Health risk assessment of chlorobenzenes in the air of residential houses using probabilistic techniques

Concentrations, profiles, emission inventory, and risk assessment of chlorinated benzenes in bottom ash and fly ash of municipal and medical waste incinerators in northern Vietnam

Concentrations and congener profiles of seven di- to hexachlorinated benzenes (CBzs) were characterized in bottom ash and fly ash samples collected simultaneously from one medical waste incinerator (MEWI) and one municipal waste incinerator (MUWI) in northern Vietnam. Total concentrations of seven CBzs in the fly ash samples ranged from 6.98 to 34.4 (median 19.1) ng g^-1 in the MEWI, and ranged from 59.1 to 391 (median 197) ng g^-1 in the MUWI. Concentrations of CBzs in the bottom ash samples of the MEWI (median 1.95; range 1.53-5.98 ng g^-1) were also lower than those measured in the MUWI samples (median 17.4; range 14.5-42.6 ng g^-1). Levels of CBzs in the fly ash samples were significantly higher than concentrations measured in the bottom ash samples, partially indicating the low-temperature catalytic formation of these pollutants in post-combustion zone. In general, higher chlorinated congeners (e.g., hexachlorobenzene, pentachlorobenzene, and 1,2,4,5-tetrachlorobenzene) were more abundant than lower chlorinated compounds. However, compositional profiles of CBzs were different between the ash types and incinerators and even between the same sample types of different sampling days, suggesting that the formation of CBzs in these incinerators is complicated and influenced by many factors. Emission factors and annual emission amounts of CBzs were estimated for the two incinerators by using actually measured data of CBz concentrations in the ash. Daily intake doses and cancer risks of ash-bound CBzs estimated for workers in the two incinerators were generally lower than critical values, but cancer risks caused by other relevant pollutants (e.g., polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and dioxin-related compounds) were not considered.

Ethylene glycol assisted synthesis of hierarchical Fe-ZSM-5 nanorods assembled microsphere for adsorption Fenton degradation of chlorobenzene

A unique zeolite catalyst, Fe doped ZSM-5 microsphere assembled by uniform nanorod-like crystals with hierarchical pore structure, was successfully synthesized and applied for the adsorption and degradation of trace chlorobenzene (CB) in the presence of H₂O₂. The organic ferric salts as the precursors, ethylene glycol as a chelating/reducing agent and the dynamic two-stage temperature-varied hydrothermal technique, together made the synthesized hierarchical Fe-ZSM-5 nanorods assembled microspheres (FZ-CA-5EG) to be characterized by abundant highly dispersed and valency-controlled framework Fe^3+/2+ species. As a result of these features, the FZ-CA-5EG showed excellent ability of adsorption and degradation efficiency of CB, and enhanced durability due to negligible leaching of framework Fe species. Moreover, the hydroxyl radicals were determined as the main the reactive oxygen species of CB oxidation degradation, and a possible adsorption-oxidation degradation pathway was proposed.

A novel highly selective electrochemical chlorobenzene sensor based on ternary oxide RuO2/ZnO/TiO2 nanocomposites

