Assessment of health risks due to hazardous air pollutant emissions from electric utilities

Exposure to intranasal chromium triggers dose and time-dependent behavioral and neurotoxicological defects in rats

The extensive recorded environmental and occupational dispersal of hexavalent chromium (CrVI) dust contributes to an increased interest in its toxicological consequences. A previous study of our team described a brain injury induced by acute intranasal instillation of Cr(VI) in rats, which was characterized by oxidative stress and inflammation. This proposed a high risk of brain damage among Cr(VI) exposed individuals either environmentally or occupationally especially through the nasal cavity. Accordingly, the main aim of this study was to evaluate the effects of subacute/subsubacute/subchronic exposure to intranasal potassium dichromate (inPDC) solution in three dose levels (0.125, 0.25, or 0.5 mg/kg/day for five successive days/week) for 3 different intervals/dose: two weeks, one month, and two months, on the brain of rats. The rats were sacrificed 24 h following the last inPDC dose. The locomotor activity, motor coordination, and object recognition behavior of the rats have been measured. Evaluation of oxidative stress; evidenced by lipid peroxidation and reduced glutathione, and inflammatory markers; evidenced by interleukin 1-beta in the brain tissues, as well as the brain PI3K and PKB contents were performed. Furthermore, the brain anti-glial fibrillary acidic protein (GFAP); marker of neurotoxicity was assessed immunohistochemically. Brain histopathological alterations were also studied. The findings of the current study revealed a dose- and time-dependent inPDC-induced brain toxicity in rats, as displayed by the biochemical, immunohistochemical and histopathological evaluation. Behaviorally, the major toxic effects of inPDC were observed on the locomotor and cognition functions, however, minor effects were observed on the motor coordination. The results suggest that short-term exposure to intranasal Cr(VI), in theses doses, does not trigger a major brain injury in rats; however, observation of more toxic alterations in a time-dependent manner is a threat of more sever toxicity upon longer exposure.

Intranasal Chromium Induces Acute Brain and Lung Injuries in Rats: Assessment of Different Potential Hazardous Effects of Environmental and Occupational Exposure to Chromium and Introduction of a Novel Pharmacological and Toxicological Animal Model

Chromium (Cr) is used in many industries and it is widely distributed in the environment. Exposure to Cr dust has been reported among workers at these industries. Beside its hazardous effects on the lungs, brain injury could be induced, as the absorption of substances through the nasal membrane has been found to provide them a direct delivery to the brain. We investigated the distribution and the effects of Cr in both brain and lung following the intranasal instillation of potassium dichromate (inPDC) in rats. Simultaneously, we used the common intraperitoneal (ipPDC) rat model of acute Cr-toxicity for comparison. Thirty male Wistar rats were randomly allocated into five groups (n = 6); each received a single dose of saline, ipPDC (15 mg/kg), or inPDC in three dose levels: 0.5, 1, or 2 mg/kg. Locomotor activity was assessed before and 24 h after PDC administration, then, the lungs and brain were collected for biochemical, histopathological, and immunohistochemical investigations. Treatment of rats with ipPDC resulted in a recognition of 36% and 31% of the injected dose of Cr in the brain and lung tissues, respectively. In inPDC-treated rats, targeting the brain by Cr was increased in a dose-dependent manner to reach 46% of the instilled dose in the group treated with the highest dose. Moreover, only this high dose of inPDC resulted in a delivery of a significant concentration of Cr, which represented 42% of the instilled dose, to the lungs. The uppermost alteration in the rats locomotor activity as well as in the brain and lung histopathological features and contents of oxidative stress biomarkers, interleukin-1β (IL-1β), phosphorylated protein kinase B (PKB), and cyclooxygenase 2 (COX-2) were observed in the rats treated with inPDC (2 mg/kg). The findings revealed that these toxic manifestations were directly proportional to the delivered concentration of Cr to the tissue. In conclusion, the study showed that a comparably higher concentrations of Cr and more elevated levels of oxidative stress and inflammatory markers were observed in brain and lung tissues of rats subjected to inPDC in a dose that is just 0.13 that of ipPDC dose commonly used in Cr-induced toxicity studies. Therefore, the study suggests a high risk of brain-targeting injury among individuals environmentally or occupationally exposed to Cr dust, even in low doses, and an additional risk of lung injury with higher Cr concentrations. Moreover, the study introduces inPDC (2 mg/kg)-instillation as a new experimental animal model suitable to study the acute brain and lung toxicities induced by intranasal exposure to Cr compounds.

