Water Pollution

Heavy metal pollution in water is one of the most significant public health risks around the world. Pollutants including lead, mercury, and nickel can enter water supplies through a number of methods including improper disposal of waste, industrial manufacturing, and mining. When solubilized, they have the ability to cause environmental and health problems. These heavy metals are acutely toxic at high concentrations and carcinogenic with long-term exposure even at low concentrations. Methods exist to remove heavy metals from water supplies, but these methods create other hazardous wastes and are more effective in waters with high concentrations of metals. Due to the high affinity of binding proteins, a biological based filtration system can be more effective at treating water contaminated with lower concentrations of heavy metals without generating large volumes of toxic waste.

Existing Technologies

Given the extremely harmful nature of heavy metal contaminants, government agencies and researchers have already developed many techniques for remediation. Current techniques commonly employed to remove lead range from reverse osmosis and distillation to activated carbon water filters. However, these methods are generally energy intensive and result in more acidic water ^[1]. Mercury found in soil is typically removed by dredging or thermal desorption. Both methods are time and resource intensive and do not guarantee complete removal of mercury. In addition to reverse osmosis and ion exchange, nickel has been removed by plants in photoremediation. Again, these methods have proven to be constrained by resources and time.

Other researchers have also worked on metal remediation using synthetic biology. Just this year, Wei et al. developed a whole-cell biosensing and bioremediation platform for lead using a regulatory metalloprotein from a heavy-metal resistant bacterium known as Cupriavidus metallidurans CH34. Their system displays the metalloprotein on the cell surface and produces RFP in response to lead detection. Their work demonstrates synthetic biology’s immense potential to alleviate this issue. However, their system uses a metal-binding protein with a high affinity for lead, but with a very significant affinity for copper, zinc, iron, and other ions that, under normal environmental conditions, are likely to be present in much higher concentrations than lead. The disparity in concentration is immense; the EPA limits for copper, zinc, and iron are 1.3 mg/L, 5.0 mg/L, and 0.3 mg/L, whereas for lead it is only 0.015 mg/L ^[2]. Therefore, a field-deployable lead sequestration system for water must be extremely selective for lead in order to be effective.

Protein-based filtration systems have been extensively studied for purifying heavy metals. At Cornell University, our advisor, Dr. David Wilson, has developed bioremedial systems consisting of metal-specific transporters and a metal binding protein called metallothionein. The two metals targeted were mercury and nickel. We plan to work to improve the efficiency and lifespan of these filtration systems. We will also be developing a novel sequestration system for lead by utilizing a putative lead transport protein from Nicotiana tabacum.

Sequestration Systems

Further information about the toxic effects of our targeted heavy metals and the transport proteins can be found by clicking the icons below.

Lead System

Mercury System

Nickel System

References

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1. Distillation - Pros and Cons. (2010). Retrieved October 18, 2014, from http://www.historyofwaterfilters.com/distillation-pc.html
2. Drinking Water Contaminants. (2013, June 3). Retrieved October 18, 2014, from http://water.epa.gov/drink/contaminants/