Environmental Exposure Assessment and Cancer Risk Among Residents Near Petroleum Refinery Operations in Kaduna State, North West Nigeria

Petroleum refineries emit a complex mixture of carcinogenic and toxic substances, and the cancer risk for communities in proximity to refinery operations in Nigeria has not been systematically quantified. This study conducted an environmental exposure assessment and cancer risk estimation for communities adjacent to the Kaduna Refinery and Petrochemical Company, North West Nigeria. Ambient air concentrations of benzene, polycyclic aromatic hydrocarbons, hydrogen sulfide, and nitrogen oxides were measured at twelve monitoring stations arranged in concentric rings at distances of 500 metres, one kilometre, and two kilometres from the refinery perimeter. Soil and groundwater samples were analyzed for petroleum hydrocarbons and trace metals. Exposure assessment was conducted using inhalation, ingestion, and dermal contact pathways. Cancer risk and hazard quotients were calculated using US EPA Risk Assessment Guidelines. Results indicated that benzene concentrations exceeded the WHO annual guideline of 1.7 micrograms per cubic metre at monitoring stations within one kilometre of the refinery in seventy-three percent of measurement periods. Incremental lifetime cancer risk from benzene inhalation exceeded the 10 to the power of negative five threshold for all residents within one kilometre. Non-cancer hazard quotients for hydrogen sulfide were above unity for sensitive subpopulations in the 500-metre zone. The study provides the first comprehensive multi-pathway cancer risk assessment for a Nigerian refinery community and offers a methodological template for future assessments. Recommendations include community buffer zone redesign, continuous air quality monitoring, and enhanced community health screening. Keywords: petroleum refinery, cancer risk assessment, benzene, Kaduna, environmental exposure.