Long-term follow-up after methyl chloride intoxication

Increased cardiovascular mortality and suicide after methyl chloride exposure

OBJECTIVES

Methyl chloride leakage from a refrigerator occurred on board an Icelandic fishing vessel in 1963. Many of the crew members were hospitalized due to various neurological symptoms and signs. The aim was to study long-term mortality.

METHODS

This is a cohort study. Five referents were selected from registries of deckhands and officers matched to each crew member according to age and occupation. Follow-up was through record linkage of personal identifiers with the nation-wide mortality registry. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated in Cox proportional hazards model.

RESULTS

The intoxicated crew was composed of 20 deckhands and 7 officers; the reference group counted 100 deckhands and 35 officers. Follow-up to the end of 2010; 14 of the exposed deckhands and 6 of the officers had died, versus 49 deckhands and 26 officers among the reference group. For all cardiovascular events, the HR was 2.06 (95% CI 1.02-4.15), for acute coronary heart disease, the HR was 3.12 (95% CI 1.11-8.78), for cerebrovascular diseases, the HR was 5.35 (1.18-24.35), and for suicide, the HR was 13.76 (1.18-160.07).

CONCLUSIONS

Follow-up showed increased mortality due to cardiovascular diseases after 47 years. The suicide cases had developed severe depression after the methyl chloride intoxication that was related to the exposure. The use of the personal identifiers and the population registries strengthen the study. Detailed information on risk factors for chronic diseases is lacking in this study; however, the matching by occupation renders some similarity to the groups compared in the study.

Potential health effects of occupational chlorinated solvent exposure

Based on toxicology, metabolism, animal studies, and human studies, occupational exposure to chlorinated aliphatic solvents (methanes, ethanes, and ethenes) has been associated with numerous adverse health effects, including central nervous system, reproductive, liver, and kidney toxicity, and carcinogenicity. However, many of these solvents remain in active, large-volume use. This article reviews the recent occupational epidemiology literature on the most widely used solvents, methylene chloride, chloroform, trichloroethylene, and tetrachloroethylene, and discusses other chlorinated aliphatics. The impact of studies to date has been lessened because of small study size, inability to control for confounding factors, particularly smoking and mixed occupational exposures, and the lack of evidence for a solid pathway from occupational exposure to biological evidence of exposure, to precursors of health effects, and to health effects. International differences in exposure limits may provide a "natural experiment" in the coming years if countries that have lowered exposure limits subsequently experience decreased adverse health effects among exposed workers. Such decreases could provide some evidence that higher levels of adverse health effects were associated with higher levels of solvent exposure. The definitive studies, which should be prospective biomarker studies incorporating body burden of solvents as well as markers of effect, remain to be done.