ENVIRONMENTAL RISK
The burden of disease can be reduced by reducing environmental risks to health, If we can estimate the burden of disease from environmental risks, we also can find the most important priorities for targeted environmental protection, while helping to promote the idea that sound environmental management plays a key role in protecting people’s health. Early estimates of the global disease burden attributable to the environment, derived partly on the basis of expert opinion, were in general agreement (WHO, 1997: 23%; Smith, Corvalàn and Kjellström, 1999: 25—33%). A third major study of OECD countries, however, yielded significantly different results, concluding that only 2.1%-5.0% of the overall disease burden was attributable to the environment (Melse and de Hollander, 2001). This lower estimate can be explained both by the methodology used and research scope (e.g. occupational risk factors were not considered), and the different impact environmental risks have on health in developed countries – as compared to developing ones. Even more recently, WHO developed a framework for a much more rigorous approach to burden of disease estimations. This project, known as the Comparative Risk Assessment (CRA), considered 6 environmental and occupational risk factors among a set of 26 environmental, occupational, social and behavioural risk factors having a major impact on population health (WHO, 2002). The total disease burden attributable to these risk factors was estimated across all 14 WHO subregions, 8 age groups, and by gender. The six environmental and occupational risk factors considered in the CRA were factors for which there was clear causal evidence that could be applied globally; for which global estimates of exposure could be obtained; and which had large impacts on people's health. However, this assessment remained limited in terms of the range of environmental risks assessed, and with respect to quantification of impacts in terms of specific health conditions. The present analysis goes a step further, providing timely new estimates of burden of disease from a much broader range of environmental risk factors, and in terms of the categories of diseases and health conditions affected. The analysis makes use of the results from the CRA, complemented by extensive literature reviews and standardized surveys of expert opinions, in an approach that aims to improve scientific rigour and transparency. Focusing on modifiable environmental risks, the current assessment examines "how much" such factors affect various diseases and injuries – both in terms of premature mortality and in terms of overall disease burden as measured by DALY's (disability adjusted life years), a weighted measure of death and disability. The definition of "modifiable" environmental risk factors include those reasonably amenable to management or change. Factors not readily modifiable were not considered here. The analysis considered most environmental risks and related diseases that could be quantified from available evidence. In some cases, however, disease burden from a known environmental risk was not quantifiable. This included certain diseases associated with changed, damaged or depleted ecosystems, and diseases associated with exposures to endocrine disrupting substances. The resulting analysis thus remains a conservative estimate of environmental disease burden.