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 [Fe++] which is
soluble. It is easily oxidized to ferric iron [Fe+++] or insoluble iron upon
exposure to air. This precipitate is orange-colored and often turns streams
Environmental Impact: Iron is a trace element required by both plants
and animals. It is a vital part of the oxygen transport mechanism in the blood
(hemoglobin) of all vertebrate and some invertebrate animals. Ferrous Fe++ and
ferric Fe+++ ions are the primary forms of concern in the aquatic environment.
Other forms may be in either organic or inorganic wastewater streams. The
ferrous form Fe++ can persist in water void 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. 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
an 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. (It is one of the few for which the criteria is not
calculated based on hardness.)
Aluminum and Water Quality
Aluminum: Aluminum is one of the most abundant elements in the earth's
crust and occurs in many rocks and ores, but never as a pure metal. The presence
of aluminum ions in streams may result from industrial wastes but is more likely
to come from the wash water of drinking water treatment plants. Many aluminum
salts are readily soluble; however, there are some that are very insoluble.
Those that are insoluble will not exist long in surface water, but will
precipitate and settle. Waters containing high concentrations of aluminum can
become toxic to aquatic life if the pH is lowered (as in acid rain).
Criteria: No criteria exist for this metal.
Cadmium and Water Quality
Cadmium: Cadmium is a non-essential element and it diminishes
plant growth. It is considered a potential carcinogen. It also has been shown to
cause toxic effects to the kidneys, bone defects, high blood pressure, and
Cadmium is widely distributed in the environment at low concentrations. It
can be found in fairly high concentrations in sewage sludge. Primary industrial
uses for cadmium are plating, battery manufacture, pigments, and plastics.
Criteria: The standard for domestic water supply is <0.01 mg/L. The
allowable level for aquatic life is derived using a formula involving hardness.
At a hardness of 100, 0.001 mg/L is considered protective.
Lead and water quality
Lead: Theprimary natural source of lead is in the
mineral galena (lead sulfide). It also occurs as carbonate, as sulfate and in
several other forms. The solubility of these minerals and also of lead oxides
and other inorganic salts is low. Major modern day uses of lead are for
batteries, pigments, and other metal products. In the past lead was used as an
additive in gasoline and became dispersed throughout the environment in the air,
soils, and waters as a result of automobile exhaust emissions. For years this
was the primary source of lead in the environment. However, since the
replacement of leaded gasoline with unleaded gasoline in the mid-1980's, lead
from that source has virtually disappeared. Mining, smelting and other
industrial emissions and combustion sources and solid waste incinerators are now
the primary sources of lead. Another source of lead is paint chips and dust from
buildings built before 1978 and from bridges and other metal structures.
Lead is not an essential element. In humans it can affect the kidneys, the
blood and most
importantly the nervous system and brain. Even low levels in the blood have
been associated with high blood pressure and reproductive effects. It is stored
in the bones.
Lead reaches water bodies either through urban runoff or discharges such as
sewage treatment plants and industrial plants. It also my be transferred from
the air to surface water through precipitation (rain or snow). Toxic to both
plant and animal life, lead's toxicity depends on its solubility and this, in
turn, depends on pH and is affected by hardness.
Criteria: The level considered protective for aquatic life at a
hardness of 100 is less than 0.003 mg/L. Use as a domestic water source requires
less than 0.05 mg/L. Drinking water must contain less than 0.015 mg/L.
Zinc and Water Quality
Zinc: Zincis found naturally in many rock-forming
minerals. Because of its use in the vulcanization of rubber, it is generally
found at higher levels near highways. It also may be present in industrial
discharges. It is used to galvanize steel, and is found in batteries, plastics,
wood preservatives, antiseptics and in rat and mouse poison.
Zinc is an essential element in the diet. It is not considered very toxic to
humans or other organisms.
Criteria: Criteria for aquatic life has been set at less than 0.106
mg/L based on hardness of 100 mg/L.