Hexavalent chromium-contaminated soils: options for risk assessment and risk management

Semi-quantitative health risk assessment of heavy metal dust exposure among nail technicians using the SQRA technique and Monte Carlo simulation

Nail technology, including the application of artificial nails and nail care, is a developing sector of the global beauty industry. Nail technicians are exposed to a variety of chemical substances through inhalation, as they spend extended periods of time in close proximity to these materials. This study aimed to evaluate the semi-quantitative health risk of dust-containing heavy metals among nail technicians. This analytical descriptive study employed the risk assessment method provided by the Singapore Occupational Health Department to evaluate the health hazards of lead, cadmium, nickel, chromium, and manganese. Dust samples from nail filing were collected from the respiratory zone of 20 nail technicians following the NIOSH 7300 method. The samples were analyzed using ICP-OES instrumentation. Monte Carlo simulation was utilized to characterize the risk and its uncertainties. Manganese and cadmium had the highest and lowest mean concentrations, respectively. The risk scores of the metals ranked from highest to lowest were as follows: N i > C r > C d > M n > P b . All five metals had risk rankings below 2.8, signifying a minimal risk level. Sensitivity analysis using Spearman's correlation coefficient demonstrated a positive relationship between concentration, daily hours of exposure, and the number of workdays per week with the risk score (RR) and exposure level (ER). Conversely, the variable of weekly working hours (W) showed a negative correlation with these parameters. Despite the low-risk level of the examined metals, continuous exposure and potential long-term effects on nail technicians warrant preventive measures. Recommendations include implementing local exhaust ventilation systems, using table fans, establishing work-rest cycles, wearing N95 dust masks, and using reputable and high-quality nail polishes.

Ecological-health risks assessment and source apportionment of heavy metals in agricultural soils around a super-sized lead-zinc smelter with a long production history, in China

Smelting activities are considered as the primary cause of heavy metal (HM) accumulation in soils, and the human health around the smelter has been a great concern worldwide. In this study, a total of 242 agricultural soil samples were collected around a large scale Pb/Zn smelter in China, and eight HMs (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) were analyzed to assess HMs status, ecological -health risks, and identify source. Monte Carlo simulation was utilized to evaluate the probabilistic health risks, and positive matrix factorization (PMF) was employed to identify sources. The results revealed the average contents of five heavy metals (Cd 5.28 mg/kg, Pb 203.36 mg/kg, Hg 0.39 mg/kg, Zn 293.45 mg/kg, Cu 37.14 mg/kg) are higher than their background values in Hunan province. Cd had the highest mean pollution index (PI) of 41.8 and the greatest average ecological risk index (E_r) of 1256.34, indicating that Cd was the primary enriched pollutant and had a higher ecological risk than other HMs. The mean hazard index (HI) through exposure to eight HMs was 2.95E-01 and 9.74E-01 for adults and children, respectively, with 35.94% of HI values for children exceeding the risk threshold of 1. Moreover, the mean total cancer risks (TCR) were 2.75E-05 and 2.37E-04 for adults and children, respectively, with 75.48% of TCR values for children exceeding the guideline value of 1E-04. In addition, the positive matrix factorization results showed smelting activities, natural sources, agricultural activities and atmospheric deposition were the three sources in soils, with the contribution rate of 48.62%, 22.35%, and 29.03%, respectively. The uncertainty analysis of the PMF indicated that the three-factor solution is reliable. This work will provide scientific reference for the comprehensive prevention of soil HM pollution adjacent to the large smelter.

High efficiency of calcined anionic clay to remove the chromate anions CrO42-from polluted water

Calcined anionic clay based on zinc and aluminum was used to remove the pollutant CrO42- from wastewater. This adsorbent material derived from layered double hydroxide (LDH) was chosen for its higher adsorption capacity, its affinity for most pollutants, and its non-toxicity. The kinetic study suggesting a high affinity between the pollutant and calcined LDH (CLDH). The pollutant is retained in multilayer and follows the Freundlich model. Thermodynamic study indicates a physical interaction. The elimination reaches 100% with a retention capacity of 3333 mg/g. After cycles of regeneration and in comparison with other adsorbents, CLDH has proven its efficiency and high performances to remove CrO42- anions.

