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Inorganic mercury releases can be globally distributed through the atmosphere and major ocean currents, and some is converted by microbes to MeHg in aquatic ecosystems (Cossa et al.
The USEPA completed a risk assessment in 1986, and produced a Record of Decision in 1987, which identified Hg and MeHg as contaminants of concern (USEPA 2012).
To understand the findings of the study and its environmental implications, it's first important to understand why MeHg is harmful to both humans and ecosystems.
The high susceptibility of the developing brain to MeHg damage compared to the mature brain can be explained by the fact that MeHg affects three processes unique to the developing brain: cell proliferation, differentiation, and migration.
In order to investigate trends in contaminant loads, we measured the concentrations of aluminum (Al), arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), nickel (Ni), total mercury (THg), MeHg, selenium (Se), silver (Ag), and Zn in liver of Harbor Seals stranded dead in the southern Puget Sound (SPS) and eastern Strait of Juan de Fuca (SJF) between 2004 and 2007.
This effect should be incorporated into policy and management efforts aimed at reducing human health risks from MeHg exposure," they added.
The conclusion suggested interventions need to be conducted to reduce prenatal exposure to MeHg.
Existing Health Canada blood MeHg guidance values were recently expanded to include a harmonized provisional guidance value for children, pregnant women and women of childbearing age (16-49 years).
If we convert the effects of MeHg on developing brains into IQ points then the benefits of controlling MeHg pollution equate to 700,000 points per year and monetary benefits of 8,000 million to 9,000 million per year for the whole of the EU," said Philippe Grandjean, one of the authors of the study.
Ingested MeHg is almost completely absorbed and crosses the placenta and blood-brain barrier (Xue, Holzman, Rahbar, Trosko, & Fischer, 2007).
Overall, changes in flow regimes likely affect rates of methyl-Hg (MeHg) production through a combination of factors such as high pH, which favors MeHg demethylation, and the occurrence of relatively high concentrations of Group VI oxyanions that could interfere with microbial SO4 reduction and MeHg production (Bonzongo, Nemer, & Lyons, 2006).