Chromium's Impact: Water Pollutant Or Not?

Chromium is a metallic element that occurs naturally in rocks, plants, animals, and soil. It is also a potentially toxic metal that can contaminate water supplies as a result of natural and human-made sources. Chromium-6, the most toxic form of chromium, has been detected in the water supplies of over 200 million Americans and is known to cause adverse health effects such as skin burns, pneumonia, and an increased risk of cancer. With no federal standard for the maximum amount of chromium-6 in water, the Environmental Protection Agency (EPA) is responsible for setting standards for drinking water contaminants to prevent potential health problems. This raises the question: is chromium a significant water pollutant, and what are the implications for human health and the environment?

Chromium-3 is a human dietary element found in many foods

Chromium is a metallic element that is odourless and tasteless. It is found naturally in rocks, plants, soil, water, and animals. Chromium exists in water in a number of valence states, the most stable forms being Cr (VI) and Cr (III). While Cr (III) is a human dietary element found in many foods, Cr (VI) is a toxic compound that poses health risks to humans, animals, plants, and microorganisms.

Chromium-3, or trivalent chromium, is an essential human dietary element found in many vegetables, fruits, meats, grains, and yeast. It is naturally present in most water supplies. Chromium-3 is also found in the environment, particularly in chromite ore (FeCr2O4), which is present in mafic and ultramafic rocks.

Chromium-3 is an important mineral that can be obtained through a well-balanced diet. It is abundant in vegetables, fruits, and whole grains. For example, a cup of cooked broccoli provides 22 micrograms of chromium, while a cup of grape juice contains about 7.5 micrograms. Brewer's yeast, used in beer-making and nutritional supplements, is also a good source of chromium, providing 3.3 micrograms per tablespoon.

Meats such as lean beef, turkey, and chicken breast are also good sources of chromium. Lean beef contains the highest amount, with 2 micrograms per 3-ounce serving, followed by turkey with 1.7 micrograms, and chicken with 0.5 micrograms per 3-ounce serving. Shellfish, including mussels, oysters, and shrimp, are also notable sources of chromium.

While chromium-3 is essential for human nutrition, excessive intake may have adverse effects. Too much chromium may worsen insulin sensitivity and lead to kidney or liver damage. Therefore, it is important to be cautious and consult a doctor before taking chromium supplements, especially for individuals with kidney or liver disease, or those taking medications for diabetes.

Chromium-6 is produced by industrial processes and occurs naturally

Chromium-6, also known as hexavalent chromium, is a form of the metallic element chromium. It occurs naturally in the environment due to the erosion of chromium deposits. It can be found in water supplies, rocks, animals, plants, and soils. While Chromium-3 is an essential human dietary element, Chromium-6 is not, and it has been linked to adverse health effects such as skin burns, pneumonia, complications during childbirth, and an increased risk of stomach cancer.

Chromium-6 is also produced by industrial processes. It is commonly used for anti-corrosion metal coating, wood preservation, and textile dyeing. Industrial activities that use chromium compounds, especially those involving heating processes, can release chromium vapour into the air, leading to air and water pollution. Chromium-6 has been detected in groundwater due to industrial pollution and from natural gas compression stations that use it as an anti-corrosion agent.

The release of chromium-6 into the environment can occur through wastewater generated during equipment cleaning, chemical spills, and cooling water used in heating procedures. If this wastewater is not treated or disposed of properly, it can contaminate local water supplies. Chromium-6 has been detected in drinking water supplies across the United States, affecting millions of people.

To address the presence of chromium-6 in drinking water, the Environmental Protection Agency (EPA) has set standards and regulations. The national primary drinking water regulation for total chromium, including chromium-6, was established at 0.1 milligrams per liter (mg/l) or 100 parts per billion (ppb). However, there is ongoing debate about the appropriate standard to protect human health, as the current standard is based on potential dermatological effects rather than other health risks associated with chromium-6 exposure.

While natural sources of chromium-6 exist, human activities, particularly industrial processes, have significantly contributed to its presence in the environment, specifically in water supplies. The health risks associated with chromium-6 exposure have led to increasing concerns and efforts to reduce its impact on human health.

Chromium discharge limits in water are regulated on a national scale

Chromium is a transition metal that exhibits complex chemistry. In water, chromium exists with oxidation states ranging from +6 to −2. The most stable forms are the hexavalent Cr (VI) and trivalent Cr (III), which can interconvert with each other. Depending on the solution's pH values, chromium can be encountered mainly as Cr (III) or Cr (VI).

Chromium is a potentially toxic metal that occurs in water and groundwater as a result of natural and anthropogenic sources. It is found naturally in rocks, plants, soil, and animals. The most common forms of chromium that occur in natural waters are chromium-3 and chromium-6. Chromium-3 is an essential human dietary element found in many vegetables, fruits, meats, grains, and yeast. Chromium-6 occurs naturally in the environment due to the erosion of natural chromium deposits. It can also be produced by industrial processes.

