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Redman A.D.,ExxonMobil | Mcgrath J.A.,HydroQual | Stubblefield W.A.,Oregon State University | Maki A.W.,Maki Consulting | Di Toro D.M.,University of Delaware
Environmental Toxicology and Chemistry | Year: 2012

Dissolved constituents of crude oil, particularly polycyclic aromatic hydrocarbons (PAHs), can contribute substantially to the toxicity of aquatic organisms. Measured aqueous concentrations of high-molecular weight PAHs (e.g., chrysenes, benzo[a]pyrene) as well as long-chain aliphatic hydrocarbons can exceed the theoretical solubility of these sparingly soluble compounds. This is attributed to the presence of a "microdroplet" or colloidal oil phase. It is important to be able to quantify the dissolved fraction of these compounds in oil-in-water preparations that are commonly used in toxicity assays because the interpretation of test results often assumes that the compounds are dissolved. A method is presented to determine the microdroplet contribution in crude oil-in-water preparations using a comparison of predicted and measured aqueous concentrations. Measured concentrations are reproduced in the model by including both microdroplets and dissolved constituents of petroleum hydrocarbons. Microdroplets were found in all oil-water preparation data sets analyzed. Estimated microdroplet oil concentrations typically ranged from 10 to 700μg oil/L water. The fraction of dissolved individual petroleum hydrocarbons ranges from 1.0 for highly soluble compounds (e.g., benzene, toluene, ethylbenzene, and xylene) to far less than 0.1 for sparingly soluble compounds (e.g., chrysenes) depending on the microdroplet oil concentration. The presence of these microdroplets complicates the interpretation of toxicity test data because they may exert an additional toxic effect due to a change in the exposure profile. The implications of the droplet model on toxicity are also discussed in terms of both dissolved hydrocarbons and microdroplets. © 2012 SETAC. Source

Adams W.J.,Rio Tinto Alcan | Blust R.,University of Antwerp | Borgmann U.,Environment Canada | Brix K.V.,University of Miami | And 7 more authors.
Integrated Environmental Assessment and Management | Year: 2011

As part of a SETAC PellstonWorkshop, we evaluated the potential use of metal tissue residues for predicting effects in aquatic organisms. This evaluation included consideration of different conceptual models and then development of several case studies on how tissue residues might be applied for metals, assessing the strengths and weaknesses of these different approaches.We further developed a new conceptual model in which metal tissue concentrations from metal-accumulating organisms (principally invertebrates) that are relatively insensitive to metal toxicity could be used as predictors of effects in metal-sensitive taxa that typically do not accumulate metals to a significant degree. Overall, we conclude that the use of tissue residue assessment for metals other than organometals has not led to the development of a generalized approach as in the case of organic substances. Species-specific and site-specific approaches have been developed for one or more metals (e.g., Ni). The use of gill tissue residues within the biotic ligand model is another successful application. Aquatic organisms contain a diverse array of homeostatic mechanisms that are both metal- and species-specific. As a result, use of whole-body measurements (and often specific organs) for metals does not lead to a defensible position regarding risk to the organism. Rather, we suggest that in the short term, with sufficient validation, species- and site-specific approaches for metals can be developed. In the longer term it may be possible to use metal-accumulating species to predict toxicity to metal-sensitive species with appropriate field validation. © 2010 SETAC. Source

Redman A.D.,HydroQual | Mihaich E.,Environmental and Regulatory Resources | Woodburn K.,Dow Corning | Paquin P.,HydroQual | And 3 more authors.
Environmental Toxicology and Chemistry | Year: 2012

Cyclic volatile methyl siloxanes (cVMS) are important consumer materials that are used in personal care products and industrial applications. These compounds have gained increased attention in recent years following the implementation of chemical legislation programs worldwide. Industry-wide research programs are being conducted to characterize the persistence, bioaccumulation, and toxicity (PBT) properties of cVMS materials. As part of this larger effort, a tissue-based risk assessment was performed to further inform the regulatory decision-making process. Measured tissue concentrations of cVMS compounds in fish and benthic invertebrates are compared with critical target lipid body burdens (CTLBBs) as estimated with the target lipid model (TLM) to evaluate risk. Acute and chronic toxicity data for cVMS compounds are compared with data for nonpolar organic chemicals to validate application of the TLM in this effort. The analysis was extended to estimate the contribution from metabolites to the overall cVMS-derived tissue residues using a food chain model calibrated to laboratory and field data. Concentrations of cVMS materials in biota from several trophic levels (e.g., invertebrates, fish) are well below the estimated CTLBBs associated with acute and chronic effects. This analysis, when combined with the limited biomagnification potential for cVMS compounds that was observed in the field, suggests that there is little risk of adverse effects from cVMS materials under present-day emission levels. © 2012 SETAC. Source

Brix K.V.,EcoTox | Brix K.V.,University of Miami | Keithly J.,Parametrix Inc. | Santore R.C.,HydroQual | And 2 more authors.
Science of the Total Environment | Year: 2010

Zinc (Zn) risks from stormwater runoff to an aquatic ecosystem were studied. Monitoring data on waterborne, porewater, and sediment Zn concentrations collected at 20 stations throughout a stormwater collection/detention facility consisting of forested wetlands, a retention pond and first order stream were used to conduct the assessment. Bioavailability in the water column was estimated using biotic ligand models for invertebrates and fish while bioavailability in the sediment was assessed using acid volatile sulfide-simultaneously extracted metal (AVS-SEM). The screening level assessment indicated no significant risks were posed to benthic organisms from Zn concentrations in sediments and pore water. As would be expected for stormwater, Zn concentrations were temporally quite variable within a storm event, varying by factors of 2 to 4. Overall, probabilistic assessment indicated low (5-10% of species affected) to negligible risks in the system, especially at the discharge to the first order stream. Moderate to high risks (10-50% of species affected) were identified at sampling locations most upgradient in the collection system. The largest uncertainty with the assessment is associated with how best to estimate chronic exposure/risks from time-varying exposure concentrations. Further research on pulse exposure metal toxicity is clearly needed to assess stormwater impacts on the environment. © 2009 Elsevier B.V. All rights reserved. Source

Redman A.D.,ExxonMobil | Parkerton T.F.,ExxonMobil | McGrath J.A.,HydroQual | Di Toro D.M.,University of Delaware
Environmental Toxicology and Chemistry | Year: 2012

A spreadsheet model (PETROTOX) is described that predicts the aquatic toxicity of complex petroleum substances from petroleum substance composition. Substance composition is characterized by specifying mass fractions in constituent hydrocarbon blocks (HBs) based on available analytical information. The HBs are defined by their mass fractions within a defined carbon number range or boiling point interval. Physicochemical properties of the HBs are approximated by assigning representative hydrocarbons from a database of individual hydrocarbons with associated physicochemical properties. A three-phase fate model is used to simulate the distribution of each structure among the water-, air-, and oil-phase liquid in the laboratory test system. Toxicity is then computed based on the predicted aqueous concentrations and aquatic toxicity of each structure and the target lipid model. The toxicity of the complex substance is computed assuming additivity of the contribution of the individual assigned hydrocarbons. Model performance was evaluated by using direct comparisons with measured toxicity data for petroleum substances with sufficient analytical characterization to run the model. Indirect evaluations were made by comparing predicted toxicity distributions using analytical data on petroleum substances from different product categories with independent, empirical distributions of toxicity data available for the same categories. Predictions compared favorably with measured aquatic toxicity data across different petroleum substance categories. These findings demonstrate the utility of PETROTOX for assessing environmental hazards of petroleum substances given knowledge of substance composition. © 2012 SETAC. Source

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