Chromium-6

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Summary

The Environmental Working Group (EWG) reported in December 2010 that hexavalent chromium (chromium-6 or Cr-6) was detected in the drinking water in a number of U.S. cities. Cr-6 was also the exposure of concern in the Erin Brockovich controversy.

The scare about Cr-6 in drinking water is dubious as:

  • There is no credible evidence that ingestion of Cr-6 causes cancer or increases cancer risk in humans.
  • The levels of Cr-6 detected in drinking water were well below already extra-safe regulatory standards set by the U.S. Environmental Protection Agency.

The EWG is well-known for efforts to scare the public through reports of the mere detection of substances in drinking water. This practice, however, ignores the well-established principle of toxicology that "the dose makes the poison."

News Timeline

Studies and Reports

  • Kerger B et al, Cancer mortality in chinese populations surrounding an alloy plant with chromium smelting operations, J Toxicol Environ Health A. 72(5):329-44, 2009.
    • Abstract. " This report is a further characterization of data from an ecological cancer mortality study of a population (about 10,000) exposed to groundwater contaminated by hexavalent chromium [Cr(VI)] up to 20 mg/L near JinZhou City in the LiaoNing Province of China between 1960 and 1978. Prior reports showed an elevation in all-cancer mortality from 1970 to 1978 averaged across five agricultural villages with Cr(VI) in groundwater relative to average cancer rates for the district and province. The current study compares the cancer rates during the same time period for the same five exposed villages to those of four nearby areas with no Cr(VI) in groundwater. The use of a local comparison group is considered superior to the use of district or province averages because of the expected improved similarity among unmeasured covariates in nearby areas. The average lung-, stomach-, and all-cancer mortality rates for the three agricultural villages without Cr(VI) in groundwater were not statistically different from those of the five agricultural villages with Cr(VI) in groundwater. Also, three surrogate measures of village drinking-water Cr(VI) dose did not significantly correlate with cancer mortality rates in the five exposed villages. Further, the industrial town in which the Cr(VI) source was located had different demographics and a different pattern of stomach and lung cancers compared to the adjacent agricultural villages, regardless of Cr(VI) groundwater exposure. The results of other local investigations on cancer mortality and genotoxicity in the exposed populations are reviewed. The overall findings in the studied population do not indicate a dose-response relationship or a coherent pattern of association of lung-, stomach-, or all-cancer mortality with exposure to Cr(VI)-contaminated groundwater."
  • Cole P and Rodu B., Epidemiologic studies of chrome and cancer mortality: a series of meta-analyses, Regul Toxicol Pharmacol. 2005 Dec;43(3):225-31. Epub 2005 Aug 15.
    • Abstract. "We used 49 epidemiologic studies based on 84 papers published since 1950 to develop an array of meta-analyses relating exposure to chrome-six compounds with 10 causes of death. Most exposures occurred in occupational settings. Studies were assessed for quality, and for control of smoking or economic status if they related to lung or stomach cancer. There was no excess mortality from all causes combined among chrome-exposed persons. A minimal excess of cancer (SMR=112), overall, was due primarily to an excess of lung cancer (SMR=141) but the SMR was 112 among the better-quality, smoking-controlled studies. The overall SMR for stomach cancer was 113 but it was 82 among the studies that were controlled for economic status. Findings were unremarkable for the six other cancers evaluated: prostate, kidney, and central nervous system cancer and leukemia, Hodgkin's disease and other lymphatohematopoietic cancer. This series of meta-analyses indicates that chrome-six is a weak cause of lung cancer and is not a cause of any of the other seven forms of cancer evaluated."
  • Crump C et al., Dose-response and risk assessment of airborne hexavalent chromium and lung cancer mortality, Risk Anal. 23(6):1147-63, December 2003.