The Toxicological Analysis of Ni and Cr in Prescription Food for Special Medical Purposes and Modified Milk Products for Babies in Infancy Available in Pharmacies in Poland

Prescription food for special medical purposes (FSMPs) and modified milk products (MMPs) for babies in the infancy period available in pharmacies are increasingly frequently used for newborns and infants-especially in cases where allergies and food-borne diseases are diagnosed. However, there is a lack of scientific study around the safety assessment of the elemental impurities in these products. Importantly, the allergen Ni and the problematic metal Cr are little considered. Hence, the aim of this article was the toxicological analysis of Ni and Cr impurities in prescription FSMPs (n = 6) and MMPs (n = 6) for newborns and infants available in Polish pharmacies. For the best safety assessment, we include three approaches including (1) the levels of Ni and Cr in powdered products, (2) assessment of the daily dose depending on age and body weight of newborns and infants, and (3) the weekly intake of Ni and Cr in samples in comparison to provisional tolerable weekly intake (PTWI). Our results show that, on the basis of our data, the products from pharmacies in Poland investigated in this study do not represent a real health hazard to newborns and infants, although there may be a requirement for the monitoring of levels of Ni. Our results are pioneer and provide valuable data for other scientists and manufacturers.

Status assessment and probabilistic health risk modeling of metals accumulation in agriculture soils across China: A synthesis

Heavy metal accumulation in agriculture soils is of particular concern in China, while the status and probabilistic health risks of metal contamination in Chinese agriculture soils have been rarely studied at the national scale. In this study, we compiled a database of heavy metal concentrations in Chinese agriculture soils and selected six heavy metals for pollution assessment and risk screening: arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni), lead (Pb) and Zinc (Zn). Monte Carlo simulation was employed to assess the probabilistic health risks, the associated uncertainties, as well as variations in toxicity parameters, ingestion rate and body weight. Results indicated that the concentrations of Cd were elevated above their reference standard and Cd had the highest mean geo-accumulation index (I_geo) of 1.79. Moreover, the mean hazard index (HI) through exposure to six heavy metals was 1.85E-01 and 2.87E-02 for children and adults, respectively, with 2.2% of non-cancer risks for children that exceeded the guideline value of 1. In contrast, 95.0% and 90.0% of the total cancer risks (TCR) through exposure to six heavy metals for children and adults, respectively, exceeded the guideline value of 1E-06. Six metals were ranked based on their percent of risk outputs exceeding the guideline values. Arsenic had the high exceedance of both cancer and non-cancer risks, while both Cr and Cd were metals with high concern that had high exceedance of cancer risk. Sensitivity analyses indicated that metal concentrations and ingestion rate of soil were the predominant contributors to total risk variance. Overall, the adverse health risks induced by exposure to heavy metals contaminated farmland were elevated. Results from this study may provide valuable implications for public health professionals and policy-makers to design effective strategy to manage nation-wide farmland and reduce heavy metal exposure.

Removal of hexavalent chromium ions by core-shell sand/Mg-layer double hydroxides (LDHs) in constructed rapid infiltration system

This study aimed to determine the efficiencies and mechanisms of hexavalent chromium (Cr(VI)) removal with modified sand coated by Mg-LDHs in constructed rapid infiltration system (CRIS). Mg-LDHs (MgAl-LDHs, MgFe-LDHs) were prepared by co-precipitation method and in situ coated onto the surface of original sand. Scanning Electron Microscope (SEM) and X-Ray Fluorescence Spectrometer (XRFS) were used to analyze physicochemical properties of sand/Mg-LDHs composites. Results obtained confirmed the successful LDHs-coating modification. During the purification experiments, the average removal rates of Cr(VI) were 47.62% for sand/MgAl-LDHs, 34.15% for sand/MgFe-LDHs and 11.61% for original sand, respectively. The sand/Mg-LDHs had a higher Langmuir adsorption capacity and desorption capability for Cr(VI) compared to original sand. The adsorption kinetic data of different adsorbents were better described by pseudo-second-order model. Intra-particle diffusion model was also used to elucidate the adsorption mechanism. Moreover, extracellular polymeric substances, biomass and enzymatic activity of microbes on the modified and original sand were testified and analyzed to study microbial effect on Cr(VI) removal in test columns. Through a rough economic estimation, the reagent cost of sand/MgAl-LDHs synthesis was only RMB ¥ 0.24/Kg. It could be concluded that MgAl-LDHs modified sand is an efficient and economical substrate of CRIS for Cr(VI) removal.

