Residues of three insecticides in tea leaves, soil and rainwater runoff

Insecticide residues in tea have attracted much attention, and the means to reduce the level of residues in tea and the surrounding environment is a serious issue. Reducing the usage or dose of insecticide may be a viable option to address this problem. We analyzed the possible dietary intake risks and the effects of regular dose versus reduced dose of bifenthrin, deltamethrin, and chlorfenapyr on their residues in fresh tea leaves, soil, and rainwater runoff in tea plantations of the green tea variety 'Fenglv' (Camellia sinensis Yutakmitor). Field trials using bifenthrin, deltamethrin, and chlorfenapyr were conducted in the tea plantations of Yucha Village, Shaoxing City, Zhejiang Province in China. The local regular dose and 30% dose reduction of bifenthrin, deltamethrin, and chlorfenapyr were considered as the experimental treatments group, which included dosages of bifenthrin at 150 mL·hm^-2 and 105 mL·hm^-2, deltamethrin at 750 mL·hm^-2 and 525 mL·hm^-2, and chlorfenapyr at 750 mL·hm^-2 and 525 mL·hm^-2, respectively. Samples of tea leaves and soil were collected on the 1^st, 3^rd, 7^th, and 10^th day after spraying, and rainwater runoff was similarly collected on the 4^th and 8^th day after spraying. The data related to insecticide residues in all the collected samples were used to evaluate the behavioral pattern of residue and risk assessment of the three insecticides. The results indicated that no significantly different residues present in fresh tea leaves was observed sprayed with regular dosage and 30%-reduced dose. The half-lives of bifenthrin in fresh tea leaves sprayed with regular dosage and reduced dosage were 5.89 d and 4.61 d, respectively, and the half-lives of deltamethrin with regular dosage and reduced dosage were 5.75 d and 2.55 d, respectively; and those of chlorfenapyr with regular dosage and reduced dosage were 3.72 d and 2.70 d, respectively. The residue levels of bifenthrin, deltamethrin, and chlorfenapyr in soil were lower than the primary standard value (≤ 0.05 mg·kg^-1) of organochlorine insecticide, hexachlorocyclohexane, as stated in Environmental Quality Standard for Soils (GB15618-1995). The residue levels of bifenthrin and chlorfenapyr in rainwater runoff were lower than the value (≤ 0.005 mg·L^-1) of organochlorine insecticide hexachlorocyclohexane as stated in Standards for Drinking Water Quality (GB5749-2006). The residue levels of deltamethrin in rainwater runoff were lower than the value (≤ 0.02 mg·L^-1) of deltamethrin as stated in Standards for Drinking Water Quality (GB5749-2006). Dietary exposure risk assessment referred to the risk assessment of exposure to insecticides and other harmful substances ingested through food. The results related to the assessment of risk of dietary exposure to the three insecticides in tea indicated that the maximum exposures of bifenthrin, deltamethrin and chlorfenapyr were 0.5×10^-4-1.7×10^-4, 1.0×10^-6-7.3×10^-6, 1.0×10^-5-8.3×10^-5 mg·kg^-1(bw)·d^-1. Risk quotient was expressed as the ratio of maximum exposure to acceptable daily intake. The risk quotients of bifenthrin, deltamethrin and carbonitrile were 0.005-0.017, 0.000 2-0.001, 0.000 2-0.003, respectively, which meant the risk to consumers was within an acceptable range. Reducing sprayed dosages of the above three insecticides in the tea plantations made no significant differences to the residues in tea and the environment.