Uptake Behavior of Terbufos in Different Greenhouse Soils by Lettuce

Terbufos is a soil-applied organophosphorus insecticide whose residue definition includes the parent compound and relevant oxidative metabolites. This study investigated the uptake behavior of terbufos and its metabolites in lettuce cultivated under two greenhouse soil conditions and evaluated dietary exposure. A 3% granular formulation was applied once before transplanting at single (0.18 kg a.i. 10a−1) and double (0.36 kg a.i. 10a−1) application rates. Soil and lettuce samples collected at 21, 28, and 35 days after treatment (DAT) were extracted using a modified QuEChERS method and analyzed by LC–MS/MS. At 21 DAT, maximum total terbufos residues in lettuce were 0.59 and 0.66 mg kg−1 for the single and double application rates in Field I, respectively, and 0.17 and 0.40 mg kg−1 in Field II. Terbufos sulfoxide and terbufos oxon sulfoxide were major residue components in lettuce, indicating the contribution of oxidative metabolites to total residues. Terbufos, terbufos sulfoxide, and terbufos sulfone were major residue components in soil. Differences in residue levels and composition between the two fields may reflect combined effects of field-related soil and environmental conditions on terbufos residue behavior. Estimated dietary exposure ranged from 0.43% to 12.49% of the acceptable daily intake. These results indicate that relevant metabolites and field-related conditions should be considered when assessing terbufos residues in lettuce following soil application.