Degradation Kinetics and Subcellular Distribution of Six Pesticides During the Grape Growth Period

Objective One of the key problems restricting the green development of grape industry is that systematic researches are still lacking on the dissipation rules of multiple pesticide residues and their subcellular distribution characteristics at different growth and development stages of grapes. This study investigated the degradation and subcellular distribution characteristics of six pesticides during the growth period of grapes in Xinjiang were investigated, so as to provide a theoretical basis for risk control and safety evaluation of pesticide residues in table-grape production in Xinjiang.

Methods A field experiment was carried out in a Thompson Seedless grape vineyard in Turpan City, Xinjiang, from May to September 2024. Six pesticides including bifenthrin, lambda-cyhalothrin, pyraclostrobin, difenoconazole, prochloraz and dimethomorph were sprayed, and fruit samples at different growth stages were collected. Pesticide residue contents were determined according to GB/T 20769-2008 and NY/T 761-2008. The subcellular fractionation method was adopted to analyze the distribution characteristics of pesticides in different cellular components.

Results The degradation processes of all six pesticides fitted the first-order kinetic model, with half-lives ranging from 2.46 d to 4.78 d, showing a trend of rapid degradation followed by slow degradation. Dimethomorph degraded the fastest with a half-life of 2.46 d, while pyraclostrobin degraded relatively slowly with a half-life of 4.78 d. At the expanding stage, dimethomorph had the highest proportion in soluble tissues. At the green-ripe stage, the proportion of pesticides in the cell walls increased, whereas the proportions in soluble tissues and organelles decreased. At the color-changing stage, the distribution order of difenoconazole and prochloraz among subcellular components was cell wall > organelle > soluble tissue. At the maturity stage, the total pesticide residues in grape fruits were extremely low, and pesticides were mainly enriched in cell wall and organelle fractions.

Conclusion The degradation of the six pesticides conformed to the first-order kinetic equation. The subcellular distribution of pesticides varied with grape growth stages, and pesticides were mainly enriched in cell wall and organelle fractions at the maturity stage.