Modeling assessments, coupled with indoor laboratory experiments, have shown that the herbicide risks to forest workers are insignificant, even if the fires occur immediately after
A field validation study was conducted in Georgia in August-October 1988 to measure breathing zone concentrations of smoke particles, herbicide residues, and carbon monoxide (CO) on 14 operational
site-preparation prescribed fires. The sites were operationally burned within a time period between 30 and 169 days after herbicide application. Smoke was monitored on sites treated at labeled rates with Arsenal (imazapyr); Garlon
4 (trichlorpyr); Pronone 10G granular and Velpar ULW granular (hexazinone); and Tordon K liquid (picloram). Tract size ranged from 3 to 380 acres.
Personal monitors and area monitors employing glass fiber filters and polyurethane
foam collection media were developed and validated for use in the study. The personal monitors were worn by forest workers and "respirable" smoke particulate matter under a normal operational scenario. The area monitors
were placed in zones of high smoke concentrations to measure airborne herbicide and total smoke particulate matter concentrations under a worst-case operational scenario.
Seventy personal monitors and 70 area monitors were
employed in the study. The sensitivity of the monitoring methods used were in a range that is several hundred to several thousand times below any known herbicide inhalation risk level. No herbicide residues were detected in the
smoke samples from any of the fires in the study.
As expected, particulate matter and CO concentrations varied highly. The effects depend on the fire condition and the location of the personnel. Research personnel experienced
discomfort when deploying the area monitors at some test sites. The particulate concentrations there often exceeded those tolerable for long-duration working conditions. The respiratory distress and eye irritation associated with
the higher values would prompt most workers to retreat to areas of lower smoke concentration after only a few minutes' exposure.
Worker exposure to CO ranged from 6 parts per million per hour to 30 ppm per hour, while working on
the fires. These values are well below the permissible exposure limit for CO of 35 ppm per hour, on the basis of an 8-hour shift. The cited limits are those of the Occupational Safety and Health Administration, U.S.
Department of Labor.
The results of this study further support the "no significant herbicide risk" findings of earlier USDA Forest Service studies.
McMahon, C. K.; Bush; 1990. Final
Report. Evaluation of worker respiratory exposure to herbicide residues in the smoke from prescribed fire in the South. FS-SO-4105-1.21 NAPIAP Project SO-30. Available from senior author, 60 p.
McMahon, Charles K.; Bush, Parshall
B. [In Press] Forest worker expose to airborne herbicide residues in smoke from prescribed fires in the Southern United States. American Industrial Hygiene Association Journal.
The use of trade names in this publication is for
reader information and does not imply endorsement by the U. S. Department of Agriculture of any product.
The authors would like to thank Larry M. Bishop, Forest Management and Taxation
Specialist for reviewing this report and facilitating its publication and distribution. The authors also thank the National Agricultural Pesticide Impact Assessment Program for Sponsoring this Research