Occurrence and distribution of atrazine in groundwater from agricultural areas in China.

There has been heavy application of chemical pesticides to farmland worldwide. As a state with a heavy emphasis on farming, China has extensively applied chemical pesticides to farmlands. Atrazine (ATZ), one of the most widely used herbicide in the world, has been used in large quantities in weed control in many crops, which poses a relatively large threat to groundwater utilization and agricultural safety. A nationwide sampling and analysis of ATZ in 8146 groundwater monitoring wells from 10 main grain producing areas were conducted during 2019. The results showed that the detection rate of ATZ in groundwater was 40.79 %, with detected concentrations up to 2.86 μg/L. ATZ detection rate was significantly higher in phreatic aquifers than confined aquifer. The concentration of ATZ decreased significantly with the depth increasing, the detected depth of ATZ in groundwater was varied from 5 to 1100 m, and 70.27 % of the detected ATZ was distributed in the depth of 0-51.8 m. The detection rate of ATZ in most north regions lower than south regions in China, and ATZ with high concentration was mainly occurred in southern regions. ATZ is more likely to migrate into the groundwater in the water resource rich areas. The concentration of ATZ decreased with TDS increasing, 74.39 % of the ATZ was detected in groundwater with TDS concentration <1 g/L. The hydrochemical type of groundwater in ATZ-enrichment environment were mainly Ca-HCO3 and Mixed type. According to classification and regression tree analysis, the high ATZ detection rate were closely related with groundwater depth (<51.8 m) and high organic matter content.