© 1981 Oxford University Press
research-article |
Potential Exposure of Humans to 2,4,5-T and TCDD in the Oregon Coast Ranges
AProfessor of Forest Ecology, Oregon State University Corvallis BChief Research Chemist, USDA Forest Service Corvallis, Oregon
Potential Exposure of Humans to 2,4,5-T and TCDD in the Oregon Coast Ranges1 Newton, M. and Norris, L.A. (1981).Fundam. Appl. Toxicol. 1:339–346. Research on the use of 2,4,5-trichlorophenoxyacetic acid (2,4,5–T) contaminated with 2.5 x10-8 parts 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in forests of the Oregon Coast Ranges permits estimates of human exposures for both compounds. Estimated total exposure of nearby (
l/8 mile distant) residents during the first week after application is 0.0039 mg/kg of 2,4,5-T for a 70-kg adult. Exposure to TCDD in the same episode would be 1.9 x 10–10 mg/kg. Nearly half the total exposure, i.e. 0.0019 mg/kg 2,4,5-T and 5.0 X 10–11 mg/kg TCDD would occur the first day. Based on published and unpublished acute no-effect estimates of 40 mg/kg for 2,4,5-T and 0.0001 mg/kg for TCDD, the smallest safety factors for the two chemicals are 20 000:1 for 2,4,5-T for 1 day and 1 000 000:1 for TCDD for 1 week. Applicators are far more heavily exposed, with daily maximum actual intake for helicopter loaders (the highest exposure group if they do not wear gloves) of 0.063 mg/kg per day 2,4,5-T and 1.6 X 10–9 mg/kg per day TCDD. Minimum safety factors for the most heavily exposed workers based on these data are estimated at 635:1 for one-time exposure to 2,4,5-T; 83 333:1 for onetime exposure to TCDD; 318:1 for daily exposure to 2,4,5-T; and 625:1 for daily exposure to TCDD. Nearly all exposure to 2,4,5-T in forestry operations is through dermal contact. Inhalation appears minor. Urine is a reliable indicator of exposure to 2,4,5-T if collected within 1 to 4 days of exposure (depending on the degree of exposure). Human skin exposed to a concentrated spray mixture containing 38.4 g 2,4,5-T per liter, as the ester, transmitted 0.0013 mg/cm2 per hr during the period of saturated contact.