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Fantke P.,Technical University of Denmark | Arnot J.A.,ARC Arnot Research and Consulting | Arnot J.A.,University of Toronto | Doucette W.J.,Utah State University
Journal of Environmental Management | Year: 2016

Experimental data and models for plant bioaccumulation of organic contaminants play a crucial role for assessing the potential human and ecological risks associated with chemical use. Plants are receptor organisms and direct or indirect vectors for chemical exposures to all other organisms. As new experimental data are generated they are used to improve our understanding of plant-chemical interactions that in turn allows for the development of better scientific knowledge and conceptual and predictive models. The interrelationship between experimental data and model development is an ongoing, never-ending process needed to advance our ability to provide reliable quality information that can be used in various contexts including regulatory risk assessment. However, relatively few standard experimental protocols for generating plant bioaccumulation data are currently available and because of inconsistent data collection and reporting requirements, the information generated is often less useful than it could be for direct applications in chemical assessments and for model development and refinement. We review existing testing guidelines, common data reporting practices, and provide recommendations for revising testing guidelines and reporting requirements to improve bioaccumulation knowledge and models. This analysis provides a list of experimental parameters that will help to develop high quality datasets and support modeling tools for assessing bioaccumulation of organic chemicals in plants and ultimately addressing uncertainty in ecological and human health risk assessments. © 2016 Elsevier Ltd Source

Mackay D.,Trent University | Arnot J.A.,University of Toronto | Arnot J.A.,ARC Arnot Research and Consulting | Gobas F.A.P.C.,Simon Fraser University | Powell D.E.,Dow Corning
Environmental Toxicology and Chemistry | Year: 2013

Five widely used metrics of bioaccumulation in fish are defined and discussed, namely the octanol-water partition coefficient (KOW), bioconcentration factor (BCF), bioaccumulation factor (BAF), biomagnification factor (BMF), and trophic magnification factor (TMF). Algebraic relationships between these metrics are developed and discussed using conventional expressions for chemical uptake from water and food and first-order losses by respiration, egestion, biotransformation, and growth dilution. Two BCFs may be defined, namely as an equilibrium partition coefficient KFW or as a nonequilibrium BCFK in which egestion losses are included. Bioaccumulation factors are shown to be the product of the BCFK and a novel equilibrium multiplier M containing 2 ratios, namely, the diet-to-water concentration ratio and the ratio of uptake rate constants for respiration and dietary uptake. Biomagnification factors are shown to be proportional to the lipid-normalized ratio of the predator/prey values of BCFK and the ratio of the equilibrium multipliers. Relationships with TMFs are also discussed. The effects of chemical hydrophobicity, biotransformation, and growth are evaluated by applying the relationships to a range of illustrative chemicals of varying KOW in a linear 4-trophic-level food web with typical values for uptake and loss rate constants. The roles of respiratory and dietary intakes are demonstrated, and even slow rates of biotransformation and growth can significantly affect bioaccumulation. The BCFKs and the values of M can be regarded as the fundamental determinants of bioaccumulation and biomagnification in aquatic food webs. Analyzing data from food webs can be enhanced by plotting logarithmic lipid-normalized concentrations or fugacities as a linear function of trophic level to deduce TMFs. Implications for determining bioaccumulation by laboratory tests for regulatory purposes are discussed. © 2013 SETAC. Source

Costanza J.,U.S. Environmental Protection Agency | Lynch D.G.,U.S. Environmental Protection Agency | Boethling R.S.,U.S. Environmental Protection Agency | Arnot J.A.,University of Toronto | Arnot J.A.,ARC Arnot Research and Consulting
Environmental Toxicology and Chemistry | Year: 2012

