Fate in the environment and long-range atmospheric transport of the organophosphorus insecticide, chlorpyrifos and its oxon.

The fate and movement of the organophosphorus insecticide chlorpyrifos (CPY;CAS No.2921-88-2) and its metabolite chlorpyrifos-oxon (CPYO; CASNo.5598-15-2) determine exposures in terrestrial and aquatic environments.Detectable concentrations of the organophosphorus insecticide CPY in air, rain,snow and other environmental media have been measured in North America and other locations at considerable distances from likely agricultural sources, which indicates the potential for long range transport (LRT) in the atmosphere. This issue was addressed by first compiling monitoring results for CPY in all relevant environmental media. As a contribution to the risk assessment of CPY in remote regions, a simple mass balance model was developed to quantify likely concentrations at locations ranging from local sites of application to more remote locationsup to hundreds of km distant. Physical-chemical properties of CPY were reviewed and a set of consistent values for those properties that determine partitioning and reactivity were compiled and evaluated for use in the model. The model quantifies transformation and deposition processes and includes a tentative treatment of dispersion to lesser atmospheric concentrations. The model also addressed formation and fate of CPYO, which is the major transformation product of CPY. The Characteristic Travel Distance (CTD) at which 63% of the original mass of volatilized CPY is degraded or deposited-based on a conservative concentration of •OHradicals of 0.7 x 106 molecules cm-3 and a half-life of 3 h, was estimated to be 62 km. At lesser concentrations of •OH radical, such as occurs at night and at lesser temperatures, the CTD is proportionally greater. By including monitoring data from a variety of media, including air, rain, snow and biota, all monitored concentrations can be converted to the equilibrium criterion of fugacity, thus providing asynoptic assessment of concentrations of CPY and CPYO in multiple media. The calculated fugacities of CPY in air and other media decrease proportionally with increasing distance from sources, which can provide an approximate prediction of downwind concentrations and fugacities in media and can contribute to improved risk assessments for CPY and especially CPYO at locations remote from points of application, but still subject to LRT. The model yielded estimated concentrations that are generally consistent with concentrations measured, which suggests that the canonical fate and transport processes were included in the simulation model. The equations included in the model enable both masses and concentrations of CPY and CPYO to be estimated as a function of distance downwind following application.While the analysis provided here is useful and an improvement over previous estimates of LRT of CPY and CPYO, there is still need for improved estimates of the chemical-physical properties of CPYO.Based on the persistence in water, soils, and sediments, its bioconcentration and biomagnification in organisms, and its potential for long-range transport, CPY and CPYO do not trigger the criteria for classification as a POP under the Stockholm convention or a PB chemical under EC 1107/2009. Nonetheless, CPY is toxic at concentrations less than the trigger for classification as T under EC 11 07 /2009; however,this simple trigger needs to be placed in the context of low risks to non-target organisms close to the areas of use. Overall, CPY and CPYO are judged to not trigger the PBT criteria of EC 1107/2009.

Scalable, sustainable cost-effective surgical care: a model for safety and quality in the developing world, part I: challenge and commitment.

BACKGROUND: With an estimated backlog of 4,000,000 patients worldwide, cleft lip and cleft palate remain a stark example of the global burden of surgical disease. The need for a new paradigm in global surgery has been increasingly recognized by governments, funding agencies, and professionals to exponentially expand care while emphasizing safety and quality. This three-part article examines the evolution of the Operation Smile Guwahati Comprehensive Cleft Care Center (GCCCC) as an innovative model for sustainable cleft care in the developing world. METHODS: The GCCCC is the result of a unique public-private partnership between government, charity, and private enterprise. In 2009, Operation Smile, the Government of Assam, the National Rural Health Mission, and the Tata Group joined together to work towards the common goal of creating a center of excellence in cleft care for the region. RESULTS: This partnership combined expertise in medical care and training, organizational structure and management, local health care infrastructure, and finance. A state-of-the-art surgical facility was constructed in Guwahati, Assam which includes a modern integrated operating suite with an open layout, advanced surgical equipment, sophisticated anesthesia and monitoring capabilities, central medical gases, and sterilization facilities. CONCLUSION: The combination of established leaders and dreamers from different arenas combined to create a synergy of ambitions, resources, and compassion that became the backbone of success in Guwahati.

