Longitudinal Analysis of Occupational Carcinogen Exposure and Cancer Incidence Among Petroleum Workers in the Niger Delta Region

The carcinogenic risk posed by occupational exposure to petroleum-associated substances including benzene, polycyclic aromatic hydrocarbons, and hydrogen sulfide among workers in the Niger Delta has never been established through longitudinal epidemiological investigation in Nigeria. This dissertation presents a ten-year retrospective cohort analysis of cancer incidence among petroleum industry workers in Rivers, Delta, and Bayelsa states, South South Nigeria. A cohort of 4,800 workers was constructed from employment records of six oil and gas operating companies, with exposure classification based on job exposure matrices constructed from industrial hygiene records, historic personal monitoring data, and expert judgment. Cancer outcomes were ascertained through linkage with state cancer registries, company medical records, and national death registration data. Cumulative exposure metrics were calculated for benzene (ppm-years) and benzo[a]pyrene-equivalent PAH (mg/m3-years). Standardized incidence ratios and multivariate Cox proportional hazards regression were applied to estimate exposure-response relationships. Results demonstrated significantly elevated standardized incidence ratios for leukemia (SIR 2.7), non-Hodgkin lymphoma (SIR 1.9), and bladder cancer (SIR 2.1) compared to the general male Nigerian population. A significant dose-response relationship was established between cumulative benzene exposure and leukemia risk. Smoking status was a significant effect modifier for lung cancer risk. The dissertation makes an original contribution as the first longitudinal occupational carcinogen-cancer cohort study in the Nigerian petroleum sector. Recommendations include mandatory biological monitoring, exposure reduction interventions, and a national occupational cancer registry. Keywords: occupational carcinogens, petroleum workers, cancer incidence, Niger Delta, benzene.