Speciation of chromium compounds from humic acid-zeolite Y to an ionic liquid during extraction

By synchrotron X-ray absorption spectroscopy, chemical structures of hexavalent chromium (Cr(VI))/trivalent chromium (Cr(III)) adsorbed on humic acid (HA)-zeolite Y and extracted in an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim][BF₄])) have been studied. By combining the competitive adsorption results and reduction of Cr(VI)-HA with the carboxyl groups of HA, Cr(III)-HA (58%) was shown to be the major compound in HA-zeolite Y using synchrotron X-ray absorption near-edge structure (XANES) spectroscopy. In an ionic liquid phase, the reduction of Cr(VI)-HA to Cr(III)-HA and the desorption of Cr(III) from HA were caused by [C₄mim][BF₄]. The ⁹F nuclear magnetic resonance (NMR) spectra show that the perturbation of the [C₄mim][BF₄] anion was affected by the extractable chromium species. The formation of a Cr(III) ion affected the increase in the bond distance for the 1st shell CrO of the chromium species in [C₄mim][BF₄] using extended X-ray absorption fine structure (EXAFS) spectroscopy. The changes in the non-extractable chromium species remaining in HA-zeolite Y were also caused by [C₄mim][BF₄] during extraction. The desorption of the absorbed Cr(III) on HA and zeolite Y was observed to form Cr(III) ions. As the percentage of Cr(III) ions remaining in HA-zeolite Y increased, a slightly greater bond distance for CrO was found at 2.01 Å. The enhanced reduction of Cr(VI)-HA and desorption of Cr(III) adsorbed on the HA and zeolite Y to form Cr(III) ions were affected by [C₄mim][BF₄]. Increased mobility of Cr(III) in the simulated soil can promote the migration of Cr(III) ions into the H₂O during soil washing for remediation.

CoQ10 Deficiency May Indicate Mitochondrial Dysfunction in Cr(VI) Toxicity

To investigate the toxic mechanism of hexavalent chromium Cr(VI) and search for an antidote for Cr(VI)-induced cytotoxicity, a study of mitochondrial dysfunction induced by Cr(VI) and cell survival by recovering mitochondrial function was performed. In the present study, we found that the gene expression of electron transfer flavoprotein dehydrogenase (ETFDH) was strongly downregulated by Cr(VI) exposure. The levels of coenzyme 10 (CoQ10) and mitochondrial biogenesis presented by mitochondrial mass and mitochondrial DNA copy number were also significantly reduced after Cr(VI) exposure. The subsequent, Cr(VI)-induced mitochondrial damage and apoptosis were characterized by reactive oxygen species (ROS) accumulation, caspase-3 and caspase-9 activation, decreased superoxide dismutase (SOD) and ATP production, increased methane dicarboxylic aldehyde (MDA) content, mitochondrial membrane depolarization and mitochondrial permeability transition pore (MPTP) opening, increased Ca²⁺ levels, Cyt c release, decreased Bcl-2 expression, and significantly elevated Bax expression. The Cr(VI)-induced deleterious changes were attenuated by pretreatment with CoQ10 in L-02 hepatocytes. These data suggest that Cr(VI) induces CoQ10 deficiency in L-02 hepatocytes, indicating that this deficiency may be a biomarker of mitochondrial dysfunction in Cr(VI) poisoning and that exogenous administration of CoQ10 may restore mitochondrial function and protect the liver from Cr(VI) exposure.

