The Danger of PFAS Chemicals
Water pollution is a global challenge that has been prevalent since the Industrial Revolution. There are many factors that pollute and contaminate our water, such as PFAS, which is the main focus of our project. Globally, every ninth person accesses drinking water from unsafe sources. Over two billion people reside in countries that are have contaminated water systems. Moreover, over 80% of global wastewater is not cleaned and filtered. Thus, people who drink this water are consuming toxic chemicals, human waste, and more. In San Diego, the situation is similar, as the water is contaminated by toxic chemicals such as Arsenic, PFAS, and Radium. Causes of water pollution, such as global warming and industrial waste, are sometimes challenging to reverse or stop. As a result, many people will continue to suffer the consequences of unsafe drinking water if nothing is done.
iGEM teams USAFA and NTHU Taiwan have previously worked to degrade Perfluorooctane Sulfonate (PFOS), Per- and Polyfluorinated Substances (PFAS), and Perfluorooctanoic Acid (PFOA). Specifically, the USAFA team worked to detect PFOS and PFOA by creating a biosensor and to search for a dehalogenase in order to defluoridate them. The NTHU Taiwan team worked on the degradation of PFOA and transportation of fluoride. With our project, we have worked to improve upon their work.
Chemical Structure of PFAS
Having clean access to water is a fundamental right all citizens should have. As young innovators of the future, we want to do our part to raise awareness and improve upon the quality of nearby water systems in the San Diego region. Starting in the 1960s, the US Navy “used certain PFAS to develop life-saving firefighting foams with support from 3M.” It was used to create substances that addressed the life-threatening challenges facing the military in live combat missions and training exercises. PFAS has not only made its way into homes from water, but also in kitchen supplies such as nonstick pans which have a Teflon coating that contains PFAS. It is even used in food containers and packaging, further increasing the risk of exposure to this toxic forever chemical. PFAS later entered water systems used for drinking when products containing them were used or spilled onto the ground or into lakes and rivers. Once in groundwater, PFAS are easily transported large distances, contaminating drinking wells. PFAS compounds have been shown to impact human health through altered kidney and thyroid function, immunosuppression and deleterious effects on reproduction and development.
Chronic diseases including kidney and testicular cancers, ulcerative colitis, and high cholesterol have also been observed. There is no doubt that many of us have some concentration of PFAS in our body. EWG's analysis suggests that up to 110 million Americans could have PFAS in their water Unfortunately, the effects of PFAS may not even show up until the next generation. "Babies born to mothers who were exposed to PFAS can be exposed before they are born, while breastfeeding, or while drinking formula mixed with PFAS contaminated water."" If the mother was exposed to PFAS, the baby's growth and development may be harmed.
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Diagram of How PFAS Has Moved From Industrial Settings to Our Environment
Our team saw the prevalence of these contaminants in everyday civilian lives. The government and large corporations promised to make our environment a better place, however these man-made chemicals were a result of their careless mistakes and their illegal practices. PFAS are forever chemicals meaning our next generation will start to see a mass impact of the chemical as they are carcinogenic and cause trailing effects. Removal of these now chemicals is important to save the future generations.
Sources of PFAS
Currently there are several methods, including filtration, adsorption, thermal, chemical oxidation/reduction, soil washing, and bioremediation technologies in place to remove forever-chemicals from water and soil. Filtration is a system using reverse osmosis or nanofiltration. Reverse osmosis means to use pressure to allow unfiltered water to go through a semipermeable membrane. This membrane is permeable to water, but blocks PFAS. Carbon filtration and adsorption work hand in hand to remove PFAS. The filters contain activated carbon and have many pores along its surface. When water runs through, PFAS is captured through adsorption, and clean water goes all the way through. Thermal technologies include vaporizing these contaminants. Soil washing is a method of detaching PFAS from soil using water. Additionally, another method is ion exchange. An anion resin captures negatively charged ions like PFAS and a cation resin captures the positively charged ions. Even boiling water at home to remove this chemical does not break it down, rather concentrates it and renders it more dangerous. Unfortunately, none have been able to completely eliminate these contaminants. Many of these solutions are time-consuming, costly, and don’t work for all the variety of PFAS chemicals that exist. Their field applicability and feasibility are open to question. However, even with these setbacks, “some of these technologies have shown promising outcomes in laboratory-based studies” (Shahsavari 2021). For example, bioremediation, or the use of a biological agent to break down chemicals, represents a “simple, environmentally safe, and cost-effective technology” (Shahsavari 2021). It has already been used to remediate many organic contaminants like pesticides, chlorinated substances, and petroleum hydrocarbons.
