Steady State of Arsenic Levels in Natural Waters

A model for the mass balance of arsenic in a typical large water body, in this case Lake Ontario, is shown in Figure 15-8. The lake receives 161 tonnes of As per year, almost all of it from river and lake flows originating with land-based sources; the rest comes from the atmosphere, mainly in the form of arsenic dissolved in rain and snow. About three-quarters of the annual input quantity leaves the lake by outflow (to the St. Lawrence River). The other quarter corresponds to the net deposited into the surface sediment, after correction for the arsenic redissolved in the water column from this source. Over time, the sediment arsenic, with a concentration of about 10 ppm, becomes buried. The net input and output of arsenic into Lake Ontario are equal, so it is in a steady state, and the concentration of the element in the water, about 0.5 ppb, remains constant with time.

Continue reading here: Arsenic in Organic and Other Molecular Forms

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