In Europe, the admissible concentration values of Cr (VI) as mg L−1 range from 0.05 to 2 according to the environmental policies of Norway, Poland, and the Netherlands. Chromium discharge in European Union (EU) waters is subject to nationwide recommendations, which vary depending on the type of industry and receiving water body. Traditional approaches for Cr (VI) removal from water and wastewaters include physico-chemical methods such as chemical reduction, adsorption on porous surfaces with sites for ion exchange, and electrocoagulation. However, these methods have limitations related to sludge production and the large amount of chemicals required. To address these issues, bioremediation can be a valid alternative, especially for lower and moderate concentrations of Cr (VI) in large volumes of wastewater.

Chromium is released into the environment through wastewater

Chromium is a transition metal that can exist in water with oxidation states ranging from +6 to −2. The most stable forms of chromium are hexavalent Cr (VI) and trivalent Cr (III). These two forms can interconvert with each other. In nature, the oxidation of Cr (III) is not favoured, and only manganese oxide seems to be an effective oxidant in the environment. On the other hand, Cr (VI) can be easily reduced to Cr (III) by different reducing agents, including Fe (II), phosphate, sulphide, and organic matter.

The discharge of chromium in water is regulated on a national scale and often varies depending on the type of industry and receiving water body. For example, in Europe, the admissible concentration values of Cr (VI) as mg L−1 range from 0.05 to 2 according to the environmental policies of Norway, Poland, and the Netherlands. In the United States, the national primary drinking water regulation established a maximum contaminant level (MCL) for total chromium of 0.1 milligrams per liter (mg/l) or 100 parts per billion (ppb). This regulation includes all forms of chromium, including chromium-6.

The release of chromium into the environment through wastewater can have significant health risks. Public concerns with chromium are primarily related to hexavalent compounds due to their toxic effects on humans, animals, plants, and microorganisms. Chromium-6 is classified as a known carcinogen, and exposure to it, even in small amounts, can cause skin burns, pneumonia, complications during childbirth, and stomach cancer.

Chromium pollution can be removed from water using physio-chemical methods

Chromium is a metallic element that is odorless and tasteless. It is found naturally in rocks, plants, animals, soil, and volcanic dust. Chromium is also used in the production of a wide range of goods and materials, including refined metals and alloys, leather, paints, pigments, wood preservatives, electronics, and chemicals. As a result of natural and anthropogenic sources, chromium can be released into water and groundwater. The most common forms of chromium found in natural waters are trivalent chromium (chromium 3) and hexavalent chromium (chromium 6). While chromium 3 is an essential human dietary element found in many vegetables, fruits, meats, grains, and yeast, chromium 6 is a byproduct of industrial and manufacturing processes. Chromium 6 is toxic to humans, animals, plants, and microorganisms, and its presence in drinking water is regulated by organizations like the EPA in the US and similar bodies in Europe.

Due to the potential health risks associated with chromium pollution in water, it is important to remove it using effective methods. Physio-chemical methods have been proven to be successful in removing chromium from water. One such method is chemical precipitation, which involves adding chemical precipitants to a liquid stream to drive contaminant ions out of the solution, allowing for physical separation. This process is generally economical, simple, and popular for treating chromium-contaminated water. While chemical precipitation effectively removes trivalent chromium, an additional reduction step is required for hexavalent chromium. This can be achieved by adding a reducing agent such as sodium bisulfate, sodium metabisulfate, iron sulfate, or gaseous sulfur dioxide, which reduces hexavalent chromium to trivalent chromium.

Another physio-chemical method for removing chromium from water is ion exchange (IX). IX is a process that selectively removes contaminants from a solution by swapping out ions of similar electrical charges. For trivalent chromium removal, strong acid cation (SAC) resins, weak acid cation (WAC) resins, or chelating resins can be used. On the other hand, hexavalent chromium removal can be achieved using strong base anion (SBA) resins. Regular maintenance and resin regeneration cycles are necessary to ensure consistent and adequate chromium removal. Additionally, facilities may need to implement a brine waste minimization strategy to optimize system performance and reduce the use of regenerant chemicals.

In addition to chemical precipitation and ion exchange, other physio-chemical methods such as adsorption, electrocoagulation, and bioremediation can be employed to remove chromium from water. Adsorption is a simple, effective, and versatile process that utilizes low-cost agricultural wastes like waste tea leaves, coconut coir, and rice husks as adsorbents. Bioremediation, which involves using microorganisms to uptake chromium, has gained interest due to its effectiveness, ecological soundness, and economical advantages. These physio-chemical methods offer a range of options for removing chromium pollution from water, each with its own advantages and considerations.

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