Potential toxicity of pesticides in freshwater environments: passive sampling, exposure and impacts on biofilms: the PoToMAC project.

Abstract

The use of a large array of organic and inorganic micropollutants has been leading to an increasing pollution of surface and ground waters (Schwarzenbach et al. 2006). Headwater streams are highly dynamic systems exposed to the transport and dilution of anthropogenic inputs from agricultural land use of their watershed, where periphytic microorganisms (biofilms) play a key role in river functioning. At the basis of these ecosystems, these complex communities composed of photosynthetic organisms (both eukaryotes and cyanobacteria), bacteria, and fungi significantly contribute to primary production, nutrient cycling, and biodiversity (Lear et al. 2012). Thus, biological impairment due to pollution may cause irremediable environmental damage. Improving pesticide assessment tools in surface waters is required to implement appropriate risk mitigation measures and ultimately contribute to the preservation or restoration of aquatic resources water quality. For this purpose, French regulations aim for a 50 % reduction in the use of pesticides within 10 years. Besides, the European Water Framework Directive (WFD) (2000/60/EC) outlines a strategy for the protection and restoration of European waters, which should reach a chemical and ecological ‘good status’ by 2015. The chemical state of French freshwater bodies is more or less extensively monitored (i.e., 5 to 12 spot samplings per year, depending on types of monitoring programs), especially for the molecules defined as ‘priority substances’ (2013/39/EU). To better characterize the occurrence and fate of pesticides, large efforts are made to improve analytical methods in terms of reliability and accuracy. However, the sampling step is also a crucial part of the monitoring process, and the uncertainty attached to it is still largely neglected (Allan et al. 2006). Besides, environmental quality standards (EQS) defined to protect human health or the ecosystem (2013/39/EU) is only a measure of the state of a specific environmental medium, in regard to a specific pollutant. Both improving risk evaluation procedures and characterizing pesticide effects in aquatic environments require the consideration of the interactions of substances in mixtures, such as found in the environment. The flagrant lack of knowledge in this area has been recently stressed by many researchers (Brock et al. 2006; Chevre et al. 2006; Knauert et al. 2009). Complementarily, the impacts of the detected substances have to be evaluated on selected living organisms or ‘key biological indicators’ as defined by the WFD. Biofilm, and in particular its diatom component, is one of these key compartments used in Europe to assess water quality, as an indicator of nutrient enrichment and other pressures (Coste et al. 2009; Kelly et al. 2014; Kelly et al. 2012). To date, diatom-based indices properly diagnose nutrient inputs, but fail to unequivocally assess toxic pollutions. However, the diversity of organisms in biofilms confers to this microbial community a great capacity of response to different environmental factors and thus a potential for contamination assessment. Because of their structural complexity, Responsible editor: Philippe Garrigues