Occurrence and differential spatiotemporal distribution of pesticides in a plateau lake basin with intensive vegetable cultivation: A case study in Qilu Lake Basin.

Pesticide pollution poses a substantial threat to the ecological well-being of plateau lakes in China. This study monitored the occurrence characteristics of 79 pesticides in the Qilu Lake Basin (QLB), with 50 pesticides detected in the area, comprising 27 insecticides, 13 herbicides, and 10 fungicides. The top 13 pesticides (such as imidacloprid, clothianidin, thiamethoxam, chlorpyrifos, and napropamide) accounted for 91.73 %-93.61 % of the total concentration across the four seasons. Cumulative pesticide concentrations (Σ50 pesticides) in rivers ranged from 10,369.03 to 15,131.02 ng/L, while those in lake shore and lake waters varied from 2355.34 to 5271.75 ng/L and 1504.95 to 1918.35 ng/L, respectively. The source apportionment indicated virtually no recent use of the banned organochlorine pesticides in the QLB post the enforcement of the Stockholm Convention in 2001. The strong positive correlations among most pesticides hint at possible similar application timings and transport pathways within the QLB. The attenuation patterns of key pesticides in the QLB indicated a notable reduction in their environmental impact from rivers to the lake region. However, ten pesticides posed high ecological risks in rivers, with 8-9 pesticides posing high risks in lake shore and lake areas. The presence of high-risk pesticides in various water bodies was highly consistent, suggesting that risks persisted despite the decrease in pesticide concentrations during migration.