The importance of bioconcentration into the pelagic food web base for methylmercury biomagnification: A meta-analysis

Abstract

Methylmercury (MeHg) transfer from water into the base of the food web (bioconcentration) and subsequent biomagnification in the aquatic food web leads to most of the MeHg in fish. But how important is bioconcentration compared to biomagnification in predicting MeHg in fish? To answer this question we reviewed articles in which MeHg concentrations in water, plankton (seston and/or zooplankton), as well as fish (planktivorous and small omnivorous fish) were reported. This yielded 32 journal articles with data from 59 aquatic ecosystems at 22 sites around the world. Although there are many case studies of particular aquatic habitats and specific geographic areas that have examined MeHg bioconcentration and biomagnification, we performed a meta-analysis of such studies. Aqueous MeHg was not a significant predictor of MeHg in fish, but MeHg in seston i.e., the base of the aquatic food web, predicted 63% of the variability in fish MeHg. The MeHg bioconcentration factors (i.e., transfer of MeHg from water to seston; BCF) varied from 3 to 7 orders of magnitude across sites and correlated significantly with MeHg in fish. The MeHg biomagnification factors from zooplankton to fish varied much less (logBMF, 0.75 ± 0.31), and did not significantly correlate with fish MeHg, suggesting that zooplanktivory is not as important as bioconcentration in the biomagnification of fish MeHg across the range of ecosystems represented in our meta-analysis. Partial least square (PLS) and linear regression analyses identified several environmental factors associated with increased BCF, including low dissolved organic carbon, low pH, and oligotrophy. Our study reveals the widespread importance of MeHg bioconcentration into the base of the aquatic food web for MeHg at higher trophic levels in aquatic food webs, as well as the major influences on the variability in this bioconcentration.

Mercury cycling in freshwater systems - An updated conceptual model

“…The focus of research on the compartments and fluxes in this long-standing conceptual model may be resulting in a failure to focus research attention on critical zones of MeHg production/degradation that have come to light in recent years, and make targeted measurements of the most important biotic and abiotic factors regulating Hg methylation that would allow for more a direct mechanistic link between MeHg production and MeHg in biota. A redirection of attention towards factors that truly regulate the supply of MeHg to the base of the food web will improve our ability to mechanistically model biotic exposure to MeHg in freshwater systems under current conditions (Wu et al, 2019), but will even more importantly provide a roadmap for understanding Hg cycling in a future non-stationary climate. In this review we posit that the persistence of this conceptual model is in large part, a function of the geographic scope of research on freshwater Hg biogeochemical cycling.…”

One health in the circumpolar North

“…Since the 1970s, contaminants from the industrialized world have entered the Arctic food web, where through the processes of bioaccumulation and biomagnification, they endanger the health and well-being of Indigenous peoples who depend heavily on marine species [31][32][33][34][35]. In addition to the direct and indirect impacts of such contamination on the health of individual humans, the knowledge of such threats to human health and to the future of Indigenous peoples and cultures contributes to mental stress [23].…”

Terrestrial diet influences mercury bioaccumulation in zooplankton and macroinvertebrates in lakes with differing dissolved organic carbon concentrations

“…The high abundance of cladocerans across oligotrophic lakes is strongly exposed to terrestrial food sources (Berggren et al, 2014) and, once ingested, Hg may be equally transferred via such terrestrial as well as algal food sources, as seen in this study. However, the extent of zooplankton or macroinvertebrates uptake of terrestrial OM was restrained in high DOC lakes, as was the case for MeHg bioaccumulation (Wu et al, 2019). This likely suggests that zooplankton depends on essential nutrients from algal food sources to sustain their somatic growth and reproduction (Karlsson et al, 2012;Masclaux et al, 2012;Wenzel et al, 2012).…”

“…The method has a detection limit of 0.05 ng L -1 and a quantitation limit of 0.1 ng L -1 . An estimation of total Hg bioconcentration factors (BCF) was calculated using the log ratio of bioaccumulated total Hg concentrations and aqueous total Hg concentrations (Rolfhus et al, 2011;Wu et al, 2019).…”