An assessment of the environmental fate and exposure of benzene and the chlorobenzenes in Canada

Transformation of chlorobenzene by Mn(III) generated in MnO2/organic acid systems

Chlorobenzene (CB) is a prevalent organic contaminant in water and soil environments. It presents high chemical stability and is resistant to both oxidation and reduction. In this study, we showed that CB was substantially removed by soluble Mn(III) produced during the reductive dissolution of colloidal MnO2 by naturally-occurring organic acids such as formate (FOR), oxalate (OX), and citrate (CIT). The removal rate was dependent on the physicochemical properties of organic acids. With strong electron-donating and coordination ability, OX and CIT promoted MnO2 dissolution and Mn(III) generation compared to FOR, but had adverse effects on the stability and reactivity of Mn(III). As a result, CB removal followed the order: MnO2/CIT > MnO2/FOR > MnO2/OX. Analysis of the transformation products showed that Mn(III) complexes acted as strong electrophiles, attacking the ortho/para carbons of the benzene ring and transforming CB to chlorophenols via an electrophilic substitution mechanism. The theoretical foundation of this proposed reaction mechanism was supplemented by quantum mechanical calculations. Together, the findings of this study provide new insights into the transformation of CB in natural environments and hold the potential to offer a novel strategy for the development of manganese oxide/ligand systems for CB elimination.

Computational models to confront the complex pollution footprint of plastic in the environment

The threat posed by plastic in the environment is poorly characterized due to uncertainties and unknowns about sources, transport, transformation and removal processes, and the properties of the plastic pollution itself. Plastic creates a footprint of particulate pollution with a diversity of composition, size and shape, and a halo of chemicals. In this Perspective, we argue that process-based mass-balance models could provide a platform to synthesize knowledge about plastic pollution as a function of its measurable intrinsic properties.

Estimating household exposure to moth repellents p-dichlorobenzene and naphthalene and the relative contribution of inhalation pathway in a sample of Japanese children

p-Dichlorobenzene (DCB) and naphthalene (NP) used as moth repellents in indoor environments are suspected to be carcinogenic. To evaluate their adverse effects on health with chronic exposure in the general population, especially children, we need to know their amounts absorbed by the body and the relationships between their amounts and air quality in residences. At present, little is known worldwide about them. This study examined the daily intakes of DCB and NP by Japanese children via all exposure pathways and the contribution of indoor air quality to the intakes. First-morning void urine samples from the subjects aged 6 to 15 years and air samples in their bedrooms were collected. Airborne NP and DCB and their urinary metabolites were measured. Significant correlations were detected between their airborne concentrations and the urinary excretion amounts of their corresponding metabolites. The absorption amounts of DCB and NP by inhalation of the children while at home were calculated to be 26 and 2.0 ng/kg b.w./h, respectively, as median values. The daily intake was estimated to be 2.4 and 0.90 μg/kg b.w./d (median), respectively. The fractions (median) of inhalation absorption amounts to overall absorption amounts for DCB and NP were 30% and 5%, respectively. In children living in residences where the indoor air concentrations of these compounds were more than half the level of each guideline value for indoor air quality, the main exposure route for their absorption was considered to be inhalation while at home. The indoor concentrations of DCB exceeded the lifetime excess cancer risk level of 10^-4 in 22% of the residences and 10^-3 in 9% of them. Our findings indicate the need to further reduce airborne concentrations of DCB in Japanese residences to prevent its adverse effects on the health of Japanese children.

Quercetin attenuated the Benzene-induced hemato- and hepatotoxicity in mice

The protective effects of Quercetin (QCN) on Benzene (BNZ)-induced hemato- and hepatotoxicy were investigated. To reach this goal, 36 adult male mice were divided into 6 groups (n = 6). The control group was not exposed to BNZ, while animals in BNZ group were exposed to BNZ (30 ppm) and the animals of QCN group were received QCN (50 mg/kg, orally), the fourth, fifth and sixth groups were exposed to 30 ppm BNZ and received 10, 50 and 100 mg/kg QCN one h before the BNZ exposure, for 28 days. The day after the last exposure following anesthesia and the blood collection, the liver and femur tissues were collected. The bone marrow samples were extracted and subjected to micronucleus assay. The blood samples were processed for hematological and biochemical analyses. Histopathological examinations were performed on the liver samples. QCN reduced significantly (p < 0.05) the BNZ-elevated hepatic enzymes and ameliorated the BNZ-induced WBC and RBC reduction. The BNZ-elevated micronucleus percentage both in the bone marrow and peripheral blood was remarkably declined in the QCN-received groups. QCN improved the BNZ-induced histopathological changes and oxidative status in the liver and serum. Our results suggest that QCN could be a protective supplement to reduce the BNZ-induced hemato- and hepatotoxicities.

