Potential Indoor Air Exposures and Health Risks from Mercury Off-Gassing of Coal Combustion Products Used in Building Materials

Coal combustion products (CCPs), including coal fly ash (CFA) and flue gas desulfurization (FGD) gypsum, have gained accepted use as substitutes for traditional substances in building materials. Because of the presence of mercury (Hg) in CCP materials, some concerns have been raised regarding the potential for Hg to off-gas from building materials into indoor air. Risk assessment offers a well-accepted, objective framework in which to determine whether such off-gassing could result in humanexposures of health concern. We thus conducted a screening-level human health risk assessment to estimate worst-case inhalation risks from indoor air exposures to Hg for multiple CCP utilization scenarios: (1) FGD-gypsum wallboard used in a school classroom or home, and (2) CFA concrete blocks used in a school classroom. For CFA concrete, published experimental data for Hg emissions during dry curing of concrete were used to calculate a high-end emission rate, and based on extrapolation of these data, an emission rate considered to be more representative of long-term emissions. For wallboard, Hg emission rates were estimated using published data from flux chamber experiments measuring Hg volatilization from FGDgypsum wallboard samples. Together with the estimated emission rates and conservative values for other parameters (e.g., building characteristics, exposure conditions), a steady-state indoor air model was used to predict indoor air Hg concentrations. Even for parameters intended to overstate potential exposures, predicted indoor air Hg concentrations were typically below background indoor Hg levels. Additionally, estimated Hg air concentrations were well below established inhalation toxicity criteria (noncancer hazard quotients [HQs] ranged from 0.00004 to 0.016). Based on our findings, we conclude that potential indoor air Hg exposures associated with the use of CCPs in concrete and wallboard building materials in either classroom settings or residential homes are associated with negligible human health risks.