Frank A. P. C. Gobas

Relationship between bioconcentration in fish and steric factors of hydrophobic chemicals

Abstract Most polychlorinated naphthalones (PCN) accumulate rapidly according to their hydrophobicity. The uptake and ellmination rate constants are comparable to those of chlorinated benzenes and biphenyls. For most PCN-congeners the resulting bioaccumulation factors show an increase with increasing hydrophobicity. For higher K d,oct -values (>10 5 ) however, no further increase of K c is observed (K c. max. = 3.5.10 4 ). For the two hepta- and the octachloronaphthalenes no detectable concentrations are found in the fishes, although no restricted blo-availability could be expected. Based on these observations and on data obtained from the literature. a loss of membrane permeation is suggested for hydrophobic molecules with widths over 9.5 A. In addition a membrane permeation model, as part of the accumulation process of hydrophobic chemicals. Is proposed, which is based on diffusion and partition processes.

A food web bioaccumulation model for organic chemicals in aquatic ecosystems

The present study examines a new bioaccumulation model for hydrophobic organic chemicals in aquatic food webs. The purpose of the model is to provide site-specific estimates of chemical concentrations and associated bioconcentration factors, bioaccumulation factors, and biota-sediment accumulation factors in organisms of aquatic food webs using a limited number of chemical, organism, and site-specific data inputs. The model is a modification of a previous model and incorporates new insights regarding the mechanism of bioaccumulation derived from laboratory experiments and field studies as well as improvements in model parameterization. The new elements of the model include: A model for the partitioning of chemicals into organisms; kinetic models for predicting chemical concentrations in algae, phytoplankton, and zooplankton; new allometric relationships for predicting gill ventilation rates in a wide range of aquatic species; and a mechanistic model for predicting gastrointestinal magnification of organic chemicals in a range of species. Model performance is evaluated using empirical data from three different freshwater ecosystems involving 1,019 observations for 35 species and 64 chemicals. The effects of each modification on the models performance are illustrated. The new model is able to provide better estimates of bioaccumulation factors in comparison to the previous food web bioaccumulation model while the model input requirements remain largely unchanged.

A model for predicting the bioaccumulation of hydrophobic organic chemicals in aquatic food-webs: application to Lake Ontario

Abstract A simple model is presented for estimating concentrations of hydrophobic organic substances in various organisms of aquatic food-webs from chemical concentrations in water and sediments. The model is applied to the Lake Ontario food-web and shown to be in satisfactory agreement with field data. Model confidence is determined by Monte-Carlo simulation. Since the model only requires basic data to characterize the organisms of the food-web, chemical properties and environmental conditions, the model is an easy-to-apply and practical tool for the management of organic contaminants on an “ecosystem” level.

Dynamics of dietary bioaccumulation and faecal elimination of hydrophobic organic chemicals in fish

A compilation of available literature data on uptake efficiencies of hydrophobic, organic chemicals from food by fish is presented. It is shown that the uptake efficiency of chemical from food (EO) follows a relationship with the 1-octanol-water partition coefficient (KOW), i.e., 1EO = 5.3.10−8.KOW + 2.3. A model is derived for chemical uptake from food, which is shown to be consistent with the observed food-uptake data. The equations provide an explanation for the phenomenon of food chain accumulation, which is observed in natural ecosystems for several hydrophobic halogenated aromatic hydrocarbons.

Intestinal absorption and biomagnification of organic contaminants in fish, wildlife, and humans

Methods for the regulatory assessment of the bioaccumulation potential of organic chemicals are founded on empirical measurements and mechanistic models of dietary absorption and biomagnification. This study includes a review of the current state of knowledge regarding mechanisms and models of intestinal absorption and biomagnification of organic chemicals in organisms of aquatic and terrestrial food chains and also includes a discussion of the implications of these models for assessing the bioaccumulation potential of organic chemicals. Four mechanistic models, including biomass conversion, digestion or gastrointestinal magnification, micelle-mediated diffusion, and fat-flush diffusion, are evaluated. The models contain many similarities and represent an evolution in understanding of chemical bioaccumulation processes. An important difference between the biomagnification models is whether intestinal absorption of an ingested contaminant occurs solely via passive molecular diffusion through serial resistances or via facilitated diffusion that incorporates an additional advective transport mechanism in parallel (i.e., molecular ferrying within gastrointestinal micelles). This difference has an effect on the selection of physicochemical properties that best anticipate the bioaccumulative potential of commercial chemicals in aquatic and terrestrial food chains. Current regulatory initiatives utilizing Kow threshold criteria to assess chemical bioaccumulation potential are shown to be unable to identify certain bioaccumulative substances in air-breathing animals. We urge further research on dietary absorption and biomagnification of organic chemicals to develop better models for assessing the bioaccumulative nature of organic chemicals.

