At what level the heavy metals such as Cr and Cd toxic to the environment?

Answer 1

They are both extremely toxic to humans Cromium and Cadmium.

Cr(VI) compounds are emitted into the air, water, and soil by a number of different industries. In the air, chromium compounds are present mainly as fine dust particles that eventually settle over the land and water.

The Report on Carcinogens, published by the National Toxicology Program, says the atmospheric total chromium concentration in U.S. air is typically less than 0.01 µg per cubic meter (m3) in rural areas and 0.01-0.03 µg/m3 in urban areas. Chromium in ambient air is not regulated.

The Report on Carcinogens also indicates that typical tap water can contain 0.4-8.0 µg per liter (L) total chromium, and that chromium in rivers and lakes usually falls between 1 and 10 µg/L. Cr(VI) by itself is not regulated in drinking water. The U.S. Environmental Protection Agency (EPA) regulates only total chromium in drinking water and has set a maximum contaminant level of 100 µg/L (more stringent state limits are often set at half that amount).


Soil, meanwhile, contains on average 400 parts per million total chromium, but this depends on the balance of oxidizing and reducing agents in the soil. Chromium can change valence state in soil and sediments depending upon the local physical, chemical, and biological conditions. For instance, says Paul Lioy, deputy director of the Environmental and Occupational Health Sciences Institute in Piscataway, New Jersey, in soils with a high pH, Cr(III) can convert to Cr(VI). According to the EPA's 1998 Toxicological Review of Hexavalent Chromium, Cr(VI) found in the soil is generally converted to Cr(III) by organic matter. Soil concentrations are not strictly regulated by the EPA, but rather are subject to soil screening levels. These levels are devised on a site-by-site basis according to the pathways present at the site (for example, whether people are likely to handle the soil) and certain site characteristics (for example, whether the soil is loamy or sandy) to determine whether investigation or cleanup is warranted.

Answer 2

Extremely! Cad is now proven to be a carcinogen and chromium is highly toxic to the human liver!