Environmental exposure of aquatic and sediment organisms to lipophilic compounds may occur through the water column, diet, and/or sediment. At a recent SETAC Pellston workshop on bioaccumulation processes, primarily in aquatic systems, it was proposed that bioaccumulative substances be defined as "substances which biomagnify in the food web" - i.e., lipid-normalized concentrations increase with increasing trophic position (SETAC, 2008). Based on this definition, it was concluded that the most relevant criterion for assessing the potential of a chemical to bioaccumulate was the trophic magnification factor (TMF), and that the most conclusive evidence to demonstrate that a chemical substance biomagnifies was a TMF > 1. TMFs are increasingly being used to assess bioaccumulation and biomagnification of chemicals in the environment (Houde et al., 2008) and data suggest that TMFs may be broadly applied across systems that differ considerably in their location and characteristics.
In summary, the TMF is considered to be a valuable parameter for proper assessment of a compound's potential to bioaccumulate/biomagnify in aquatic food webs. A general hierarchical ranking of bioaccumulation measures for highly lipophilic chemicals (log Kow >5), particularly in aquatic systems, has been proposed (Gobas et al., 2008): (1) TMF, (2) biomagnification factors (BMF), and (3) bioconcentration factors (BCF).
Currently, TMF values are calculated from chemical residues in field-collected biota. For new chemicals, alternative methods must be developed for assessment of TMF. A range of tools are known to exist, such as solid-phase microextraction (SPME) methods for rapid measurement of residue concentrations (lipid-adjusted), a variety of in silico and in vitro methods to determine metabolism, and computer models that purport to predict biota concentrations in aquatic species of a constructed food web (e.g., AQUAWEB, ACC-Human, and TAO). Such methods may be used together or with other approaches to produce an estimation of a chemical's TMF.
(1) Literature search and appraisal of existing techniques that could be employed for estimating TMFs.
(2) Current assessment methods to determine a chemical's TMF involve extensive field sampling and analytical residue analysis of a large number of food web organisms across several trophic levels, a process which is expensive, time-consuming, and animal intensive (e.g., Houde et al., 2008). This overall aim of this proposal is to develop a scheme and tools for estimating a chemical's TMF value, using laboratory testing, computer modeling and/or field methods.
(3) The project should involve a detailed and verifiable testing plan examining a range of chemicals with previously-determined field-measured TMFs. The selected compounds should encompass a range of TMFs, from <1 to >1. The test plan should consider: (1) estimation of TMFs for existing chemicals with field residues in aquatic systems; and (2) estimation of TMFs for "new" chemicals via a combination of modelling, in vitro, and/or in vivo testing methods.
(4) In addition, the predictive tools should be evaluated using selected chemicals for which there is no existing data on TMF.
Gobas F, de Wolf W, Verbruggen E, and Plotzke K. 2008. SETAC Pellston Workshop-Revisiting Bioaccumulation Criteria. 29th Annual Meeting of the Society of Environmental Toxicology and Chemistry; Tampa, Florida, 16-20 November 2008.
Houde M, Muir DCG, Kidd KA, Guildford S, Drouillard K, Evans, MS, Wang X, Whittle DM, Haffner D, and Kling H. 2008. Influence of lake characteristics on the biomagnification of persistent organic pollutants in lake trout food webs. Environ. Toxicol. Chem. 27: 2169-2178.
SETAC. 2008. Pellston Workshop: Science-based Guidance for the Evaluation and Identification of PBTs and POPs, 27-31 January 2008, Pensacola, FL, USA. Proceedings to be published in Integrated Environmental Assessment and Management in 2009.