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

Abstract

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 and trophic dilution of human pharmaceuticals across trophic positions of an effluent-dependent wadeable stream

“…Chemicals with BMFs greater than unity are suggested to accumulate from prey to predator. However, if predators are able to metabolize a compound which is poorly biotransformed by organisms at lower TPs, it is difficult to evaluate the bioaccumulation between different predator -prey pairs without accurate biotransformation rates of chemicals in each species [37]. Clearly, comparative biotransformation of pharmaceuticals and other CECs are needed in fish [10].…”

Application of stable isotope mixing models for defining trophic biomagnification pathways of mercury and selenium

“…The lower regression strength observed in THg-d 15 N std regressions against MeHg-d 15 N std would appear to be the product of a number of factors. These include (1) selective uptake of MeHg over inorganic Hg within the guts of predators as a result of cellular partitioning (Mason et al 1995), (2) bioaccumulation of inorganic species of Hg through dissolved or sedimentary phases (Borgå et al 2012;Coelho et al 2013), (3) the fraction of THg as MeHg in invertebrates varying widely as a result of feeding strategies and speciesspecific habits (Evers et al 2008;Coelho et al 2013), and (4) the insolubility of inorganic Hg, such as mercury selenide (HgSe), contained within prey, making it unavailable for dietary absorption (Ralston and Raymond 2010). All of these conditions would reduce regression strength.…”

Aquatic bioaccumulation and trophic transfer of tetrabromobisphenol-A flame retardant introduced from a typical e-waste recycling site

“…Biotransformation of TBBP-A in fish species have been reported previously (Shen et al 2012), although it is occurred in different species from our fish. Besides biotransformation and assimilation efficiencies, the relative importance of exposure routes other than dietary uptake, e.g., respiratory uptake, in organisms at lower TLs could also result in trophic dilution of a chemical (Borgå et al 2004(Borgå et al , 2012. When assessing the TMF for a chemical, it is presumed that the major exposure route for a species is through its diet.…”

“…When assessing the TMF for a chemical, it is presumed that the major exposure route for a species is through its diet. However, for aquatic species that take up chemicals through other exposure pathways such as respiratory surfaces can highly likely affect the determination of TMF in an aquatic food web (Borgå et al 2004(Borgå et al , 2012. Although there is, to our knowledge, no such a study demonstrating the relative fractions of respiratory uptake of TBBP-A in aquatic species, it is likely occurring because of the relatively high water solubility of TBBP-A (63 μg/l) (European Chemicals Bureau 2008).…”