Mortality risk associated to arsenic exposure after a major disaster. Results from the Manfredonia occupational cohort study 1976-2021.

Background: On September 1976, due to the explosion of an ammonia-washing column at the petrochemical plant in Manfredonia (Italy), 39 tonnes of arsenic were released into the atmosphere, contaminating the plants and the neighbourhoods close to it. The aim of this study is to present the results of a 45-year follow up of exposed workers with a focus on residential exposure.

Methods: We contacted Italian General Registries Offices and updated the vital status of persons involved in the clean-up activities following the disaster. The outcome of interest was the overall and cause-specific mortality. An accelerated failure time (AFT) approach was used when appropriate to model the risk of mortality.

Results: 1772 workers contributing 67,743 person years were considered in the analysis. For overall mortality, results of the age-adjusted AFT model show an accelerator factor of 0.89 (95%CI 0.80-0.99) among contract workers, which means a shortening of survival in comparison to the reference category (plastic area workers). When accounting for latency greater than 20 years, higher mortality rates for lung cancer were observed among workers residing in Manfredonia.

Discussion: An increased risk of mortality among workers who were more exposed to arsenic during the clean-up activities has been observed. In fact, a loss of 5 years of life among more exposed workers was calculated. Furthermore, the mortality rates of residents in Manfredonia were higher than those of workers residing elsewhere.