Sediments may act as sink and exposure route of lipophilic pesticides, potentially giving rise to adverse ecological effects on benthic populations and communities (Warrant et al. 2003; Nowell et al. 2016; Boyle et al. 2016; Brock, et al. 2016; McKnight et al. 2015). To assess benthic organisms from potential exposure to pesticides that accumulate in sediments, prospective effect assessment procedures for sediment organisms have been proposed (EFSA 2015; Diepens et al. 2017). Nevertheless, information on effects of sediment-exposure of pesticides on benthic organisms others than standard test species is relatively scarce (Diepens et al. 2014; EFSA 2015; Yin et al. 2018; Brock et al. 2020). In China, an ERA approach for sediment-dwelling organisms is not yet implemented in the authorization procedure of pesticides if they are predicted to accumulate in the sediment compartment. Consequently, results of sediment-spiked toxicity tests with pesticides and benthic invertebrates are not often published in Chinese regulatory reports until now.
Compared to insecticides and herbicides, the potential environmental risks of fungicides received less attention in the open literature (Köhler and Triebskorn 2013; Wightwick et al. 2012; Zubrod et al. 2019), although fungicides may enter surface waters by spray drift, surface run-off and drainage (Komarek et al. 2010; Kookana et al. 1998; Wightwick et al. 2012). Particularly if the Kow and lipophilicity of the fungicide is high, risks to sediment-dwelling organisms cannot be excluded (EFSA 2015). In addition, many fungicides may have biocidal properties, affecting different taxonomic groups and ecological processes in aquatic ecosystems (Maltby et al. 2009; Rico et al. 2019).
Fludioxonil was selected as benchmark compound in this study, since in China this fungicide is extensively used for reducing the disease caused by various fungi in crops like grapes, rice and wheat (Hui 2016). In addition, recent experimental experience on environmental fate and ecotoxicological effects of fludioxonil in the Netherlands could be used to design the Chinese experiments presented in this paper (Yin et al. 2018; Brock et al. 2020). Furthermore, this also offered the possibility for a geographical comparison of the sensitivity of benthic and pelagic species and communities between the Netherlands and China.
Fludioxonil is a non-systemic and broad-spectrum fungicide. It strongly interferes with mycelia growth and stimulates glycerol synthesis via the mitogen-activated protein kinase pathway(Kanetis et al. 2008, Duan et al. 2013). Fludioxonil is stable to hydrolysis but may rapidly photodegrade in water. It has a low solubility in water (1.8 mg/L) and a high mean partitioning coefficient between soil organic carbon and water (Koc = 145,600 mL/g OC) (EFSA 2007), implying that, when present in surface water, fludioxonil will rapidly adsorb to sediment from the water phase. It was found that fludioxonil has a long persistence in sediments of edge-of-field surface waters since residues of this fungicide were present up to 2 years after its use in grape vineyards (Bermúdez-Couso et al. 2007). Fludioxonil is persistent in aerobic aquatic water-sediment systems, with half-lives of 737 and 643 days in pond and river systems (Health Canada 2016). Several publications showed that fludioxonil has biocidal properties and that in aquatic ecosystems several taxonomic groups, including sediment-dwelling organisms, may be relatively sensitive (Brock et al. 2020; Höss et al. 2019; Yin et al. 2018).
In China, the application rate of fludioxonil reported for rice crops is 0.026 a.s. kg/ha while that is 0.126 a.s. kg/ha for grapes, 0.0088 for wheat and maize and 0.15 kg a.s./ha for tomato (see http://www.chinapesticide.org.cn/). Moreover, in China the fungicide fludioxonil was identified as emerging chemical of concern because of its high or increasing use rates and ferquent detection in surface waters (Zhang et al. 2015; Zhang et al. 2017). For this reason, the studies presented in this paper focused the aquatic risks of fludioxonil, with reference to responses of benthic macroinvertebrates and zooplankton in sediment-spiked test systems.
The purpose of this paper is fourfold; (i) to generate chronic toxicity values for benthic invertebrates typical for the Yangtze River Delta in sediment-spiked single species toxicity tests, (ii) to study the fate of sediment-spiked fludioxonil and population- and community-levels responses of benthic invertebrates and zooplankton from the Yangtze River Delta in laboratory microcosms, (iii) compare the treatment-related responses observed in our test systems with those of similar experiments conducted in the Netherlands, and (iv) to evaluate possible environmental risks of fludioxonil application in the crops grapes, rice, wheat, maize and tomato for sediment-dwelling macroinvertebrates and zooplankton in Chinese edge-of-field surface ponds.