SUMMARY. The causes of vegetarian fires are reviewed and their potential risk is documented. Strategies for reducing the risks are listed. The specific health risks of vegetation fires are also analysed. High concentrations of inhalable particulate matter are found in smoke from vegetation fires, constituting a health risk. Suspended particulate matter has been associated with increased mortality, and morbidity. Asthmatics are particularly at risk. A series of health guidelines for vegetation fire events is presented.
Vegetation fires, whether man-made or natural as a consequence of extreme drought, occur in many parts of the world. Fires are caused by slash and burn land clearing, by clearing of plantations following logging operations, and by natural events such as lightning or extreme drought. During dry seasons, fires usually reach a peak and can present a transboundary problem when prevailing winds disperse the smoke to other countries. It can happen that extensive fire fighting activities do not help to extinguish the fires, especially when peat soil is burning.
The smoke from vegetation fires seriously affects exposed populations. Examples in case are the concentrations of PM10 as monitored in Malaysia and Singapore during the outbreak of the vegetation fires in Indonesia from July to October 1997 which substantially exceeded the air quality guidelines recommended previously by WHO and national air quality standards. Increased numbers of incidences of respiratory diseases and hospital admissions were reported. Contingency plans harmonized between countries to the utmost extent possible would help to mitigate the air pollutant burden suffered by the general public.
The recurrence of transboundary smoke originating from uncontrolled vegetation fires in many countries around the world causing acute and long-term respiratory health problems requires a comprehensive strategy based on broad international consensus. Any comprehensive strategy must include:
Environmental as well as health aspects, cause-effect relationships, long-range pollution transport, etc. must be taken into consideration.
Smoke from biomass burning contains a large and diverse number of chemicals, many of which have been associated with adverse health impacts. Nearly 200 distinct organic compounds have been identified in wood smoke aerosol, including polycyclic aromatic hydrocarbons. Available data indicate high concentrations of inhalable particulate matter in the smoke of vegetation fires. Since particulate matter produced by incomplete combustion of biomass is mainly less than 1 Ìm in aerodynamic diameter, both PM10 and PM2.5 concentrations increase during air pollution episodes caused by vegetation fires.
Inhalable and thoracic suspended particulate matter moves further down into the lower respiratory airways and can remain there for a longer period and deposit. The potential for health impacts in an exposed population depends on individual factors such as age, the pre-existence of respiratory and cardiovascular diseases and infections, and particle size. Gaseous compounds ad- or absorbed by particles can play a role in long-term health effects (cancer) but short-term health effects are essentially determined through particle size. The quantitative assessment of health impacts of air pollution associated with vegetation fires in developing countries is often limited by the availability of baseline morbidity and mortality information. Air pollutant data are of relatively higher availability and quality but sometimes even these data are not available or reliable.
Epidemiological studies have also indicated that levels of suspended particulate matter currently monitored in many urban areas in the world are associated with increased daily mortality, increased out-patient emergency room visits and hospital admissions, and an exacerbation and increase in the number of respiratory diseases. Increases in restricted activity days and in school absenteeism have been observed with increased levels of fine particulate matter as well as increases in the frequency of coughs and the use of bronchodilators. Infants are a particularly sensitive group with respect to acute respiratory infections (ARI) exacerbated in the presence of smoke.
The association between increases in daily mortality and particulate matter concentrations existed primarily in the elderly and in individuals with pre-existing respiratory and/or cardiovascular illness. No threshold was found for the onset of health effects in suspended particulate matter in the general population. Therefore, the expert task force of the WHO for updating and revising the WHO Air Quality Guidelines for Europe did not derive a guideline value for PM10 and PM2.5 but rather recommended these associations to be used as guidance for deriving air quality standards (WHO 2000).
Specific studies of exposure to biomass smoke or “haze” indicate a consistent relationship between exposure and increased respiratory symptoms, increased risk of respiratory illness, and decreased lung function (see WHO-UNEP-WMO 1999b). These studies have mainly been focused on children; some studies on adults have shown compatible results. A limited number of studies also indicate an association between biomass smoke exposure and visits to hospital emergency rooms. Asthmatics are a particularly sensitive group. During the smoke episode caused by vegetation fires in Indonesia, the Malaysian Ministry of Health indicated a two- to three-fold increase in the number of out-patient visits for respiratory diseases during high PM10 concentration events. A study by Universiti Kebangsaan Malaysia demonstrated a 14% lung function decrease in a group of Kuala Lumpur schoolchildren during the smoke episode. A crude analysis of surveillance monitoring of ARI, asthma, and conjunctivitis incidents in August-September 1997 at three hospitals in the Klang Valley, in comparison to the Malaysian air pollution index (API), indicated a clear relationship between incidents and PM10 concentration. The Indonesian Ministry of Health indicated a total of 210,000 clinically affected individuals as of 22 October 1997, one month after the peak of the episode.
There is no evidence that particles from biomass smoke would have a health impact different from those due to particulate matter from other combustion processes.
The World Health Organization convened in October 1998 in Lima, Peru, a group of high-level experts with personal experience covering collectively all pertinent aspects of the problem, including:
Based on background papers, this meeting developed the WHO-UNEP-WMO Health Guidelines on Vegetation Fire Events. These guidelines refer to:
Three documents of the Health Guidelines for Vegetation Fire events have been published: Guideline Document (WHO-UNEP-WMO 1999a); Background Papers (WHO-UNEP-WMO 1999b), and a Teachers’ Guide (WHO-UNEP-WMO 1999c).
The Guideline Document, in a chapter on air pollution from vegetation fires and health, discusses the following topics:
In its chapter on the guidelines, the Guideline Document describes the acute and chronic health effects of particulate matter from the smoke of biomass and gives public advisories on how to inform the public with respect to:
Mitigation measures are then discussed in detail, such as:
Methodologies are also given for the assessment of forest-fire-induced health effects treating the issues of:
A final chapter of the Guideline Document elaborates on the prevention of future health-affecting events by discussing the source of the problem - land-use and fire policies - and addressing gaps in knowledge, technologies, and programmes.
The document of Background Papers contains the 18 background papers, prepared by experts of the different scientific communities, which cover the following issues:
The goal of the Teachers’ Guide is to enable national trainees of the guidelines to become trainers, and disseminate the information in the guidelines to the staff of national fighters and other stakeholders involved in the fighting, suppression, and prevention of vegetation fires. The Teachers’ Guide contains the complete set of slides used in a first training course convened in Kuala Lumpur, Malaysia, in December 1998.
The Guideline Document has been translated into French and Spanish. In 2001, a CD-ROM is being prepared to contain all three documents in English, and the French and Spanish editions of the Guideline Document. The CD-ROM will also contain the slides in English and Spanish used in the above-mentioned first training course and in a second course held in Brasilia, Brazil, in June 1999.
RESUME L’Auteur considère les causes des incendies de la végétation et leur risque potentiel est documenté. Les stratégies et les risques spécifiques pour la santé sont analysés. Une haute concentration de matière inhalable est observée dans la fumée provoquée par les incendies de végétation, et cela constitue un danger pour la santé. La matière suspendue particulée a été associée à une mortalité et une morbidité plus élevée. Les personnes atteintes d’asthme sont particulièrement exposées à ce risque. L’Auteur présente en conclusion une série de lignes directrices pour les incendies de végétation.