Mercury is one of the most hazardous contaminants that may be present in the aquatic environment, but its ecological and toxicological effects are strongly dependent on the chemical species present. Species distribution and transformation processes in natural aquatic systems are controlled by various physical, chemical, and biological factors. Depending on the prevailing environmental conditions, inorganic mercury species may be converted to many times more toxic methylated forms such as methylmercury, a potent neurotoxin that is readily accumulated by aquatic biota. Despite a considerable amount of literature on the subject, the behavior of mercury and many of the transformation and distribution mechanisms operating in the natural aquatic environment are still poorly understood. This review examines the current state of knowledge on the physicochemical behavior of mercury in the aquatic environment, and in particular the environmental factors influencing its transformation into highly toxic methylated forms.

Mercury in the Aquatic Environment: A Review of Factors Affecting Methylation

Mercury methylation in aquatic systems affected by acid deposition

A method was developed to measure mercury methylation and demethylation rate constants simultaneously in aquatic samples. Solutions containing stable isotope tracers of 199 Hg 2+ and CH 3 202 Hg + were spiked into lake sediments at subambient concentrations. The formation of CH 3 199 Hg + and the decrease in CH 3 202 Hg were measured simultaneously in time series experiments using gas chromatographic separation and isotope-specific detection by inductively coupled plasma mass spectrometry. Specific rate constants for the two processes were calculated and compared to rate constants obtained by monitoring changes in concentration of the ambient methylmercury in the same sample. The inorganic mercury tracer 199 Hg 2+ was methylated at a faster rate compared with the ambient inorganic Hg 2+ , which indicates that the added tracer Hg 2+ is more available for transformation reaction than the ambient Hg 2+ . The degradation of tracer and ambient methylmercury proceeded at a similar rate, showing no significant differences between added tracer and ambient methylmercury. The calculated half-life for methylmercury in sediments was 1.7 d, suggesting a rapid turnover and low persistence of methylmercury in lake sediments. Different Hg species were investigated regarding their availability for methylation reactions. Compared to Hg(NO 3 ) 2 , Hg-fulvate showed reduced availability and freshly precipitated HgS was hardly available.

Constants of mercury methylation and demethylation rates in sediments and comparison of tracer and ambient mercury availability

Literature on the long-range atmospheric transport of both anthropogenic and naturally occurring mercury (Hg) to terrestrial and aquatic ecosystems was reviewed for the purpose of assessing the qua...

https://www.researchgate.net/profile/Togwell_Jackson/publication/237154471_Long-range_atmospheric_transport_of_mercury_to_ecosystems_and_the_importance_of_anthropogenic_emissions_-_A_critical_review_and_evaluation_of_the_published_evidence/links/0deec51decac7ba0d3000000.pdf

Long-range atmospheric transport of mercury to ecosystems, and the importance of anthropogenic emissionsa critical review and evaluation of the published evidence

Mercury (Hg) is one of the most toxic heavy metals. From a biological perspective it has no redeeming virtue, for, unlike a number of other heavy metals, it is not known to perform any essential biochemical function (Bowen, 1966). Traces of Hg are ubiquitous in soils, natural waters, sediments, organisms and air (Jonasson and Boyle, 1972), and anomalously high Hg concentrations occur in many ecosystems owing to Hg pollution (a serious, widespread problem), natural Hg enrichment in certain rocks, distinctive properties of Hg such as its tendency to form highly stable complexes and compounds (including species that are easily taken up by organisms but not readily excreted), natural processes (e.g. methylation) which enhance the bioavailability of Hg, increased bioavailability of Hg due to environmental changes caused by human activities, and efficient accumulation of Hg by organisms and certain natural materials, such as soil organic matter and fine-grained sediments. Moreover, Hg is a relatively volatile element, and this accounts, in large part, for its wide distribution.

Mercury in aquatic ecosystems

Seasonal and regional variations in the speciation, sediment-water partitioning, and dynamics of mercury (Hg) were studied at selected sites along the Hg-polluted Wabigoon River, and at unpolluted headwater and tributary sites, during April–September, 1979. ‘Dissolved’ and ‘particulate’ forms of Hg in the water were separated by continuous-flow centrifugation in the field. The Hg and other pollutants such as wood chips and salt had been discharged from a chlor-alkali plant and paper mill at Dryden, Ontario.

T. A. Jackson

Papers

Dissolved and suspended mercury. species in the Wabigoon River (Ontario, Canada): seasonal and regional variations