Global Warming Science and Public Policy - Section 18: Man-Made vs. Natural Sources of Mercury

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Section 18: Man-Made vs. Natural Sources of Mercury

[D]ecision makers need more than mercury concentrations to be able to ensure defensible interpretation of the indicators, such as MeHg in fish.

- Mason, et al., 2005

Chicago Tribune:

It doesn't matter who catches or sells the fish. The mercury is everywhere - oceans, rivers and lakes - thanks mainly to man-made pollution. (December 15, 2005)

Response:

The Kafkaesque attribution to “man-made pollution” in this statement is scientifically indefensible, and is addressed throughout this critique (see Sec. 5). We repeat,

“The weights of several scientific facts crumble the footings underlying their entire construction: one such fact is that annual total mercury entering the bio-sphere from natural sources dwarfs anthropogenic sources into near insignificance. These sources are not only immense and overwhelming, but are persistent over geological time. This stubborn fact has been resolute in the literature for decades, and doggedly ignored by mercury activists.”

Further, it is well recognized that the processes of bio-conversion from Hg to MeHg is reversible, depending on multiple factors, including levels of sulfate, organic matter and even selenium levels in a particular ecosystem. According to Mason et al. (2005), the correlated factors of sulfate-organic-matter and bacterial activity alone could “possibly cause an increase in fish mercury concentration even as atmospheric deposition decreases”. [Emphasis added]

The decisive point is that science-based observations reveal that both the production and destruction processes of MeHg ending up in fish are not exclusively dependent on the amount of Hg available in a water system.

Hence, key biological, geological and chemical processes driving Hg environmental abundance, methylation/demethylation and the ultimate bioaccumulation of MeHg in fish tissue overwhelm the relatively insignificant contributions of elemental, ionic and particulate Hg from U.S. power plant emissions.

This is because there are already extant millions of tons of naturally occurring Hg in Earth’s waters, crust, soils and sediments ever available for conversion into MeHg. This explains why it is neither difficult nor surprising to find high, even extremely high, levels of MeHg in both fish and humans in the past several centuries, at times lacking mercury emissions from power plants or other industrial activities.

For example, a comparison of MeHg levels in ancient and modern Alaskans found a higher mean level in 550-year old mummies.

Figure 18-A shows pregnant Alaskan women today with mean hair levels of 0.7 ppm, compared to 550-year old mummified adults with a mean of 1.2 ppm and one as high as 4.6 ppm. While this sample number is small, it demonstrates the point and is supported by other Arctic Circle remains dating some as long ago as the fifth century A.D. (see Sec. 15).

So, while CT is correct about mercury being naturally ubiquitous, it is clearly incorrect to categorically state that anthropogenic sources of mercury are predominant.

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