A Robust Approach to Risk Assessment Based on Species Sensitivity Distributions

Abstract

The guidelines for setting environmental quality standards are increasingly based on probabilistic risk assessment due to a growing general awareness of the need for probabilistic procedures. One of the commonly used tools in probabilistic risk assessment is the species sensitivity distribution (SSD), which represents the proportion of species affected belonging to a biological assemblage as a function of exposure to a specific toxicant. Our focus is on the inverse use of the SSD curve with the aim of estimating the concentration, HCp, of a toxic compound that is hazardous to p% of the biological community under study. Toward this end, we propose the use of robust statistical methods in order to take into account the presence of outliers or apparent skew in the data, which may occur without any ecological basis. A robust approach exploits the full neighborhood of a parametric model, enabling the analyst to account for the typical real-world deviations from ideal models. We examine two classic HCp estimation approaches and consider robust versions of these estimators. In addition, we also use data transformations in conjunction with robust estimation methods in case of heteroscedasticity. Different scenarios using real data sets as well as simulated data are presented in order to illustrate and compare the proposed approaches. These scenarios illustrate that the use of robust estimation methods enhances HCp estimation.

Taxon-toxicity study of fish to typical transition metals: Most sensitive species are edible fish

“…The screening standards of toxicity data used in the study were based on the strict rules as detailed in Text S1. The lethal concentration affecting 50% of individuals (LC50) or the effective concentration affecting 50% of individuals (EC50) were selected as the acute toxicity endpoint (Wang et al, 2017a), while the no observed effect concentration (NOEC) or the lowest observed effect concentration (LOEC) were selected as the chronic toxicity endpoint (Monti et al, 2018). The species mean acute/ chronic value (SMAV/SMCV) was calculated by use of geometric means when more than one toxicity data for the same species were available (Stephen et al, 1985).…”

Systematic Consideration of Parameter Uncertainty and Variability in Probabilistic Species Sensitivity Distributions

“…The NOEC was criticized for having no biological meaning because it is not a measure of toxicity but rather of nontoxicity. The NOEC considerably depends on the study design that can lead to higher variability (Laskowski 1995;Isnard et al 2001;Jager 2012;Fox and Landis 2016;Monti et al 2018). Thus, the measure of ECx was proposed to replace the NOEC, whereas the selected value for x depends on jurisdiction and risk management objectives (Isnard et al 2001;Beasley et al 2015).…”

“…Yet, the biological community does not necessarily follow 1 single distribution (Xu et al 2015). Nonparametrical SSD approaches have been developed to tackle this challenge (Newman et al 2000;Wang et al 2015;Monti et al 2018). One of these approaches is the probabilistic species sensitivity distribution (PSSD) (Gottschalk and Nowack 2013).…”

“…Environmental and ecological risk assessments of a substance require the comparison of an environmental concentration, which can be measured or predicted, with the predicted no‐effect concentration (PNEC). The calculation of a species sensitivity distribution (SSD) is a commonly accepted approach to derive the PNEC of a substance (Monti et al ). Generally, the SSD approach considers several environmental species that are assumed to be representative of the biological community of an environmental compartment.…”

“…Thus, the measure of EC x was proposed to replace the NOEC, whereas the selected value for x depends on jurisdiction and risk management objectives (Isnard et al ; Beasley et al ). Still, the NOEC and EC 10 represent the conservative values for assessing the PNEC, which are proposed by the Registration, Evaluation, Authorisation and Restriction of Chemicals regulation (REACH) (ECHA ; Monti et al ).…”