T10 PM Advances in Bioaccumulation Assessment|
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in 341-342
385 (BON-1116-519513) Addressing PBT program needs for new and existing substances in Canada.
Start time: 1:50 PM
Bonnell, M1, Morin, D1, 1 Environment Canada, Gatineau, Quebec, Canada
The assessment of persistence, bioaccumulation and inherent toxicity (PBiT) is currently being performed in Canada for new and existing substances. Categorization of 23,000 existing substances on the Canadian Domestic Substances List (DSL) for PBiT is nearing completion, but further examination of PBiT properties will be performed at the risk assessment stage for those substances meeting the criteria, as is done for new substances. The criteria in the Persistence and Bioaccumulation Regulations (Canada Gazette 2000) are used by both programs to identify very persistent and very bioaccumulative substances. Inherent toxicity criteria are defined within each program, but are consistent. Obtaining reliable and accurate estimates of these three hazard properties presents challenges to regulators and non-regulators alike. Regarding ′B′, practical and scientific difficulties can arise when examining inventories of chemicals given the large number of substances to be examined, limitations of QSAR training set domains and the general lack of experimental data. Consequently, modeled values of bioaccumulation are often used as BCF testing is often cost prohibitive, requires animal testing and may not result in reliable results (e.g., poorly soluble, highly sorptive substances). However, QSAR models for ′B ′are driven by logKow input and most currently do not account for absorbtion, distribution, metabolism, and excretion (ADME) process, although some models are moving in that direction (e.g., Mekenyan′s POPs model, Gobas mass-balance BCF/BAF model). A tiered approach to bioaccumulation assessment, that includes ADME considerations, has been proposed by the ILSI-HESI (Health and Environmental Sciences Institute) Emerging Issues Committee for Bioaccumulation to help improve bioaccumulation assessment. Accurate assessment of bioaccumulation values, whether they are modeled or experimental, are needed by risk assessors for the examination of′B′ as it relates to the benchmark criteria as well as for determining the potential trophic transfer of contaminants in aquatic and terrestrial systems using food web and exposure based models. This presentation will discuss how the ILSI-HESI tiered approach may be applied in risk assessment of new and existing substances in Canada.
386 (MCE-1117-774861) Influence of metabolism on organic contaminant bioaccumulation–How should we be addressing this?
Start time: 2:10 PM
McElroy, A1, Rust, A1, Brownawell, B1, 1 Stony Brook University, Stony Brook, NY, USA
It is well known that many sediment-associated contaminants are bioavailable to benthic organisms, and that some of these contaminants can be transferred through aquatic food chains, thus posing both ecological and human health risks. Early efforts to predict bioaccumulation based on octanol water partitioning behavior, sediment organic carbon, and organism lipid provide a good first approximation for potential bioaccumulation , but recent work has pointed out the important influence of factors such as soot (or black) carbon, and gut surfactancy in influencing bioavailability. Another often overlooked process is the role of in vivo metabolism of target chemical in affecting observed bioaccumulated levels. We have shown highly species-specific rates of PAH metabolism that are inversely correlated with biota sediment bioaccumulation factors in benthic invertebrates. Further, we have shown that PAH metabolites in tissues are available for food chain transfer to aquatic consumers. The influence of metabolism should be taken into account in the choice of species used for bioaccumulation tests, and in predicting the fate and risk of bioavailable contaminants. Future needs in this area should include development of paradigms to predict metabolic susceptibility of contaminants, indices of metabolic competence in guilds of exposed organisms, methods for directly measuring metabolite body burdens in infaunal and consumer organisms, and an assessment of the toxicological significance of metabolites.
387 (DIM-1117-798314) BCF Base Line Model and Effect of Mitigating Factors.