Scalable, sustainable cost-effective surgical care: a model for safety and quality in the developing world, part II: program development and quality care.

BACKGROUND: The Guwahati Comprehensive Cleft Care Center (GCCCC) is committed to free medical and surgical care to patients afflicted with facial deformities in Assam, India. A needs-based approach was utilized to assemble numerous teams, processes of care, and systems aimed at providing world-class care to the most needy of patients, and to assist them with breaking through the barriers that prohibit them from obtaining services. METHODS: A team of international professionals from various disciplines served in Guwahati full time to implement and oversee patient care and training of local counterparts. Recruitment of local professionals in all disciplines began early in the scheme of the program and led to gradual expansion of all medical teams. Emphasis was placed on achieving optimal outcome for each patient treated, as opposed to treating the maximum number of patients. RESULTS: The center is open year round to offer full-time services and follow-up care. Along with surgery, GCCCC provides speech therapy, child life counseling, dental care, otolaryngology, orthodontics, and nutrition services for the cleft patients under one roof. Local medical providers participated in a model of graded responsibility commiserate with individualized skill and progress, and gradually assumed all leadership positions and now account for 92% of the workforce. Institutional infrastructure improvements positioned and empowered teams of skilled local providers while implementing systemized perioperative processes. CONCLUSION: This needs-based approach to program development in Guwahati was successful in optimization of quality and safety in all clinical divisions.

Scalable, sustainable cost-effective surgical care: a model for safety and quality in the developing world, part III: impact and sustainability.

BACKGROUND: The Guwahati Comprehensive Cleft Care Center (GCCCC) utilizes a high-volume, subspecialized institution to provide safe, quality, and comprehensive and cost-effective surgical care to a highly vulnerable patient population. METHODS: The GCCCC utilized a diagonal model of surgical care delivery, with vertical inputs of mission-based care transitioning to investments in infrastructure and human capital to create a sustainable, local care delivery system. Over the first 2.5 years of service (May 2011-November 2013), the GCCCC made significant advances in numerous areas. Progress was meticulously documented to evaluate performance and provide transparency to stakeholders including donors, government officials, medical oversight bodies, employees, and patients. RESULTS: During this time period, the GCCCC provided free operations to 7,034 patients, with improved safety, outcomes, and multidisciplinary services while dramatically decreasing costs and increasing investments in the local community. The center has become a regional referral cleft center, and governments of surrounding states have contracted the GCCCC to provide care for their citizens with cleft lip and cleft palate. Additional regional and global impact is anticipated through continued investments into education and training, comprehensive services, and research and outcomes. CONCLUSION: The success of this public private partnership demonstrates the value of this model of surgical care in the developing world, and offers a blueprint for reproduction. The GCCCC experience has been consistent with previous studies demonstrating a positive volume-outcomes relationship, and provides evidence for the value of the specialty hospital model for surgical delivery in the developing world.

Activity-based concept for transport and partitioning of ionizing organics.

Ionizing chemicals, including pesticides, pharmaceuticals, and personal care products, are care products, are widely used chemicals of commerce and have been detected in the environment in large numbers. These "ionics" are subject to a variety of processes, such as dissociation, ion trap, and electrical interactions with organic matter and biota. Conventional chemodynamic concepts and models designed to treat neutral compounds do not necessarily address these processes. A new system of equations, based on activity and analogous to the fugacity approach, is suggested to describe the fate of organic ionics. The total concentration of all molecule species in a bulk compartment is determined from the product of activity 'a' and a bulk activity capacity 'B'. The concentration ratio between compartments in equilibrium depends on the activity ratio and the capacity ratio. Changes in partitioning due to pH, ionic strength, and the ion trap effect are quantified. The calculation is illustrated for two pharmaceuticals, namely the monovalent acid ibuprofen and the monovalent base trimethoprim, in a multimedia lake system. Trimethoprim is neutral at high pH but ionized at low pH, while ibuprofen exhibits the opposite. The concentration ratios of air and biota to water are shown to depend on pH. The activity approach may be used to describe transport and partitioning of multivalent ionizable organic compounds and to build multimedia fate models.

