Captan

Captan was developed by Standard Oil Company in 1949 and became one of the most widely used fungicides in American agriculture for the following 70 years [1]. Structurally it contains a trichloromethylthio (-SCCl₃) group that releases reactive sulfur species when it reacts with cellular thiols — the same functional group found in the related fungicide folpet [2]. EPA's 1989 reregistration review triggered controversy when dietary risk calculations showed potential cancer risk above the then-threshold; EPA cancelled many food uses in 1989, but the cancellation was subsequently partially reversed based on updated risk calculations [1]. Today, captan remains registered for use on strawberries, stone fruits, apples, grapes, and ornamentals. It is one of the highest-use fungicides in California — consistently in the top 10 by weight applied in strawberry production [2].

Dietary residues on treated fruits and vegetables represent the primary exposure for most people — strawberries, apples, cherries, and peaches have the most consistent residue presence [1]. Agricultural workers applying captan or working in recently treated fields face inhalation and dermal exposure [2]. Home gardeners using captan formulations on roses and fruit trees have direct handling exposure [1]. Captan is moderately persistent — washing fruit reduces but does not eliminate residues [2].

Captan's trichloromethylthio group reacts with cysteine residues in cellular proteins and with glutathione, generating reactive oxygen species and thiophosgene-related intermediates [1]. In high-dose gavage rodent studies, it induced duodenal tumors (in mice) and kidney tumors, leading to EPA and IARC Group B2/Group 2B probable/possible carcinogen classification [2]. However, the duodenal tumors are likely a rodent-specific cytotoxicity mechanism (local tissue injury from the bolus dose) rather than a genotoxic mechanism relevant to dietary human exposure [1]. Captan is also a skin sensitizer and causes contact dermatitis in agricultural workers [2].

Strawberry, apple, and stone fruit farmworkers with repeated application and harvest-season exposure are most at risk for sensitization and acute effects [1]. Infants and toddlers who consume relatively more fruit per body weight may have higher dietary exposure [2]. Home gardeners using captan dust on roses and ornamental plants have direct handling exposure [1].

1. Wash fruit thoroughly under running water and, for high-residue fruits like strawberries, consider choosing organic [1]. 2. Home gardeners should use gloves and a dust mask when applying captan powder — skin sensitization is a real risk [2]. 3. Farmworkers should use PPE as specified on the label and follow restricted-entry intervals [1]. 4. EPA's Pesticide Data Program annual report shows captan residue levels — check at apps.ams.usda.gov/PDP [2].