Abstract
We conducted a probabilistic ecological risk assessment of the herbicide simetryn which is used in Japanese paddy fields. The EC50 values for 31 algal genera were fitted to log-normal distribution, and the hazardous concentration for 5% of algal genera (HC5) was estimated to be 8.2 μg/l. The predicted environmental concentration (PEC) of simetryn was calculated to be 0.71 μg/l using an environmental model and the standard scenario defined by the Ministry of Environment, Japan. The distribution of PEC was quantified using Monte Carlo analysis, and the mean of PEC was 0.77 μg/l and the 95 percentile was 2.8 μg/l. The joint probability curve was derived by comparing the species sensitivity distribution and the distribution of PECs, and the probability of exceeding HC5 was estimated to be 1.5%.
