Refined exposure assessment for ingestion of tapwater contaminated with hexavalent chromium: consideration of exogenous and endogenous reducing agents.

Laboratory studies were conducted to determine how rapidly and completely chromium (VI) [Cr(VI)] is reduced upon contact with common beverages mixed with tapwater. Studies were performed for five common beverages (coffee, tea, orange juice, Kool Aid, and powdered lemonade) spiked with either 10 or 50 mg Cr(VI)/l. The concentrations of Cr(VI) were measured at several time intervals for up to four hours. It was demonstrated that each of these beverages had the capacity to reduce a concentration of > or = 8 mg Cr(VI)/l within a 15-minute time frame, and that continued monitoring of the beverages revealed greater reduction of the Cr(VI). These findings are consistent with the observation that many foods and beverages, as well as endogenous body fluids such as saliva and gastric juices, are capable of reducing substantial quantities of Cr(VI) to Cr(III). Our exposure assessment shows that the estimated high-end ingested dose of Cr(VI) from tapwater at both 1 and 5 mg Cr(VI)/l is generally two to three orders of magnitude below doses shown to have no adverse health effect in animal studies. When considered in conjunction with studies demonstrating that the reductive capacity of gastric juices may exceed 50 mg Cr(VI) daily, these observations suggest that little or no Cr(VI) is likely to be absorbed orally at a reasonable water concentration of Cr(VI), since tapwater is bright yellow at 5 mg Cr(VI)/l.

Assessment of airborne hexavalent chromium in the home following use of contaminated tapwater.

Field studies were conducted to estimate the plausible uptake of hexavalent chromium [Cr(VI)] aerosols inhaled during indoor residential use of a shower or an evaporative cooler supplied with water containing Cr(VI). In the evaporative cooler study, water concentrations of 20 mg Cr(VI)/L did not produce an increased concentration of airborne Cr(VI). The indoor air concentration of Cr(VI), measured over 24 hours of use, was 0.3-2.7 ng/m3, about the same as the concurrent outdoor concentrations. In the shower study, the average airborne concentrations of Cr(VI) aerosols at breathing-zone height ranged from 87 to 324 ng Cr(VI)/m3 when the water concentration of Cr(VI) was 0.89 to 11.5 mg/L. The Cr(VI) concentration in air was correlated directly to water concentration. The lifetime average daily doses and incremental cancer risk estimates corresponding to 30-year residential exposures were calculated using the measurements in this study and published exposure guidelines. The plausible upperbound lifetime cancer risk associated with continuous exposure to "background" Cr(VI) in outdoor air was estimated at 6.9 per million for a person exposed during ages 0-30, and 4.0 per million for ages 30-60. Similarly estimated upperbound cancer risks due to inhalation of shower aerosols from water containing 2-10 mg Cr(VI)/L over the same exposure period ranged from 0.9 to 5.5 per million. Our calculations demonstrate that shower aerosols do not contribute appreciably to background Cr(VI) exposures and risks, even at concentrations exceeding 2 mg Cr(VI)/L, which exhibit a discernible and unaesthetic yellow color that may limit the potential for long-term exposures of this type. We conclude that exposure to indoor aerosols from water containing Cr(VI) is unlikely to create a health hazard at concentrations up to 10 mg Cr(VI)/L. Furthermore, these aerosol measurements may be relevant to estimating airborne exposures to other nonvolatile chemicals.