This is a newly redesigned Water-Research.net page
Page Archive

Metals in the Environment


Iron is the fourth most abundant element, by mass, in the earth's crust (not all of Earth’s iron is in its core). 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 more soluble ferrous or bivalent form [Fe++]. It is easily oxidized to the less soluble ferric iron [Fe+++] form upon exposure to air. This gelatinous ferric hydroxide precipitate is orange-colored and often turns streams orange.

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 vertebrates and some invertebrate animals. Ferrous Fe++ and ferric Fe+++ ions are the primary ions of concern in the aquatic environment although other significant ions may be in either organic or inorganic wastewater streams. The ferrous ion (Fe++) can persist in water devoid of dissolved oxygen and usually originates from groundwater or mines that are pumped or drained. Ferric iron (Fe+++) 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 because that is the concentration at which ferric iron will begin to precipitate. Black or brown swamp waters may contain iron concentrations of several mg/L in the presence (ferric iron) or absence (ferrous iron) of dissolved oxygen, but these iron ions have little effect on aquatic life.

Standard for Iron

The current aquatic-life standard for iron is less than 1.0 mg/L based on toxic effects. (It is one of the few iron standards for which the standard is not calculated based on hardness.)

Learn more by visiting the Iron page in our Indoor Drinking Water Section.


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 dissolved aluminum can become toxic to aquatic life if the pH is lowered (as in acid rain). For water wells, we have seen elevated levels of aluminum in the well water in the following cases: movement of grout materials for geothermal or ground source heating and cooling systems, turbid waters (the aluminum is leached from sediment particles when the sample is preserved by adding acid), leaching from cooking materials (pots, pans, and some cups), leaching from piping caused by corrosion or microbiologically-induced corrosion, corrosion of a water heater, and very low pH waters. The highest level we have ever detected was 80 mg/L in a leachate from a coal spoil pile and in well water it was 8 mg/L, associated with corrosion and nuisance bacteria; the water was gray.

Standard for Aluminum

Surface water - 0.75 mg/L . The secondary drinking water standard set for aesthetic issues is 0.2 mg/L.

Learn more by visiting the Aluminum page in our Indoor Drinking Water Section.


Cadmium is a non-essential element which diminishes plant growth. It is considered to be a potential carcinogen. It also has been shown to have toxic effects on the kidneys and reproductive organs and to cause bone defects and high blood pressure.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.

Standard for Cadmium

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, a cadmium limit of 0.001 mg/L is considered protective.

Learn more by visiting the Cadmium page in our Indoor Drinking Water Section.


The primary natural source of lead is the mineral galena (lead sulfide, PbS). It also occurs as a carbonate, a sulfate, and in several other compounds. 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 from discharges such as those from sewage treatment plants and industrial plants. It may also 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 the pH and hardness.

Standard for Lead

The level considered protective for aquatic life at a hardness of 100 mg/L as CaCO3, is less than 0.003 mg/L. The standard for a domestic water source is less than 0.005 mg/L, but the drinking water at the point of use must be less than 0.015 mg/L of lead. Since private water wells are directly linked to the water source, we use the standard of 0.005 mg/L. However, there is really no safe level when we are talking about long-term exposure.

Learn more by visiting the Lead page in our Indoor Drinking Water Section.


Zinc is 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 and sewage sludge. 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.

Standard for Zinc

The standard for aquatic life has been set at less than 0.106 mg/L, based on a hardness of 100 mg/L.

Learn more by visiting the Zinc page in our Indoor Drinking Water Section

Additional Pages

Learn more by visiting these additional Metals pages in our Drinking Water Section.





Additional Resources

Get Tested

Level 1
Level 2
Level 3
Level 4

Get Treatment

Short Term
Archive Page Reference
This is a newly redesigned Water-Research.net page. To reference related archived Water-Research.net page(s) click the link(s) below:
No items found.