Residues of Lindane and Chlorpyrifos in Firewood and Woodsmoke

Pine bark beetle insecticide treatment plots were established on the Ocala National Forest, in central Florida. Each plot consisted of five sand pine, pinus clausa (Chapm. Ex. Engelm) Vassey ex. Sarg., trees treated with either 0.5% lindane (benzene hexachloride) or 2% chlorpyrifos (O,O-diethyl O-(3,5,6-trichloro-2-pgridyl) phosphorothioate). After 4 months, mean residue levels ranged from 0.32 to 35.8 mg/kg for lindane and < 0.1 to 76.1 mg/kg for chlorpyrifos. Chlorpyrifos was more persistent in wood than lindane. In a separate laboratory study, lindane or chlorpyrifos were applied to powdered wood and then burned under controlled conditions to determine carryover in combustion products. With slow heating to 500°C (20”C/min.), 42.7% of the lindane and 28.3% of the chlorpyrifos were recovered in the smoke stream. With rapid combustion at 600°C all lindane and chlorpyrifos residues were thermally degraded. These findings were related to the risk of burning insecticide treated wood as firewood inside houses. Even under the worst case slow burning conditions, human exposure to airborne residues would be well under “safe-sided” threshold limit values and less than 0.2% of the acceptable daily intake established by the World Health Organization.