Evaluation of probabilistic ecological risk assessment methodology using aquatic microcosms and azinphos-methyl

Takacs, Peter
Journal Title
Journal ISSN
Volume Title
University of Guelph

The general trend toward probabilistic risk assessment in aquatic toxicology relies on some key assumptions, several of which are questionable. At present, only a few studies have been carried out to evaluate the probabilistic approach. To this end, a multi-species outdoor microcosm study was conducted using the organophosphorus insecticide azinphos-methyl, the freshwater fish ' Pimephales promelas' and 'Lepomis gibbosus', as well as zooplankton. A regression design was used with 5 treatment levels (0.1-100 [mu]g/L) and a control. Comparison of the 96 hr LC50s for fish (31.7 and 3.2 [mu]g/L, respectively) with the 10th percentile of the acute sensitivity distribution (0.9 [mu]g/L) indicates that this extrapolated value would not correspond to acute toxicity in these species. Based on literature data, the multi-species no observable effect concentration (NOEC) for ' Daphnia' sp. (0.1 [mu]g/L) coincides with the chronic and acute 10 th centiles (0.092 and 0.15 [mu]g/L) of the single species invertebrate sensitivity distributions. For fish, the multi-species NOEC for survival (0. 17 [mu]g/L is below the acute 10th centile of 0.9 [mu]g/L, which is not protective. Probabilistic risk assessment of azinphos-methyl in Southern Ontario surface waters indicates that up to 30% of fish and 50-70% of invertebrate species may be acutely impacted. The applicability of probabilistic extrapolation to ecosystem level effects is highly uncertain and thus difficult to reconcile.

probabilistic risk assessment, aquatic toxicology, multi-species outdoor microcosm study, organophosphorus, insecticide, azinphos-methyl, freshwater fish, Pimephales promelas, Lepomis gibbosus, zooplankton