Estimating Health Risk from Exposure to Volatile Organic Compound Emission Profiles from Wastewater Treatment Technologies Used in South Africa

Abstract

Exposure to volatile organic compounds (VOCs), particularly benzene, toluene, ethylbenzene, and xylene (BTEX), poses significant health risks, even at concentrations below occupational exposure limits. Wastewater treatment plants (WWTPs) are recognized sources of VOC emissions due to the composition of influent wastewater and treatment processes. This study assesses the health risks associated with inhaling BTEX compounds at five (5) WWTPs employing chemical, physical, and biological treatment technologies. Atmospheric area monitoring and personal exposure assessments were conducted at selected sites using Radiello passive samplers. Personal exposure monitoring was performed on five (5) occupations following the methodology outlined in the occupational exposure sampling strategy manual, while ten (10) area monitoring points were established at various treatment stages, including four (4) parameter sampling poles. Sampling devices were deployed at selected locations for a duration of 30 days. VOC concentrations were analysed and compared against occupational exposure limits (OEL). Additionally, a human health risk assessment was conducted using U.S. EPA methodologies, with benzene-related cancer risks estimated and hazard quotients calculated for other BTEX compounds. Results indicate significant variability in BTEX emissions across different wastewater treatment technologies. Chemical treatment processes exhibited higher VOC concentrations during early treatment stages, whereas biological and physical treatment processes displayed fluctuating patterns influenced by site-specific factors. Factors such as plant size, operational capacity, and surrounding environmental conditions were found to substantially impact VOC emissions. Personal exposure results, calculated as 8-hour time-weighted averages, revealed that no BTEX compound exceeded OELs across all occupations in the five (5) selected WWTPs. However, the health risk assessment revealed that benzene exceeded the carcinogenic risk threshold of 1.0 × 10⁻⁶ at all five (5) sites, indicating potential cancer risks. Non-carcinogenic risks exceeded the health hazard index of 1 at Site A due to xylene and at Sites B and D due to benzene. The carcinogenic and non-carcinogenic risk assessment results emphasize the necessity for stringent monitoring and mitigation strategies. ii A comparative analysis of chemical, biological, and physical treatment processes provides critical insights for selecting effective control measures to reduce VOC exposure risks. These findings support the identification of wastewater treatment technologies associated with lower health risks, reinforcing the need for regulatory frameworks to address long-term exposure to low-level VOC emissions.