Preliminary assessment of avian stomach oils: a vector of contaminants to chicks and potential for diet analysis and biomonitoring.

Bird species from the order Procellariiformes or petrels, including the northern fulmar (Fulmarus glacialis), produce high lipid and high energy content stomach oils from the prey they consume, which enables them to exploit distant marine food sources. Stomach oils are also used as a food source for chicks and for defensive purposes. Samples of stomach oils from two Arctic colonies, St. George Island Alaska, USA and Cape Vera, Devon Island Nunavut, Canada, were collected and analyzed for organochlorine contaminants. SigmaPCB concentrations ranged from 13 to 236 ng g(-1) wet weight (ww) and SigmaDDT concentrations from 5 to 158 ng g(-1) ww and were similar in both sites, though differences in chemical signatures were apparent. Stomach oils are a rich energy source; however, they may also provide a higher dose of contaminants per unit energy than the direct consumption of prey items, as illustrated using mass and energy balance calculations to estimate chick exposure to SigmaDDT for hypothetical stomach oil and whole prey diets. The results of this study suggest that stomach oils are an important vector of organochlorine contaminants to chicks and should be considered in future risk assessments of northern fulmars and other species of petrels. To our knowledge this is the first study of stomach oils as an overlooked vector of organochlorine contaminants to chicks and as a potentially valuable medium for dietary analysis and noninvasive biomonitoring both of petrel dietary exposure and of marine contaminant concentrations.

Multimedia modeling of human exposure to chemical substances: the roles of food web biomagnification and biotransformation.

The Risk Assessment IDentification And Ranking (RAIDAR) model is refined to calculate relative human exposures as expressed by total intake, intake fraction (iF), and total body burden (TBB) metrics. The RAIDAR model is applied to three persistent organic pollutants (POPs) and six petrochemicals using four mode-of-entry emission scenarios to evaluate the effect of metabolic biotransformation estimates on human exposure calculations. When biotransformation rates are assumed to be negligible, daily intake and iFs for the nine substances ranged over six orders of magnitude and TBBs ranged over 10 orders of magnitude. Including biotransformation estimates for fish, birds, and mammals reduced substance-specific daily intake and iF by up to 4.5 orders of magnitude and TBB by more than eight orders of magnitude. The RAIDAR iF calculations are compared to the European Union System for the Evaluation of Substances (EUSES) model iF calculations and differences are discussed, especially the treatment of food web bioaccumulation. Model selection and application assumptions result in different rankings of human exposure potential. These results suggest a need to critically consider model selection and to include reliable biotransformation rate estimates when assessing relative human exposure and ranking substances for priority setting. Recommendations for further model evaluations and revisions are discussed.

Modeling bioaccumulation using characteristic times.

A new formulation of existing mass balance models for bioaccumulation is derived and applied to organisms that respire either water or air. This model employs characteristic time parameters and equations that are mathematically equivalent to those used in existing concentration-rate constant and fugacity models. The equivalence of these traditional formulations and the novel formulation is demonstrated. In all three formulations, the required information includes various physiological and dietary parameters as well as chemical concentrations in food and in the respired medium of water or air. Chemical properties are described by the octanol-water or octanol-air partition coefficient and a metabolic biotransformation half-life. Bioaccumulation, biomagnification, and all uptake and loss rates are expressed using characteristic times that have readily identifiable chemical or biological significance. The ability of the characteristic time formulation to provide an evaluation of the bioenergetic consistency of organism properties is briefly discussed. The model is applied illustratively to a trout as a water-respiring organism and to a wolf as an air-respiring organism, and the results are discussed. It is concluded that the use of characteristic time parameters and equations provides valuable additional insights regarding the relative importance of the various uptake and loss processes and, thus, is complementary to the conventional approaches for modeling bioaccumulation phenomena in a variety of organisms.

