Survey of Organic Pollutants in River Water by a Target Screening Method and a Bioassay in Heavy Rainfall Disasters

In July 2020, heavy rains caused floods in the Kyushu region, resulting in an accidental spillage of 12 pesticides from a pesticide storehouse upstream of the Chikugo River tributary. In this study, we analyzed the spilled pesticides by a target screening method using GC/MS and LC/MS/MS. Some of the spilled pesticides (iminoctadine,diquat,paraquat) were measured by direct injection using LC/MS/MS. The toxicity of the pesticides to aquatic organisms was assessed by bioassays using algae (Raphidocelis subcapitata), water fleas (Daphnia magna), and fish (Danio rerio) embryos. As a result, no spilled pesticides were detected and no toxic effects were observed on aquatic organisms. The screening method using GC/MS and LC/MS/MS determined chemicals in 1 day, i.e., from sampling to reporting the survey results. The recovery tests of pesticides, using river water in a heavy rain disaster by a target screening method, were at generally acceptable levels (recovery rate: 44-110 %) compared with the target recovery rates (50-150 %). However, the recovery rate of highly hydrophilic pesticides (iminoctadine,diquat,paraquat) was 0.29-0.75 %. Therefore, it is necessary to develop a screening method for hydrophilic substances used in heavy rain disasters.