Acute toxicology of components of vegetation smoke.

Only in recent times, systematic attention has been paid to the occupational health of forest firefighters and workers who manage prescribed fire. Two parts of the effort to learn the impact on worker health are medical observation of those workers, and study of occupational hygiene. It is also necessary to learn what components of smoke are most likely to affect firefighters, and to learn something of the manner in which those substances might compromise health; this review is a step toward that end. The number of possible products of vegetation combustion is almost limitless, and every fuel and condition of burning produces a unique pattern. Nonetheless, it is possible and practical to select a limited number of products that are most likely to be involved in the acute toxicity of smoke. Two products that are almost certainly important are formaldehyde and acrolein. Both appear to occur in all smoke. The toxicology of both is well studied; in particular both are powerful mucosal irritants. Estimates of exposure suggest strongly that concentrations are high enough in smoke to contribute some or all of the irritant activity. There seems to be a reasonable prospect that free radical precursors with half-lives in the tens of minutes are produced when cellulosic materials burn. If so, they will reach the respiratory tract, and liberate free radicals that react immediately on or in pulmonary cells. Ozone is not produced in the fire, but the various hydrocarbons of smoke are substrates for reactions that eventually produce ozone, and that production may continue for miles down-plume. Some measured plume concentrations approach the threshold for human health effects. The effects of the best known component, the particulate material, are unknown in isolation from all of the other substances in smoke. In spite of that ignorance, particulate loading is the principal index of smoke pollution for regulatory purposes, and sometimes is incorrectly used to represent smoke emissions regardless of source. The need to understand health impacts of these components of smoke seems obvious. Perhaps less obvious is the need to use such knowledge in management of both prescribed burning and wildfire. To some extent, it is possible to either manage fire itself to alter emission patterns, or control exposures in certain situations. Whether that should be done to protect worker health can only be judged if enough is known about health effects to direct the management decisions.