A novel electrochemical (EC) chlorobenzene (CBZ) sensor was fabricated using a ternary oxide RuO₂/ZnO/TiO₂ nanocomposite (NC)-decorated glassy carbon electrode (GCE). The nanoparticles (NPs) were synthesized by a wet-chemical method and characterized by X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and ultraviolet-visible (UV-vis) spectroscopy. The synthesized RuO₂/ZnO/TiO₂ NC was layered as thin film on a GCE with Nafion (5% suspension in ethanol) adhesive, and the as-prepared sensor was subjected to CBZ analysis using an electrochemical approach. The calibration of the proposed CBZ sensor was executed with a linear relation of current versus concentration of CBZs known as the calibration curve. The sensitivity (32.02 μA μM⁻¹ cm⁻²) of the CBZ sensor was calculated from the slope of the calibration curve by considering the active surface area of the GCE (0.0316 cm²). The lower detection limit (LD; 98.70 ± 4.90 pM) was also calculated at a signal-to-noise ratio of 3. Besides these, the response current followed a linear relationship with the concentration of chlorobenzene and the linear dynamic range (LDR) was denoted in the range of 0.1 nM to 1.0 μM. Moreover, the CBZ sensor was found to exhibit good reproducibility, reliability, stability, and fast response time. Finally, the sensing mechanism was also discussed with the energy-band theory of ternary doped semiconductor materials. The sensing activity of the proposed sensor was significantly enhanced due to the combined result of depletion layer formation at the heterojunction of RuO₂/ZnO/TiO₂ NCs as well as the activity of RuO₂ NPs as oxidation catalysts. The proposed CBZ sensor probe based on ternary oxide RuO₂/ZnO/TiO₂ NCs was developed with significant analytical parameters for practical application in monitoring the environmental pollutants of CBZs for the safety of environmental fields on a large scale.

A novel electrochemical (EC) chlorobenzene (CBZ) sensor was fabricated using a ternary oxide RuO₂/ZnO/TiO₂ nanocomposite (NC)-decorated glassy carbon electrode (GCE).

Use of toxicant sensitivity distributions (TSD) for development of exposure guidelines for risk to human health from benzene

This technique for setting guideline values differs from that currently used by regulatory agencies throughout the world. Data for benzene were evaluated from epidemiological studies on human populations (29 studies). Exposure durations were evaluated in terms of Long Term Exposure (LTE) and Lifetime Exposure. All data was reported as Lowest Observed Adverse Effect Levels (LOAEL) and converted into exposure doses using Average Daily Dose (ADD) and Lifetime Average Daily Dose (LADD). These values were plotted as a Toxicant Sensitivity Distribution (TSD) which was the cumulative probability of LOAEL-ADD and LOAEL-LADD. From the TSD plots, linear regression equations gave correlation coefficients (R²) ranging from 0.69 to 0.97 indicating normal distributions. Guideline Values (GVs) for LTE (8hr/day) and Lifetime (24hr/70yrs) exposure to benzene were calculated using data from human epidemiological studies as 5% level of cumulative probability (CP) of LOAEL-ADD and LOAEL-LADD from the cumulative probability distributions (CPD). The derived guideline values from the human epidemiological studies were 92 μg/kg/day for LTE and 3.4 μg/kg/day for lifetime exposure. GV for LTE is appropriate for occupational exposure and GV derived for lifetime exposure appropriate for the general population. The guideline value for occupational exposure limit was below all the guideline values developed by regulatory agencies. But the general population guideline is within the range of values formulated by European Union, ATSDR, EPAQS, USEPA and OEHHA for air quality for the general population. This is an alternative method which eliminates the application of safety factors and other sources of errors in deriving guideline values for benzene.

Health risk assessment for exposure to benzene in petroleum refinery environments

The health risk resulting from benzene exposure in petroleum refineries was calculated using data from the scientific literature from various countries throughout the world. The exposure data was collated into four scenarios from petroleum refinery environments and plotted as cumulative probability distributions (CPD) plots. Health risk was evaluated for each scenario using the Hazard Quotient (HQ) at 50% (CEXP50) and 95% (CEXP95) exposure levels. Benzene levels were estimated to pose a significant risk with HQ50 > 1 and HQ95 > 1 for workers exposed to benzene as base estimates for petroleum refinery workers (Scenario 1), petroleum refinery workers evaluated with personal samplers in Bulgarian refineries (Scenario 2B) and evaluated using air inside petroleum refineries in Bulgarian refineries (Scenario 3B). HQ50 < 1 were calculated for petroleum refinery workers with personal samplers in Italian refineries (Scenario 2A), air inside petroleum refineries (Scenario 3A) and air outside petroleum refineries (Scenario 4) in India and Taiwan indicating little possible adverse health effects. Also, HQ95 was < 1 for Scenario 4 however potential risk was evaluated for Scenarios 2A and 3A with HQ95 > 1. The excess Cancer risk (CR) for lifetime exposure to benzene for all the scenarios was evaluated using the Slope Factor and Overall Risk Probability (ORP) methods. The result suggests a potential cancer risk for exposure to benzene in all the scenarios. However, there is a higher cancer risk at 95% (CEXP95) for petroleum refinery workers (2B) with a CR of 48,000 per 106 and exposure to benzene in air inside petroleum refineries (3B) with a CR of 28,000 per 106.