Start time: 2:30 PM
Mekenyan, Ovanes1, Dimitrov, Sabcho1, Parkerton, T2, Comber, M3, Bonnell, M4, 1 Laboratory of Mathematical Chemistry, University "Prof. As. Zlatarov", Bourgas, Bulgaria2 Toxicological and Environmental Sciences Division, ExxonMobil Biomedical Sciences, Inc., Annandale, NJ, USA3 ExxonMobil Biomedical Sciences, Machelen, Belgium4 New Chemicals Evaluation Division, New Substances Branch, Environment, Gatineau, Quebec, Canada
The base-line modeling concept is based on the assumption of maximum cut off for BCF and set of mitigating factors reducing it. The maximum potential of bioconcentration is assumed to be a result of passive diffusion conditioned by chemical lipofilicity, only. The multi-compartment partitioning model is used as the theoretical justification for this concept. The significance of different mitigating factors associated either with interactions with an organism or bioavailability were investigated. The most important mitigating factor was found to be metabolism. Accordingly, a metabolism simulator for fish liver was used in the model, which has been trained to reproduce fish metabolism based on related mammalian metabolic pathways. It contains 382 Phase I and 48 Phase II metabolic transformations. The probabilities of occurrence of transformations were regressed on the basis of 515 experimental BCF values. Other significant mitigating factors, depending on the chemical structure, e.g. molecular size and ionization are also taken into account in the model. The current structural domain of the model includes a variety of chemical classes such as low molecular chain-like, carbo-monocyclic, carbo-polycyclic heterocyclic organic compounds and pharmacopoeial chemical substances. The results (R2 = 0.84) obtained for a training set of 515 chemicals demonstrate the usefulness of the BCF base line concept. The predictability of the model was evaluated on the basis of 176 chemicals not used in the model building. The correctness of predictions for 59 chemicals identified to belong to the model applicability domain was 80%.
388 (MUI-1117-834358) Approaches for measurements of field bioaccumulation of POPs and their application to less persistent chemicals.
Start time: 2:50 PM
Muir, D.1, Burkhard, L.2, 1 NWRI, Environment Canada, Burlington, ON, Canada2 Mid-Continent Ecology Division, US Environmental Protection Agency, Duluth, MN, USA
Careful field measurements of PCBs, persistent organochlorines pesticides (POPs) and PCDD/Fs have yielded biota-water (BAFs), biota-sediment (BSAFs) accumulation factors and trophic magnification factors (TMFs) that are consistent across ecosystems and have predictive power. However, the most consistent values are from larger well mixed ecosystems (e.g. large lakes and marine environments) while smaller heterogeneous ecosystems (e.g. rivers) exhibit more temporal and spatial variability. Field BAFs for fish and zooplankton are consistently higher than lab BCFs even for compounds with intermediate or low Kows (Log Kow 3-5). Key reasons may be additional trophic transfer and low degradation rates in microbial and invertebrate food webs. The database on BAFs/BSAFs and TMFs are almost exclusively derived from studies of POPs. Can the field based approaches be used for predicting bioaccumulation of the thousands of existing chemicals in commerce? Many of these substances such as substituted aromatics, current use pesticides, and phthalate esters may have low bioaccumulation due to metabolism. TMFs for metabolizable chemicals such as endosulfan, lindane and phthalate esters have negative values i.e. trophic dilution, in marine food webs, particularly when mammals are included as top predators. This has implications for assessments of bioaccumulation potential of new chemicals which, when lacking information on metabolism, currently assume it is zero for modeling purposes. Broader surveys of different classes of chemicals under field conditions would provide the ultimate validation of lab measured or predicted BCFs generated for these chemicals. However, field measurements are ultimately dependent on analytical methodologies which are typically not developed for most "existing" chemicals or their metabolites. This is probably the limiting factor on broader use of field BAFs, BSAFs, and TMFs for bioaccumulation assessment. This abstract does not necessarily reflect EPA policy.
Start time: 3:10 PM
389 (TOR-1117-856586) Bioaccumulation in Small Mammals.
