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Iron and water quality
Iron: Iron is the fourth most abundant element, by weight, in the earth's crust. Natural waters
contain variable amounts of iron depending on the geological area and other chemical
components of the waterway. Iron in groundwater is normally present in the ferrous or bivalent
form [Fe2+] which is soluble. It is easily oxidized to ferric iron [Fe3+] or insoluble iron upon
exposure to air. This precipitate is orange-colored and often turns streams orange.
Environmental Impact: Iron is a trace element required by both plants and animals. It is also a vital
part of the oxygen transport mechanism in the blood (hemoglobin) of all vertebrate and some
invertebrate animals. Ferrous Fe2+ and ferric Fe3+ ions are the primary forms of concern in the
aquatic environment, but other forms may be in either organic or inorganic wastewater streams. The
ferrous form Fe2+can persist in water devoid of dissolved oxygen, and usually originates from
groundwater or mines that are pumped or drained. Iron in domestic water supply systems stains
laundry and porcelain and it appears to be more of a nuisance than a potential health hazard. Taste
thresholds of iron in water are 0.1 mg/L for ferrous iron and 0.2 mg/L ferric iron, giving a bitter
or astringent taste. Water to be used in industrial processes should contain less than 0.2 mg/L
iron. Black or brown swamp waters may contain iron concentrations of several mg/L in the
presence or absence of dissolved oxygen, but this iron form has little effect on aquatic life.
Criteria: The current aquatic life standard is less than 1.0 mg/L based on toxic effects.
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