Abstract
The ecological risk for chemicals should be evaluated from the viewpoint of population-level impact. To date, however, there are still no practical approaches to the assessment of the population-level impact of chemicals in order to develop appropriate plans for chemical management. In an attempt to address this urgent issue, we firstly proposed two population-level approaches based on state-of-the-art approaches to population-level risk assessment. Thereafter, as a case study, we applied the two approaches to the quantitative assessment of the potential impact of 4-nonylphenol (4-NP) on medaka (Oryzias latipes) in terms of reduction of population growth rate (λ). An age-classified projection matrix (daily time-step) model was developed and used as a tool for incorporating life-cycle survivorship and fecundity data obtained for individual-level responses of medaka exposed to 4-NP into population-level responses such as λ. Based on the resulting λs, the two proposed population-level approaches were then examined. The predicted no-effect concentration (PNEC) for population-level impact based on the threshold concentration (defined as the concentration at λ=1), as well as the lowest-observed-effect concentration (LOEC), the non-observed-effect concentration (NOEC), and the maximum-acceptable-toxic concentration (MATC) were then derived. The results suggest values for PNEC ranging between 0.82 and 2.10μg·l-1 for medaka population growth impact under 4-NP exposure. Although these two approaches still have limitations, current knowledge indicates that they are reasonable and practical approaches to the evaluation of population-level impact.