Analysis of Organochlorine Pesticide Residues in Various Vegetable Oils Collected in Chinese Markets

Organochlorine pesticides (OCPs), chemicals frequently used in agriculture, are a group of highly toxic and persistent organic pollutants. This study assesses the distribution and congener profiles of residual OCPs in 11 types of vegetable oils collected from Chinese markets. All samples were extracted using the modified QuEChERS method prior to analysis by gas chromatography-triple quadrupole mass spectrometry. The sesame oil samples had the highest concentration of OCPs, within the range of 15.30-59.38 ng/g, whereas the peanut oil samples had the lowest OCP concentrations, within the range of 10.83-35.65 ng/g. The possible effect of the processing technology on the pesticide residues in these vegetable oils was also evaluated. It was found that the pressing method leaves more OCPs in vegetable oils than the aqueous extraction and cold-pressing, but the result for leaching was not obvious. In light of the obtained results, it was estimated that the average daily intake of different pesticides is between 0.01 and 2.20 ng/kg bw/day for urban and rural households. Hence, it can be affirmed that, given the amount of the concentration of OCPs detected in the vegetable oils collected from Chinese markets, there are no obvious health risks for urban and rural households by intake.

Assessment of Industry-Induced Urban Human Health Risks Related to Benzo[a]pyrenebased on a Multimedia Fugacity Model: Case Study of Nanjing, China

Large amounts of organic pollutants emitted from industries have accumulated and caused serious human health risks, especially in urban areas with rapid industrialization. This paper focused on the carcinogen benzo[a]pyrene (BaP) from industrial effluent and gaseous emissions, and established a multi-pathway exposure model based on a Level IV multimedia fugacity model to analyze the human health risks in a city that has undergone rapid industrialization. In this study, GIS tools combined with land-use data was introduced to analyze smaller spatial scales so as to enhance the spatial resolution of the results. An uncertainty analysis using a Monte Carlo simulation was also conducted to illustrate the rationale of the probabilistic assessment mode rather than deterministic assessment. Finally, the results of the case study in Nanjing, China indicated the annual average human cancer risk induced by local industrial emissions during 2002–2008 (lowest at 1.99×10^–6 in 2008 and highest at 3.34×10^–6 in 2004), which was lower than the USEPA prescriptive level (1×10^–6–1×10^–4) but cannot be neglected in the long term.The study results could not only instruct the BaP health risk management but also help future health risk prediction and control.

Effects of input uncertainty and variability on the modelled environmental fate of organic pollutants under global climate change scenarios

Global climate change (GCC) is expected to influence the fate, exposure and risks of organic pollutants to wildlife and humans. Multimedia chemical fate models have been previously applied to estimate how GCC affects pollutant concentrations in the environment and biota, but previous studies have not addressed how uncertainty and variability of model inputs affect model predictions. Here, we assess the influence of climate variability and chemical property uncertainty on future projections of environmental fate of six polychlorinated biphenyl congeners under different GCC scenarios using a spreadsheet version of the ChemCAN model and the Crystal Ball® software. Regardless of emission mode, results demonstrate: (i) uncertainty in degradation half-lives dominates the variance of modelled absolute levels of PCB congeners under GCC scenarios; (ii) when the ratios of predictions under GCC to predictions under present day climate are modelled, climate variability dominates the variance of modelled ratios; and (iii) the ratios also indicate a maximum of about a factor of 2 change in the long-term average environmental concentrations due to GCC that is forecasted between present conditions and the period between 2080 and 2099. We conclude that chemical property uncertainty does not preclude assessing relative changes in a GCC scenario compared to a present-day scenario if variance in model outputs due to chemical properties and degradation half-lives can be assumed to cancel out in the two scenarios.