Start time: 3:50 PM
Torres, K1, Johnson, M2, 1 Tetra Tech, Inc., Lafayette, CA, United States2 John Muir Institute of the Environment, UC Davis, Davis, CA, United States
Accurate predictions of chemical concentrations in tissues of small mammals are important for reducing uncertainty in ecological risk assessments. Small mammals are a key pathway for the trophic transfer of contaminants to predators. Bioaccumulation modeling can also be useful to improve our understanding of mechanisms involved in bioaccumulation, including absorption, distribution, metabolism, and excretion. Two general types of bioaccumulation models will be reviewed, statistic-based empirical models (e.g., bioaccumulation factors and regressions) and mechanistic models. The relative prevalence, advantages, and shortcomings of available modeling tools will be discussed. Direct measurements of tissue concentrations for risk assessments and monitoring are preferred over modeling in certain situations. Model testing with empirical measurements will be reviewed in the context of a study of bioaccumulation of arsenic, cadmium, copper, lead, and nickel body in house mice (Mus musculus) inhabiting a seasonal wetland in California. Published soil-to-small mammal bioaccumulation regression models produced accurate estimates of arsenic and lead body burdens, but failed to adequately predict copper and nickel levels in mice. A simple mechanistic model for cumulative assimilation of ingested metals overpredicted lead levels in mice generally by less than one order of magnitude, but greatly overpredicted concentrations of arsenic, copper, and nickel. Recommendations for further research and applications of bioaccumulation advancements in ecological risk assessments will be proposed.
390 (ROS-1117-725988) Reducing uncertainties in biotransfer modeling in meat and milk.
Start time: 4:10 PM
Rosenbaum, R1, McKone, T2, Jolliet, O1, 1 Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland2 University of California, Berkeley, California, United States of America
Improving indirect (human) exposure assessment with respect to biotransfer into biota is the main objective of this study. Much of the overall uncertainty in exposure is attributable to the estimation of biotransfers. Biotransfer factor (BTF) and carry over rate (CR) are measures of the fraction of ingested contaminant transferred to animal tissue. The most commonly used BTF model dates back seventeen years and in spite of its widespread use in multimedia exposure models few attempts have been made to advance or improve the highly uncertain Kow regressions. Furthermore, in the range of Kow where meat and milk become the dominant human exposure pathways these models provide clearly unrealistic CRs. Quantitative structure-property relationships, such as the molecular connectivity index (MCI), derived from the structural formula of a chemical and then correlated to experimentally determined BTFs/CRs, are explored for possible combination with an improved Kow regression further decreasing indirect exposure uncertainty. Literature suggests that MCI-methods significantly increase the accuracy of BTF/BCF estimations, reducing at the same time uncertainties linked to unreliable Kow measurements. A dynamic six compartment cow model has been developed to track the transport of a chemical into meat fat and milk within the cow. First results demonstrate that steady state is almost never reached in meat which in some cases also holds true for milk. Degradation within animal tissue is a currently neglected but important fate process to be included. Another problem of current biotransfer models was identified as they typically adopt single measured data points which often do not represent steady state concentrations, as the feeding experiment duration was not long enough. The dynamic cow model can assist in reinterpreting experimental data, including predicting the extension of experimental time series and the according (non-steady state) concentration reached during the cow lifetime. This leads to more consistent, less varying data points to derive a less uncertain CR-prediction regression model, combining Kow and MCI.
391 (HEN-1117-745179) U.S. EPA's methodology for developing national bioaccumulation factors.
Start time: 4:30 PM
Henry, T1, Cook, P2, Burkhard, L2, Endicott, D3, Sappington, K4, Winchester, E5, 1 U.S. EPA, Office of Water, Office of Science & Technology, Washington, DC, USA2 U.S. EPA, Office of Research & Development, National Health and Envrionmental Effects Research Laboratory, Duluth, MN, USA3 Great Lakes Environmental Center, Traverse City, MI, USA4 U.S. EPA, Office of Research & Development, National Center for Environmental Assessment, Washington, DC, USA5 U.S. EPA, Office of Research & Development, Office of Science Policy, Washington, DC, USA
In 2000, the U.S. Environmental Protection Agency (EPA)'s Office of Water published the Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health. This methodology incorporates a number of scientific advancements made over the past two decades, one of which is in the assessment of chemical exposure to humans through the food chain pathway. EPA's methodology uses trophic level-specific bioaccumulation factors (BAFs) and fish ingestion rates to account for exposure to chemicals from the consumption of freshwater and estuarine fish and shellfish. Although national-scale estimates, EPA's national BAFs are intended to account for major chemical and biological attributes that can affect bioaccumulation and can vary between regions and ecosystems. Therefore, within the EPA framework for deriving national BAFs, different procedures are used for deriving BAFs for different types of chemicals. Each procedure is specifically suited for the class and properties of chemicals to which the procedure applies. The BAF derivation methods used within EPA's framework range from empirically-based measurements of organism and media concentrations to mechanistically-based predictions based on chemical properties combined with food web modeling. To provide transparency, clarity and consistency, EPA has published the national BAF framework, including detailed discussion of the scientific basis, advantages, and limitations of each BAF derivation method. EPA's use of BAFs, which account for chemical accumulation in fish and shellfish from all potential exposure routes, ultimately results in more accuracy and certainty in setting national 304(a) ambient water quality criteria.
