Vegetated and shallow areas such as wetlands and salt marshes, as well as freshwater lakes and rivers, have been identified as hotspots for Hg methylation. The presence of aquatic macrophytes, the predominant primary producers in shallow waters, plays an important but still poorly understood role in the fate of Hg in these environments. The present review focuses on the influences of macrophytes on Hg speciation and distribution in sediments, the rhizosphere, and the water column; on Hg transformation; and on Hg release to the environment, including transfer to the trophic web. Future research will require an improved understanding of the mechanisms and the factors controlling these aspects as well as a broader general view. Thus, the main gaps in knowledge are also discussed.

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.