22/6/22/19/20, dithiocarbamates: n = 6/3/6/6/6, strobilurins: n = 9/4/9/9/9, for A, B, C, D, and E, respectively; extracted from the Pesticide Properties DataBase). See caption of Figure 1 for more details.

Figure 3

Boxplots of fungicide concentrations compiled from the literature (see SI Table S1 for details) separated by continent. Number of detections per continent are provided and different letters indicate statistical significance.

Figure 4

Overview of maximum detected global field concentrations (SI Table S1), toxicity to different organism groups according to the literature (including acute and chronic end points; SI Table S2), and regulatory acceptable concentrations (RACs; SI Table S3) derived during the EU’s ERA for (A) demethylation inhibitors, (B) strobilurins, (C) benzimidazoles, (D) chloronitriles (i.e., chlorothalonil), and (E) dithiocarbamates. Field concentrations and toxicities are presented up to the highest detected concentrations and down to the lowest effect concentrations, respectively. Y-axis limit was set to 1000, concentrations exceeding 1000 were cut. nd = not detected; na = not available.

Figure 5

Risk quotients for algae (squares), fish (circles), and invertebrates (triangles) as ratios of maximum detected global field concentrations (SI Table S1; substances with ≥10 observations) and acute standard toxicity data (i.e., the base set; provided by the Pesticide Properties DataBase). Open symbols indicate that toxicity was provided as “greater than” values. Risk quotients >0.01 (dashed line) and >0.1 (solid line) indicate moderate and high risks, respectively. Substances are ordered from highest to lowest risk according to the classification: high risk for several test organisms > high risk for one test organism and moderate risk for two test organisms > high risk for one test organism and moderate risk for one test organism > high risk for one test organism > moderate risk for three test organisms > moderate risk for two test organisms > moderate risk for one test organisms > unclear risk (i.e., toxicity value provided as “greater than” value) > all test organisms low risk. If substances scored equal, the mean risk quotient determined ranking. For risk quotients sorted by continent, see SI Table S4.