Theoretical study on thermochemical parameters and IR spectra of chlorinated isomers of nitrobenzene

Thermochemical and geometrical parameters and internal rotation barriers of all chlorinated nitrobenzene isomers were calculated with the G3MP2B3 composite method. Standard entropies, standard Gibbs free energies of formation, standard enthalpies of formation, and heat capacities were calculated and compared with their corresponding available experimental data. Our calculated enthalpy values agree well with the corresponding experimental data. The temperature dependence of entropy and heat capacity has been analysed. All isomers with ortho-chlorine substituents were found to be less stable than other corresponding isomers. Rotational barriers and distortions of the benzene rings were incorporated in the calculations of values for entropy and heat capacity. The IR spectra were calculated and found to be in reasonable agreement with the experimental spectra.

A dynamic multimedia environmental and bioaccumulation model for brominated flame retardants in Lake Huron and Lake Erie, USA

Polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) may pose a worldwide pollution problem because of their persistence, long-range transport capability, and predisposition to bioaccumulate. The ubiquitous presence of PBBs and PBDEs has heightened interest in determination of their fate. We report results for a fugacity-based dynamic environmental and bioaccumulation model of the fate of hexabromobiphenyl (hexaBB) discharged into the Saginaw Bay region of Lake Huron, USA. We calculated transient fugacity profiles of hexaBB in Lake Huron and Lake Erie water and sediment during the 1970s, 1980s, and 1990s. The hexaBB concentrations in the environmental compartments were used as inputs for a dynamic bioaccumulation model of Lake Huron and Lake Erie aquatic biota. The model results indicate that the sediment compartments of Lakes Huron and Erie serve as reservoirs for the accumulation and slow transfer of hexaBB to the food web constituents of these lakes. We present bioaccumulation factors (BAFs) and compare the predicted hexaBB concentrations in lake trout from the bioaccumulation model with measurements during the period 1980 to 2000. An uncertainty analysis for this model suggests that errors associated with input parameter uncertainty can be reduced by refining estimates of the sediment degradation half-life of hexaBB. The corroborated PBB model has carryover application for modeling the fate of polybrominated diphenyl ether (PBDE) contaminants in the Great Lakes. By fitting model outputs to field measurement data using the transformed least square fit method, we report estimations of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) emission rates into the Lake Huron and Lake Erie watershed areas.

ATSDR evaluation of potential for human exposure to benzene

As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of portions of the toxicological profile for benzene. The primary purpose of this article is to provide interested individuals with environmental information on benzene that includes production data, environmental fate, potential for human exposure, analytical methods, and a listing of regulations and advisories.

Microbial degradation of chlorinated benzenes

Chlorinated benzenes are important industrial intermediates and solvents. Their widespread use has resulted in broad distribution of these compounds in the environment. Chlorobenzenes (CBs) are subject to both aerobic and anaerobic metabolism. Under aerobic conditions, CBs with four or less chlorine groups are susceptible to oxidation by aerobic bacteria, including bacteria (Burkholderia, Pseudomonas, etc.) that grow on such compounds as the sole source of carbon and energy. Sound evidence for the mineralization of CBs has been provided based on stoichiometric release of chloride or mineralization of (14)C-labeled CBs to (14)CO(2). The degradative attack of CBs by these strains is initiated with dioxygenases eventually yielding chlorocatechols as intermediates in a pathway leading to CO(2) and chloride. Higher CBs are readily reductively dehalogenated to lower chlorinated benzenes in anaerobic environments. Halorespiring bacteria from the genus Dehalococcoides are implicated in this conversion. Lower chlorinated benzenes are less readily converted, and mono-chlorinated benzene is recalcitrant to biotransformation under anaerobic conditions.

Influence of the large grid size used in a multimedia mass balance model (POPsME) on the exposure assessment of polychlorinated dibenzo-p-dioxins and dibenzofurans

A multimedia mass balance model (MMM), POPsME, was evaluated for its performance to assess the fate and transport of 2,3,7,8-substituted PCDD/Fs in Seoul and a neighboring area (150 km x 150 km) in Korea. As part of the evaluation, the effects of the grid size with the homogeneous mixing assumption were estimated on the sign and magnitude of the prediction bias. The prediction compared with the monitoring data generally within 1 order of magnitude. In the presence of a concentration gradient within individual cells of 30 km x 30 km,the prediction bias for air and soil tended to increase with the distance from the sources. It was observed that the ratio of the predicted to the measured values could vary more than 4 times with the location of the monitoring site. Use of the large grid size in POPsME (and perhaps other MMMs) resulted in overpredictions for a major portion of the model domain at the cost of underprediction for limited areas nearthe sources. Beyond the source areas, a substantial contribution of the total prediction bias originated from the congeners with a large atmospheric loss rate and small TEF value. On a TEQ basis, therefore, the magnitude of the overpredictions could be significantly reduced as compared to that of the underprediction for the source areas.

