Biomagnification of OPFRs: Aquatic Ecosystem Impacts and Health Risks

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Introduction

Biomagnification is a contaminant’s potential to transfer through the food web and accumulate at the highest concentrations in apex predators (Dodder et al., 2014). Biomagnification at each trophic level will result in high concentrations of FRs in top predators (Iqbal et al., 2017) and is affected by hydrophobicity of the compounds and biotransformation properties in the organisms at different trophic levels (Wang et al., 2019). Limited data, as well as different aspects expressed about the biomagnifications of OPFRs have led to contradictory results.

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Trophic Magnification Factors (TMFs)

Trophic magnification factors (TMFs) were calculated for OPFRs as the regression coefficient of the trophic level versus the logarithm of the concentration in organisms from the benthic and pelagic food webs of the Western Scheldt estuary, The Netherlands. The food web was consisted of invertebrates, fish and birds and OPFRs determined in whole organism. Trophic magnification was observed only in the benthic food web (macro interbrates), with TMFs >1 (calculated on wet basis) for TCEP (2,6), TCIPP (2,2) and TBOEP (3,5) (Brandsma et al.

, 2015). However, according to the author these values are assigned as tentative due to high uncertainty resulted from the relatively small number of samples.

Formula for TMFs Calculation

TMFs are typically calculated using the formula: TMF=Log (Concentration in Predator)Log (Concentration in Prey)TMF=Log (Concentration in Prey)Log (Concentration in Predator)

Another study on trophic magnification of OPFRs referred that no accumulation was observed for nine OPFRs, with exception of TPHP in demersal species. Kim et al. (2011) suggested that exposure to bottom sediments enriched in TPHP has caused the accumulation of TPHP in bottom dwelling species.

This may also explain the trophic magnification, observed previously in the benthic food web for TCEP, TCIPP and TBOEP (Brandsma et al., 2015). EHDPP also biomagnified in a fish food web in Taihu Lake (China) with a TMF of 3.61, maybe due to its relatively high hydrophobicity. In contrast, Hallanger et al. (2015) observed that OPFRs in seabirds, mammals, as well as capelin (their major food source), were all detected in similar levels. As a result, OPFRs do not biomagnify, according to this study.

It is possible that the choice of tissues from the different organism groups were not the appropriate for assessing biomagnification of OPFRs and further studies should focus on analyzing similar tissues in different animal groups.

Dietary Exposure to OPFRs

Recent studies have focused on estimating the impact of OPFRs on human health, but data is only available about exposure assessments through inhalation and ingestion. Exposure to OPFRs via diet has been assessed recently regarding the risk to human health, but limited data is recorded (Hou et al., 2016). The available literature data is referred to the calculation of OPFRs intake through human diet by the consumption of fish, using the following equation:

EDI = (DC x MC)/BW

where:

EDI = Estimated daily intake (ng kg^-1 bw d^-1)
DC = Daily consumption rate (g day^-1)
MC = Concentration of OPFRs (ng g^-1 wet weight)
BW = Body weight (kg)

Risk Assessment through Oral Reference Dose (RfD)

Liu et al., (2019) estimated the potential dietary risk of 8 OPFRs residue levels in fish for humans living along the Pearl River Delta (China) and it ranged from 17 to 98 ng kg−1 bw d−1. Previously, Kim et al. (2011) calculated the total dietary intake of OPFRs (22 ng kg−1 bw d−1) in fish from Philippines. Even much lower value was measured for TCIPP, TPHP, EHDPHP, TBOEP, TDCIPP and TCEP ( The oral reference dose (RfD) is a major parameter in health risk assessment on human exposure to toxic substances. RfD is used to characterize the non-carcinogenic risk of a toxic substance via environmental exposure. Most studies about the health risk OPFRs were based on the reference dose from Van den Eede et al. (2011) and Ali et al. (2012), which were calculated by the following equation:

RfD = NOAEL/SF

where:

NOAEL = No observed adverse effect level (mg kg^-1 day^-1)
SF = Safety factor

Recently, RfD values have been updated by the United States Environmental Protection Agency (USEPA), after new toxicological studies (USEPA, 2017). Table S2 shows the difference between the RfD values from Van den Eede et al. (2011) and Ali et al. (2012), which is due to that the authors have used different SFs (10,000 for Van den Eede et al. (2011) and 1000 Ali et al. (2012)). The differences among the estimated RfD values are below one order of magnitude for most OPFRs and are probably due to the different calculation equations of RfDs; the calculation equations to derive RfD used by USEPA (2017) is different than that of Ali et al. (2012). Based on the advancement of toxicological science, the calculation equation of RfD has been upgraded in recent years.

It should be noted that exposure assessment based only on parent OPFRs may underestimate the risk through food consumption. The presence and toxicity of OPFRs metabolites should be considered. Moreover, RFDs are relatively high due to low acute toxicity of OPFRs; however, information on their chronic toxicity is limited. It is also important to bear in mind that the consumption of OPFRs is expected to increase in the future due to restriction of brominated flame retardants in consumer products.

Conclusion

The biomagnification of OPFRs in aquatic ecosystems poses potential risks to both wildlife and human populations. While trophic magnification factors provide insight into the accumulation of these substances in the food web, the estimated daily intake formula helps assess the risk to human health from dietary exposure. However, the complexity of biomagnification processes and variability in study results necessitate further research, especially focusing on similar tissues across different organism groups for accurate biomagnification assessment. Additionally, updated RfD values and the inclusion of OPFR metabolites in risk assessments could offer a more comprehensive understanding of the health implications of these compounds.