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Understanding Our Planet Through Chemistry

Industrial Sources of Contamination

A similar cause for environmental concern is the presence of mercury in the agricultural soils of the Panoche Fan. To the west of the San Joaquin Valley, a major, mercury mineralization district is located near the town of Idria. The New Idria Mine, operated between 1858 and 1972, was the second largest mercury producer in North America.

Streams that drain the north, east, and south sides of the mining district all contribute sediment to the Panoche Fan. Chemical analyses of soil samples from the Fan clearly show that the soil contains elevated mercury levels. These high levels of mercury could be caused by a combination of natural geochemical dispersion and mining activity, considering the time period of major mercury production at the New Idria Mine (see the discussion of dispersion halos in Chapter IIIa again).

Like the selenium, the mercury data were generated using AAS. The rocks were digested and the solution was then reduced to form elemental mercury, which was separated as mercury vapor and measured with AAS. This method is called the cold vapor-AAS method.

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