Assessment of the human health risks posed by exposure to chromium-contaminated soils

Speciation of chromium in water samples using microfluidic paper-based analytical devices with online oxidation of trivalent chromium

Speciation of chromium (Cr) was demonstrated using microfluidic paper-based analytical devices (μ-PADs) that permit the colorimetric determination of hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) via online oxidation. The μ-PADs consist of left and right channels that allow the simultaneous measurements of Cr(VI) and total Cr based on the colorimetric reaction of Cr(VI) with 1,5-diphenylcarbazide (DPC). For the determination of Cr(VI), a sample solution was directly reacted with DPC in the left channels whereas total Cr was determined in the right channels, which permitted online oxidation in the pretreatment zone containing cerium (IV) (Ce(IV)) followed by a colorimetric reaction with DPC. We found that the online oxidation of Cr(III) proceeded 100% whereas Ce(IV) inhibited the reaction of Cr(VI) with DPC. Therefore, speciation can be achieved by measuring the Cr(VI) and total Cr in the left and right channels followed by the subtraction of Cr(VI) from total Cr. The limits of detection and quantification were 0.008 and 0.02 mg L^-1 for Cr(VI) and 0.07 and 0.1 mg L^-1 for Cr(III) or total Cr, respectively. The linear dynamic ranges were 0.02-100 mg L^-1 and 0.1-60 mg L^-1 for Cr(VI) and Cr(III), respectively. The RSDs were less than 7.5%. The results obtained using μ-PADs were in good agreement with those obtained via ICP-OES with recoveries of 92-108% for Cr(III) and 108-110% for Cr (VI) using μ-PADs, and 106-110% for total Cr using ICP-OES. Thus, the μ-PADs could potentially be utilized for the speciation of chromium in developing countries where environmental pollution and the availability of sophisticated instruments are significant problems.

Chromium Distribution and Spatial Variations in the Finer Sediment Grain Size Fraction and Unfractioned Surficial Sediments on Nyanza Gulf, of Lake Victoria (East Africa)

Surficial sediments collected from the Nyanza Gulf of Lake Victoria (East Africa) were used to determine spatial concentrations of Cr and determine differences in contents of the unfractioned (whole sediment) and the finer grain size sediments, establishing any changes in Cr enrichment and potential ecological risks using sediment quality guidelines. A single pollution index was also used to evaluate level of Cr contamination. The spatial mean Cr contents in the <63 µm (silt-clay) fraction were found to be significantly lower than those in the unfractioned sediments, but with a strong linear positive correlation. The study results show decreasing spatial amounts of Cr in surficial sediments of the Nyanza Gulf, when compared to a study done 20 years earlier. However, the 95% confidence limits of the overall mean Cr in unfractioned sediments exceed the threshold effect concentration (TEC), indicating the potential for Cr remobilization from sediments. In general the sediment enrichment is evidence of possible dominance of lithogenous sources of Cr in the surface lake sediments, with potential anthropogenic sources from the drainage system and nearshore urban areas. The sediments are unpolluted with respect to geoaccumulation index, and sediment enrichment factors suggest a minor to moderate enrichment of Cr in surficial sediments of three sites around the Nyanza Gulf zones and around the river mouth in the main lake.

Influence of soil geochemical and physical properties on chromium(VI) sorption and bioaccessibility

The Department of Defense (DoD) is faced with the daunting task of possible remediation of numerous soil-Cr(VI) contaminated sites throughout the continental U.S. The primary risk driver at these sites is hand-to-mouth ingestion of contaminated soil by children. In the following study we investigate the impact of soil geochemical and physical properties on the sorption and bioaccessibility of Cr(VI) in a vast array of soils relevant to neighboring DoD sites. For the 35 soils used in this study, A-horizon soils typically sorbed significantly more Cr(VI) relative to B-horizon soils. Multiple linear regression analysis suggested that Cr(VI) sorption increased with increasing soil total organic C (TOC) and decreasing soil pH. The bioaccessibility of total Cr (CrT) and Cr(VI) on the soils decreased with increasing soil TOC content. As the soil TOC content approached 0.4%, the bioaccessibility of soil bound Cr systematically decreased from approximately 65 to 10%. As the soil TOC content increased from 0.4 to 4%, the bioaccessibility of Cr(VI) and CrT remained relatively constant at approximately 4% and 10%, respectively. X-ray absorption near edge structure (XANES) spectroscopy suggested that Cr(VI) reduction to Cr(III) was prevalent and that the redox transformation of Cr(VI) increased with increasing soil TOC. XANES confirmed that nearly all bioaccessible soil Cr was the Cr(VI) moiety. Multiple linear regression analysis suggested that the bioaccessibility of Cr(VI) and its reduced counterpart Cr(III), decreased with increasing soil TOC and increasing soil pH. This is consistent with the observation that the reduction reaction and formation of Cr(III) increased with increasing soil TOC and that Cr(III) was significantly less bioaccessible relative to Cr(VI). The model was found to adequately describe CrT bioaccessibility in soils from DoD facilities where Cr(VI) contaminated sites were present. The results of this study illustrate the importance of soil properties on Cr(VI) sorption and bioassessability and help define what soil types have the greatest risk associated with Cr(VI) exposure.