An ionic liquid as a solvent for headspace single drop microextraction of chlorobenzenes from water samples

A headspace single-drop microextraction (HS-SDME) procedure using room temperature ionic liquid and coupled to high-performance liquid chromatography capable of quantifying trace amounts of chlorobenzenes in environmental water samples is proposed. A Plackett-Burman design for screening was carried out in order to determine the significant experimental conditions affecting the HS-SDME process (namely drop volume, aqueous sample volume, stirring speed, ionic strength, extraction time and temperature), and then a central composite design was used to optimize the significant conditions. The optimum experimental conditions found from this statistical evaluation were: a 5 microL microdrop of 1-butyl-3-methylimidazolium hexafluorophosphate, exposed for 37 min to the headspace of a 10 mL aqueous sample placed in a 15 mL vial, stirred at 1580 rpm at room temperature and containing 30% (w/v) NaCl. The calculated calibration curves gave a high level of linearity for all target analytes with correlation coefficients ranging between 0.9981 and 0.9997. The repeatability of the proposed method, expressed as relative standard deviation, varied between 1.6 and 5.1% (n=5). The limits of detection ranged between 0.102 and 0.203 microg L(-1). Matrix effects upon extraction were evaluated by analysing spiked tap and river water as well as effluent water samples originating from a municipal wastewater treatment plant.

Empirical evaluation of spatial and non-spatial European-scale multimedia fate models: results and implications for chemical risk assessment

Multimedia environmental fate models are commonly-applied tools for assessing the fate and distribution of contaminants in the environment. Owing to the large number of chemicals in use and the paucity of monitoring data, such models are often adopted as part of decision-support systems for chemical risk assessment. The purpose of this study was to evaluate the performance of three multimedia environmental fate models (spatially- and non-spatially-explicit) at a European scale. The assessment was conducted for four polycyclic aromatic hydrocarbons (PAHs) and hexachlorobenzene (HCB) and compared predicted and median observed concentrations using monitoring data collected for air, water, sediments and soils. Model performance in the air compartment was reasonable for all models included in the evaluation exercise as predicted concentrations were typically within a factor of 3 of the median observed concentrations. Furthermore, there was good correspondence between predictions and observations in regions that had elevated median observed concentrations for both spatially-explicit models. On the other hand, all three models consistently underestimated median observed concentrations in sediment and soil by 1-3 orders of magnitude. Although regions with elevated median observed concentrations in these environmental media were broadly identified by the spatially-explicit models, the magnitude of the discrepancy between predicted and median observed concentrations is of concern in the context of chemical risk assessment. These results were discussed in terms of factors influencing model performance such as the steady-state assumption, inaccuracies in emission estimates and the representativeness of monitoring data.

Analysis of chloro- and nitrobenzenes in water by a simple polyaniline-based solid-phase microextraction coupled with gas chromatography

A simple solid-phase microextraction (SPME) device, coupled with gas chromatography-electron capture detection (GC-ECD) was developed to detect trace levels of chloro- and nitrobenzene compounds in environmental water samples. Polyaniline (PANI) was chosen as the extraction material for the SPME device, and was electrochemically deposited on a stainless steel wire to achieve high mechanical stability. Due to the peculiar pi-pi conjugated structure, PANI coating shows a stable performance in high temperature (to 350 degrees C) and solvents (organic and inorganic). The porous structure of PANI film characterized by scanning electron microscopy (SEM) revealed high extraction efficiency. The possible extraction mechanism was explained by the study carried out using electrochemical impedance spectroscopy (EIS). Eight chloro- and nitrobenzene compounds were selected to evaluate the SPME-GC procedures. The key parameters such as extraction and desorption temperature and time, and the ionic strength were investigated and optimized. The method was applied to the detection of environmental water samples collected from Taihu Lake, representing nowadays contamination level under industrial impact. The whole PANI-SPME-GC method offers high accuracy and precision, high sensitivity and low detection limits. Thus, the method developed could be used as a new way to monitor the trace levels of chloro- and nitrobenzene compounds in real water bodies.