A quantitative structure-activity relationship for predicting metabolic biotransformation rates for organic chemicals in fish.

An evaluated database of whole body in vivo biotransformation rate estimates in fish was used to develop a model for predicting the primary biotransformation half-lives of organic chemicals. The estimated biotransformation rates were converted to half-lives and divided into a model development set (n=421) and an external validation set (n=211) to test the model. The model uses molecular substructures similar to those of other biodegradation models. The biotransformation half-life predictions were calculated based on multiple linear regressions of development set data against counts of 57 molecular substructures, the octanol-water partition coefficient, and molar mass. The coefficient of determination (r2) for the development set was 0.82, the cross-validation (leave-one-out coefficient of determination, q2) was 0.75, and the mean absolute error (MAE) was 0.38 log units (factor of 2.4). Results for the external validation of the model using an independent test set were r2 = 0.73 and MAE = 0.45 log units (factor of 2.8). For the development set, 68 and 95% of the predicted values were within a factor of 3 and a factor of 10 of the expected values, respectively. For the test (or validation) set, 63 and 90% of the predicted values were within a factor of 3 and a factor of 10 of the expected values, respectively. Reasons for discrepancies between model predictions and expected values are discussed and recommendations are made for improving the model. This model can predict biotransformation rate constants from chemical structure for screening level bioaccumulation hazard assessments, exposure and risk assessments, comparisons with other in vivo and in vitro estimates, and as a contribution to testing strategies that reduce animal usage.

Estimating metabolic biotransformation rates in fish from laboratory data.

A method is proposed for estimating metabolic biotransformation rate constants for nonionic organic chemicals from measured laboratory bioconcentration and dietary bioaccumulation data in fish. Data have been selected based on a quality review to reduce uncertainty in the measured values. A kinetic mass balance model is used to estimate rates of chemical uptake and elimination. Biotransformation rate constants are essentially calculated as the difference between two quantities, a measured bioconcentration factor or elimination rate constant, and a model-derived bioconcentration factor or elimination rate constant estimated assuming no biotransformation. Model parameterization exploits key empirical data when they are available and assumes default values when study specific data are unavailable. Uncertainty analyses provide screening level assessments for confidence in the biotransformation rate constant estimates. The uncertainty analyses include the range for 95% of the predicted values and 95% confidence intervals for the calculated biotransformation values. Case studies are provided to illustrate the calculation and uncertainty methods. Biotransformation rate constants calculated by the proposed method are compared with other published estimates for 31 chemicals that range in octanol-water partition coefficients from approximately 10(1) to 10(8) and represent over four orders of magnitude in biotransformation potential. The comparison of previously published values with those calculated by the proposed method shows general agreement with 82% of the estimated values falling within a factor of three.

A database of fish biotransformation rates for organic chemicals.

Biotransformation is a key process that can mitigate the bioaccumulation potential of organic substances and is an important parameter for exposure assessments. A recently published method for estimating whole-body in vivo metabolic biotransformation rate constants (kM) is applied to a database of measured laboratory bioconcentration factors and total elimination rate constants for fish. The method uses a kinetic mass balance model to estimate rates of chemical uptake and elimination when measured values are not reported. More than 5400 measurements for more than 1000 organic chemicals were critically reviewed to compile a database of 1535 kM estimates for 702 organic chemicals. Biotransformation rates range over six orders of magnitude across a diverse domain of chemical classes and structures. Screening-level uncertainty analyses provide guidance for the selection and interpretation of kM values. In general, variation in kM estimates from different routes of exposure (water vs diet) and between fish species is approximately equal to the calculation uncertainty in kM values. Examples are presented of structure-biotransformation relationships. Biotransformation rate estimates in the database are compared with estimates of biodegradation rates from existing quantitative structure-activity relationship models. Modest correlations are found, suggesting some consistency in biotransformation capabilities between fish and microorganisms. Additional analyses to further explore possible quantitative structure-biotransformation relationships for estimating kM from chemical structure are encouraged, and recommendations for improving the database are provided.

