Mercury Inhalation Risks in Indoor Air from Use of Coal Combustion Products(CCPs)in Building Materials

摘要

Coal combustion products(CCPs),including coal fly ash(CFA)and flue gasdesulfurization(FGD)products,are increasingly being used as substitutes for traditionalsubstances in building materials.For example,approximately 30%of US wallboard isnow manufactured from FGD gypsum,while CFA has gained widespread use as apartial replacement for Portland cement in concrete.Given concerns that have beenraised regarding the presence of mercury(Hg)in CCPs,and the potential for Hgreleases from CCP materials into indoor air,we conducted a risk assessment toestimate inhalation risks from indoor air exposures to Hg for two CCP utilizationscenarios:(1)CFA concrete blocks used in a school classroom,and(2)FGD gypsumwallboard used in a school classroom or home.For CFA concrete,we relied on datafrom recent laboratory studies of Hg emissions during dry curing of concrete at near-ambient temperatures to calculate two Hg release rates to indoor air,one based on themaximum 28-day curing rate from these studies to represent a high-end estimate ofpotential emissions and one based on extrapolated longer-term curing emissions torepresent an upper-bound estimate of more typical,long-term emissions.Forwallboard,we calculated a Hg release rate based on laboratory flux chambermeasurements for gypsum wallboard samples.We estimated indoor air Hgconcentrations using these Hg release rates and conservative values for otherparameters(e.g.,air exchange rates,material loading ratios)in a steady-state indoor airmodel.Even using parameters intended to overstate potential exposures,we predictedindoor air Hg concentrations that are generally consistent with or below ambientbackground Hg levels.Moreover,predicted indoor Hg concentrations were well belowestablished inhalation toxicity criteria(hazard indices ranged from 0.00003 to 0.015).Thus,based on our findings,we conclude that CCPs in concrete and wallboard buildingmaterials are unlikely to result in Hg exposures in either classroom settings or inresidential homes that pose a health concern.Key results are displayed graphicallybelow.