Long-Term Follow-Up after Methyl Chloride Intoxication

Abstract

In this study, the authors investigated mortality and cancer patterns among a group of individuals accidentally exposed to methyl chloride 32 y earlier. This group of 24 persons had survived the immediate intoxication, which had occurred on a trawler during a fishing trip. The authors selected a reference group, which contained five times as many individuals as the study group, from registers of crews, and they controlled for age, occupation, social class, and lifestyle factors. The authors established a record linkage through personal identification numbers with the national death register and cancer register, thus securing 100% follow-up. The Mantel-Haenszel point estimate (M-H) was 2.2, and the 95% confidence interval (CI) was 1.3–3.1 for all causes of death. There was an excess of deaths from cardiovascular diseases (M-H = 2.1, 95% CI = 1.2–3.8). This excess mortality was more prominent among deckhands who had been subject to higher exposure; risk ratios (RRs) were elevated for all causes of death (RR = 2.5, 95% CI = 1.0–5.7), as well as for cardiovascular diseases (RR = 3.9, 95% CI = 1.0–14.4). In addition, the authors noted elevated risks for all cancers (M-H = 1.5, 95% CI = 0.3–5.6) and for lung cancer (M-H = 2.7, 95% CI = 0.1–52.6). The authors concluded that exposure to methyl chloride may have contributed to the risk of cardiovascular disease. Investigators need to conduct further studies on groups exposed to methyl chloride to refute or confirm this result.