Mass balance modelling of contaminants in river basins: application of the flexible matrix approach.

It is useful to have available a variety of catchment-scale water quality models that range in complexity, spatial resolution and data requirements. In a previous paper [Warren, C., Mackay, D., Whelan, M., Fox, K., 2005. Mass balance modelling of contaminants in river basins: a flexible matrix approach. Chemosphere 61, 1458-1467] a series of simple to intermediately complex mass balance models was presented which can be used for tiered exposure assessments in river basins. The connectivity of the segments is expressed using a matrix that permits flexibility in application, enabling the model to be re-segmented and applied to different catchments as required. In this paper, the intermediate models, QWASI matrix-rate constant (QMX-R) and QWASI matrix-fugacity (QMX-F) are used to estimate concentrations of linear alkylbenzene sulfonates (LAS) in the rivers Aire and Calder, UK, and of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the Fraser River basin, Canada. The results compare satisfactorily with monitoring data, suggesting that these QWASI-based models for exposure and risk assessment may be applicable under data-limited conditions. The use of QWASI-based models for regulatory purposes in an evaluative river system is also discussed with reference to assessments of para-dichlorobenzene (pDCB), trichloroethylene (TCE), bis(2-ethylhexyl) phthalate (DEHP) and toluene. It is shown that multi-media QWASI model predictions can be usefully depicted graphically on chemical space diagrams and used to highlight regions in which advection, partitioning to sediments and volatilization may be important determinants of chemical fate in river systems.

Can the unit world model concept be applied to hazard assessment of both organic chemicals and metal ions?

A unit world model that has the potential to be used for the hazard assessment of both metal ions and organic chemicals is described and discussed, with an emphasis on the problems that arise when treating metal ions. It is based on the steady-state equilibrium criterion model that is designed to simulate the fate of organic chemicals in a 100,000-km(2) region and comprises four well-mixed compartments: Air, water, soil, and sediment. To be applicable to metal ions, modifications are required. The single soil and sediment layers should be replaced by two layers to accommodate aerobic and anaerobic conditions. The more complex and variable partitioning of metals resulting from dependence on pH, redox conditions, ionic oxidation state, and presence of sulfide also must be addressed, but preferably in a separate geochemical model, because these factors can result in nonlinearity. For metals, a dynamic as well as a steady-state model is desirable. It is shown that the resulting model can be applied to both organics and metals. Rather than seeking to apply the hazard criterion of persistence to metal ions, the model can be used to deduce a critical loading that results in a defined toxic end point, thus integrating the hazard criteria of persistence, toxicity, and possibly, bioaccumulation. This approach is applied illustratively to naphthalene as a typical organic substance and to four environmentally relevant metal ions. Results are discussed and recommendations made for further development. Specifically, the absence of metal degradation can result in large, steady-state quantities in soils and sediments corresponding to residence times of many centuries. Consequently, the dynamic calculations are more relevant for fate assessments of metals over a period of years, and more focus on the aquatic environment is justified.

Mass balance modelling of contaminants in river basins: a flexible matrix approach.

A novel and flexible approach is described for simulating the behaviour of chemicals in river basins. A number (n) of river reaches are defined and their connectivity is described by entries in an n x n matrix. Changes in segmentation can be readily accommodated by altering the matrix entries, without the need for model revision. Two models are described. The simpler QMX-R model only considers advection and an overall loss due to the combined processes of volatilization, net transfer to sediment and degradation. The rate constant for the overall loss is derived from fugacity calculations for a single segment system. The more rigorous QMX-F model performs fugacity calculations for each segment and explicitly includes the processes of advection, evaporation, water-sediment exchange and degradation in both water and sediment. In this way chemical exposure in all compartments (including equilibrium concentrations in biota) can be estimated. Both models are designed to serve as intermediate-complexity exposure assessment tools for river basins with relatively low data requirements. By considering the spatially explicit nature of emission sources and the changes in concentration which occur with transport in the channel system, the approach offers significant advantages over simple one-segment simulations while being more readily applicable than more sophisticated, highly segmented, GIS-based models.