Evaluation of the SO(2) and NH(3) gas adsorption properties of CuO/ZnO/Mn(3)O(4) and CuO/ZnO/NiO ternary impregnated activated carbon using combinatorial materials science methods

Impregnated activated carbons (IAC) are widely used materials for the removal of toxic gases in personal respiratory protection applications. The combinatorial method has been employed to prepare IACs containing different types of metal oxides in various proportions and evaluate their adsorption performance for low molecular weight gases, such as SO(2) and NH(3), under dry conditions. Among the metal oxides used for the study, Mn(3)O(4) was found to have the highest capacity for retaining SO(2) gas under dry conditions. NiO and ZnO were found to have similar NH(3) adsorption capacities which are higher than the NH(3) capacities observed for the other metal oxide impregnants used in the study. Although Cu- or Zn-based impregnants and their combinations have been extensively studied and used as gas adsorbents, neither Mn(3)O(4) nor NiO have been incorporated in the formulations used. In this study, ternary libraries of IACs with various combinations of CuO/ZnO/Mn(3)O(4) and CuO/ZnO/NiO were studied and evaluated for their adsorption of SO(2) and NH(3) gases. Combinations of CuO, ZnO, and Mn(3)O(4) were found to have the potential to be multigas adsorbents compared to formulations that contain NiO.

An efficient ultrasound assisted approach for the impregnation of room temperature ionic liquid onto Dowex 1×8 resin matrix and its application toward the enhanced adsorption of chromium (VI)

The work discussed in this paper is based on the utilization of ultrasound in conjunction with an ionic liquid (Aliquat 336) impregnated Dowex 1×8 resin for the effective adsorption of chromium. Ionic liquids are known for their selectivity toward metal extraction and ultrasonic medium offers efficient energy transfer for impregnating the ionic liquid in the resin matrix. The molecular interaction between the ionic liquid impregnated resin and chromium was studied through various physicochemical and spectroscopic techniques. The influence of various analytical parameters on the adsorption of Cr(VI) such as pH, adsorbent dosage, temperature and interference of foreign ions was studied in detail. Chromium (VI) was quantitatively adsorbed in the pH range of 3.5-4, with a high adsorption capacity of 230.9 mg g(-1) in conformity with the Langmuir isotherm model. The study of thermodynamic parameters showed that the adsorption process is exothermic and spontaneous. The adsorbent could be regenerated using 1 mol L(-1) HCl-0.28 mol L(-1) ascorbic acid mixture. Chromium could be effectively detoxified from an industrial effluent and finally the developed method was validated with the analysis of a certified reference material (BCR-715). The obtained results indicated that the ultrasonic assisted impregnation of the room temperature ionic liquid significantly enhances and improves the removal efficiency of Cr(VI).

Gas adsorption properties of the ternary ZnO/CuO/CuCl(2) impregnated activated carbon system for multigas respirator applications assessed through combinatorial methods and dynamic adsorption studies

A ternary library of 64 ZnO/CuO/CuCl(2) impregnated activated carbon samples was synthesized and screened automatically using a combinatorial (combi) method. The ability of the samples to adsorb toxic gases was screened gravimetrically. The stoichiometric ratio of reaction (SRR) between the moles of toxicant and the total moles of impregnant was obtained from the calculated mass increase of the samples after chemisorption, with a high SRR indicating high efficiency of toxicant removal. The combi samples that exhibited good dry SO(2) and NH(3) adsorption were prepared in bulk using the incipient wetness method and were evaluated for multigas respirator function by dynamic adsorption studies of SO(2), NH(3), HCN, and C(6)H(12) gases in either dry or humid conditions at ambient temperature. The bulk samples showed equivalent gas adsorption capacities when exposed to the different challenge gases indicating the value of the combi method for initial screening. Cu(2)Cl(OH)(3) was identified to be a potential multigas adsorbent.

The content of elements in rainwater and its relation to the frequency of hospitalization for gastric and duodenal peptic ulcers in Opole Voivodship, Poland, during 2000-2002

The relationship between chemical elements in rainwater and the frequency of hospitalizations for gastric and duodenal peptic ulcers was studied on the population of the province (Voivodship) of Opole, Poland, during the years 2000-2002. There is a high positive correlation between hospitalized cases of gastric peptic ulcers with chromium in rainwater (r = 0.71), cadmium (r = 0.63), and lead (r = 0.70). Mild positive correlations were found with zinc (r = 0.55), copper (r = 0.56), iron (r = 0.57), chloride (r = 0.60), and sulfate (r = 0.52). These correlations were higher on men, suggesting that there are gender correlations involved. In duodenal peptic ulcers, we observed a high positive correlation between chromium in rainwater and hospitalized cases (r = 0.61) and mild positive correlations with lead (r = 0.57), copper (r = 0.52), and cadmium (r = 0.51). Significant gender differences were not found. These positive correlations may be due to the biological activity of the elements, such as their cytotoxic activity, enhanced local adrenergic stimulation on mucosal vasculature, ion channel (mainly calcium channels) remodeling, and, for example promoting infection by Helicobacter pylori.

Identifying soil cleanup criteria for dioxins in urban residential soils: how have 20 years of research and risk assessment experience affected the analysis?