The fish bioconcentration factor (BCF), as calculated from controlled laboratory tests, is commonly used in chemical management programs to screen chemicals for bioaccumulation potential. The bioaccumulation factor (BAF), as calculated from field-caught fish, is more ecologically relevant because it accounts for dietary, respiratory, and dermal exposures. The BCFBAF™ program in the U.S. Environmental Protection Agency's Estimation Programs Interface Suite (EPI Suite™ Ver 4.10) screening-level tool includes the Arnot-Gobas quantitative structure-activity relationship model to estimate BAFs for organic chemicals in fish. Bioaccumulation factors can be greater than BCFs, suggesting that using the BAF rather than the BCF for screening bioaccumulation potential could have regulatory and resource implications for chemical assessment programs. To evaluate these potential implications, BCFBAF was used to calculate BAFs and BCFs for 6,034U.S. high- and medium-production volume chemicals. The results indicate no change in the bioaccumulation rating for 86% of these chemicals, with 3% receiving lower and 11% receiving higher bioaccumulation ratings when using the BAF rather than the BCF. All chemicals that received higher bioaccumulation ratings had log KOWvalues greater than 4.02, in which a chemical's BAF was more representative of field-based bioaccumulation than its BCF. Similar results were obtained for 374 new chemicals. Screening based on BAFs provides ecologically relevant results without a substantial increase in resources needed for assessments or the number of chemicals screened as being of concern for bioaccumulation potential. © 2012 SETAC. Source

Papa E.,University of Insubria | van der Wal L.,REACH Mastery | Arnot J.A.,ARC Arnot Research and Consulting | Arnot J.A.,University of Toronto | Gramatica P.,University of Insubria
Science of the Total Environment | Year: 2014

Bioaccumulation in fish is a function of competing rates of chemical uptake and elimination. For hydrophobic organic chemicals bioconcentration, bioaccumulation and biomagnification potential are high and the biotransformation rate constant is a key parameter. Few measured biotransformation rate constant data are available compared to the number of chemicals that are being evaluated for bioaccumulation hazard and for exposure and risk assessment. Three new Quantitative Structure-Activity Relationships (QSARs) for predicting whole body biotransformation half-lives (HLN) in fish were developed and validated using theoretical molecular descriptors that seek to capture structural characteristics of the whole molecule and three data set splitting schemes. The new QSARs were developed using a minimal number of theoretical descriptors (n=9) and compared to existing QSARs developed using fragment contribution methods that include up to 59 descriptors. The predictive statistics of the models are similar thus further corroborating the predictive performance of the different QSARs; Q2 ext ranges from 0.75 to 0.77, CCCext ranges from 0.86 to 0.87, RMSE in prediction ranges from 0.56 to 0.58. The new QSARs provide additional mechanistic insights into the biotransformation capacity of organic chemicals in fish by including whole molecule descriptors and they also include information on the domain of applicability for the chemical of interest. Advantages of consensus modeling for improving overall prediction and minimizing false negative errors in chemical screening assessments, for identifying potential sources of residual error in the empirical HLN database, and for identifying structural features that are not well represented in the HLN dataset to prioritize future testing needs are illustrated. © 2013 Elsevier B.V. Source

Mackay D.,Trent University | Mccarty L.S.,Ls Mccarty Scientific Research And Consulting | Arnot J.A.,ARC Arnot Research and Consulting | Arnot J.A.,University of Toronto
Environmental Toxicology and Chemistry | Year: 2014

There is continuing debate about the merits of exposure-based toxicity metrics such as median lethal concentration (LC50) versus organism-based metrics such as critical body residue (CBR) as indicators of chemical toxicity to aquatic organisms. To demonstrate relationships and differences between these 2 metrics, the authors applied a simple one-compartment toxicokinetic mass-balance model for water-exposed fish for a series of hypothetical organic chemicals exhibiting baseline narcotic toxicity. The authors also considered the influence of several toxicity-modifying factors. The results showed that the results of standard toxicity tests, such as the LC50, are strongly influenced by several modifying factors, including chemical and organism characteristics such as hydrophobicity, body size, lipid content, metabolic biotransformation, and exposure durations. Consequently, reported LC50s may not represent consistent dose surrogates and may be inappropriate for comparing the relative toxicity of chemicals. For comparisons of toxicity between chemicals, it is preferable to employ a delivered dose metric, such as the CBR. Reproducible toxicity data for a specific combination of chemical, exposure conditions, and organism can be obtained only if the extent of approach to steady state is known. Suggestions are made for revisions in test protocols, including the use of models in advance of empirical testing, to improve the efficiency and effectiveness of tests and reduce the confounding influences of toxicity-modifying factors, especially exposure duration and metabolic biotransformation. This will assist in linking empirical measurements of LC50s and CBRs, 2 different but related indicators of aquatic toxicity, and thereby improve understanding of the large existing database of aquatic toxicity test results. © 2014 SETAC. Source

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