Uncertainty Analysis of Risk Estimation in Human Health Risk Assessment of Black Soot Pollution Exposure in Warri Metropolis, Nigeria

Abstract

This study analyses uncertainty associated with environmental health risk extraction from black soot pollution on the exposed population in Warri metropolis, using the USEPA (1989) environmental health risk assessment equation approach. The study was aimed at providing informed confidence in risk assessment for the exposed population to black soot pollution and to develop a "comfort level" with the approach. The aim was achieved through the adoption of point estimate, parametric variance propagation, and a ninety-five percent (95%) confidence interval-based context. In this context, three hundred and eighty-five (385) samples were collected for each input parameter. A risk extract was obtained using the point estimate approach. However, a nominal range sensitivity analysis of the model inputs identified exposure duration as the most influential risk driver, with a swing weight of 3.4×10−1, whereas human body mass had the least influence, with a swing weight of 3.7×10−6. Input parametric probability distribution functions (PDFs) for the propagation were developed using sample statistics and graphics, while the selections were based on certain probability density function models. To effectively utilize the law of parametric uncertainties propagation for the study, the complex multiplicative equation was transformed into an additive functional equation using a logarithmic transformation approach. Also, the log mean and variances of input parameters were obtained using logarithmic distribution algorithms, while the model’s uncertainty was propagated as the “root-sum-of-squares” of input log variances to be 2.7. Consequently, the estimated risk was bounded by a 95% confidence interval of 3.7 × 10⁻² to 3.3 × 10⁻¹, with the lower and upper confidence limits determined using the quotient and product of the geometric mean and the square of the geometric standard deviation, respectively. The estimated risk values indicate that although the non-carcinogenic risk remains below the regulatory threshold (HI < 1), prolonged exposure to black soot may still constitute a potential public health concern, particularly for vulnerable populations such as children, the elderly, and individuals with pre-existing respiratory conditions.