This article reviews the scientific evidence and methodologies that have been used to assess the risks posed by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and presents a probabilistic analysis for identifying virtually safe concentrations of TCDD toxicity equivalents (TEQ) in residential soils. Updated data distributions that consider state-of-the-science cancer and noncancer toxicity criteria, child soil ingestion and dermal uptake, bioavailability in soil, and residential exposure duration are incorporated. The probabilistic analysis shows that the most sensitive determinants of dose and risk are childhood soil ingestion, exposure duration, and the selected TCDD cancer potency factor. It also shows that the cancer risk at 1 per 100,000 predicted more conservative (lower) soil criteria values than did the noncancer hazard (e.g., developmental and reproductive effects). In this analysis, acceptable or tolerable soil dioxin concentrations (TCDD TEQ) ranged from 0.4 to 5.5 ppb at the 95th percentile for cancer potency factors from 9600 to 156,000 (mg/kg/d)(-1) with site-specific adjustments not included. Various possible soil guidelines based on cancer and noncancer risks are presented and discussed. In the main, the current toxicology, epidemiology, and exposure assessment data indicate that the historical 1 ppb TEQ soil guidance value remains a reasonable screening value for most residential sites. This analysis provides risk managers with a thorough and transparent methodology, as well as a comprehensive information base, for making informed decisions about selecting soil cleanup values for PCDD/Fs in urban residential settings.

Health risk communication using comparative risk analyses

The ability to communicate effectively the degree or magnitude of public exposures or health risks is essential for risk assessors and risk managers. Various guidelines exist for communicating environmental and public health risks, including recommended approaches for putting risk data into proper context. Although it remains unclear as to which approach is the most useful or appropriate under different circumstances, risk comparisons are a popular choice for conveying the significance of or providing a better perspective on a particular chemical exposure or health risk. In this paper, several different types of risk comparisons are described that are frequently used in the private and public sectors, and these are illustrated using a variety of examples from the literature. These approaches include: (1) intrachemical comparisons, (2) interchemical comparisons, (3) comparisons to background levels of risk, (4) comparisons to theoretical risks or safety levels, and (5) comparisons to other actions or activities. The primary purpose of this paper is to summarize and briefly discuss the advantages and limitations of these risk communication approaches. The evolving field of risk communication is also discussed, including ongoing research on public risk perceptions and alternative methods for communicating risk magnitudes and data uncertainties.

Mutagens in contaminated soil: a review

The intentional and accidental discharges of toxic pollutants into the lithosphere results in soil contamination. In some cases (e.g., wood preserving wastes, coal-tar, airborne combustion by-products), the contaminated soil constitutes a genotoxic hazard. This work is a comprehensive review of published information on soil mutagenicity. In total, 1312 assessments of genotoxic activity from 118 works were examined. The majority of the assessments (37.6%) employed the Salmonella mutagenicity test with strains TA98 and/or TA100. An additional 37.6% of the assessments employed a variety of plant species (e.g., Tradescantia clone 4430, Vicia faba, Zea mays, Allium cepa) to assess mutagenic activity. The compiled data on Salmonella mutagenicity indicates significant differences (p<0.0001) in mean potency (revertents per gram dry weight) between industrial, urban, and rural/agricultural sites. Additional analyses showed significant empirical relationships between S9-activated TA98 mutagenicity and soil polycyclic aromatic hydrocarbon (PAH) concentration (r2=0.19 to 0.25, p<0.0001), and between direct-acting TA98 mutagenicity and soil dinitropyrene (DNP) concentration (r2=0.87, p<0.0001). The plant assay data revealed excellent response ranges and significant differences between heavily contaminated, industrial, rural/agricultural, and reference sites, for the anaphase aberration in Allium cepa (direct soil contact) and the waxy locus mutation assay in Zea mays (direct soil contact). The Tradescantia assays appeared to be less responsive, particularly for exposures to aqueous soil leachates. Additional data analyses showed empirical relationships between anaphase aberrations in Allium, or mutations in Arabidopsis, and the 137Cs contamination of soils. Induction of micronuclei in Tradescantia is significantly related to the soil concentration of several metals (e.g., Sb, Cu, Cr, As, Pb, Cd, Ni, Zn). Review of published remediation exercises showed effective removal of genotoxic petrochemical wastes within one year. Remediation of more refractory genotoxic material (e.g., explosives, creosote) frequently showed increases in mutagenic hazard that remained for extended periods. Despite substantial contamination and mutagenic hazards, the risk of adverse effect (e.g., mutation, cancer) in humans or terrestrial biota is difficult to quantify.

Influence of organic ligands on Cr desorption from hydroxy-Cr intercalated montmorillonite

Retention of metals as hydroxy precipitates on mineral surfaces is an important process maintaining environmental quality. Hydroxy precipitates of Cr(III) are particularly important because appreciable mobilisation of intercalated, hydrolysed Cr from montmorillonite is currently thought to occur only via oxidative dissolution. The present study examines the potential of oxalate, tartrate, and citrate to desorb Cr from both hydroxy-Cr and hydroxy Al-Cr precipitates sorbed to montmorillonite. For all intercalated clays there was an initial very rapid dissolution, followed by a slow but sustained Cr release that more closely followed a parabolic rate law, the latter indicative of transport-controlled dissolution. The initial rapid dissolution persisted longer for the pure Cr clay ( approximately 48 h) than for the coprecipitated Al-Cr clay ( approximately 24 h). At the end of the 30 d reaction, however, most Cr remained sorbed to the montmorillonite in all systems. Citrate, for example, solubilised only approximately 10% of the total sorbed Cr from the pure Cr clays. Aluminum presence decreased Cr solubilisation rate due to Al accumulation at the polymer margins. Moreover, Al presence maintained the integrity of the intercalated polymers and prevented c-axis expansion beyond 1.4 nm, thus restricting the supply of organic ligand to the inter-layer region. Oxalate, tartrate, and citrate were shown to be effective chelators of sorbed Cr and these ligands may therefore play an important role in the mobilisation and cycling of this metal in soils and sediments.