Modelling the long-term fate of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) in the Grenland Fjords, Norway

The development and application of a predictive fate model (DIG--Dioxins in Grenland) for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in the marine environment of the Norwegian Grenland Fjords are described. The objective of the modelling study was to predict long-term future changes in PCDD/F concentrations in the fjord following the cessation of point source emissions. To assess the reliability of the model, the model performance was evaluated by comparing model results to field measurements collected between 1989 and 2001. Model bias (defined as the ratio of median predicted concentration and median observed concentration) for prediction of concentrations for three different PCDD/F congeners (2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 1,2,3,6,7,8-hexadibenzofuran (HxCDF) and octachlorodibenzofuran (OCDF)) in the fjord was between 0.53 and 24, which was deemed a satisfactory result for models of this type. The model was run to determine the dynamic change in concentrations between 1950 and 2050 and to examine the key fluxes of PCDD/Fs in the fjord. Between 1990 and 2050 sediment concentrations of TCDD, HxCDF and OCDF were predicted to fall at fairly constant but gradually slowing rates to concentrations 52, 98 and 88 times lower, respectively, of their 1990 values. Losses of PCDD/Fs from the bottom sediments in the Frierfjord were predicted to be a combination of sediment burial and net resuspension to the water column. Sediment burial was shown to be relatively more important in the fjord's deep-water sediments, whereas resuspension was relatively more important in the shallow sediments. For the shallower sediments, a net water-to-sediment flux was predicted for all three congeners up until the mid-1970s, when emission reductions were initiated, and thereafter a net sediment-to-water flux was predicted. The shallow sediments acted as net sources to the deeper sediments and to the fishing areas in the outer fjord.

Evaluating the fate of p,p'-DDT in Tianjin, China using a non-steady-state multimedia fugacity model

Studies showed that DDT levels were still high in Tianjin, China, even though its use was banned in 1983. To estimate current risk of DDT to human health in Tianjin area, a non-steady-state (Level IV) multimedia fugacity model was used to simulate the fate and transfer of p,p'-DDT before and after the ban. The ordinary linear equations of Level IV model were solved with a matrix approach. The calculated p,p'-DDT concentration in air, water, soil, and sediment reached a maximum in the 1980s and then decreased, and agree well with those measured. The biggest bulk sinks of p,p'-DDT were soil and sediment, which accounted for 90% of total amount of p,p'-DDT in the environment. Air deposition and diffusions through the interfaces of water-air and water-sediment were the major intermedia transfer processes, while the degradation in soil and sediment were the key eliminating routes for p,p'-DDT in the environment.

Hexachlorobenzene in the global environment: emissions, levels, distribution, trends and processes

Hexachlorobenzene (HCB) is considered here as a 'model persistent organic pollutant.' Data on its sources, emissions, environmental levels and distributions and trends are compiled and used to assess its fate and behaviour in the global environment. Consideration is given as to the extent to which it has undergone repeated air-surface exchange or 'hopping' to become globally dispersed, the balance between primary and secondary sources in maintaining ambient levels, and its ultimate sinks in the environment. Global production exceeded 100,000 tonnes and primary emissions to atmosphere probably peaked in the 1970s. There has been a consistent downward trend in the environment over the past 20 years. Temporal trends of HCB in the environment vary, dependent on time period measured, media studied and study location, but the average half-life from all the studies is approximately 9 years. Estimates are made of the contemporary burden in the environment; these range between 10,000 and 26,000 tonnes and are dominated by the loadings in treated and background soils, sediments and oceans. Estimates of the trends of HCB emissions from treated soils are derived. At its peak, the amount of HCB emitted from soil to air may have been in the hundreds to thousands of tonnes per year, which would have made it a significant source of HCB to the environment. Whilst the amount of HCB being emitted from contemporary soil is much lower, only a small amount of re-emission of HCB from soil to air is required to maintain contemporary air concentrations under the current primary emission scenario.