    • Abstract. "This study evaluates the dose-response relationship for inhalation exposure to hexavalent chromium [Cr(VI)] and lung cancer mortality for workers of a chromate production facility, and provides estimates of the carcinogenic potency. The data were analyzed using relative risk and additive risk dose-response models implemented with both Poisson and Cox regression. Potential confounding by birth cohort and smoking prevalence were also assessed. Lifetime cumulative exposure and highest monthly exposure were the dose metrics evaluated. The estimated lifetime additional risk of lung cancer mortality associated with 45 years of occupational exposure to 1 microg/m3 Cr(VI) (occupational exposure unit risk) was 0.00205 (90%CI: 0.00134, 0.00291) for the relative risk model and 0.00216 (90%CI: 0.00143, 0.00302) for the additive risk model assuming a linear dose response for cumulative exposure with a five-year lag. Extrapolating these findings to a continuous (e.g., environmental) exposure scenario yielded an environmental unit risk of 0.00978 (90%CI: 0.00640, 0.0138) for the relative risk model [e.g., a cancer slope factor of 34 (mg/kg-day)-1] and 0.0125 (90%CI: 0.00833, 0.0175) for the additive risk model. The relative risk model is preferred because it is more consistent with the expected trend for lung cancer risk with age. Based on statistical tests for exposure-related trend, there was no statistically significant increased lung cancer risk below lifetime cumulative occupational exposures of 1.0 mg-yr/m3, and no excess risk for workers whose highest average monthly exposure did not exceed the current Permissible Exposure Limit (52 microg/m3). It is acknowledged that this study had limited power to detect increases at these low exposure levels. These cancer potency estimates are comparable to those developed by U.S. regulatory agencies and should be useful for assessing the potential cancer hazard associated with inhaled Cr(VI)."
  • Paustenbach D et al., Human health risk and exposure assessment of chromium (VI) in tap water, J Toxicol Environ Health A. 25;66(14):1295-339, July 2003.
    • Abstract. "Hexavalent chromium [Cr(VI)] has been detected in groundwater across the United States due to industrial and military operations, including plating, painting, cooling-tower water, and chromate production. Because inhalation of Cr(VI) can cause lung cancer in some persons exposed to a sufficient airborne concentration, questions have been raised about the possible hazards associated with exposure to Cr(VI) in tap water via ingestion, inhalation, and dermal contact. Although ingested Cr(VI) is generally known to be converted to Cr(III) in the stomach following ingestion, prior to the mid-1980s a quantitative analysis of the reduction capacity of the human stomach had not been conducted. Thus, risk assessments of the human health hazard posed by contaminated drinking water contained some degree of uncertainty. This article presents the results of nine studies, including seven dose reconstruction or simulation studies involving human volunteers, that quantitatively characterize the absorbed dose of Cr(VI) following contact with tap water via all routes of exposure. The methodology used here illustrates an approach that permits one to understand, within a very narrow range, the possible intake of Cr(VI) and the associated health risks for situations where little is known about historical concentrations of Cr(VI). Using red blood cell uptake and sequestration of chromium as an in vivo metric of Cr(VI) absorption, the primary conclusions of these studies were that: (1) oral exposure to concentrations of Cr(VI) in water up to 10 mg/L (ppm) does not overwhelm the reductive capacity of the stomach and blood, (2) the inhaled dose of Cr(VI) associated with showering at concentrations up to 10 mg/L is so small as to pose a de minimis cancer hazard, and (3) dermal exposures to Cr(VI) in water at concentrations as high as 22 mg/L do not overwhelm the reductive capacity of the skin or blood. Because Cr(VI) in water appears yellow at approximately 1-2 mg/L, the studies represent conditions beyond the worst-case scenario for voluntary human exposure. Based on a physiologically based pharmacokinetic model for chromium derived from published studies, coupled with the dose reconstruction studies presented in this article, the available information clearly indicates that (1) Cr(VI) ingested in tap water at concentrations below 2 mg/L is rapidly reduced to Cr(III), and (2) even trace amounts of Cr(VI) are not systemically circulated. This assessment indicates that exposure to Cr(VI) in tap water via all plausible routes of exposure, at concentrations well in excess of the current U.S. Environmental Protection Agency (EPA) maximum contaminant level of 100 microg/L (ppb), and perhaps those as high as several parts per million, should not pose an acute or chronic health hazard to humans. These conclusions are consistent with those recently reached by a panel of experts convened by the State of California."
  • Modl A and Paustenbach D, Airborne concentrations of benzene due to diesel locomotive exhaust in a roundhouse, J Toxicol Environ Health A. 13;65(23):1945-64, December 2002.