Ageing of chromium(III)-bearing slag and its relation to the atmospheric oxidation of solid chromium(III)-oxide in the presence of calcium oxide

Slag arising in ferrochromium and stainless steel production is known to contain residual levels of trivalent chromium. As the chromium is normally bound in the slag matrix in various silicate or spinel phases, and hence not easily mobilised, utilisation or controlled disposal of such slag is generally considered unproblematic. Experimental test work with a number of slag materials indicates, however, that very gradual oxidation of trivalent to hexavalent chromium does occur when the slag is exposed to atmospheric oxygen, rendering a quantifiable but small portion of chromium in this much more mobile and toxic form. Mechanisms and rates of the oxidation reaction were investigated in a number of long-term studies using both original slag materials and artificial mixes of chromium and calcium oxides. Powders of these materials, some of them rolled into balls, were left to age under different conditions for periods of up to 12 months. In the slag samples, which contained between 1 and 3 wt.% chromium, 1000-10000 microg Cr(VI) were found per gram of chromium within 6-9 months of exposure to an ambient atmosphere. The rate of the oxidation reaction decreased exponentially, and the reaction could generally be said to have ceased within 12 months. In mixtures of calcium and chromium oxides the oxidation reaction is presumed to occur at the boundaries between chromium oxide and calcium oxide phases through diffusion of oxygen along the grain boundaries and of Cr(3+) across the boundaries, resulting in the formation of calcium chromate. In the slags, where calcium and chromium oxide can form a solid solution, the oxidation is likely to occur at the exposed surface of grains containing this solution.

Influence of soil geochemical and physical properties on the sorption and bioaccessibility of chromium(III)

There are numerous Cr(III)-contaminated sites on Department of Defense (DoD) and Department of Energy (DOE) lands that are awaiting possible clean up and closure. Ingestion of contaminated soil by children is the risk driver that generally motivates the likelihood of site remediation. The purpose of this study was to develop a simple statistical model based on common soil properties to estimate the hioaccessibility of Cr(III)-contaminated soil upon ingestion. Thirty-five uncontaminated soils from seven major soil orders, whose properties were similar to numerous U.S. DoD contaminated sites, were treated with Cr(III) and aged. Statistical analysis revealed that Cr(III) sorption (e.g., adsorption and surface precipitation) by the soils was strongly correlated with the clay content, total inorganic C, pH, and the cation exchange capacity of the soils. Soils with higher quantities of clay, inorganic C (i.e., carbonates), higher pH, and higher cation exchange capacity generally sequestered more Cr(III). The amount of Cr(III) bioaccessible from the treated soils was determined with a physiologically based extraction test (PBET) that was designed to simulate the digestive process of the stomach. The bioaccessibility of Cr(III) varied widely as a function of soil type with most soils limiting bioaccessibility to <45 and <30% after I and 100 d soil-Cr aging, respectively. Statistical analysis showed the bioaccessibility of Cr(III) on soil was again related to the clay and total inorganic carbon (TIC) content of the soil. Bioaccessibility decreased as the soil TIC content increased and as the clay content decreased. The model yielded an equation based on common soil properties that could be used to predict the Cr(III) bioaccessibility in soils with a reasonable level of confidence.

Risk characterization: principles and practice

In the field of risk assessment, characterizing the nature and magnitude of human health or environmental risks is arguably the most important step in the analytical process. In this step, data on the dose-response relationship of an agent are integrated with estimates of the degree of exposure in a population to characterize the likelihood and severity of risk. Although the purpose of risk characterizations is to make sense of the available data and describe what they mean to a broad audience, this step is often given insufficient attention in health risk evaluations. Too often, characterizations fail to interpret or summarize risk information in a meaningful way, or they present single numerical estimates of risk without an adequate discussion of the uncertainties inherent in key exposure parameters or the dose-response assessment, model assumptions, or analytical limitations. Consequently, many users of risk information have misinterpreted the findings of a risk assessment or have false impressions about the degree of accuracy (or the confidence of the scientist) in reported risk estimates. In this article we collected and integrated the published literature on conducting and reporting risk characterizations to provide a broad, yet comprehensive, analysis of the risk characterization process as practiced in the United States and some other countries. Specifically, the following eight topics are addressed: (1) objective of risk characterization, (2) guidance documents on risk characterization, (3) key components of risk characterizations, (4) toxicity criteria for evaluating health risks, (5) descriptors used to characterize health risks, (6) methods for quantifying human health risks, (7) key uncertainties in risk characterizations, and (8) the risk decision-making process. A brief discussion is also provided on international aspects of risk characterization. A number of examples are presented that illustrate key concepts, and citations are provided for approximately 100 of the most relevant papers.