Headspace single-drop microextraction for the analysis of chlorobenzenes in water samples

Exposing a microlitre organic solvent drop to the headspace of an aqueous sample contaminated with ten chlorobenzene compounds proved to be an excellent preconcentration method for headspace analysis by gas chromatography-mass spectrometry (GC-MS). The proposed headspace single-drop microextraction (SDME) method was initially optimised and the optimum experimental conditions found were: 2.5 microl toluene microdrop exposed for 5 min to the headspace of a 10 ml aqueous sample containing 30% (w/v) NaCl placed in 15 ml vial and stirred at 1000 rpm. The calculated calibration curves gave a high level of linearity for all target analytes with correlation coefficients ranging between 0.9901 and 0.9971, except for hexachlorobenzene where the correlation coefficient was found to be 0.9886. The repeatability of the proposed method, expressed as relative standard deviation varied between 2.1 and 13.2% (n = 5). The limits of detection ranged between 0.003 and 0.031 microg/l using GC-MS with selective ion monitoring. Analysis of spiked tap and well water samples revealed that matrix had little effect on extraction. A comparative study was performed between the proposed method, headspace solid-phase microextraction (SPME), solid-phase extraction (SPE) and EPA method 8121. Overall, headspace SDME proved to be a rapid, simple and sensitive technique for the analysis of chlorobenzenes in water samples, representing an excellent alternative to traditional and other, recently introduced, methods.

Tissue-dependent distribution and accumulation of chlorobenzenes by vegetables in urban area

Five seasonal vegetables from three growing sites in Hangzhou city, Zhejiang Province, were studied for the levels of four chlorobenzenes(CBs): o-dichlorobenzene (o-DCB), p-dichlorobenzene (p-DCB), m-dichlorobenzene (m-DCB), and 1,2,4-trichlorobenzene (1,2,4-TCB). Samples of each vegetable from each site were subdivided into leaves, stems, and roots, and these subsamples were analyzed separately for the levels of accumulated CBs. Relations between the levels of CBs in vegetables with the total organic carbon (TOC) of the soil, the lipid content of the vegetable, and the physicochemical properties of CBs were established. Results showed that o-DCB, p-DCB, m-DCB, 1,2,4-TCB were present in all vegetables analyzed. For spinaches (Spinacia oleracea), Chinese cabbages (Brassica rapa var. pekinensis), and celery (Apium graveolens var. dulce), the highest level of CBs was with roots, followed by leaves. While for radishes (Raphanus sativus), and carrots (Daucus carota subsp. sativus), the highest level was with leaves, followed by stems. The accumulation of CBs was found to have a good correlation with the plant-tissue lipid content, the contaminant air-water Henry's coefficient (H), the contaminant octanol-water partition coefficient (K(ow)), and the physiological characteristics of the vegetables.

Regional differences in chemical fate model outcome

The fate of anthropogenic substances in the environment is increasingly determined using multimedia mass balance models. It is, therefore, critical to fully understand how such models work and what their limitations are. The effects of uncertainty and variation in the chemical properties, discharges, and landscape parameters on model outcome have been examined by other researchers. Here, the role of landscape properties in controlling region-to-region differences in chemical fate is examined. Specifically, regions of Canada and the ChemCAN model are used to explore the region-to-region difference in fate for benzo[a]pyrene, hexachlorobenzene, tetrachloroethylene, alpha-hexachlorocyclohexane, 2,2',5,5'-tetrachlorobiphenyl (PCB 52), and atrazine emitted individually to air, water, and soil. To facilitate the same analysis in other places a description of the model and the methods for obtaining the landscape parameters used here are given. Differences in fate are the unique result of combining the input parameters of chemical properties, emission data, and landscape parameters. While region-to-region differences are small compared to the chemical-to-chemical differences that may span many orders of magnitude for physical-chemical or degradation properties, chemical fate is not the same for regions of differing landscape parameters. It is therefore concluded that the quality of results obtained from regional environmental fate models can be improved by the use of region-specific landscape parameters.