    • Abstract. "Concentrations of airborne benzene due to diesel exhaust from a locomotive were measured during a worst-case exposure scenario in a roundhouse. To understand the upper bound human health risk due to benzene, an electromotive diesel and a General Electric four-cycle turbo locomotive were allowed to run for four 30-min intervals during an 8-h workshift in a roundhouse. Full-shift and 1-h airborne concentrations of benzene were measured in the breathing zone of surrogate locomotive repairmen over the 8-h workshift on 2 consecutive days. In addition, carbon monoxide was measured continuously; elemental carbon (surrogate for diesel exhaust) was sampled with full-shift area samples; and nitrogen dioxide/nitric oxide was sampled using full-shift and 15-min (nitrogen dioxide only) area samples. Peak concentrations of carbon monoxide ranged from 22.5 to 93 ppm. The average concentration of elemental carbon for each day of the roundhouse study was 0.0543 and 0.0552 microg/m(3 )for an 8-h workshift. These were considered "worst-case" conditions since the work environment was intolerably irritating to the eyes, nose, and throat. Short-term nitrogen dioxide concentrations ranged from 0.81 to 2.63 ppm during the diesel emission events with the doors closed. One-hour airborne benzene concentrations ranged from 0.001 to 0.015 ppm with 45% of the measurements below the detection limit of 0.002-0.004 ppm. Results indicated that the 8-h time-weighted average for benzene in the roundhouse was approximately 100-fold less than the current threshold limit value (TLV) of 0.5 ppm. These data are consistent with other studies, which have indicated that benzene concentrations due to diesel emissions, even in a confined environment, are quite low."
  • Fryzek J et al., Cancer mortality in relation to environmental chromium exposure, J Occup Environ Med. 43(7):635-40, July 2001.
    • Abstract. "From the 1950s to the 1980s, hexavalent chromium compounds were used as additives at certain water-cooling towers at three southern California gas compressor facilities. Claims of potential residential chromium exposure prompted the examination of age-adjusted mortality rates during 1989 to 1998 for lung cancer, all cancer, and all deaths for neighborhoods near versus distant from the plants. Differences in the rates between areas tended to be small and not statistically significant. The only significant difference was a lower, rather than higher, rate of total cancer among women in the potentially exposed areas. Study limitations preclude a definitive assessment of risk, but similar to previous investigations of cancer in relation to environmental chromium exposure in other locations, this study found no evidence of a cancer hazard among residents living near these California gas compressor facilities."
  • Blot W et al., A cohort mortality study among gas generator utility workers, J Occup Environ Med. 42(2):194-9, February 2000.
    • Abstract. "An earlier cohort study tracked the mortality experience through 1988 of male employees at five utility companies in the United States. Workers employed by the Pacific Gas and Electric Company (PG&E) were part of that study, but results for PG&E employees overall or for those involved in gas generator plant operations where hexavalent chromium compounds were used in open and closed systems from the 1950s to early 1980s were not reported. To evaluate risk of lung cancer and other diseases, a cohort of 51,899 PG&E male workers was followed for mortality from 1971 through 1997. Observed numbers of deaths were compared with those expected based on rates in the general California population, with standardized mortality ratios (SMR) and corresponding 95% confidence intervals (CI) calculated for the total cohort and for subsets defined by potential for gas generator plant exposure. A total of 10,591 deaths were observed, a number significantly less than expected (SMR, 0.89; 95% CI, 0.87 to 0.91). No significant excesses of total or specific cancers were observed, with SMR typically near or below 1.0. Lung cancer mortality in the entire cohort was close to expected (SMR, 0.98; 95% CI, 0.92 to 1.05), with no excess detected among persons who worked (SMR, 0.81; 95% CI, 0.35 to 1.60) or trained (SMR, 0.57; 95% CI, 0.12 to 1.67) at gas generator facilities. Furthermore, risk of lung cancer did not increase with increasing duration of employment or time since hire. The study thus provides no evidence that occupational exposures at PG&E facilities resulted in increased risk of lung cancer or any other cause of death. The results indicate that any chromium exposures were of insufficient magnitude to result in increased risk of lung cancer."
  • Fowler J et al., An environmental hazard assessment of low-level dermal exposure to hexavalent chromium in solution among chromium-sensitized volunteers, J Occup Environ Med. 41(3):150-60, March 1999.
