The authors have reviewed studies of human health effects that resulted from exposure to methyl isocyanate gas that leaked from the Union Carbide plant in Bhopal, India, in 1984. The studies were conducted during both the early and late recovery periods. Major organs exposed were the eyes, respiratory tract, and skin. Although mortality was initially high, it declined over time, but remained elevated among the most severely exposed population. Studies conducted during the early recovery period focused primarily on ocular and respiratory systems. Major findings included acute irritant effects on the eyes and respiratory tract. In follow-up studies, investigators observed persistent irritant effects, including ocular lesions and respiratory impairment. Studies conducted during the late recovery period focused on various systemic health endpoints. Significant neurological, reproductive, neurobehavioral, and psychological effects were also observed. Early and late recovery period studies suffered from several clinical and epidemiological limitations, including study design, bias, and exposure classification. The authors herein recommend long-term monitoring of the affected community and use of appropriate methods of investigation that include well-designed cohort studies, case-control studies for rare conditions, characterization of personal exposure, and accident analysis to determine the possible components of the gas cloud.

Our results suggest that persistent small airways obstruction among survivors of the 1984 disaster may be attributed to gas exposure.

Nine years after the Bhopal methyl isocyanate disaster, we examined the effects of exposures among a cross-section of current residents and a subset of those with persistent symptoms. We estimated individual exposures by developing exposure indices based on activity, exposure duration, and distance of residence from the plant. Most people left home after the gas leak by walking and running. About 60% used some form of protection (wet cloth on face, splashing water). Mean and median values of the exposure indices showed a declining trend with increasing distance from the plant. For those subjects reporting any versus no exposure, prevalence ratios were elevated for most respiratory and nonrespiratory symptoms. We examined exposure-response relationships using exposure indices to determine which were associated with health outcomes. The index total exposure weighted for distance was associated with most respiratory symptoms, one measure of pulmonary function in the cross-sectional sample [mid-expiratory flow (FEF)(25-75), p = 0.02], and two measures of pulmonary function in the hospitalized subset [forced expiratory volume (FEV)(1), p = 0.02; FEF(25-75), p = 0.08). Indices that correlated with FEV(1) and forced vital capacity in the hospitalized subset did not correlate with the cross-sectional sample, and most indices (except total exposure) that correlated with the hospitalized subset did not correlate with the cross-sectional sample. Incorporation of distance into every index increased the number of symptoms associated; an improvement was also noted in the strength of the association for respiratory symptoms, but not for pulmonary function. The sum of duration (p = 0.02) and total exposure (p = 0.03) indices independently demonstrated stronger associations with percent predicted FEF(25-75) than the distance variable (p = 0.04). The results show that total exposure weighted for distance has met the criteria for a successful index by being associated with most respiratory symptoms as well as FEF(25-75), features of obstructive airways disease.

No abstract

This study was undertaken to determine risk factors associated with hazardous substance releases (at fixed facilities or during transport) that have public health consequences. Data from nine states with surveillance systems for such releases and their consequences were analyzed. Risk factors were determined for releases resulting in (1) injuries or (2) evacuations. Both outcomes were more likely to occur as a result of facility releases (odds ratio [OR] = 1.89, 95% confidence interval [CI] = 1.44, 2.47, for injuries; OR = 3.29, 95% CI = 2.28, 4.74, for evacuations). Releases of ammonia, chlorine, and acids resulted in injuries and evacuations more frequently than releases of other substances.