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Diffuse pressures: pesticides

To quantify the effects of pesticides on the freshwater ecosystems, he chronic multi-substance Potentially Affected Fraction (msPAF) was used, derived from Europe-wide integrated exposure and effect modelling for the year 2013 (van Gils et al., 2020). The msPAF specifies the potential share of the aquatic species community affected by pesticide toxicity. The model includes two components:
   (1) a spatio-temporally resolved model for emissions and fate-transport of chemicals driven by a hydrological model (van Gils et al., 2020), yielding Europe-wide daily predicted environmental concentrations (freely dissolved part) of 332 pesticides in water bodies to obtain a “real-life” mixture exposure scenario for each FEC, and
   (2) species sensitivity distributions (SSD) based on effect models considering chronic non-observed-effect concentrations (NOEC) of each studied chemical as effect endpoint (Posthuma et al., 2019). Combining (1) and (2), and adding a step of mixture modelling yields the mixture toxic pressure metric, which is expressed as multi substance Potentially Affected Fraction of species (msPAF) (de Zwart & Posthuma, 2005; Posthuma et al., 2020), being an estimate of the likelihood (values between 0 and 1) of direct effects of chemical exposure to effect-endpoints of aquatic organisms such as growth and reproduction (Posthuma et al., 2019). In this study, the msPAF-NOEC based on 99^th percentile predicted environmental concentrations of the daily concentration estimates was used, representing an acute toxic stress level exceeded at four days per year (Figure 4).

Figure 4: Geographical distribution of the fraction of aquatic species in Europe potentially affected by pesticides, calculated by FEC