Emissions and risks associated with oxyfuel combustion: state of the science and critical data gaps

Oxyfuel combustion is a promising technology that may greatly facilitate carbon capture and sequestration by increasing the relative CO2 content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants (e.g., acid gases, particulates, metals and organics) is not well studied. It is possible that combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry (e.g., by changing the valence state of metals). The data available for addressing these concerns are quite limited and are typically derived from laboratory-scale or pilot-scale tests. A review of the available data does suggest that oxyfuel combustion may decrease the air emissions of some pollutants (e.g., SO2, NO(x), particulates) whereas data for other pollutants are too limited to draw any conclusions. The oxy-combustion systems that have been proposed to date do not have a conventional "stack" and combustion flue gas is treated in such a way that solid or liquid waste streams are the major outputs. Use of this technology will therefore shift emissions from air to solid or liquid waste streams, but the risk management implications of this potential change have yet to be assessed. Truly useful studies of the potential effects of oxyfuel combustion on power plant emissions will require construction of integrated systems containing a combustion system coupled to a CO2 processing unit. Sampling and analysis to assess potential emission effects should be an essential part of integrated system tests.

IMPLICATIONS

Oxyfuel combustion may facilitate carbon capture and sequestration by increasing the relative CO2 content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants has not been well studied. Combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry. Therefore, before moving further with oxyfuel combustion as a new technology, it is appropriate to summarize the current understanding of potential emissions risk and to identify data gaps as priorities for future research.

Air pollution and health: emerging information on susceptible populations

Outdoor air pollution poses risks to human health in communities around the world, and research on populations who are most susceptible continues to reveal new insights. Human susceptibility to adverse health effects from exposure to air pollution can be related to underlying disease; demographic or anthropometric characteristics; genetic profile; race and ethnicity; lifestyle, behaviors, and socioeconomic position; and location of residence or daily activities. In health research, an individual or group may have an enhanced responsiveness to a given, identical level of pollution exposure compared to those who are less susceptible. Or, people in these different groups may experience varying levels of exposure (for example, a theoretically homogeneous population whose members differ only by proximity to a road). Often the information available for health research may relate to both exposure and enhanced response to a given dose of pollution. This paper discusses the general direction of research on susceptibility to air pollution, with a general though not an exclusive focus on particulate matter, with specific examples of research on susceptibility related to cardiovascular disease, diabetes, asthma, and genetic and epigenetic features. We conclude by commenting how emerging knowledge of susceptibility can inform policy for controlling pollution sources and exposures to yield maximal health benefit and discuss two areas of emerging interest: studying air pollution and its connection to perinatal health, as well as land use and urban infrastructure design.

Strategies for chromium bioremediation of tannery effluent

Bioremediation offers the possibility of using living organisms (bacteria, fungi, algae,or plants), but primarily microorganisms, to degrade or remove environmental contaminants, and transform them into nontoxic or less-toxic forms. The major advantages of bioremediation over conventional physicochemical and biological treatment methods include low cost, good efficiency, minimization of chemicals, reduced quantity of secondary sludge, regeneration of cell biomass, and the possibility of recover-ing pollutant metals. Leather industries, which extensively employ chromium compounds in the tanning process, discharge spent-chromium-laden effluent into nearby water bodies. Worldwide, chromium is known to be one of the most common inorganic contaminants of groundwater at pollutant hazardous sites. Hexavalent chromium poses a health risk to all forms of life. Bioremediation of chromium extant in tannery waste involves different strategies that include biosorption, bioaccumulation,bioreduction, and immobilization of biomaterial(s). Biosorption is a nondirected physiochemical interaction that occurs between metal species and the cellular components of biological species. It is metabolism-dependent when living biomass is employed, and metabolism-independent in dead cell biomass. Dead cell biomass is much more effective than living cell biomass at biosorping heavy metals, including chromium. Bioaccumulation is a metabolically active process in living organisms that works through adsorption, intracellular accumulation, and bioprecipitation mechanisms. In bioreduction processes, microorganisms alter the oxidation/reduction state of toxic metals through direct or indirect biological and chemical process(es).Bioreduction of Cr6+ to Cr3+ not only decreases the chromium toxicity to living organisms, but also helps precipitate chromium at a neutral pH for further physical removal,thus offering promise as a bioremediation strategy. However, biosorption, bioaccumulation, and bioreduction methods that rely on free cells for bioremediation suffer from Cr6 toxicity, and cell damage. Therefore, immobilization of microbial cell biomass enhances bioremediation and renders industrial bioremediation processes more economically viable from reduced free-cells toxicity, easier separation of biosorbents from the tannery effluent, ability to achieve multiple biosorption cycles, and desorption (elution) of metal(s) from matrices for reuse. Thus, microbial bioremediation can be a cost competitive strategy and beneficial bioresource for removing many hazardous contaminants from tannery and other industrial wastes.

