Trichlorfon and Dichlorvos: Their Residues and Toxicity in Rodent Bait for Flea Control

An analytical chemical procedure was used to determine residues of trichlorfon and dichlorvos in rodent baits, in feces from rodents fed the treated baits, and in the vapors arising from both materials. Also, the effects of these vapors on oriental rat fleas, Xenopsylla cheopis (Rothschild), were determined. The residues of the 0.3% trichlorfon used to treat corn-milo bait decreased from 2190 to 1250 ppm in 8 days while the residues of dichlorvos were increasing from 34.1 to 90.9 ppm; also, 10 g of this 8-day-old bait emitted 365 ng of trichlorfon and 3000 ng dichlorvos in vapor when the bait was swept with air (50 ml per min.) for 8 hr. A composite sample of rat feces collected for 6 days from rats fed on the same bait contained residues of trichlorfon and dichlorvos of 179 and 12.8 ppm, respectively; also, 1040 ng of dichlorvos was emitted in the vapor from 10 g of the feces in 8 hr (no trichlorfon was detected). In addition, the vapor from ground laboratory chow treated with 0.3% trichlorfon contained 24 ng per liter of dichlorvos but no trichlorfon when it was swept for 1 hr after standing for 24 hr in closed jars. The mortality of fleas exposed to these vapors during the 24 hr was 60%.