Health risk assessment of ambient air concentrations of benzene, toluene and xylene (BTX) in service station environments

A comprehensive evaluation of the adverse health effects of human exposures to BTX from service station emissions was carried out using BTX exposure data from the scientific literature. The data was grouped into different scenarios based on activity, location and occupation and plotted as Cumulative Probability Distributions (CPD) plots. Health risk was evaluated for each scenario using the Hazard Quotient (HQ) at 50% (CEXP50) and 95% (CEXP95) exposure levels. HQ50 and HQ95 > 1 were obtained with benzene in the scenario for service station attendants and mechanics repairing petrol dispensing pumps indicating a possible health risk. The risk was minimized for service stations using vapour recovery systems which greatly reduced the benzene exposure levels. HQ50 and HQ95 < 1 were obtained for all other scenarios with benzene suggesting minimal risk for most of the exposed population. However, HQ50 and HQ95 < 1 was also found with toluene and xylene for all scenarios, suggesting minimal health risk. The lifetime excess Cancer Risk (CR) and Overall Risk Probability for cancer on exposure to benzene was calculated for all Scenarios and this was higher amongst service station attendants than any other scenario.

Biodegradation of chlorobenzene, 1,2-dichlorobenzene, and 1,4-dichlorobenzene in the vadose zone

Much of the microbial activity in nature takes place at interfaces, which are often associated with redox discontinuities. One example is the oxic/anoxic interface where polluted groundwater interacts with the overlying vadose zone. We tested whether microbes in the vadose zone can use synthetic chemicals as electron donors and thus protect the overlying air and buildings from groundwater pollutants. Samples from the vadose zone of a site contaminated with chlorobenzene (CB), 1,2-dichlorobenzene (12DCB), and 1,4-dichlorobenzene (14DCB) were packed in a multiport column to simulate the interface of the vadose zone with an underlying groundwater plume. A mixture of CB, 12DCB, and 14DCB in anoxic water was pumped continuously through the bottom of column to an outlet below the first sampling port to create an oxic/anoxic interface and a capillary fringe. Removal to below the detection limits by rapid biodegradation with rates of 21 ± 1 mg of CB • m(-2) • d(-1), 3.7 ± 0.5 mg of 12DCB • m(-2) • d(-1), and 7.4 ± 0.7 mg of 1.4 DCB • m(-2) • d(-1) indicated that natural attenuation in the capillary fringe can prevent the migration of CB, 12DCB, and 14DCB vapors. Enumeration of bacteria capable of degrading chlorobenzenes suggested that most of the biodegradation takes place within the first 10 cm above the saturated zone. Biodegradation also increased the upward flux of contaminants and thus enhanced their elimination from the underlying water. The results revealed a substantial biodegradation capacity for chlorinated aromatic compounds at the oxic/anoxic interface and illustrate the role of microbes in creating steep redox gradients.