Is PM More Toxic Than the Sum of Its Parts? Risk-Assessment Toxicity Factorsvs.PM-Mortality “Effect Functions”

Epidemiology studies of populations living in areas with good air quality report correlations between levels of ambient particulate matter (PM) and mortality rates. These associations occur at low PM concentrations that are below current air quality standards. Can such concentrations cause mortality, given the toxicity of PM chemical constituents? We examined chemical-specific, dose-response data typically used in U.S. EPA human health risk assessments. These assessments rely on established, no-effect thresholds for noncancer health endpoints. We found that chemicals identified as constituents of ambient PM are present at concentrations considerably below the regulatory thresholds used in risk assessment (i.e., below the RfCs and RfDs that identify levels for which no adverse health effects are anticipated). From the perspective of risk assessment, exposure to the concentrations of chemicals in ambient PM (e.g., sulfate, nitrate, and elemental carbon) cannot be expected to cause death. Hence, the health effects attributed to ambient PM in "regulatory impact analyses" appear to be at odds with what would be predicted from a standard U.S. EPA health-risk assessment for PM chemicals. Four possible resolutions of this paradox are that (1) the mixtures of chemicals present in ambient PM are vastly more toxic than the sum of individual components, (2) small portions of the general population are vastly more sensitive to certain ambient PM chemicals than reflected in U.S. EPA toxicity factors, (3) the toxicity of ambient PM is unrelated to its chemical constituents, or (4) PM mass concentration is not the causal factor in the reported associations. The associations may arise because ambient PM concentrations (1) are a surrogate for unmeasured copollutants (e.g., HAPs), (2) covary with confounding factors that cannot be fully controlled (e.g., weather, demographics), or (3) covary with unmeasured (e.g., societal, behavioral, or stress) factors.

Single pollutant versus surrogate measure approaches: do single pollutant risk assessments underestimate the impact of air pollution on lung cancer risk?

Cancer risk as a result of air pollution may be quantified by different approaches. We compared the sum of unit risk based effects of single pollutants with an epidemiology-based method by using PM(10) as a surrogate of the total air pollution. The excess rate for lung cancer cases attributable to an increase of 10 microg/m3 in average PM(10) exposure was estimated from available cohort studies. Applying the epidemiology-based risk method to the air pollution situation in the Basel area (Switzerland) resulted in 13.3 (95% CI = 6.9-19.8) excess lung cancer cases per 100,000 person years. This estimate was considerably higher than the unit risk-based estimate yielding 1.1 (range, 0.45-2.8) cancer cases per 100,000 person years. We discuss these discrepancies in light of inherent differences between approaches in toxicology and epidemiology.

Developments in terrestrial bacterial remediation of metals

Recent advances in understanding the role and application of bacteria to the remediation of toxic metal and radionuclide contaminated terrestrial environments have come from several avenues. Novel species capable of mobilization and immobilization of metal ions have been discovered. Remediation of toxicity has been accelerated by nutrient amendment, the use of chelating agents and novel methods for phosphate amendment. Major advances in the use of natural and genetically engineered species for bioprotection and remediation of organic co-contaminants have been reported. Construction of wetland function continues to be developed for containment and decontamination of wastewaters.

Characterization of risks posed by combustor emissions

Risk characterization is the final step of the risk assessment process as practiced in the U.S. EPA. In risk characterization, the major scientific evidence and "bottom-line" results from the other components of the risk assessment process, hazard identification, dose-response assessment, and exposure assessment, are evaluated and integrated into an overall conclusion about the risks posed by a given situation. Risk characterization is also an iterative process; the results of a specific step may require re-evaluation or additional information to finalize the risk assessment process. Risks posed by atmospheric emissions are an example of an involuntary human health risk which typically receives a great deal of public attention. Characterization of the risks posed by atmospheric emissions typically requires the use of mathematical models to evaluate: 1) the environmental fate of emitted pollutants, 2) exposures to these pollutants, and 3) human dose-response. Integration of these models results in quantitative risk estimates. The confidence in a quantitative risk estimate is examined by evaluating uncertainty and variability within individual risk assessment components. Variability arises from the true heterogeneity in characteristics within a population or an event; on the other hand, uncertainty represents lack of knowledge about the true value used in a risk estimate. U.S. EPA's 1997 Mercury Study will illustrate some aspects of the risk characterization process as well as the uncertainty and variability encountered in the risk assessment process.