Evaluating multimedia/multipathway model intake fraction estimates using POP emission and monitoring data

This paper presents a structured evaluation of a novel multimedia chemical fate and multi-pathway human exposure model for Western Europe, IMPACT 2002, using data for PCDD/F congeners. PCDD/F congeners provide an illustration of the potential use of POPs (Persistent Organic Pollutant) data for the evaluation of such models. Based on available emission estimates, model predictions with and without spatial resolution are evaluated at three different stages against monitored data: at environmental contamination levels, food exposure concentration, and in terms of human intake fractions (iF): the fraction of an emission that is taken in by the population. The iF is approximately 3.5.10(-3) for emissions of dioxin in Western Europe. This iF compares well to the traditional non-spatial multi-media/-pathway model predictions of 3.9.10(-3) for the same region and to 2.10(-3) for the USA. Approximately 95% of the intake from Western European emissions occurs within the same region, 5% being transferred out of the region in terms of food contaminants and atmospheric advective transport.

1,4-Dichlorobenzene-Induced liver tumors in the mouse: evaluation of the role of chlorohydroquinones

1,4-Dichlorobenzene (1,4-DCB) is a wide-spread environmental contaminant and well-described hepatotoxicant for rats and mice. The prolonged oral or inhalation exposure to 1,4-DCB is associated with an increased frequency of hepatic tumors in mice, but not in rats. Evidence is lacking of direct genotoxicity with 1,4-DCB or its metabolites, and no generally accepted mechanism has been found to account for the increased numbers of 1,4-DCB-induced hepatic tumors in mice. No information is available on the carcinogenic effects of 1,4-DCB in humans. Here we consider evidence that the biotransformation of 1,4-DCB to substituted hydroquinone species contributes to hepatic adenoma and carcinoma formation in mouse liver. This phenomenon has implications for human carcinogenesis.

Evaluating and expressing the propagation of uncertainty in chemical fate and bioaccumulation models

First-order analytical sensitivity and uncertainty analysis for environmental chemical fate models is described and applied to a regional contaminant fate model and a food web bioaccumulation model. By assuming linear relationships between inputs and outputs, independence, and log-normal distributions of input variables, a relationship between uncertainty in input parameters and uncertainty in output parameters can be derived, yielding results that are consistent with a Monte Carlo analysis with similar input assumptions. A graphical technique is devised for interpreting and communicating uncertainty propagation as a function of variance in input parameters and model sensitivity. The suggested approach is less calculationally intensive than Monte Carlo analysis and is appropriate for preliminary assessment of uncertainty when models are applied to generic environments or to large geographic areas or when detailed parameterization of input uncertainties is unwarranted or impossible. This approach is particularly useful as a starting point for identification of sensitive model inputs at the early stages of applying a generic contaminant fate model to a specific environmental scenario, as a tool to support refinements of the model and the uncertainty analysis for site-specific scenarios, or for examining defined end points. The analysis identifies those input parameters that contribute significantly to uncertainty in outputs, enabling attention to be focused on defining median values and more appropriate distributions to describe these variables.

A regionally segmented national scale multimedia contaminant fate model for Canada with GIS data input and display

Regional scale mass balance models are valuable tools for describing the fate of chemicals in areas with defined and fairly homogeneous environmental characteristics and chemical use patterns. These models often show that contaminant inflows from outside the region of interest are significant compared with local emissions. This is most likely for persistent chemicals and those that are efficiently transported in air or water. As a result regional levels of environmental contamination are controlled by external factors and meaningful evaluation requires assessment of contaminant fate in neighboring regions. A linked set of regional models thus has the potential to describe quantitatively the impact of chemical emissions over a wider geographic scale with significant spatial differences in environmental characteristics and chemical use patterns. We describe here a national scale contaiminant fate model for Canada based on the existing 24-region ChemCAN model. The ecological regions, which were previously treated individually, are linked with flows of air and water deduced from GIS analysis to provide a comprehensive description of contaminant fate over the entire country, including long-range transport between regions. The model is applied to describe the national-scale fate of three chemicals in Canada, benzene, trichloroethene, and diethylhexyl phthalate, exploiting GIS analysis for interpretation and presentation of model results. Agreement between predicted multimedia environmental concentrations and measured values is satisfactory for all three chemicals. In total this work represents an initial attempt to address the different processes of both linking a regional model and using GIS as a tool for data analysis and management.

