Temporal dynamics of total petroleum hydrocarbon contamination in rainwater storage systems in Nigeria: seasonal patterns and mitigation strategies

This study assessed total petroleum hydrocarbons (TPH) in rainwater from Okitipupa, Nigeria between April and August 2023. TPH concentrations ranged from 0.00 to 3.78 µg/L, with peaks in April and May, a mid-season decline, and a slight rebound in August. This pattern reflects atmospheric washout of pollutants from gas flaring, vehicle emissions and generator use. Dominant compounds included dodecane, pentadecane and dotriacontane. Rainwater pH increased from 4.20 ± 0.15 to 6.60 ± 0.22 while electrical conductivity remained stable. TPH correlated positively with conductivity (r = 0.83) and negatively with pH (r = −0.34). Health risk assessment indicated low chronic daily intake. The maximum Hazard Quotient was 4.76 × 10⁻², well below the threshold of 1, suggesting minimal non-carcinogenic risk. Hexadecane and tetradecane contributed most to exposure. Cancer risk could not be quantified due to limited toxicity data for aliphatic TPH, but hydrocarbon presence warrants monitoring. Results support first-flush diversion, proper storage timing and basic treatment before domestic use of rainwater in hydrocarbon-impacted areas.