Effects of dentifrice containing hydroxyapatite on dentinal tubule occlusion and aqueous hexavalent chromium cations sorption: a preliminary study

In order to endow environmental protection features to dentifrice, hydroxyapatite (HA) was added to ordinary dentifrice. The effects on dentinal tubule occlusion and surface mineralization were compared after brushing dentine discs with dentifrice with or without HA. The two types of dentifrice were then added to 100 µg/ml of hexavalent chromium cation (Cr⁶⁺) solution in order to evaluate their capacities of adsorbing Cr⁶⁺ from water. Our results showed that the dentifrice containing HA was significantly better than the ordinary dentifrice in occluding the dentinal tubules with a plugging rate greater than 90%. Moreover, the effect of the HA dentifrice was persistent and energy-dispersive spectrometer (EDS) revealed that the atomic percentages of calcium and phosphorus on the surface of dentine discs increased significantly. Adding HA to ordinary dentifrice significantly enhanced the ability of dentifrice to adsorb Cr⁶⁺ from water with the removal rate up to 52.36%. In addition, the sorption was stable. Our study suggests that HA can be added to ordinary dentifrice to obtain dentifrice that has both relieving dentin hypersensitivity benefits and also helps to control environmental pollution.

Cancer prevention: a global perspective

This review will be restricted to measures aimed at primary prevention of cancer; reduction of the death rate through screening will not be covered. In many instances, cancer prevention is just one outcome of the benefits of good health practices, which may also benefit cardiovascular, lung, infectious, and metabolic diseases. Thus, reducing tobacco smoking will bring benefits in heart disease, neonatal and maternal health, stroke, and peripheral vascular disease as well as a variety of cancers, while dietary advice appropriate to cancer risk reduction will bring benefits in diabetes, stroke, kidney, and heart disease.

Biofilm hydrous manganese oxyhydroxides and metal dynamics in acid rock drainage

Biofilms in shallow, tailings-associated acid rock drainage (ARD) accumulated metals from May to September, indicating scavenging is stable within these biological solids over seasonal time frames. Results indicate a doubling (Mn, Cr) to over a 6-fold increase (Ni, Co) in biofilm metal concentrations. Biofilm oxygen and pH gradients measured over diel time scales with microelectrodes were observed to be both spatially and temporally variable, indicating that biofilms are highly dynamic geochemical environments. Biofilm metal retention and affinities were element specific indicating different processes control their sequestration. Metals were specifically scavenged by the organic constituents of the biofilm itself (Ni, Co) and associated biominerals of amorphous Mn oxyhydroxides (HMO; Ni, Co, and Cr). Results are consistent with sorption and coprecipitation processes controlling Ni and Co biofilm association, while Cr dynamics appear linked to those of Mn through redox processes. Biofilm HMO concentrations increased seasonally but showed significant diel fluctuations, indicating that both formation and dissolution processes occurred over rapid time scales in these biofilms. Biofilm HMO concentrations increased nocturnally but decreased during daylight hours to late afternoon minima. Under the geochemical conditions of the streams, observed HMO formation rates can only be explained by microbial catalysis. These results are the first to quantitatively examine microbial biofilm metal dynamics using microscale, geochemical techniques at both diel and seasonal time scales. They provide strong evidence for the significant role that microbial activity can play in metal geochemistry in natural environments.

Chromate content versus particle size for aircraft paints

Many industries rely on the corrosion inhibiting properties of chromate-containing primer paints to protect metal from oxidation. However, chromate contains hexavalent chromium (Cr(6+)), a known human carcinogen. The concentration of Cr(6+) as a function of paint particle size has important implications to worker health and environmental release from paint facilities. This research examines Cr(6+) content as a function of particle size for three types of aircraft primer paints: solvent-based epoxy-polyamide, water-based epoxy-polyamide, and solvent-based polyurethane. Cascade impactors were used to collect and separate paint particles based on their aerodynamic diameter, from 0.7 to 34.1 microm. The mass of the dry paint collected at each stage was determined and an atomic absorption spectrometer was used to analyze for Cr(6+) content. For all three paints, particles less than 7.0 microm contained disproportionately less Cr(6+) per mass of dry paint than larger particles, and the Cr(6+)concentration decreased substantially as particle size decreased. The smallest particles, 0.7 to 1.0 microm, contained approximately 10% of the Cr(6+) content, per mass of dry paint, compared to particles larger than 7.0 microm. The paint gun settings of air to paint ratio was found to have no influence on the Cr(6+) bias.

