Ecological risk assessment of imidacloprid in surface water from rice- vegetable rotation areas by using interspecies correlation estimation

Imidacloprid is widely detected in surface water from sub-tropical or tropical agricultural regions of China. However, there is scanty information on the ecological risk assessment of imidacloprid in surface water near tropical crop systems due to the lack of toxicity data on local aquatic organisms. In this study, the acute toxicity risk threshold-hazardous concentration at the 5^th percentile of the species (HC₅) -of imidacloprid to local aquatic organisms in surface water was obtained based on web-interspecific correlation estimation (Web-ICE) and species sensitivity distribution (SSD) models, then its ecological risk assessment in surface water near rice-vegetable practice in Chengmai (Hainan) was temporally and spatially assessed by risk quotient (RQ). The results showed that the risk threshold HC₅ of imidacloprid in the aquatic environment around the rice-vegetable rotation in Chengmai is 4.30 μg/L, 41.7% of water samples with the RQ of higher than 1. Also, the RQ values corresponding to the median and maximum concentrations of imidacloprid in surface water from our study were significantly higher than the RQ values in surface water from other regions of China, indicating that imidacloprid residues had higher potential ecological risks to aquatic organisms in surface water from tropical rice-vegetable rotation field. In addition, there was the highest potential ecological risk occurring in April, the sowing time (RQ>1 in 92.3% surface water), vegetable planting period (mean RQ=2.53 with RQ>1 with 68% water surface water), and the central regions of Chengmai during the practice of rice-vegetable rotation, indicating that there were significant spatiotemporal and crop-related characteristics of the ecological risk of imidacloprid in surface water. It thus contrives to limit and reasonably use imidacloprid by planting period and region in the practice of rice-vegetable rotation in Chengmai, Hainan.