    • Abstract. "To evaluate the potential for elicitation of allergic contact dermatitis from contact with standing water in the environment, 26 persons known to be allergic to hexavalent chromium [Cr(VI)] were exposed to 25 to 29 mg/L Cr(VI) by immersion of one arm for 30 minutes per day on 3 consecutive days in a potassium dichromate bath. Sixteen of the 26 volunteers demonstrated either no or an equivocal response to the Cr(VI) challenge. Ten of the volunteers developed a few papules or vesicles (1 to approximately 15), mild redness, and pruritus on the Cr(VI)-challenged arm. Histopathological examination of the papules revealed spongiosis and perieccrine and perivascular inflammation. The responses were diagnosed as acute perieccrine reactions. It was concluded that exposure to similar concentrations of Cr(VI) in the environment does not pose an allergic contact dermatitis hazard, even to Cr-sensitized persons."
  • Finley B et al., Assessment of airborne hexavalent chromium in the home following use of contaminated tapwater, J Expo Anal Environ Epidemiol. 6(2):229-45, April-June 1996.
    • Abstract. "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."
  • Paustenbach D et al., An assessment and quantitative uncertainty analysis of the health risks to workers exposed to chromium contaminated soils, Toxicol Ind Health. 7(3):159-96, May 1991.
    • Abstract. "Millions of tons of chromite-ore processing residue have been used as fill in various locations in Northern New Jersey and elsewhere in the United States. The primary toxicants in the residue are trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. The hazard posed by Cr(III) is negligible due to its low acute and chronic toxicity. In contrast, Cr(VI) is considered a inhalation human carcinogen at high concentrations. Approximately 40 commercial and industrial properties in Northern New Jersey have been identified as containing chromite ore processing residue in the soil. One site, a partially-paved trucking terminal, was evaluated in this assessment. The arithmetic mean and geometric mean concentrations of total chromium in soil were 977 and 359 mg/kg, respectively. The data were log-normal distributed. The arithmetic mean and geometric mean concentrations of Cr(VI) in surface soil were 37.6 and 3.1 mg/kg, respectively. The data could not be fit to a standard distribution, likely due to the large number of samples with concentrations below the method detection limit (65%). Dose was calculated for each exposure route using a Monte Carlo statistical simulation. Probability distributions of most exposure parameters were incorporated into the analyses to predict the range and probability of uptake for persons in the exposed population. The exposure parameter distributions included in this assessment are: the concentrations of Cr(VI) and total chromium in air and soil, fraction of the year when suspension of airborne soil particulates is likely to occur due to weather conditions, fraction of Cr(VI) in air which is respirable (less than 10 microns), soil loading rate on skin, occupational tenure, and body weight. The techniques used in this assessment are applicable for evaluating the human health risks posed by most industrial sites having contaminated soil. The estimated average daily dose (ADD) via ingestion and dermal absorption for the individual exposed at the 95th percentile was about 48,000- and 91-fold below the U.S. EPA reference dose (RfD) for Cr(III) and Cr(VI), respectively. Since inhalation of Cr(VI) contaminated dust (but not ingestion or dermal contact) poses a cancer hazard, the lifetime average daily doses (LADDs) associated with exposure at the 50th and 95th percentile were calculated to be 9.8 x 10(-8) and 1.3 x 10(-6), respectively. Based on this analysis, industrial sites having soil concentrations of Cr(VI) below 230 ppm do not pose a significant noncarcinogenic or carcinogenic health hazard following acute or chronic exposure. These risks would be even smaller if the sites were paved."
  • Paustenbach D et al., The health hazards posed by chromium-contaminated soils in residential and industrial areas: conclusions of an expert panel, Regul Toxicol Pharmacol. 13(2):195-222, April 1991.
