Evaluation of Bioaccumulation Using In Vivo Laboratory and Field Studies

Abstract

A primary consideration in the evaluation of chemicals is the potential for substances to be absorbed and retained in an organism's tissues (i.e., bioaccumulated) at concentrations sufficient to pose health concerns. Substances that exhibit properties that enable biomagnification in the food chain (i.e., amplification of tissue concentrations at successive trophic levels) are of particular concern due to the elevated long‐term exposures these substances pose to higher trophic organisms, including humans. Historically, biomarkers of in vivo chemical exposure (e.g., eggshell thinning, bill deformities) retrospectively led to the identification of such compounds, which were later categorized as persistent organic pollutants. Today, multiple bioaccumulation metrics are available to quantitatively assess the bioaccumulation potential of new and existing chemicals and identify substances that, upon or before environmental release, may be characterized as persistent organic pollutants. This paper reviews the various in vivo measurement approaches that can be used to assess the bioaccumulation of chemicals in aquatic or terrestrial species using laboratory‐exposed, field‐deployed, or collected organisms. Important issues associated with laboratory measurements of bioaccumulation include appropriate test species selection, test chemical dosing methods, exposure duration, and chemical and statistical analyses. Measuring bioaccumulation at a particular field site requires consideration of which test species to use and whether to examine natural populations or to use field‐deployed populations. Both laboratory and field methods also require reliable determination of chemical concentrations in exposure media of interest (i.e., water, sediment, food or prey, etc.), accumulated body residues, or both. The advantages and disadvantages of various laboratory and field bioaccumulation metrics for assessing biomagnification potential in aquatic or terrestrial food chains are discussed. Guidance is provided on how to consider the uncertainty in these metrics and develop a weight‐of‐evidence evaluation that supports technically sound and consistent persistent organic pollutant and persistent, bioaccumulative, and toxic chemical identification. Based on the bioaccumulation information shared in 8 draft risk profiles submitted for review under the United Nations Stockholm Convention, recommendations are given for the information that is most critical to aid transparency and consistency in decision making.

Proposal for a harmonised PBT identification across different regulatory frameworks

“…In some cases, inefficient or nonexistent detoxification processes may be responsible for high BCF values (e.g. TBT in molluscs) [41,42]. -Non-lipid-based accumulation for substances such as perfluorinated acids, which bioaccumulate in blood plasma proteins [43,44].…”

“…[47]) are being developed and using information from field studies and TMF (e.g. [42,48]) is being considered. Taking into account these various aspects will improve the assessment of bioaccumulation.…”

Assessment of PBTs in the European Union: a critical assessment of the proposed evaluation scheme with reference to plant protection products

“…The important concept that needs to be considered when assessing exposures is that P and B are dependent on the properties of the chemical and its environment. Thus, while basic properties such as K OW or K OA may predict bioconcentration, metabolism in organisms [24] or degradation in the environment by processes such as photolysis may negate this, as in the example of the pyrethroid insecticides, which have large K OW s but are not bioaccumulated or biomagnified [25]. Similarly, persistence in one environment should not be extrapolated to other environments.…”

“…The European Chemical Agency (ECHA) proposed the value of log K OW > 4.5 as a criterion for B [82]. However, K OW does not account for metabolic transformation and active excretion processes [24]. Therefore, false positives are highly probable and K OW must be assumed only as an indicator of worst-case conditions of the 'potential' for bioconcentration.…”

“…Field methods Considering the limitations and weaknesses of laboratory bioconcentration tests, the TMF has been proposed as the best and most reliable tool for assessing bioaccumulation and biomagnification of chemicals [24,76]. However, at this time, reliable TMF values need to be characterized from field studies on chemicals that have been present in the environment for enough time to allow the achievement of equilibrium in natural food webs.…”