Trophic magnification factors: Considerations of ecology, ecosystems, and study design

Recent reviews by researchers from academia, industry, and government have revealed that the criteria used by the Stockholm Convention on persistent organic pollutants under the United Nations Environment Programme are not always able to identify the actual bioaccumulative capacity of some substances, by use of chemical properties such as the octanol-water partitioning coefficient. Trophic magnification factors (TMFs) were suggested as a more reliable tool for bioaccumulation assessment of chemicals that have been in commerce long enough to be quantitatively measured in environmental samples. TMFs are increasingly used to quantify biomagnification and represent the average diet-to-consumer transfer of a chemical through food webs. They differ from biomagnification factors, which apply to individual species and can be highly variable between predator-prey combinations. The TMF is calculated from the slope of a regression between the chemical concentration and trophic level of organisms in the food web. The trophic level can be determined from stable N isotope ratios (δ(15) N). In this article, we give the background for the development of TMFs, identify and discuss impacts of ecosystem and ecological variables on their values, and discuss challenges and uncertainties associated with contaminant measurements and the use of δ(15) N for trophic level estimations. Recommendations are provided for experimental design, data treatment, and statistical analyses, including advice for users on reporting and interpreting TMF data. Interspecies intrinsic ecological and organismal properties such as thermoregulation, reproductive status, migration, and age, particularly among species at higher trophic levels with high contaminant concentrations, can influence the TMF (i.e., regression slope). Following recommendations herein for study design, empirical TMFs are likely to be useful for understanding the food web biomagnification potential of chemicals, where the target is to definitively identify if chemicals biomagnify (i.e., TMF > or < 1). TMFs may be less useful in species- and site-specific risk assessments, where the goal is to predict absolute contaminant concentrations in organisms in relation to threshold levels.

Bioaccumulation behaviour of polybrominated diphenyl ethers (PBDEs) in a Canadian Arctic marine food web

A comparative analysis of the bioaccumulation behaviour of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) was conducted involving simultaneous measurements of PBDE and PCB concentrations in organisms of a Canadian Arctic marine food web. Concentrations of individual PBDE congeners (BDE-28, -47, -99, -153, -154 and -183) in Arctic marine sediments (0.001-0.5 ng.g(-1) dry wt) and biota (0.1-30 ng.g(-1) wet wt) were low compared to those concentrations in biota from urbanized/industrial regions. While recalcitrant PCB congeners exhibited a high degree of biomagnification in this food web, PBDE congeners exhibited negligible biomagnification. Trophic magnification factors (TMFs) of PCBs ranged between 2.9 and 11, while TMFs of PBDEs ranged between 0.7 and 1.6. TMFs of several PBDE congeners (BDE-28, -66, -99, -100, -118, -153 and -154) were not statistically greater than 1, indicating a lack of food web magnification. BDE-47 was the only PBDE with a TMF (i.e. 1.6) statistically greater than 1, hence showing evidence of biomagnification in the food web. However, the TMF of BDE-47 (1.6) was substantially lower than TMFs of recalcitrant Cl(5)-Cl(7) PCBs (TMFs~9-11). Species-specific bioaccumulation factors (BAFs) of PBDEs in homeotherms were much smaller than those for PCBs. This further indicates the low degree or absence of biomagnification of PBDEs compared to PCBs in this food web. The field observations suggest PBDEs exhibit a relatively rapid rate of depuration though biotransformation in Arctic marine organisms, which is consistent with laboratory studies in fish and rats.

A simple, novel method for the quantitative analysis of coplanar (non-ortho substituted) polychlorinated biphenyls in environmental samples

Abstract A novel method is presented for the analysis of coplanar (i.e. non-ortho substituted) polychlorinated biphenyls (PCBs) in environmental samples. The new procedure combines methylene chloride extraction, gel permeation and Florisil chromatography. Recovery efficiencies and resolution of the Florisil column method are reported and compared to the carbon column method. It is shown that both the Florisil column and the Carbon column techniques give comparable results with recovery efficiencies for PCBs 77, 126 and 169 of nearly 100%. Excellent resolution and reproducibility for quantitative analysis of coplanar PCBs are obtained in complex PCB mixtures. The Florisil method is considerably simpler than the carbon column technique and better suited for routine analysis.

The sorptive capacity of animal protein

Partition coefficients that are used to predict concentrations of hydrophobic organic chemicals in biota (e.g., the bioconcentration factor) often assume that the sorptive capacity of an organism or tissue is adequately represented by its lipid content. In lean organisms and tissues, however, theory suggests that partitioning may be strongly influenced by the sorptive capacity of nonlipid materials, such as protein. Little is known about the sorptive capacity of proteins for hydrophobic organic chemicals, and methods to include proteins in bioaccumulation models do not exist. Here, we present a compilation and meta-analysis of published data to estimate the relative sorptive capacities of animal proteins and lipids for neutral organic chemicals. We found that the estimated sorptive capacity of protein in solid animal tissues ranged from around 1 to 10% that of lipid for compounds with a log octanol/water partition coefficient (K(OW)) of greater than two. The sorptive capacity of blood protein (albumin) appeared to be substantially higher than this, especially for low-K(OW) chemicals. For modeling purposes, we recommend estimating the sorptive capacity of animal protein as 5% that of lipid. According to this estimate, the sorptive capacity of an animal or tissue will be dominated by the contribution from protein if the lipid content makes up less than 5% of the dry-weight organic content. In such situations, a consideration of the sorptive capacity of nonlipid constituents, such as protein, will permit more accurate predictions of chemical accumulation and distribution.

Time Response of the Lake Ontario Ecosystem to Virtual Elimination of PCBs.

This study presents the development, application, and partial validation of an integrated time-dependent whole ecosystem environmental fate and food-chain bioaccumulation model of the time response of PCB concentrations in various media and organisms of Lake Ontario to changes in external PCB loadings to the lake. The model and observed PCB concentration time trends in herring gull eggs, lake trout, sculpins, smelt, water, and sediment data are used to reconstruct the time response and PCB loading history for Lake Ontario and to assess the past and future time response of PCB concentrations in the Lake Ontario food web to PCB inputs. Estimates of loadings, concentrations, half-lifetimes, and changes in PCB composition over time are discussed.