Physiological Impacts of Chronic Exposure to Hydrogen Sulphide on Respiratory and Cardiovascular Function Among Workers in Wastewater Treatment Plants in Lagos, South West Nigeria

Background: Hydrogen sulphide generated during organic matter decomposition in wastewater treatment represents a significant occupational inhalation hazard. Chronic low-level exposure affects respiratory mucosal integrity and may impair cardiovascular autonomic regulation. Lagos hosts several major wastewater treatment facilities whose workers lack systematic physiological health surveillance. Objectives: This study aims to compare spirometric lung function, exhaled nitric oxide as a marker of airway inflammation, and heart rate variability indices between wastewater treatment plant workers and an unexposed control group of municipal park maintenance workers in Lagos. Methods: Sixty treatment plant workers and forty controls will be recruited. Spirometry will be performed using the EasyOne Plus device. Exhaled nitric oxide will be measured by electrochemical analysis. Short-term heart rate variability will be recorded over five minutes using a validated wearable device. Ambient hydrogen sulphide concentrations will be estimated by personal dosimetry. Independent t-tests and regression analysis will model exposure-response relationships. Expected Outcomes: Treatment plant workers are anticipated to demonstrate elevated exhaled nitric oxide, reduced spirometric values, and lower parasympathetic heart rate variability indices compared to controls, with ambient hydrogen sulphide concentration predicting physiological impairment severity. Conclusion: Findings will support occupational health surveillance implementation for wastewater treatment workers in Lagos State. Keywords: hydrogen sulphide, respiratory function, heart rate variability, wastewater workers, Lagos.