Fugacity and activity analysis of the bioaccumulation and environmental risks of decamethylcyclopentasiloxane (D5).

As part of an initiative to evaluate commercial chemicals for their effects on human and environmental health, Canada recently evaluated decamethylcyclopentasiloxane (D5; CAS no. 541-02-06), a high-volume production chemical used in many personal care products. The evaluation illustrated the challenges encountered in environmental risk assessments and the need for the development of better tools to increase the weight of evidence in environmental risk assessments. The present study presents a new risk analysis method that applies thermodynamic principles of fugacity and activity to express the results of field monitoring and laboratory bioaccumulation and toxicity studies in a comprehensive risk analysis that can support risk assessments. Fugacity and activity ratios of D5 derived from bioaccumulation measures indicate that D5 does not biomagnify in food webs, likely because of biotransformation. The fugacity and activity analysis further demonstrates that reported no-observed-effect concentrations of D5 normally cannot occur in the environment. Observed fugacities and activities in the environment are, without exception, far below those corresponding with no observed effects, in many cases by several orders of magnitude. This analysis supports the conclusion of the Canadian Board of Review and the Minister of the Environment that D5 does not pose a danger to the environment. The present study further illustrates some of the limitations of a persistence-bioaccumulation-toxicity-type criteria-based risk assessment approach and discusses the merits of the fugacity and activity approach to increase the weight of evidence and consistency in environmental risk assessments of commercial chemicals.

Modeling transport and deposition of contaminants to ecosystems of concern: a case study for the Laurentian Great Lakes.

Transfer efficiency (TE) is introduced as a model output that can be used to characterize the relative ability of chemicals to be transported in the environment and deposited to specific target ecosystems. We illustrate this concept by applying the Berkeley-Trent North American contaminant fate model (BETR North America) to identify organic chemicals with properties that result in efficient atmospheric transport and deposition to the Laurentian Great Lakes. By systematically applying the model to hypothetical organic chemicals that span a wide range of environmental partitioning properties, we identify combinations of properties that favor efficient transport and deposition to the Lakes. Five classes of chemicals are identified based on dominant transport and deposition pathways, and specific examples of chemicals in each class are identified and discussed. The role of vegetation in scavenging chemicals from the atmosphere is assessed, and found to have a negligible influence on transfer efficiency to the Great Lakes. Results indicate chemicals with octanol-water (K(ow)) and air-water (K(aw)) partition coefficients in the range of 10(5)-10(7) and 10(-4)-10(-1) combine efficient transport and deposition to the Great Lakes with potential for biaccumulation in the aquatic food web once they are deposited. A method of estimating the time scale for atmospheric transport and deposition process is suggested, and the effects of degrading reactions in the atmosphere and meteorological conditions on transport efficiency of different classes of chemicals are discussed. In total, this approach provides a method of identifying chemicals that are subject to long-range transport and deposition to specific target ecosystems as a result of their partitioning and persistence characteristics. Supported by an appropriate contaminant fate model, the approach can be applied to any target ecosystem of concern.

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.

Comparison of two methods for obtaining degradation half-lives.

Given the paucity of experimental degradation half-life data for most organic chemicals, there is a compelling incentive to use available estimation software when undertaking assessments of chemical persistence and mass balance modeling studies. In this study, half-life data obtained from estimation software for a set of 233 organic chemicals in air, water, soil and sediments were shown to differ significantly from half-life data listed in handbooks. It is suggested that the widely available and used estimation software, EPIWIN (Estimations Program's Interface for Windows), overestimates the reactivity of persistent organic pollutants (POPs). Reasons for this overestimation are explored. It is concluded that the maximum "default half-life values" used by the EPIWIN software are too short for estimating half-lives of highly persistent chemicals such as PCBs. There is a need for estimation software such as EPIWIN to be more thoroughly calibrated against experimental derived half-life data for a wide range of chemicals, including potential POPs, thus improving their reliability.

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.