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sw18 - Bioaccumulative Contaminants Mercury is naturally...

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Bioaccumulative Contaminants
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The number 1 anthropogenic source is the combustion of coal Enters water bodies principally from the atmosphere 48 tons of elemental mercury to the atmosphere each year. Mercury is naturally occurring (coal, volcanism, rock weathering)
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Inorganic mercury can be converted to more toxic forms in bottom sediments under anaerobic conditions Mercury Methylation
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Mercury Methylation Methylation: conversion of inorganic forms of mercury, Hg 2+ , to an organic form: methyl mercury under anaerobic conditions Hg 2+ (CH 3 Hg + ) methylmercury Methylmercury is accumulated in organisms and is generally more toxic than inorganic Hg
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Occurs primarily in bottom sediments as a byproduct of the life processes of anaerobic sulfate-reducing bacteria (SO 4 to HS-) that live in high sulfur, low oxygen environments. Mercury Methylation When sulfur accepts electrons it is said to be “reduced”. C 6 H 12 O 6 + 3 SO 4 2- + 3H + = 6HCO 3 - + 3HS - Sulfate Respiration Requires 4 elements: anaerobic conditions a carbon source (organic matter) a source of sulfur (SO 4 - ) sulfur reducing bacteria e-
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Bioaccumulation: concentration of a chemical in organisms relative to the amount in water. Enhanced Risk Methylmercury has a half-life in human blood of about 70 days (twice as long as inorganic mercury (Hg 2+ ).
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