Risk assessment before and after solar photocatalytic degradation of BTEX contaminated groundwater at a gas station site in Korea

Health risk assessment of toxic VOCs species for the coal fire well drillers

In this study, the health risk of toxic volatile organic compounds (VOCs) species for well drillers, working at an exposure site around a well of underground coal fire site, was presented in a case of Shanxi province. The samples were collected by Teflon sampling bags and measured by gas chromatography-mass spectrometry (GC-MS). The results showed that isopropyl alcohol was the most abundant compound of VOCs, with the geometric mean concentrations of 1700.38 μg/m(3). The geometric mean concentrations of individual BTEX compounds obtained in all of the sampling campaign were 131.64, 10.15, 15.53, and 25.38 μg/m(3) for benzene, toluene, ethyl-benzene, and xylenes, respectively. Relative proportion of BTEX averaged as 8.5:0.7:1:1.6. High B/T ratio (13.0) and low T/E ratio (0.7) was observed in this study. For non-cancer risk in this study, the hazardous quotient (HQ) of 1,2-dibromoethane, 1,3-butadiene, and benzene was 17.91, 1.71, and 43.88, respectively, mean their non-cancer risk was at the level of definite concern. The HQ sum of 20 VOCs was 64.94, much higher than 1. The cancer risk values of benzene (7.01E-04), 1,2-dibromoethane (1.91E-04), carbon tetrachloride (1.55E-04), and 1,3-butadiene (1.09E-04) were greater than 10(-4), indicating that they were all definite risk. The total cancer risk of all VOCs species was 1.39E-03, almost 14 times more than the level of definite risk. The stochastic exposure assessment of all VOCs species total cancer risk using the Monte Carlo simulation analysis shows that 5 and 95 % cancer risks were predicted to be 7.60E-04 and 2.75E-03, respectively. The cancer risk for all VOCs species is unacceptable. The results of sensitivity analysis show that benzene, carbon tetrachloride, and 1,3-butadiene exposure account for more than 98 % contributions to the estimated risk for drillers, indicating that those VOCs species exposure has greater impact than other species on risk assessment. Both combined effects and independent effects of each VOCs species have to be considered.

Underestimated public health risks caused by overestimated VOC removal in wastewater treatment processes

The uncontrolled release of volatile organic compounds (VOCs) from wastewater treatment plants (WWTPs) and the adverse health effects on the public have been of increasing concern. In this study, a lab-scale bioreactor was prepared to analyze the mass distribution of three aromatic (benzene, toluene, and xylenes) and four chlorinated VOCs (chloroform, carbon tetrachloride, trichloroethylene, and tetrachloroethylene) among the air, water and sludge phases in wastewater treatment processes. The VOC distribution through a full-scale WWTP in northern China was further investigated with respect to the effects of seasonal temperature variations and treatment technologies, followed by the cancer risk assessment using a steady-state Gaussian plume model (Industrial Source Complex) to simulate the atmospheric behaviors of the VOCs emitted from the WWTP. It was found that three aromatic hydrocarbons, notably benzene, were more readily released from the wastewater into the atmosphere, whereas the chlorinated compounds except chloroform were mainly present in the water phase through the treatment processes. The primary clarifier was the technology releasing high levels of VOCs into the atmosphere from the wastewater. The extents of volatilization or biodegradation, two important mechanisms to remove VOCs from wastewater, appeared to be determined by the physicochemical characteristics of the compounds, as the influence of treatment technologies (e.g., aeration) and seasonal temperature variations was rather limited. More importantly, the people living in the areas even more than 4 km away from the WWTP were still potentially exposed to cancer risks exceeding the regulatory threshold limit. The findings described the complex nature of VOC emissions from WWTPs and quantitatively indicated that the associated health impacts on the public near the WWTPs could be severely underestimated, whereas their treatment efficiencies by wastewater treatment technologies were overestimated. Instead of fully controlling the VOC release from WWTPs, the identification and abatement of important VOC species with regard to the atmospheric emission and health concerns is one possible alternative approach to effectively minimize the environmental and public health impacts by VOCs released from this particular source.