Radioactive Decay, Phytoremediation, and Bioremediation of Metals
Radioactive Clocks
Radioactive elements are unstable and disintegrate at a precise rhythm. To measure the speed of this decay, we consider the half-life, the time it takes for a quantity of the material to reduce by half.
Isotopes:
- Chlorine-36. Half-life: 300,000 years.
- Hydrogen-3 (Tritium). Half-life: less than 1 second.
- Technetium-99. Half-life: 6 hours.
- Carbon-14. Half-life: 5,730 years.
Technetium-99 and Hydrogen-3 isotopes cannot be used to determine the age of fossils due to their short half-lives.
Sciences like endowment archaeology (study of ancient civilizations’ remains), paleontology (study of past life through fossils), and anthropology (study of humans, physically and culturally) use these methods.
Carbon-14 can be used in dating fossils because it serves to date recent objects and developments and disintegrates more rapidly. It is formed in the atmosphere by cosmic radiation and then mixes with Carbon-12. When living things absorb carbon dioxide, their tissues contain a certain proportion of Carbon-14, which remains constant until they die. After death, Carbon-14 decreases as the body disintegrates, starting the radioactive clock.
Metal-Absorbing Plants
A group of researchers from the Department of Plant Sciences, University of Oxford, found that a plant from Greece, Alyssum lesbiacum, can absorb and clean large amounts of nickel from the soil. With this discovery, Dr. Andrew Smith and Ute Kramer believe that in the future, using genetic engineering techniques, we may be able to engineer plants to remove metals from the soil more quickly and cheaply than current methods.
A. lesbiacum absorbs nickel very efficiently, accumulating it in its tissues, so the “harvest” decontaminates the soil. Like other hyperaccumulators, it absorbs this metal in amounts that would be deadly for most plants. The problem is that this plant grows very slowly and could take years to decontaminate a site. Researchers are trying to locate the genes responsible for hyperaccumulation to genetically engineer fast-growing plants with lots of greenery, such as cauliflower, to absorb the metals.
Some current methods used to decontaminate the soil use acid, which is expensive, kills microorganisms, and leaves the soil sterile. This new method is considered cheaper and more environmentally friendly.
Bacteria that “Eat” Metals
The metals industry, particularly those using plating techniques, releases waste into the environment, including heavy metals such as nickel and cadmium. These metals are a significant source of pollution in the biosphere, including water, with their environmental impact exceeding that of chlorinated compounds and radioactive waste combined. Heavy metals are spread in low concentrations everywhere, and their elimination by physical or chemical methods is very difficult.
However, some bacteria can “eat” oil, sulfur, methane, and a variety of chemicals, including iron (they incorporate and metabolize these substances).
This bacterial property can be used to clean the environment, including contaminated water. However, until recently, this could not be exploited for heavy metals like nickel and cadmium, as they are indigestible and indestructible residues. The only solution was to filter them out and store them safely.
A group of Spanish researchers led by Dr. Victor De Lorenzo created, through genetic engineering techniques, a bacterium to address this problem and invented a technology that could also be used to harvest precious metals. The initial idea was that any bacteria can retain metals because they have many negative electrical charges on the outside of their envelope. This natural ability is not enough but can be enhanced by genetic engineering. The experiment involved introducing genes from another bacterium into Escherichia coli to produce a small molecule called polyhistidine in the membrane. Polyhistidine has a high affinity for heavy metals. With this molecule in its membrane, the bacteria can hold ten times the amount of metal atoms than expected. The drawback is that the modified bacteria grow easily in the laboratory but rarely in the wild. The solution is to collect bacteria from the environment, genetically modify them, and use them to clean polluted water.