How reliable are field‐derived biomagnification factors and trophic magnification factors as indicators of bioaccumulation potential? Conclusions from a case study on per‐ and polyfluoroalkyl substances

Abstract

This review examines the usefulness of the metrics BMF (biomagnification factor) and TMF (trophic magnification factor), derived from field measurements of the levels of contaminants in naturally occurring biota, for characterizing the bioaccumulation potential ("B") of chemicals. Trophic magnification factor and BMF values greater than 1.0 are often considered to be the most conclusive indicators of B status, and the TMF criterion has been referred to as the "gold standard" for B categorization. Although not wishing to dispute the theoretical primacy of field-derived BMFs and TMFs as B metrics, we make the case that, in practice, the study-to-study (and even within-study) variability of the results is so great that they are of very restricted usefulness for assessing B status, at least in the case of the per-and polyfluoroalkyl substances (PFASs), on which we focus here. This conclusion is based on an analysis of the results of 24 peer-reviewed studies reporting field-derived BMFs or TMFs for 14 PFASs, for which BMF values often range over several orders of magnitude from <<1.0 to >>1.0, sometimes even in the same study. For TMFs, the range is a factor of approximately 20 for the most intensely studied PFASs (perfluorooctanoic acid [PFOA] and perfluorooctanesulfonic acid [PFOS]). We analyze the possible causes for such variability: To some extent it results from the differing ways in which the metrics are expressed, but most of the scatter is likely attributable to such factors as nonachievement of the tacitly assumed steady-state conditions, uncertainties in the feeding ecology, the impact of metabolism of precursor compounds, and so forth. As more trustworthy alternatives to field-derived BMFs and TMFs, we suggest the implementation of dietary BMF studies performed under strictly controlled conditions on aquatic, terrestrial, and avian species, as well as the consideration of measured elimination half-lives, which have been demonstrated to be directly related to BMF values. Integr Environ Assess Manag 2016;12:6-20.

Practical advice for selecting or determining trophic magnification factors for application under the European Union Water Framework Directive

“…PFOS is a WFD priority substance for which an EQS has been established because there is considerable evidence that it biomagnifies (reviewed by Franklin [] and Houde et al []). TMFs for PFOS in aquatic food webs that include fish and no endotherms range widely from less than 1 to 6.4 (Table S5), making it difficult to choose a specific value.…”

“…In the context of the WFD, TMF selection is therefore a critical issue, and reported values of this field‐derived metric may be quite variable for a given contaminant (Franklin ), even for well‐known and well‐studied chemicals like polychlorinated biphenyls (PCBs). The sources of TMF variability relate to the chemical properties, experimental design, and the ecosystem(s) considered.…”

Evidence for the Trophic Transfer of Perfluoroalkylated Substances in a Temperate Macrotidal Estuary

“…11,22 Other common pitfalls that may affect the validity and reliability of TMFs have been extensively reviewed by Borgå et al 19 Albeit there exists no straight answer to such conundrums, the determination of TMFs could possibly be improved via appropriate study design and robust data treatment procedures. Uncertainties due to sampling design, analytical pitfalls, and statistical issues have been articulated in recent reviews, 19,27,29 but some aspects remain yet to be addressed in practice. This constituted a first important knowledge gap to be explored.…”

Spatial and trophic biomonitoring of trace metals in aquatic environments following the Mt. Polley Mine tailings spill

“…To assess the movement of metals in the food web, and also to quantify links between the abiotic environment and the food web, "transference factors" (TF) are used, which are based on the ratio of analyte concentrations between two materials in the environment. This measure is often referred to as a "biomagnification factor" in food web studies (Franklin, 2016) (Kim and Kim, 2016). The TF index is used to assess the relationship between individual links in the environment but cannot be used to assess magnification or transfer in the food web as a whole.…”

“…Log transformation is appropriate because biomagnification is often exponential in aquatic food webs (Franklin, 2016).…”