For PFAS, there is the possibility of using enzymes to directly remove the fluorine atoms, further destabilizing the C-F bonds that make this chemical so hard to break down. This may be done by adding oxygen to the C-F bonds, via oxidation (addition of oxygen), or reduction (addition of electrons). Additionally, there are also bacteria, such as Pseudomonas, that can remediate PFAS compounds. Studies have also shown that these bacteria use PFAS as an energy source, and as a result, produce perfluoroheptanoic acid and thus, release fluorine ions. Scientists are also looking into the value of transitional metals in an enzyme reaction. This can happen when the F in the C-F bond is replaced by a transition metal, thus allowing transition metal-dependent enzymes to release the F from these bonds. This is possible because the electronegativity of fluorine “can promote attraction to transition metal cations'' (Shahsavari 2021).
Continuing on, there are a few studies that are also looking into mycroremediation, or looking into types of fungi and microorganisms that can be successful at biotransformation of toxins. Much of the research has only been done in a laboratory setting, and thus “remains to be determined whether fungi are capable of degrading PFAS in the environment” (Shahsavari 2021). However, microalgae and fungi may play another role in remediation by enhancing bacteria biodegradation. This is being done by understanding the “relationship between microalgae and bacteria and how the optimum physico-chemical conditions are crucial steps to enhance bioremediation” (Shahsavari 2021). Many scientists are still trying to understand how PFAS works in water, what are the differences between many of the chemical structures of these chemicals, how these structures contribute to their unique properties, and how these can be used to our advantage to break them down once and for all.
Current Removal Strategies
Our solution is to engineer bacteria containing specific enzymes known for defluorination and test that bacteria in water containing PFAS to see how well they can degrade this compound. Comparing our engineered bacteria with a control will allow us to effectively understand how the enzymes degrade the chemical and how well they break it up. The two enzymes we are testing are Fluoroacetate Dehalogenase (FaCD) and Haloacid Dehalogenase (HaCD) which will be inserted into E.Coli bacteria. Our end goal is to test the concentration of hydrogen ions with pH testing during experimentation to understand the effectiveness of degradation.
Future Plans
1. Test more enzymes such as P450, histine-ligated heme enzymes like TyrH and other hydroxylases or dehydrogenases
2. Understand what byrpoducts are formed after testing various enzymes and use this information to see if certain enzymes contribute to higher levels of toxicity from the creation of toxic byproducts or if there are safer enzymes that can partially degrade PFAS while also producing safe byproducts (get the best of both worlds)
3. Want to enginner our bacteria in Pseudomonas Putida (P. Putida) to test which type and strains of bacteria have a higher survival rate when degrading PFAS
4. Add a fluorescent tag to our insert will tell us if the protein is being produced. This guarantees a greater understanding of whether or not the promoter is working and helps us understand the expression of the gene
5. Protein Size (see if protein of expected size is there)
a. Protein tag
b. Western blot
c. Fast Protein Liquid Chromatography (FPLC)
PFAS Pollution is Widespread in California
WORKS CITED/ SOURCES
- https://2016.igem.org/Team:NTHU_Taiwan/Description
- https://2020.igem.org/Team:USAFA/Description
Dyjak, Analies. "Problems We Found In San Diego's Drinking Water." Hydroviv.com, 7 July 2022, www.hydroviv.com/blogs/water-smarts/problems-we-found-in-san-diegos-drinking-water. Accessed 12 Oct. 2022.
"International Initiative on Water Quality (IIWQ)." Unesco.org, en.unesco.org/waterquality. Accessed 12 Oct. 2022.
Shahsavari, Esmaeil. "Challenges and Current Status of the Biological Treatment of PFAS-Contaminated Soils." Ncbi.nlm.nih.gov, 7 Jan. 2021, www.ncbi.nlm.nih.gov/pmc/articles/PMC7817812/. Accessed 12 Oct. 2022.