Methylation is a product of complex processes that move and transform mercury. Atmospheric deposition contains the three principal forms of mercury, although inorganic divalent mercury (HgII) is the dominant form. Once in surface water, mercury enters a complex cycle in which one form can be converted to another. Mercury attached to particles can settle onto the sediments where it can diffuse into the water column, be resuspended, be buried by other sediments, or be methylated. Methylmercury can enter the food chain, or it can be released back to the atmosphere by volatilization. The concentration of dissolved organic carbon (DOC) and pH have a strong effect on the ultimate fate of mercury in an ecosystem. Studies have shown that for the same species of fish taken from the same region, increasing the acidity of the water (decreasing pH) and/or the DOC content generally results in higher mercury levels in fish, an indicator of greater net methylation. Higher acidity and DOC levels enhance the mobility of mercury in the environment, thus making it more likely to enter the food chain. Mercury and methylmercury exposure to sunlight (specifically ultra-violet light) has an …show more content…
Many substances entering organisms are eventually eliminated in wastes; whereas such others as heavy metals and fat-soluble organic substances may remain in the body for long periods of time. The U.S. Environmental Protection Agency uses the term persistent, bioaccumulative and toxic pollutants (PBTs) to categorize substances that raise human health and environmental health concerns. Depending on their affinity for fatty tissue and the length of the body's exposure, PBTs may accumulate in high concentrations and may cause physiological problems. PBTs enter the organism through a variety of active and passive means, including respiration, food intake, and epidermal (or skin)