    • Abstract. "Between 1905 and 1971, over 2 million tons of residue from chromite ore processing was generated in Hudson County, New Jersey, of which substantial amounts were used as fill and tank diking. A panel of medical, toxicology, and risk assessment experts was convened in early 1990 to evaluate the potential health hazards posed by the resulting chromium contaminated soil. The Panel concluded that soils containing concentrations of 75 ppm hexavalent chromium [Cr(VI)] and 1000 ppm total chromium compounds (about 95% was trivalent chromium [Cr(III)]) did not pose a significant health hazard to nearby residents and workers. They also determined that exposure to chromium from Hudson County sites posed a negligible cancer hazard to residents. Using risk assessment methods, the Panel estimated that the plausible incremental cancer risk to individuals at residential sites would be substantially less than 1 in 1,000,000. The average measured levels of airborne Cr(VI) at typical industrial sites were more than 1000-fold lower than the current OSHA Permissible Exposure Limit (PEL). The maximum plausible increased cancer risk for an average worker at a dusty industrial site was estimated to be less than 1 in 100,000. The Panel also concluded that chromium-containing crystals, which have occasionally been found in Hudson County buildings, do not pose a significant hazard. However, they suggested that were the concentration to exceed 5000 ppm Cr(VI) in the crystals, site-specific health risk assessments would be conducted and remediation considered. The Panel evaluated the dermal hazard posed by chromium-contaminated soil and acknowledged that there is a small group of persons (approximately 0.1% of the United States population) who currently have a dermal sensitization to Cr(VI) primarily through occupational exposure. Based on published studies of human volunteers, the Panel concluded that a small percentage (less than 5%) of persons already sensitized may respond to Cr(VI) in solution at concentrations above 35 ppm. They decided that a much higher concentration in soil, perhaps 350 ppm Cr(VI), would be necessary to elicit dermatitis because only a fraction of the chromium in soil is soluble. The Panel concluded that it was highly unlikely (if not impossible) for a person to become dermally sensitized to Cr(VI) or Cr(III) at the soil concentrations found in most areas in Hudson County..."
  • Sheehan P et al., Assessment of the human health risks posed by exposure to chromium-contaminated soils, J Toxicol Environ Health. 32(2):161-201, February 1991.
    • Abstract. "Millions of tons of chromite-ore processing residue have been used as fill in various locations in northern New Jersey and elsewhere in the United States. The primary toxicants in the residue are trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. The hazard posed by Cr(III) is negligible due to its low acute and chronic toxicity. In contrast, Cr(VI) is a human carcinogen following inhalation of high concentrations. It can also cause allergic contact dermatitis. This evaluation addresses a residential site where the arithmetic mean (x) and geometric mean (gm) concentrations of Cr(III) in soil were 2879 and 1212 mg/kg (ppm). The mean and geometric mean concentrations of Cr(VI) were 180 and 4 mg/kg, respectively. The uptake (absorbed dose) of Cr(III) via soil ingestion, consumption of homegrown vegetables, and ingestion of inspired particles was determined. The uptake of Cr(VI) via dermal absorption from contact with surface soil and building wall surfaces, as well as inhalation, was also evaluated. The techniques used in this assessment are applicable for evaluating the human health risks posed by any residential site having contaminated soil. The potential for both sensitized and unsensitized persons to develop allergic contact dermatitis due to exposure to soil contaminated at these levels was found to be negligible. The estimated average daily dose (ADD) via ingestion and dermal absorption for the maximally exposed individual (MEI) was about 1500- and 40-fold below the EPA reference dose (RfD) for Cr(III) and Cr(VI), respectively. It was shown that for residential sites, the most important route of exposure to Cr(III) was incidental soil ingestion. Although not relevant to these sites specifically, if garden vegetables could be successfully grown in these soils, then they would probably be the predominant source of uptake of Cr(III). Since inhalation of Cr(VI)-contaminated dust (but not ingestion or dermal contact) poses a cancer hazard, the doses and associated risks were assessed. The estimated cancer risks for the MEI and most likely exposed individual (MLEI) were approximately 5 x 10(-9) and 2 x 10(-9), respectively. These levels of risk have always been considered well below those that warrant regulatory concern. For persons living on residential properties, the cancer risk due to inhaling suspended particles is likely to be less than 1 in 1,000,000 if Cr(VI) levels in soil are less than 180 mg/kg (ppm). Based on this analysis, the levels of Cr(III) and Cr(VI) at this and similar sites do not pose a health hazard following acute or chronic exposure."

Analysis & Commentary

Regulatory Documents

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