Is hexavalent chromium carcinogenic via ingestion? A weight-of-evidence review

Hexavalent chromium [Cr(VI)] is recognized as a human carcinogen via inhalation, based on elevated rates of lung cancer among occupationally exposed workers in certain industries. Cr(VI) is also genotoxic in bacterial and mammalian cell lines. In contrast, scientific panels in the United States and abroad have reviewed the weight of evidence (WOE) and decided that the available data are insufficient to conclude that Cr(VI) is an oral carcinogen. A criterion of 0.2 ppb was established by a California agency for Cr(VI) in drinking water to prevent cancer, however, this criterion was withdrawn in November, 2001. This criterion was remarkably lower than the promulgated California and federal drinking-water standards for total chromium of 50 ppb and 100 ppb, respectively. Both of the promulgated standards are designed to be protective of humans who ingest Cr(VI). This article describes a WOE analysis to examine the likelihood that Cr(VI) in drinking water poses a cancer hazard at the current U.S. drinking-water standard. The results indicate that: (1) From the historical epidemiological studies, there are a few reports of increased rates of digestive system cancer among Cr(VI)-exposed workers, although most are not statistically significant; (2) the preponderance of evidence from recent epidemiological studies of Cr(VI)-exposed workers does not support an increased risk of cancer outside of the respiratory system; (3) studies of four environmentally exposed populations are negative; (4) there is only one lifetime animal feeding study, and the findings from that study are considered to be flawed and inconclusive; and (5) recent kinetics and in vivo genotoxicity data demonstrate that Cr(VI) is reduced to nontoxic Cr(III) in saliva, in the acidic conditions of the stomach, and in blood. In short, at concentrations at least as high as the current U.S. maximum contaminant level (100 ppb), and probably at least an order of magnitude higher, Cr(VI) is reduced to Cr(III) prior to or upon systemic absorption. The weight of scientific evidence supports that Cr(VI) is not carcinogenic in humans via the oral route of exposure at permissible drinking-water concentrations.

Cancer mortality in relation to environmental chromium exposure

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.

Chromium

Chromium occurs primarily in the trivalent state (III), which is the most stable form, or in the hexavalent state (VI), which is a strong oxidizing agent. Elemental chromium (0) does not occur naturally on earth. Trivalent chromium (III) is an essential trace metal necessary for the formation of glucose tolerance factor and for the metabolism of insulin. Commercial applications of chromium compounds include tanning (III), corrosion inhibition, plating, glassware-cleaning solutions, wood preservatives (VI), manufacture of safety matches, metal finishing (VI), and the production of pigments (III, VI). Hexavalent chromium (VI) contaminated local soil when chromium waste slag was part of the fill material present in residential, public, and industrial areas. In some urban areas, about two-thirds of the chromium in air results from the emission of hexavalent chromium from fossil fuel combustion and steel production. The remaining chromium in air is the trivalent form. The residence time of chromium in air is < 10 days, depending on the particle size. Trivalent compounds generally have low toxicity and the gastrointestinal tract poorly absorbs these compounds. Hexavalent chromium is a skin and mucous membrane irritant and some of these hexavalent compounds are strong corrosive agents. Hexavalent chromium compounds also produce an allergic contact dermatitis characterized by eczema. Sensitivity to trivalent compounds is much less frequent, but some workers may react to high concentrations of these compounds. Hexavalent chromium is recognized by the International Agency for Research on Cancer and by the US Toxicology Program as a pulmonary carcinogen. The increased risk of lung cancer occurs primarily in workers exposed to hexavalent chromium dust during the refining of chromite ore and the production of chromate pigments. Although individual studies suggest the possibility of an excess incidence of cancer at sites outside the lung, the results from these studies are inconsistent.

In Situ Reduction of Hexavalent Chromium in Alkaline Soils Enriched with Chromite Ore Processing Residue

In investigating chromium sites in New Jersey, it has been observed that an organic-rich 0.5- to 4-foot-thick layer of decayed vegetation (locally known as "meadowmat") underlying the chromium-containing material acts as a natural barrier to the migration of Cr(VI). The groundwater in a sand layer directly beneath the meadowmat has been shown to contain low or nondetectable levels of chromium. The meadowmat is under highly reduced conditions due to bacterial activity associated with the organic material. Based on the observed ability of the meadowmat to reduce Cr(VI) to Cr(III), the feasibility of in situ reduction of Cr(VI) to Cr(III) at chromite ore processing residue (COPR) sites was investigated in biologically-active, laboratory-scale test columns. COPR typically has a high pH (in excess of 12) and may contain total chromium concentrations as high as 70,000 mg/kg. Experimental results demonstrated that the addition of a mineral acid (to lower the pH to between 7.0 and 9.5) and a bacteria-rich organic substrate (fresh manure) resulted in the reduction of Cr(VI) to the less toxic and less mobile trivalent form. Pore water Cr(VI) was reduced from approximately 800 mg/L to less than 0.05 mg/L over a period of eight months. This is less than the U.S. Environmental Protection Agency's (EPA) Maximum Contaminant Level (MCL) for chromium in drinking water of 0.1 mg/L. Solid phase Cr(VI) concentrations decreased from approximately 2,000 mg/kg to less than 10 mg/kg in the columns over a period of 11 months while the total chromium concentrations remained unchanged. Toxicity Characteristic Leaching Procedure (TCLP) extract from the treated columns met the regulatory limit of 5 mg/L of Cr, whereas the untreated samples had TCLP extract concentrations greater than 40 mg/L. This study demonstrated the potential applicability of in situ reduction to soils contaminated with Cr(VI) by adjusting the pH to between 7.0 and 9.5 and mixing in a bacteria-rich organic substrate.

