Environmental contaminants cover U.S. grounds. These contaminants include polychlorinated biphenyls (PCBs), chlorinated organic solvents, and organochlorine pesticides. The EPA reported that more than 1500 sites are polluted and in the last decade, less than a third of them have been cleaned up. The current clean up procedure for these contaminants are costly and limited. Much environmental research has been dedicated to less costly alternatives. One alternative that has proven to be successful in laboratory research as well as field test studies is the use of nanoscale iron particles.
Nanoscale Iron Particles
Nanoscale iron particles are small in size, usually 1-100 nm, making them highly reactive because of their large surface areas. Furthermore, they are easily transportable through ground water. This attribute allows in situ treatment. The nanoparticle-water slurry can be injected into the contaminated area and stay there for long periods of time. When exposed to oxygen and water, iron oxidizes. The below equations show zero-valent iron reactions:
(1) 2Fe0(s) + 4H+(aq) + O2
(aq) → 2Fe2
+(aq) + 2H2
(2) Fe0(s) + 2H2O (aq) → Fe2+(aq) + H2(g) + 2OH-(aq)
Researchers have found that although metallic iron nanoparticles remediate contaminants well, they tend to agglomerate on the soil surfaces. Carbon nanoparticles and water-soluble polyelectrolytes have been used as supports to the metallic iron nanoparticles. The hydrophobic contaminants adsorb to these supports, improving permeability in sand and soil.
In addition to laboratory research, some researchers have conducted field studies. Many researchers agree that it is extremely important to perform these field tests and to understand the particular field where the tests occur. Wei-xian Zhang conducted an experiment in a field downhill from a waste disposal area. Ground water samples were taken before, during and after injection of iron nanoparticles. Although Zhang feels that more improved field-scale tests should be performed, the results were good. The test showed enhanced water quality and achieved total chlorinated volatile organic compounds (VOCs).
Traditional remediation procedures include incineration and landfilling. While incineration is very expensive, landfilling is becoming more and more limited. These problems delay the clean up of the contaminated sites. Incineration causes toxic emissions to be released into the air. Furthermore, contaminants can escape landfills through air channels. The pollution from the lack of clean up is affecting the public health. The inhalation of the volatized contaminants and the consumption of contaminated fish are serious health concerns. Studies have shown that exposure to these contaminants increases health risks. Some of the identified health problems from laboratory animal studies are liver damage, skin irritation, reproductive dysfunction and cancer.