Volatile and Dislodgeable Residues Following Trichlorfon and Isazofos Application to Turfgrass and Implications for Human Exposure
- K. C. Murphy,
- R. J. Cooper and
- J. M. Clark
In this study, volatile and dislodgeable residues were determined following insecticide application of trichlorfon (dimethyl 2,2,2-trichloro-1-hydroxyethyiphosphonate) or isazofos (O-5-chloro-1-isopropyl-1H-1,2,4-triazol-3-yl O,O-diethylphosphorothioate) to a 10-m radius plot of ‘Penncross’ creeping bentgrass (Agrostis palustris Huds.) to assess human exposure and possible toxicity. Trichlorfon was applied either with or without irrigation following application, whereas isazofos application was always followed by irrigation. For all applications, less than 12% of applied insecticides were lost as measured volatile residues during the experimental sampling periods. Volatile loss declined in a diphasic pattern with most loss occurring within 5 to 7 d of application. Irrigation greatly reduced initial volatile and dislodgeable residues. Subsequent volatile and dislodgeable residues, however, increased substantially on Days 2 and 3 compared with residue levels in the absence of irrigation. Trichlorfon dislodgeable residues never exceeded 1% of applied compound in the absence of irrigation, whereas with irrigation, trichlorfon, and isazofos dislodgeable residues were never greater than 0.5% of applied compound. Irrigation increased the transformation of trichlorfon to DDVP (2,2-dichlorovinyl dimethyl phosphate), a more toxic insecticide. Inhalation and dermal exposures were estimated using measured air concentrations and dislodgeable residues, respectively, and hazard quotients (HQs) were calculated. A HQ less than 1 indicated that the residue level is below a concentration that might reasonably be expected to cause adverse effects in humans. Calculated inhalation HQs for volatile residues were equal to or less than 1 for all sampling periods except Days 1 (HQ = 5.0), 2 (HQ = 4.5) and 3 (HQ = follo wing isazofos application. Calculated dermal HQs from dislodgeable residues were equal to or less than 1 except for DDVP on Day 2 (HQ = 4.6) when trichlorfon application was followed by irrigation, and on Days 2 (HQ = 14.3) and 3 (HQ = 5.7) following isazofos application.
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