Towards Mechanistic Understanding of Mercury Availability and Toxicity to Aquatic Primary Producers

Abstract

The present article reviews current knowledge and recent progress on the bioavailability and toxicity of mercury to aquatic primary producers. Mercury is a ubiquitous toxic trace element of global concern. At the base of the food web, primary producers are central for mercury incorporation into the food web. Here, the emphasis is on key, but still poorly understood, processes governing the interactions between mercury species and phytoplankton, and macrophytes, two representatives of primary producers. Mass transfer to biota surface, adsorption to cell wall, internalization and release from cells, as well as underlying toxicity mechanisms of both inorganic mercury and methylmercury are discussed critically. In addition, the intracellular distribution and transformation processes, their importance for mercury toxicity, species-sensitivity differences and trophic transfer are presented. The mini-review is illustrated with examples of our own research.

Solar irradiance and primary productivity controlled mercury accumulation in sediments of a remote lake in the Southern Hemisphere during the past 4000 years

“…Bravo et al () suggested that in eutrophic lakes receiving low inputs of terrigenous OM, sediment Hg concentrations are determined by atmospheric inputs. Besides dissolved Hg II , lipophilic Hg compounds such as uncharged HgCl 2 and CH 3 HgCl complexes are important for the uptake by algae (Mason et al ; Dranguet et al ), but binding to terrestrial DOM limits the uptake of both metals (e.g., (Brooks et al ; Schartup et al b ). Enhanced photo‐oxidation of DOM‐Hg under higher TSI might enhance Hg II uptake by algae, in a similar way as found for Cu (Moffett et al ; Sander et al ; Shank et al ).…”

“…Oxidized dissolved Hg (Hg II ‐species such as HgCl 2 ) and methylmercury (CH 3 HgX, (MeHg)) are the dominant species taken up. Lipophilic CH 3 HgCl has a higher bioaccumulation factor than other Hg II ‐species, whereas DOM‐bound Hg appears to decrease uptake by algae (Dranguet et al ; Le Faucheur et al ; Schartup et al b ). Direct uptake of dissolved or gaseous elemental mercury (GEM) by phytoplankton seems to be of minor importance as no detectable accumulation of Hg could be observed when GEM was used in bioaccumulation experiments (Le Faucheur et al ).…”

“…Transport by dissolved organic matter (DOM) is the major pathway of Hg from catchments into aquatic systems (Driscoll et al 1995). In freshwater systems and estuaries, algae have been shown to accumulate Hg from the water phase and influence Hg cycling by affecting its concentrations, speciation, and transport to the sediments (Mason et al 1996;Pickhardt et al 2002;Fitzgerald et al 2007;Pickhardt and Fisher 2007;Dranguet et al 2014;Le Faucheur et al 2014). The mechanism of Hg uptake by phytoplankton is not well understood, but could involve both, facilitated transport and diffusion (Dranguet et al 2014;Le Faucheur et al 2014).…”

Molecular Effects of Inorganic and Methyl Mercury in Aquatic Primary Producers: Comparing Impact to A Macrophyte and A Green Microalga in Controlled Conditions

“…Mercury (Hg) contamination of freshwaters arises from the deposition of atmospheric Hg (dry settling or rainfall), polluted soils runoffs, industrial effluents, gold-mining and reemission from historical contaminated systems ( [1,2]). It subsequently settles in the sediment of lakes, rivers or bays where it is transformed into methylmercury (MeHg), absorbed by primary producers, transferred to primary and secondary consumers, and accumulates especially in long-lived predatory species, e.g., shark and swordfish.…”

“…Typical environmental concentrations measured in rivers and lakes range between 0.003 and 30 nM THg ( [5]). Both IHg and MeHg are mainly bound to dissolved organic matter (DOM) ( [1,6,7]) in particular to thiol (RSH) groups. For the fraction of Hg not bound with DOM, water chemistry (e.g., pH and chloride concentration) controls its distribution among different dissolved chemical species and complexes ( [8,9]).…”