Chromate dissociation from three types of paint particles

Chromate-containing primer paints are used to inhibit corrosion on metal surfaces. Though chromate contains hexavalent chromium (Cr(6+)), a human carcinogen, there is little epidemiological evidence of increased lung cancer among spray painters. One reason may be that the paint matrix hinders the release of Cr(6+) from the paint particle during the time that the particle is within the lungs. This study measures the mass of Cr(6+) released from particles originating from three types of paint particles: solvent-borne epoxy, water-borne epoxy, and polyurethane. Impingers were used to collect paint particles into water and particles were held in the water at rest for 1 and 24 h residence times. Particles were then separated from the water by centrifugation. The supernatant was tested for dissolved Cr(6+), which was compared to the total Cr(6+) (dissolved Cr(6+) plus Cr(6+) in particles). The mean fractions of Cr(6+) released into the water after 1 and 24 hours for each primer averaged: 70 and 85 (solvent epoxy), 74 and 84% (water epoxy), and 94 and 95% (polyurethane). Correlations between particle size and the fraction of Cr(6+) released indicate that smaller particles (<5 microm) release a larger fraction of Cr(6+) versus larger particles (>5 microm).

Evaluation of toxic and genotoxic potential of stabilized industrial waste and contaminated soils

Artificial aqueous samples (eluates, percolates, immersion waters) were obtained from contaminated soils and stabilized industrial wastes. The toxicity and genotoxicity of these aqueous fractions have been evaluated in vivo in the aquatic larvae of the amphibian Xenopus laevis. Four biotests have been applied: a test of subchronic toxicity and three biomakers: (1) measurement of the activity of ethoxyresorufine-o-dealkylase in the liver, (2) detection of DNA adducts in the liver and the blood, and (3) measurement of the rate of micronuclei in the erythrocytes. Biological datas were completed through a chemical analysis. The main conclusions of this study are: The importance of integrating different toxicity criterias into a biological battery (phenotypic and genotypic criterias). Some aqueous extracts did not seem to be very toxic, whereas their genotoxic effects were rather significant [e.g. the stabilized Municipal Solid Waste (MSW) ashes]. The importance of coupling together chemical and biological approaches to refine the impact. Actually, some eluates (lixiviation or percolation) coming from polluted soils appeared to be very poorly loaded with pollutants, whereas the toxic and genotoxic impact of these complex matrices were rather noticeable. In addition, when applying the leaching standardized procedure, the hazardous potential of the two analysed soils may be underestimated if the results on percolates and on eluates have been compared. This study highligths the importance of coupling the tools of characterization and preparation of samples to be analysed according to the objectives to be reached.

Chromate concentration bias in primer paint particles

Chromate-containing primer paints are used to prevent corrosion on metal surfaces. Chromate contains hexavalent chromium (Cr6+), a human carcinogen. The objective of this research was to determine if there is a bias in the fraction of chromate found in various particle sizes generated during primer painting operations. A solvent-based, aviation primer paint was sprayed using a high-volume, low-pressure spray gun. Paint particles were collected and separated by size with seven-stage cascade impactors. It was determined that particles with a mass aerodynamic diameter < 2.0 microm contained significantly less Cr6+ per dry weight of paint than particles > 2.0 microm (P < 0.001). The median concentration of Cr6+ in particles < 2.0 microm is 18 micro g of Cr/mg of dry paint and the median concentration for particles > 2.0 microm is 70 microg of Cr/mg of dry paint. The mixed paint contains 18.75% strontium chromate, which equates to a ratio of 67 microg of Cr/mg of dry paint. Particles > 2.0 microm are more likely to impact in the upper tracheobronchial regions of the lung where mucociliary clearance is relatively rapid. Additionally, chromate emissions from spraying operations may be overestimated because larger particles, which are more easily trapped on an air filter, contain more chromate than the smaller particles, which are more likely to bypass an air filter.

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.