Environmental Biotechnology

The use of genetic engineered organisms for pollution abatement

Phytoextraction

Phytoextraction is the use of plant to take up metal contaminants from soil through the absorption by plant roots. The metal absorbed are stored or accumulated in the aerial portions of the plants (Stems & Leaves).  Plants intended for this application are called hyper accumulators. These species of plants have high tolerance to heavy metals and are capable of absorbing larger amount of metal in comparison to other plants. Today, researchers are developing genetically engineered hyper accumulators that have a higher metal accumulation and tolerance capacity.

After the plants are allowed to absorb the contaminants for some time, they are harvested to either be disposed by incineration or be composted to recycle metals. Although plants that were incinerated will be disposed off in a hazardous waste landfill, the volume of the plant ash generated will be below 10% of the volume that would be produce if contaminated soil were excavated for treatment.

The plants take up the contaminant through the system of roots and store them in the roots or transport them up into the stems and leaves. The plants will carry on absorbing contaminants until it is being harvested. After the harvest, the soil will contain a lower concentration of contaminant. As such, this growth and harvest cycle is usually repeated for a number of times to achieve a considerable clean up. After the process, the remediated soil can be put into other beneficial uses.

Gene to improve Phytoextraction

A problem in the use of phytoaccumulator is that they do not have enough biomass and growth rate to be applied in large scale practices. To resolve this problem, phytoextraction can be further improve by transfer of genetic traits from hyper accumulator into plants that has high biomass and growth rate. In this way, plants with high biomass and growth rate will also have the ability to take up high quantity of metals.

For example, Poplar and willow do not accumulate metals to high concentration. However, they are still effective remediators because of their deep root system and biomass. Hence, they became excellent candidate to be genetically engineered to have traits of hyper-accumulators.

Metals accumulated poses significant risk to consumers of plants. As such, plants capable of producing substances that deter or discourage herbivores from feeding them can be transformed to have improved metal tolerance and capabilities. With such a system in place, it will help prevent the transfer of metals to food chain.

Transfer of gene extracted from bacteria or animals into plants systems are attempts to improve the potential of remediation. Some bacteria have the genetic characteristic to detoxify toxic elements. Today, the transfer of such genes into plants had already produced promising results.

For instances, no plants have been shown to be able tolerate some elements such as mercury or lead. This can possibly be changed by transferring genes from bacteria that has the ability to detoxify these metals (mercury & lead) into plants. With the transfer of the expressing gene, plants can be genetically altered to be used clean up these metals which were once seemed to be impossible.

The use of transgenic plants also addresses the problem of mix contamination that is happening in a polluted site. Methods which involve introducing several genes at once into plants have help in the removal of complex and mixed pollutants.

Advantages:

  1. Owing to incineration, the volume of harvested plant biomass that requires disposal is dramatically reduced
  2. In some cases, additional source of revenue can be obtained by extraction of metals from metal rich ash; so therefore, it can be used to offset the cost of remediation.
  3. Cheaper than most clean-up methods
  4. In comparison to conventional methods which typically disrupt soil structure and productivity, phytoextraction is capable of remediating heavily metal contaminated soil without impairing the soil quality.

Disadvantages:

  1. As the process relies solely on plants, the remediation time is relatively longer than other anthropogenic soil clean-up processes.

 

 

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