Urinary chromium as a biological marker of environmental exposure: what are the limitations?

Public concern has mounted recently about environmental exposures to chromium in soil, tap water, and ambient air. In response, agencies charged with protecting public health have attempted to study exposure by monitoring urinary chromium levels among potentially exposed populations. While urinary biomonitoring of occupationally exposed workers has been successfully used to assess high-level inhalation exposures in the workplace, evaluating low-level environmental exposures has been problematic. Due to these problems, before an extensive biological monitoring study is conducted of those exposed to low levels of environmental chromium, several issues must be resolved. First, exposures to chromium must occur at the same time as sampling, because the biological half-life of chromium in urine is very short (less than 2 days). Second, reduced bioavailability and bioaccessibility via the oral and dermal routes of exposure limit the capacity of urinary monitoring to measure environmental exposures (e.g., systemic dose is too small to be measured). Third, the dose of chromium must be sufficient such that it may be reliably measured above background levels in urine (range of 0.2 to 2 microg/liter) and above the analytical limit of detection (0.2 microg/liter). Fourth, the inter- and intrapersonal variability in background levels of urinary chromium is known to be significant and influenced by food and beverage intake, smoking, and exercise. Thus, the role of each factor must be carefully understood. Finally, it is imperative to have developed a complete understanding of the clinical significance of elevated urinary chromium levels before a study is performed, because higher than background levels, in and of themselves, are not indicative of a significant health concern. The route of exposure, valence of chromium to which people were exposed, exposure time, and duration must all be understood before the biological data can be implemented. We have conducted a total of nine human exposure studies over the past 3 years in an attempt to understand the kinetics of chromium and the impact on urinary, red blood cell (RBC), and plasma biomonitoring programs. The results of these studies are described here and our recommendations are offered for how to design and implement a urinary chromium biomonitoring study. In our view, given some evidence that the dose of hexavalent chromium [Cr(VI)] is sufficient to be measurable above background concentrations of total chromium [Cr(III) and Cr(VI)], duplicated measurements of chromium in plasma and RBCs are, in most cases, a more definitive gauge of environmental exposure than urinary biomonitoring.

Growth and behavioral effects of early postnatal chromium and manganese exposure in herring gull (Larus argentatus) chicks

Organisms in marine environments are exposed to chromium and manganese, yet little is known of the effects of these metals on physiology and behavior. In this article we examine the effects of chromium and manganese on early neurobehavioral development in herring gulls, Larus argentatus. Each of 36 2-day-old herring gull chicks was randomly assigned to one of three treatment groups to receive either chromium nitrate (25 mg/kg), manganese acetate (50 mg/kg), or a control dose of sterile saline solution. The trios were not siblings, but were matched by age and weight. Behavioral tests examined food-begging, balance, locomotion, righting response, recognition, thermoregulation, and perception. There were significant differences in begging behavior by 5 days postinjection, and there were significant differences in weight gain throughout development until 50 days of age, when the experiment was terminated. Behavioral tests, administered from 18-48 days postinjection, indicated significant differences between control and the exposed groups for time to right themselves; thermoregulation behavior; and performance on a balance beam, inclined plane, actual cliff, and visual cliff (although not all components varied significantly). Of the 14 behavioral measures with significant differences, control birds performed best on 12.

Designing a biological monitoring program to assess community exposure to chromium: conclusions of an expert panel

The possible benefits of biological monitoring of large groups of people potentially exposed to environmental contaminants has become an area of much interest in recent years. Because chromite-ore processing residue has been found in some soils in northern New Jersey, urinary chromium monitoring of people in the community was evaluated as a potentially useful tool. In an attempt to identify those who could be exposed and to quantify the magnitude of exposure to the chromium in these soils, the New Jersey Department of Health (NJDOH) initiated a public health screening project. In 1992, the NJDOH proposed to evaluate over 4000 people who lived or worked near these sites. Volunteers were administered a questionnaire and were given a limited physical examination, and a single spot urine sample was collected. Because of the difficulties in using urinary chromium to assess low-level exposure and the potential implications of any regulatory decisions that could be based on the results of this project, a panel of experts was convened to evaluate the protocol. The panel consisted of five scientists and physicians with expertise in toxicology, dermatology, epidemiology, biological monitoring, and analytical chemistry. Like a World Health Organization group, the panel concluded that although urine biomonitoring can be useful in evaluating high levels of exposure to chromium, it is not reliable for assessing low-level exposure similar to that which may have occurred in northern New Jersey. The panel also noted that when urinary biomonitoring is to be used to assess the public's possible exposure, a large number of precautions must be taken to ensure the accuracy and usefulness of the results. The single most important recommendation was to collect a second, and perhaps a third, spot urine (or 24-h urine) sample before concluding that a person may be routinely overexposed. These suggestions are applicable to designing a biomonitoring program for nearly any environmental contaminant to which a community may be exposed. A review of scientific literature associated with biological monitoring of chromium is provided.

