Metal Mobility: Contaminant Accumulation and Rerelease

Certain contaminants, such as lead, arsenic, antimony, and radium, have been found to exist in public water supplies at the entry points to water distribution systems in trace amounts, or amounts below prescribed Maximum Contaminant Levels (MCLs). (Note: The MCL is the maximum concentration of a chemical allowed in public drinking water systems.) Under normal circumstances, trace amounts of known contaminants do not pose a health risk; however, the accumulation and rerelease of these contaminants in concentrated amounts, which may not be detected by current monitoring practices, could result in elevated levels at our taps. For this reason, many communities face potential health concerns.

Recent research has confirmed that corrosion deposits and scale (hard mineral coatings) on the inside of distribution system piping and storage facilities can serve as reservoirs where trace contaminants accumulate. Concentrated amounts of these contaminants can be rereleased into the water supply because of changes in water chemistry or mixing of waters.

Because regulated contaminants, such as arsenic, nitrite, barium, and others are regulated only at the point where the water supply leaves the treatment plant, the potential health impact from the rerelease of these contaminant-containing solids is not known.

Regulations

In 1974, Congress passed the Safe Drinking Water Act. This law requires EPA to determine safe levels of chemicals in drinking water. Currently, there are no specific rules in place to control the accumulation of trace contaminants in distribution systems. However, in response to elevated levels of arsenic in drinking water, and concerns about arsenic’s effect on consumer health, EPA recently reduced the MCL of arsenic in drinking water from 0.050 milligrams per liter (mg/L) to 0.010 mg/L.

Technical Contact:

Darren Lytle (513) 569-7432
Michael Schock (513) 569-7412

See Also:

Safe Drinking Water Act

National Primary Drinking Water Regulations

List of Drinking Water Contaminants and MCLs