Microbes : The Heavy Weights of Heavy Metal Remediation
Heavy metals are nothing but any metallic chemical element that has a relatively high molecular weight. But unlike normal metals, they are toxic or poisonous even at very low concentrations. Moreover, they have a propensity to accumulate in selective body organs (such as brain and liver) and cause irreversible damage. There are many members which can be technically counted under the broad term “heavy metal”; however, arsenic, cadmium, chromium, lead, mercury are of major concern due to common & wide occurrence in soils & water and repetitive incidences of poisoning induced thereby.
Though, we have been aware of presence of such heavy metals since ancient times, it was not until 1868; when adverse effect of heavy metals were documented as an effect of their presence in drinking water. Problem of heavy metal poising has exponentially increased since then due to industrialization; rather unethical disposal of industrial waste. There have been many incidences of heavy metal toxicity throughout the world. It has even been found out that the autism; a disease of neuro-developmental disorders in children is also triggered by exposure to high quantities of heavy metals.
Very few physico-chemical methods of remediation are available to combat this issue. The most commonly used method (after land filling) is soil washing using EDTA. This method is non specific and thus can not be classified as environmentally sustainable. Among biological methods, phytoremediation and microbial remediation are the two options; later being the more sustainable considering small size of the microbial cells.
Though being smallest living creatures, microorganisms have found to not only develop resistance to considerably high concentrations of heavy metals but, they are also able to remediate the same . The most commonly used bacteria used in the process of heavy metal remediation are members of genus Pseudomonas, Thiobacillus and Leptospirillum species. Other than these few cyanobacteria, algae and fungi are also been reported to serve the job of heavy metal remediation. Scientist have even tried taking an aid of genetic engineering to design the bacteria that can be easily grown and serve the job of heavy metal remediation more efficiently. An examples of one such attempt is the transfer of a gene from Helicobactor pylori to E coli to enhance the process. Similar studies have also been conducted using Staphylococci sp.. An example of one such genetically engineered microbe; yeast is been extensively studied by a team of Romanian and Norwegian researchers where they propose the use of this yeast for heavy metal remediation in wastewater treatment plants or contaminated soil.
Though there has been research going on this topic since decades, it is only recently that microbes have been explored for large scale remediation of soil and water contaminated with heavy metals. An Irish biotech company has even identified bacteria as only option to stabilize heavy metal flow within the ecosystems. Their microbial based products are being used extensively in agriculture to restrict the mobility of heavy metals in the plants. Recently, Indian authorities have adopted microbial route for remediation of Ganga river. The major part of this project covers remediation of heavy metals present in the water. From decades of research on microbial remediation to actual implementation in either wastewater or contaminated soils, the journey has been long and it is encouraging to see these tiny useful creatures serve this purpose. Having such versatile microbes at work, it is not irrational to expect the soil soon to be free of toxic metal concentrations; thus helping us provide a safer environment for future generations to come.