Pesticide Contamination and Environmental Health Risk Assessment in Typical Rice Growing Areas of China

Abstract

Pymetrozine has replaced the toxic organophosphate pesticides that were previously used for rice crops in China. Owing to its recent introduction, there are limited studies on the residuals and dynamics of Pymetrozine in the environment. The existing data usually pertain to application studies on artificially constructed plots. Such studies do not adequately address the behaviour of natural dynamics and residuals of Pymetrozine in actual field conditions. Therefore, it is necessary to carry out studies under field conditions to investigate the natural dynamics and residuals of Pymetrozine in typical rice-growing areas in China. In addition, residents living close to agricultural lands might be exposed to pesticides through environmental pathways including spray drift and volatilisation of pesticides beyond the treated area. Most studies about the metabolism, environmental distribution, fate and exposure of Pymetrozine have been carried out in laboratory conditions. However, these experiments cannot represent the natural dynamics and residuals and its exposure and human health risk in the field situation. Therefore, it is necessary to systematically assess Pymetrozine exposures and potential health risks through the environmental routes for residents living close to agricultural lands in field situations.\nThis study was carried out in two rice growing areas in China: Guangxi Province and Hunan Province. Surface soil and paddy water samples were collected in each area on the day prior to spraying and up to the 28th day after pesticide application in June 2019. A modified Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method was used to extract the target analyte. Parameters including linearity, linear range, LOQs, accuracy, precision and stability were considered to evaluate the method validation. Calibration curve analysis and kinetic evaluation methods were used to discuss the dynamics and residual levels of Pymetrozine. In addition, data on the registration of pesticides in China were used, along with government reports, and questionnaire interview as well as toxicological health investigations were carried out to determine the potential hazard identification of Pymetrozine as the major hazard to community health. US EPA exposure assessment and human health risk assessment methods were conducted using the soil and paddy water samples which were collected between 10 to 20 metres around the residents’ apartments. These included the calculation of Hazard Quotient (HQ) and cancer risk values to assess health risks. \nThe results of the recovery range for both the soil and water samples were between 70 % and 120 %, and the relative standard deviation (RSD) was lower than the 20 % in this study, being within the accepted level for residue determination method. Thus, this result shows satisfactory performance of the method. The initial deposit of Pymetrozine in soils was higher than in paddy water in both areas. The decay of Pymetrozine followed an exponential trend. The half-life of Pymetrozine in paddy water was determined to be 3.08 and 3.85 days in the Guangxi and Hunan samples, whereas in soil it was 3.49 and 3.73 days, respectively. The degradation of Pymetrozine in soil and paddy water in this field study was faster than reported in previous studies conducted under non-field conditions.\nThe typical loamy soil and red soil type of the rice-growing areas in China, make residues of Pymetrozine very susceptible to chemical and biological degradation, probably corresponding to the variety of microorganisms in that soil type. In addition, the partitioning behaviour of Pymetrozine between soil/sediment and water conforms to previous results and can be used in modelling studies.\nThe minimum, average, 95th percentile and maximum of the potential cancer risk from dermal contact with soil and water for adults and children; the minimum, average, 95th percentile and maximum of the potential cancer risk from ingestion of soil for adults and children; and the potential total cancer risk from soil and paddy water exposure through the dermal and ingestion pathways were less than 1×10-6, which is within the acceptable levels.\nThe potential non-cancer risk levels obtained for the minimum, average, 95th percentile and maximum of the acute dose and lifetime dose of Pymetrozine through dermal exposure to soils and paddy water; and ingestion exposure to soil for adults and children of the two study locations were below unity. Thus, the potential risks were relatively low.\nThere are no significant potential health effects of Pymetrozine exposure from environmental routes to agriculture communities in both typical rice-growing areas Hunan and Guangxi, of China.