Using human sweat to extract chromium from chromite ore processing residue: applications to setting health-based cleanup levels

Chromite ore processing residue (COPR) containing measurable levels of hexavalent and trivalent chromium. [Cr(VI) and Cr(III), respectively] has been used to fill in low-lying areas in Hudson County, N.J. While it has been demonstrated that direct dermal contact with solutions containing Cr(VI) may elicit allergic contact dermatitis (ACD) in previously sensitized individuals, it is unknown to what degree skin moisture may solubilize Cr(VI) from COPR adhering to skin. An accurate estimate of this extraction potential is necessary to establish COPR concentrations of Cr(VI) and Cr(III) that are protective of eliciting ACD in sensitized individuals. The purpose of this study was to measure the extractable fraction of Cr(VI) and total chromium [Cr(III) and Cr(VI)] in soils impacted by COPR using human sweat as the extractant. Human sweat was collected from seven male volunteers. Samples of COPR material containing the following Cr(VI) and total chromium concentrations were collected: Cr(VI), 16, 136, and 1240 ppm; total chromium, 932 and 6660 ppm. The samples were sieved to obtain a uniform particle size < 500 microns. The samples were then mixed with human sweat at 30 degrees C for 12 h, after which the sweat was filtered and analyzed to determine the dissolved concentration of Cr(VI) and total chromium. The data from these analyses show that no detectable levels (limit of detection = 0.010 ppm) of Cr(VI) were leached from COPR containing 16 ppm Cr(VI). At Cr(VI) concentrations of 136 and 1240 ppm, less than 0.1% of the Cr(VI) present in the COPR sample was extracted into sweat, and sweat concentrations were 0.133 ppm Cr(VI) or less. Similarly, the amount of Crtotal extracted was 0.3% or less at COPR concentrations as high as 6600 ppm Crtotal, and sweat concentrations were 2.3 ppm Crtotal or less. If a minimum concentration of 10 ppm (Bagdon and Hazen, 1991) to 54 ppm (Paustenbach et al., 1992) Cr(VI) in sweat is required to elicit an ACD response in chromium-sensitive individuals, the current study results suggest that a COPR Cr(VI) concentration of at least 10,000-54,000 ppm would be required to elicit ACD. If 500 ppm (or greater) of solubilized Cr(III) is required to elicit an ACD response (NJDEPE, 1992a), then a COPR concentration of 250,000 ppm Cr(III) or greater would be required to elicit an allergic response. These results suggest that ACD is unlikely to occur as a result of environmental exposure to the COPR.

Metals and the skin

Certain metals, and many metal-based compounds, are inherently toxic, and their presence in occupational and environmental settings raises appropriate questions concerning human exposure. Contact of these materials with the skin represents an important route of exposure, which is not well characterized. The purpose of this review, therefore, is to assemble the available, useful information pertinent to risk assessment following dermal contact. Specifically, we summarize here: (1) data relevant to the qualitative and (where possible) quantitative evaluation of metal compound permeation through the skin; (2) the role of each metal in metabolism, particularly with respect to the skin, and the potentially toxic effects that may result from dermal contact; and (3) the immunological characteristics (including allergenicity) of the metals and their derivatives. In total, information on 31 metals has been reviewed. It is clear that many diverse factors determine the ability of metal-based species to permeate biological membranes, not all of which have been fully defined. Therefore, considerably more experimentation, targeted at the development of high-quality transport data, will be required before the specification of practically useful structure-activity relationships are possible.

Mechanisms of chromium carcinogenicity and toxicity

Chromium, like many transition metal elements, is essential to life at low concentrations yet toxic to many systems at higher concentrations. In addition to the overt symptoms of acute chromium toxicity, delayed manifestations of chromium exposure become apparent by subsequent increases in the incidence of various human cancers. Chromium is widely used in numerous industrial processes, and as a result is a contaminant of many environmental systems. Chromium, in its myriad chemical forms and oxidation states, has been well studied in terms of its general chemistry and its interactions with biological molecules. However, the precise mechanisms by which chromium is both an essential metal and a carcinogen are not yet fully clear. The following review does not seek to embellish upon the proposed mechanisms of the toxic and carcinogenic actions of chromium, but rather provides a comprehensive review of these theories. The chemical nature of chromium compounds and how these properties impact upon the interactions of chromium with cellular and genetic targets, including animal and human hosts, are discussed.

Review of the allergic contact dermatitis hazard posed by chromium-contaminated soil: identifying a "safe" concentration

