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& Ma*cnagement Bulletin R8-MB 56 December 1991 .

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pglLSTsrrhlq United States

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Department of

Agriculture COOPERATIVE FORESTRY fill w Forest Service

%chnology Zrpdate. Southem lkgicm, USDA ForestSetvb, 1720 pegchtree Rd., N.W.. AtJwta, Ga.30367

No Herbicide Residues

Found in Smoke from Prescribed Fires

By Charles K. McMahon and P. B. Bush’

Some concerns have been expressed by forest Garlon 4 (trichlorpyr); Pronone 1OG granular and Velpar

workers conducting prescribed burns on forest lands ULW granular (hexazinone); and Tordon K liquid

treated with herbicides. The major concern has been (picloram). Tract size ranged from 3 to 380 acres.

based on speculation that hazardous levels of airborne

herbicide residues may be present in the smoke near Personal monitors and area monitors employing

breathing zones of forest workers. Much of ‘this glass fiber filters and polyurethane foam collection

speculation is based on fiie hazard caution statements media were developed and validated for use in the study.

found on product labels and material safety-data sheets. The personal monitors were worn by forest workers and

While these cautions are appropriate in connection with research personnel to measure airborne herbicide and

fires near herbicide storage sites, they were not intended “respirable” smoke particulate matter under a normal

to apply to fires following application on forest sites. In operational ‘scenario. The area monitors were placed in

these cases, on a given acre, only a few ounces or pounds zones of high smoke concentrations to measure airborne

of active ingredient are spread over several tons of herbicide and total smoke particulate matter

ground litter and forest vegetation, which becomes the concentrations under a worst-case operational scenario.

dominant fuel for the prescribed fne.

Seventy personal monitors and 70 area monitors

Modeling assessments, coupled with indoor were employed in the study. The sensitivity of the

laboratory experiments, have shown that the herbicide monitoring methods used were in arange that.is several

risks to forest workers are insignificant, even if the fires hundred to several thousand times below any known

occur immediately after herbicide application. herbicide inhalation risk level. No herbicide residues

were detected in the smoke samples from any of the

A field validation study was conducted in Georgia fires in the study.

in August-October 1988 to measure breathing zone

concentrations of smoke particles, herbicide residues, As expected, particulate matter and CO

and carbon monoxide (CO) on 14 operational site- concentrations varied highly. The effects depend on the

preparation prescribed fires. The sites were operationally fire condition and the location of the personnel. Research

burned within a time period between 30 and 169 days personnel experienced discomfort when deploying the

after herbicide application. Smoke was monitored on area monitors at some test sites. The particulate

sites treated at labeled rates with Arsenal (imazapyr); concentrations there often exceeded those tolerable for

long-duration working conditions. The respiratory

distress and eye irritation associated with the higher

‘The authors are Project Leader, USDA Forest Service, Auburn, valuei would prompt most wbkers to retreat to areas of

AL, and Co-Investigator, Cooperative Extension Service, lower smoke concentration after only a few minutes’

University of Georgia, Athens, GA, respectively. exposure.