392 (WOO-1117-631936) BCF data analysis techniques: What are the most effective and efficient tools?
Start time: 4:50 PM
Woodburn, K1, 1 The Dow Chemical Company, Midland, MI, USA
Bioconcentration studies provide critical information for both aquatic and terrestrial risk assessments to evaluate the impacts of chemicals on wildlife species and potentially for uptake into human consumers. A key parameter resulting from such experiments is the bioconcentration factor or BCF value, and this value is ideally evaluated at steady-state conditions or using toxicokinetic parameters. The former situation may be unrealistic for many highly lipophilic materials which can require extremely long exposure timeframes for achievement of steady-state conditions. Pharmacokinetic modeling techniques can allow kinetic parameter estimation over shorter periods of time and provide insight into the key issues of absorption, distribution, and metabolism. A current regulatory guideline BCF study with fish typically requires a 28-day water exposure under flow-through conditions, followed by a minimum 14-day clearance period. Data on BCF values generated via empirical steady-state conditions will be compared to kinetic parameter-estimated BCFs. An additional issue that will be examined is the relative importance of dosimetry in bioconcentration studies. Current regulatory guidelines require two separate exposure concentration studies, differing in dose by a factor of ten; these studies are time, money, and animal intensive. Bioconcentration data will be examined as to whether the use of such dual exposure experiments is warranted, or if alternatives exist requiring less intensive use of animals with an acceptable level of accuracy. Supporting examples taken from case studies will be presented and discussed. All statistical analyses involve a comparison of means using the paired t-test.
393 (HEL-1117-728750) Assessing organic contaminants in fish: evaluating non-lethal sampling techniques and mobile passive sampling devices.
Start time: 5:10 PM
Heltsley, R1, Cope, W1, Shea, D1, Bringolf, R1, Kwak, T2, Malindzak, E1, 1 North Carolina State University, Raleigh, NC, USA2 USGS, North Carolina Cooperative Fish and Wildlife Research Unit, Raleigh, NC, USA
As concerns mount over the human health risks associated with consumption of fish contaminated with bioaccumulative persistent organic pollutants, there exists a need to better evaluate fish body burdens without lethally sampling many of the important commercial and sport species of interest. The aim of this study was to investigate two novel methods for estimating organic contaminants in fish that are a concern for both fish and human health. The removal of fish adipose fins, commonly done in mark-recapture studies with salmonid species, was evaluated as a non-lethal sampling technique to estimate concentrations of selected polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in flathead catfish Pylodictis olivaris, relative to those found in muscle fillets of the same fish. We also assessed the efficacy of using polydimethylsiloxane (PDMS) as a mobile passive sampling device (PSD) attached directly to wild flathead catfish for assessing location-specific exposure of the fish to waterborne contaminants. The results of this study have demonstrated for the first time that organic contaminant concentrations in adipose fin were highly correlated (r2 = 0.87) with muscle fillet concentrations, indicating that the adipose fin of certain fishes may be used to estimate tissue concentrations without the need for lethal sampling. Moreover, mobile PSDs attached directly to fish and used here for the first time, estimated sub ppb concentrations of waterborne PCBs and OCPs without any apparent harm to the fish, indicating that there are no practical or physical barriers to the use of mobile passive samplers attached to aquatic organisms.