At least 200 sites in the United States contain soil with elevated levels of trivalent and hexavalent chromium [Cr(III) and Cr(VI)]. Although the potential cancer hazard posed by airborne Cr(VI) has been the primary concern for these sites, a soil cleanup standard based on the potential elicitation of allergic contact dermatitis has been proposed for sites in Hudson County, N.J. This paper describes the rationale for identifying a soil concentration of Cr(VI) that should not pose an allergic contact dermatitis hazard-even in sensitized persons. A literature review of eight published patch test studies that evaluated the allergic response to potassium dichromate was conducted. These studies were evaluated for clinical and statistical relevance in establishing a threshold dose of Cr(VI) to which no more than 10% of the subpopulation sensitized to chromium would respond, and that would protect at least 99.84% of the general population. Although each of the studies had certain methodological limitations when evaluated against current test methods, the data set proved useful for deriving an estimated threshold. Using computer data-fitting techniques based on truncated lognormal distributions, a weighted mean 10% threshold of approximately 150 ppm potassium dichromate or 54 ppm Cr(VI) was identified for the eight studies. Due to the types of limitations noted for these studies, this threshold is likely to be somewhat conservative. Test results have shown that between 5 and 10% of the Cr(VI) at concentrations less than about 500 ppm are released from a soil matrix into an isotonic saline solution simulating sweat. Using human sweat as the extractant, it has been shown that only 0.1% of the CR(VI) at concentrations of approximately 1,000 ppm are released from a soil matrix into sweat. Based on 10% solubilization of soil-bound Cr(VI) and the results of our statistical analysis of previous threshold studies, a concentration of approximately 350 to 500 ppm Cr(VI) in soil should be sufficiently low to protect virtually all exposed people, including children, from chromium-induced allergic contact dermatitis.

A proposed approach to regulating contaminated soil: identify safe concentrations for seven of the most frequently encountered exposure scenarios

Since 1980, more than 10,000 sites in the United States have been shown to contain soil which has elevated concentrations of various xenobiotics. Since that time, guidelines for deciding whether the level of contamination is worthy of concern have been proposed or promulgated by dozens of local, state, and federal regulatory agencies. Unfortunately, there has been little consistency in the guidelines suggested for each soil contaminant. For example, (a) the basis or rationale for some of the cleanup levels is unclear, (b) approaches to setting cleanup levels vary between states and agencies, (c) cleanup objectives often vary among agencies within the same state, and (d) the cleanup levels are usually set in a scientifically haphazard manner. This paper proposes that the most cost-effective and efficient way to quickly regulate contaminated soil is to establish "safe" concentrations for each chemical for the seven most common exposure scenarios. These exposure scenarios include (1) residential, (2) industrial, (3) agricultural, (4) recreational, (5) groundwater, (6) wildlife and aquatic species, and (7) runoff/erosion of particulates to waterways. The scientific approach and rationale for calculating the cleanup criteria are illustrated by evaluating dioxin and benzene, toluene, and xylene (BTX). The methods suggested here indicate that levels of dioxin of 25 and 50 ppb in residential and industrial soils, respectively, should be acceptable. The predominant concern for the agricultural and recreational scenarios is the runoff of particulates to waterways. For BTX, benzene will dictate the degree of cleanup and the primary hazard at most residential sites will be the inhalation of vapors. Benzene concentrations of 2.5, 14, and 250 ppm should be acceptable for residential, industrial, and recreational soils, respectively. Depending on the depth to groundwater and aquifer use, protection of groundwater may be the driving concern for establishing BTX cleanup levels and must be determined using site-specific factors.

Recent developments on the hazards posed by 2,3,7,8-tetrachlorodibenzo-p-dioxin in soil: implications for setting risk-based cleanup levels at residential and industrial sites

Since the publication of the Times Beach risk assessment in 1984, which suggested that residential soils were of concern when the level of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was in excess of 1 ppb, there has been continued interest in this topic. Studies conducted within the past 5 yr on the environmental and toxicological behavior of TCDD, as well as refinement of parameters regarding human exposure, indicate that previous assessments of the risk to humans posed by TCDD-contaminated soil were overestimated. In this paper, recent information drawn from nearly 100 recently published articles regarding the histopathology interpretation of the Kociba bioassay, environmental fate and half-life of TCDD in soil, and estimates of human exposure via soil ingestion, dermal contact, inhalation, surface runoff, and the consumption of fish were incorporated into a risk assessment. Cleanup levels for TCDD in residential and industrial soils were calculated based on most likely exposure scenarios. Probability distributions of key exposure parameters were incorporated into a Monte Carlo uncertainty analysis to predict the range and probability of TCDD uptake and corresponding cleanup levels in soil. This analysis demonstrated that the most significant route of human exposure to TCDD is through dermal contact with soil, followed by soil ingestion, fish consumption, and inhalation of airborne particulates. At residential sites, soils containing 20 parts per billion (ppb) of TCDD were found to pose a lifetime cancer risk no greater than 1 in 100,000 (10(-5) risk) under typical exposure conditions. Based on the Monte Carlo analysis, soil concentrations for the 75th and 95th percentile person were 12 and 7 ppb (10(-5) risk), respectively. In industrial soils, TCDD concentrations ranged between 131 and 582 ppb (10(-5) risk), depending on the amount of time spent outdoors under typical exposure conditions. Industrial soil concentrations of approximately 93 and 46 ppb (10(-5) risk) were calculated for the 75th and 95th percentile worker, respectively, engaged in outdoor activities. The range of TCDD concentrations in industrial soils was not reduced significantly when the consumption of fish from a neighboring waterway by off-site receptors was considered. While cleanup levels for TCDD should be derived on a site-specific basis, this analysis indicated that soil cleanup standards can be generally higher than those implemented over the past 8 yr.

An assessment and quantitative uncertainty analysis of the health risks to workers exposed to chromium contaminated soils

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.

The health hazards posed by chromium-contaminated soils in residential and industrial areas: conclusions of an expert panel

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.(ABSTRACT TRUNCATED AT 400 WORDS)