Concentrations and risks of p-dichlorobenzene in indoor and outdoor air

p-dichlorobenzene (PDCB) is a chlorinated volatile organic compound that can be encountered at high concentrations in buildings owing to its use as pest repellent and deodorant. This study characterizes PDCB concentrations in four communities in southeast Michigan. The median concentration outside 145 homes was 0.04 μg/m(3), and the median concentration inside 287 homes was 0.36 μg/m(3). The distribution of indoor concentrations was extremely skewed. For example, 30% of the homes exceeded 0.91 μg/m(3), which corresponds to a cancer risk level of 10(-5) based on the California unit risk estimate, and 4% of homes exceeded 91 μg/m(3), equivalent to a 10(-3) risk level. The single highest measurement was 4100 μg/m(3). Estimates of whole-house emission rates were largely consistent with chamber test results in the literature. Indoor concentrations that exceed a few μg/m(3) indicate the use of PDCB products. PDCB concentrations differed among households and the four cities, suggesting the importance of locational, cultural, and behavioral factors in the use patterns of this chemical. The high PDCB levels found suggest the need for policies and actions to lower exposures, for example, sales or use restrictions, improved labeling, and consumer education.

PRACTICAL IMPLICATIONS

Distributions of p-dichlorobenzene concentrations in residences are highly right-skewed, and a subset of houses has very elevated concentrations that are equivalent to an excess cancer risk of 10(-3) or higher based on the California unit risk effect estimate. House-to-house variation is large, reflecting differences in use practices. Stronger policies and educational efforts are needed to eliminate or modify indoor usage practices of this chemical.

Emissions of p-dichlorobenzene and naphthalene from consumer products

p-Dichlorobenzene (p-DCB) and naphthalene are classified as hazardous air pollutants and rank highly among chronic chemical hazards in US. residences. Sources of p-DCB and naphthalene include moth repellents and deodorizers typically used in closets, garment bags, and toilet bowls. Nearly pure concentrations of p-DCB and naphthalene are found in these products. p-DCB and naphthalene mass emission rates were determined for four different products placed in well-ventilated laboratory chambers as well as closets in a test house and in a garment bag. Concentrations were measured in bedrooms adjacent to closets where products were used. Emission rates varied considerably between products that contain p-DCB, primarily due to product packaging, and were generally suppressed when the product was used in closed closet or garments bags relative to products placed in well-ventilated chambers. This reduction appears to be due to lower air speeds in closets and garment bags as opposed to chemical accumulation. Variations in air temperature within typical ranges observed in homes can significantly influence emission rates of p-DCB and naphthalene. Concentrations of p-DCB and naphthalene in bedrooms adjacent to closets where moth repellents are used can exceed or approach odor thresholds. For this study, the concentrations exceeded or were within the upper few percentiles of those previously reported in residential indoor air. Based on a comparison of whole-house emission rates derived in a previous study, it appears that somewhere between 2% and 12% of homes in that study had active sources of p-DCB and between 5% and 15% had active sources of naphthalene.

IMPLICATIONS

Inhalation of p-DCB and naphthalene has been linked to several health effects. Several off-the-shelf consumer products are nearly pure p-DCB or naphthalene, thus leading to potential for high emission rates and gas-phase concentrations in indoor environments where such products are used. Knowledge of p-DCB and naphthalene emission rates and variability in emissions with environmental conditions should provide for improvements in predictions of indoor concentrations of these compounds, which are in turn needed to complete exposure and inhalation risk assessments.

An overall risk probability-based method for quantification of synergistic and antagonistic effects in health risk assessment for mixtures: theoretical concepts

PURPOSE

In the assessment of health risks of environmental pollutants, the method of dose addition and the method of independent action are used to assess mixture effects when no synergistic and/or antagonistic effects are present. Currently, no method exists to quantify synergistic and/or antagonistic effects for mixtures. The purpose of this paper is to develop the theoretical concepts of an overall risk probability (ORP)-based method to quantify the synergistic and antagonistic effects in health risk assessment for mixtures.

METHOD

The ORP for health effects of environmental chemicals was determined from the cumulative probabilities of exposure and effects. This method was used to calculate the ORP for independent mixtures and for mixtures with synergistic and antagonistic effects.

RESULTS

For the independent mixtures, a mixture ORP can be calculated from the product of the ORPs of individual components. For systems of interacting mixtures, a synergistic coefficient and an antagonistic coefficient were defined respectively to quantify the ORPs of each individual component in the mixture. The component ORPs with synergistic and/or antagonistic effects were then used to calculate the total ORP for the mixture.

