Trace levels of hexavalent chromium found in two cities' drinking water

JEFFERSON CITY, MO, Jan. 7, 2010 -- The Missouri Department of Natural Resources is collaborating with other state and federal agencies to determine why trace levels of hexavalent chromium are appearing in Hannibal's and Louisiana's drinking water...

JEFFERSON CITY, MO, Jan. 7, 2010 -- The Missouri Department of Natural Resources is collaborating with other state and federal agencies to determine why trace levels of hexavalent chromium are appearing in Hannibal's and Louisiana's drinking water.

Results received by the agency at approximately 2:40 p.m. on Jan. 7 confirmed an earlier sample that showed trace amounts of hexavalent chrome in the public drinking water for Hannibal and Louisiana.

The amounts in Hannibal's water exceed the health-screening level set by the Missouri Department of Health and Senior Services of 0.4 parts per billion.

Based on extensive consultations with the U.S. Environmental Protection Agency and the Missouri Department of Health and Senior Services and the public drinking water is safe to drink.

DNR notified officials in both cities shortly after the initial results came in Dec. 22 and notified city officials immediately after the most recent samples were received.

The most recent samples -- which were taken Jan. 5 -- found:

• a level of hexavalent chromium at 0.6 parts per billion (ppb) in Hannibal's finished drinking water.
• a level of hexavalent chromium at 0.3 parts per billion (ppb) in Louisiana's finished drinking water.

Information found during the most recent sampling of parts of Hannibal's drinking-water treatment process may shed some light on why the finished drinking water had higher hexavalent chromium levels than the raw water. The following list details hexavalent chromium concentrations at each step of the Hannibal drinking-water treatment process:

• Water measured at the plant's intake: 0.1 ppb
• After the pre-sedimenation basin: 0.1 ppb
• After the primary flocculation and settling basin: 0.1 ppb
• After the secondary settling basin, in which lime is added to adjust the water's pH: 0.5 ppb
• After the filter feed basin: 0.5 ppb
• After filtering: 0.5 ppb
• After final chlorination: 0.6 ppb

Currently, no state in the country has a drinking water standard for hexavalent chromium. However, the state of Missouri does have a standard for total chromium (measuring both hexavalent and trivalent chromium) of 100 parts per billion; both cities' systems are in compliance with that standard. Both cities are entirely in compliance with Missouri's public drinking water standards, as well.

On Dec. 22, DNR received heavy metals sample results for the finished drinking water from both plants and discovered extremely low amounts of hexavalent chromium. Hannibal's sample measured 0.4 parts per billion and Louisiana's sample measured 0.1 part per billion. Both of these values were higher than the hexavalent chromium levels found in the raw water taken from the cities' water supplies.

On Dec. 24, DHSS officials defined 0.4 parts per billion as a health-screening level for hexavalent chrome in drinking water. Sampling concentrations found above this level do not necessarily indicate a public health threat is present, but do indicate that further evaluation is needed. A health-screening level is a conservative measuring stick; sample concentrations below that level present no health risk and concentrations above it merit further investigation, but still may not present a public-health risk. The measurement of 0.4 parts per billion is equivalent to 80 percent of a single drop of water being diluted into a 2-meter deep Olympic-size swimming pool.

According to data from the EPA, water districts in California routinely use a level of 6 ppb of hexavalent chromium in drinking water as a target goal for drinking water distribution.

Due to existing technological limitations, testing for extremely low levels of hexavalent chromium is difficult, and the amounts found in Hannibal and Louisiana are at the low end of the detectable range. In investigating the causes for the chemical's presence in public drinking water, DNR and the Department of Health and Senior Services are taking a step beyond enforcing existing regulations to understand the implications of these low hexavalent chromium levels in drinking water to the health of all Missourians. The U.S. Environmental Protection Agency is providing technical assistance and support, as well.

Hexavalent chrome is a heavy metal that is commonly used in industrial processes, such as the making of stainless steel, textile dyes and anti-corrosive coatings. In certain amounts, it is a known carcinogen. It is also something that body needs; trivalent chromium is added to vitamins, which the body then converts to hexavalent chromium.

The detection of hexavalent chrome is a developing science. In a recent study, the state of California sampled approximately 7,000 public drinking water systems and found roughly 30 percent were at or above hexavalent chrome levels of 1 part per billion.


More in Drinking Water
Potable Water Management 4.0
Potable Water Management 4.0