Assessing the environmental fate of chemicals of emerging concern: a case study of the polybrominated diphenyl ethers

It is suggested that assessments of chemicals of emerging concern can be rationally structured around a multistage process in which fate and risk are evaluated with increasing accuracy as new data become available. An initial tentative and approximate assessment of fate and risk can identify key data gaps and justify and direct further investigations, which progressively improve the reliability of the assessment. This approach is demonstrated for a class of chemicals, the polybrominated diphenyl ethers (PBDEs), which is of increasing concern, but about which there is presently a lack of comprehensive data on properties, sources, fate and effects. Specifically, 20 PBDE congeners are investigated using the suggested approach and research needs are identified.

Evaluation and comparison of multimedia mass balance models of chemical fate: application of EUSES and ChemCAN to 68 chemicals in Japan

The European Union System for Evaluation of Substances (EUSES) and the ChemCAN chemical fate model are applied to describe the fate of 68 chemicals on two spatial scales in Japan. Emission information on the chemicals has been obtained from Japan's Pollutant Release and Transfer Registry and available monitoring data gathered from government reports. Environmental concentrations calculated by the two models for the four primary environmental media of air, water, soil and sediment agree within a factor of 3 for over 70% of the data, and within a factor of 10 for over 87% of the data. Reasons for certain large discrepancies are discussed. Concentrations calculated by the models are generally consistent with the lower range of concentrations that are observed in the environment. Agreement between modeled and observed concentrations is considerably improved by including an estimate of the advective input of chemicals in air from outside Japan. The agreement between the EUSES and ChemCAN models suggests that results of individual chemical assessments are not likely to be significantly affected by the choice of chemical fate model. Primary sources of discrepancy between modeled and observed concentrations are believed to be uncertainties in emission rates, degradation half-lives, and the lack of data on advective inflow of contaminants in air.

Temporal changes in kerosene content and composition in field soil as a result of leaching

A field experiment was designed to determine the combined effect of leaching and natural attenuation on the redistribution dynamics of kerosene--a volatile petroleum hydrocarbon mixture (VPHM)--and of its selected individual components in the soil subsurface. Variables included the composition of contaminant spilled, the soil water content before contamination and the leaching pattern. Temporal changes in the residual kerosene concentration and composition in the soil subsurface of the experimental field during 39 days and leaching by 500 mm of irrigation water were determined to a depth of 100 cm. The main processes controlling contaminant attenuation were volatilization and redistribution with depth. Soil hydration status was found to affect the attenuation, redistribution and composition of VPHM in the porous media. An initial relative increase of n-alkanes in the subsurface compared with the total VPHM in the first leaching period was a result of the volatilization of low vapor pressure compounds. The redistribution of individual components in the soil profile during leaching was in accordance with their physico-chemical properties.

Contaminant residue levels in arctic wolves (Canis lupus) from the Yukon Territory, Canada

Kidney, liver and bone samples were taken from 19 wolves (Canis lupus) collected from two locations in the Yukon Territory. Liver samples pooled by age and sex were analyzed for 22 organochlorine pesticides and 101 PCB congeners. Individual kidney and liver samples were analyzed for arsenic, cadmium, copper, lead, total mercury, selenium and zinc. Thirteen individual bone samples were analyzed for lead. While most organochlorines were not present at detectable levels in wolf liver, some chlorobenzenes, dieldrin and sigma PCB were present at low levels. PCB congeners 149, 153, 170/190, 180 and 187/182 made up 86% of the total PCBs measured in wolf liver. The hexa- and heptachlorobiphenyls dominated the pattern in wolf liver, while congeners containing less than five chlorine atoms were not detected. The pattern of chlorobenzene and PCB homologues found in wolf liver are more similar to those found in marten (Martes americana) and other carnivores than caribou (Rangifer tarandus), perhaps reflecting similarities in food habits and metabolic capacities. With the exception of cadmium, average element concentrations in all wolf tissues are similar to those found in other arctic carnivores. Cadmium concentrations in wolf liver and kidney were somewhat higher in Yukon wolves than other arctic wolves. This may reflect high cadmium concentrations found in livers and kidneys of moose and some caribou herds in the Yukon. Renal arsenic and bone lead decreased significantly with age in wolves, while renal mercury increased with age. Because the ranges seen are relatively small, and all values are within the range normally seen in wildlife, it is difficult to determine the biological significance of these relationships. Contaminant levels in Yukon wolves are generally low and are similar to those found in other arctic terrestrial carnivores. They do not approach levels that are known to potentially cause adverse effects in animals. Contaminant concentrations found in this study should be considered baseline levels.