CONCLUSIONS

An ORP-based method was developed to quantify synergistic and antagonistic effects in health risk assessment for mixtures. This represents a first method to generally quantify mixture effects of interacting toxicants.

Health risk characterisation for environmental pollutants with a new concept of overall risk probability

In health risk assessment, risk is commonly characterised by calculating a simple hazard quotient (HQ), which cannot reflect the actual distribution of exposure and health effect values. This study aimed to develop a new risk characterisation method, the overall risk probability (ORP) method based on probabilistic techniques. Exposure exceedence values were calculated to obtain an exposure exceedence curve (EEC). The area under the EEC was calculated as the ORP value to represent the risk. This method was demonstrated by a case study for two steroidal EDCs, 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) for fish in surface water. It was found that the risk probability of fish exposed to E2 (ORP, 8.1%) and EE2 (ORP, 27%) were both above the reference value of 2.5%, which was consistent with the results of HQ method. Assuming independent action of individual EDCs, a combined risk probability of 33% was obtained for the mixture effects of E2 and EE2. Our results implicated that the adverse health effects imposed by E2 and EE2 were significant for fish in surface water worldwide.

Fate simulation and risk assessment of endocrine disrupting chemicals in a reservoir receiving recycled wastewater

A fugacity based model was applied to simulate the distribution of three endocrine disrupting chemicals (EDCs), namely estrone (E1), 17β-estradiol (E2) and 17α-ethynylestradiol (EE2) in a reservoir receiving recycled wastewater in Australia. At typical conditions, the majority of estrogens were removed by degradation in the water compartment. A sensitivity analysis found that the simulated concentrations of E1, E2 and EE2 were equally sensitive to the parameters of temperature (T), reservoir water volume (V) and equivalent biomass concentration (EBC), but E1 was more sensitive to estrogen concentration in the recycled water (C(e)) and recycling rate (F(r)). In contrast, all three estrogens were not sensitive to reservoir water releasing rate (F(d)). Furthermore, a probabilistic health risk assessment showed that the simulated concentrations were below fish exposure threshold value (ETV) and human public health standard (PHS). Human equivalent dose of EDCs from fish consumption was about 10 times higher than that from drinking water consumption. The highest risk quotient among the three estrogens was found for EE2 with less than 9.5×10(-2), implying negligible health risks.

Effects of occupational exposure to 1,4-dichlorobenzene on hematologic, kidney, and liver functions

PURPOSE

To investigate the effects of 1,4-dichlorobenzene (1,4-DCB) on kidney, liver, and hematological functions of workers in insect repellent factories in Taiwan.

METHODS

A cross-sectional study was performed comparing 46 exposed workers and 29 non-exposed workers. Health information was collected using questionnaires and biochemical tests. The concentration of urinary 2,5-dichlorophenol (2,5-DCP), the major metabolite of 1,4-DCB, was analyzed by gas chromatography with electron-capture detection.

RESULTS

Urinary 2,5-DCP concentration, white blood cell (WBC) count, and serum alanine aminotransferase (ALT) level were higher in exposed workers than in non-exposed ones (P < 0.05). Furthermore, the WBC count and ALT level were significantly correlated with the concentration of 2,5-DCP in urine (P < 0.05). The blood urea nitrogen was significantly higher in on-site exposed workers (P < 0.05). Urinary 2,5-DCP concentration was significantly lower in workers who wore personal protective equipment (PPE) during work than in those who did not (P < 0.05).

CONCLUSIONS

The higher urinary 2,5-DCP concentration in exposed (105.38 μg/L) than non-exposed (1.08 μg/L) workers suggests that 1,4-DCB exposure may increase the 2,5-DCP concentration in urine. Moreover, exposure to 1,4-DCB may also increase WBC count and ALT activity, and PPE may protect workers from 1,4-DCB exposure.