Team:Northwestern/Description
What is the problem we are trying to solve?
Hexavalent Chromium -- Cr(VI) -- is a highly carcinogenic and mutagenic compound, proven in 2008 to cause cancer in laboratory mice and rats [1]. In 2010, scientists at the California Office of Environmental Health Hazard Assessment experimentally determined that ingestion of very small amounts of this toxic chromium can lead to cancer in humans, a finding backed by teams of scientists in North Carolina and New Jersey. Soon after reaching this conclusion, the California and New Jersey scientists conducted independent calculations to determine the maximum safe contaminant level of hexavalent chromium in drinking water, arriving at .02 and .06 ppb (parts per billion), respectively [2]. This evidence communicates, based on California’s data, that .02 ppb represents the maximum amount of toxic chromium that poses no more than a one-in-a-million risk of cancer for people who drink the water daily for 70 years. The EPA-set maximum contaminant level is 1.0 ppb.
Lead is another highly toxic heavy metal, identified by the World Health Organization as 1 of 10 chemicals of major public health concern. The hazards of lead poisoning are substantial; when ingested, lead invades the brain, liver, kidney, and bones. It has been shown to severely hinder brain development and contribute to behavioral disorders in young children, and exposure of lead to pregnant women can result in miscarriage, stillbirths, and malformations. Long-term effects of lead poisoning in adults include increased risk of high blood pressure and kidney damage [3]. The FDA-regulated bottled-water maximum lead contaminant level is 5 ppb, while interestingly, the EPA-set amount is 15 ppb [4]. Per the Centers of Disease Control and Prevention, “No safe blood lead level in children has been identified” [5].
Local and National Impact
Northwestern University sits on the shores of Lake Michigan in Evanston, IL, just outside of Chicago. From 2013 to 2015, in water quality tests conducted in Evanston and Chicago, hexavalent chromium contaminant levels were found to be .210 and .194 ppb respectively, 10 times more concentrated than the California-determined maximum [6]. Nationally, over 60,000 drinking water tests were conducted, with hexavalent chromium being found in more than 75% of the samples [7]. Per the Environmental Working Group’s data analysis, water supplies serving 218 million Americans contained hexavalent chromium levels above the California-determined .02 ppb maximum. In April of 2017, a local U.S. Steel spill garnered national attention when 346 pounds of chromium - 298 pounds of which were highly toxic hexavalent chromium - were dumped into a Lake Michigan tributary [8]. Total chromium discharges into the lake are restricted to 30 pounds a day, with the amount of hexavalent chromium capped at just 0.51 pounds.
Moreover, in April of 2018, results from a Chicago-wide lead test and analysis were published -- of the nearly 3,000 water-testing sites, over 70% were found to contain levels of lead, with 30% having lead levels above the FDA-set bottled-water limit of 5 ppb. Starting in May of 2016, extensive lead testing has been conducted in Chicago Public Schools. It was found that 37% of CPS schools had at least one sample with an elevated lead level, though 3.05% had samples over the 15 ppb EPA limit. It should be noted that the 15 ppb limit set by the EPA has faced criticism for being too high, as some scientists have reached conclusions that no level of lead in water is safe; the 5 ppb limit set by the FDA, some say, reflect a more accurate level for safety concern -- even 5 ppb is not completely safe, though it significantly decreases health risks [4].
Of course, with these concerning results in mind, this is more than just a local problem. Flint, Michigan has been the toxic lead capital of the United States in recent years, with levels in some areas reaching 13,000 ppb; years of tests and efforts to purify the water have done little to bring the lead levels down to a safe amount [4].
Our Proposed Solution
In response to these staggering statistics and adverse local health effects, the Northwestern iGEM Team seeks to create a biosensor that can detect toxic hexavalent chromium and lead levels in and around Lake Michigan. We will be working with a cell-free protein synthesis system (CFPS) using self-made E. coli extract. CFPS offer significant advantages over traditional in vivo biological systems, as they are abiotic, able to be blotted onto paper, and can be readily stored long-term. Ultimately, the team will be creating a paper-based biosensor that can be used safely and efficiently outside the laboratory environment, in which ‘citizen scientists’ can detect levels of these two toxic heavy metals in their own drinking water. Current city-sponsored water quality test kits are expensive and inefficient, taking weeks to arrive and for results to be published [9]. Additionally, the team aims to create an easy-to-use software-based diagnostic test, in which the colorimetric output produced by GFP reporter can be analyzed and understood in order to take further action.
Specifically, the team will begin our project by creating and selecting for two strains of E. coli that are able to successfully output GFP in the presence of either toxic hexavalent chromium or lead. Building off this in vivo success, we seek to blot these protein-synthesis mechanisms onto paper to create an in vitro orthogonal metal-detection system. Once we determine our cell-free protein-synthesis system is reliable, we will use our software-based modeling analytics to quantify the GFP output, and clearly report the toxicity levels of the the tested water.
In 2015, the Bielefeld iGEM Team had a similar undertaking; their in vivo results were promising, however they were unable to successfully and reliably implement in vitro CFPS lead and chromium detection systems [10]. We aim to build upon and further their approach, optimizing and reliably measuring these cell-free systems and their output, while blotting these systems onto paper.
References
[1]Stout, M. D.; Herbert, R. A.; Kissling, G. E.; Collins, B. J.; Travlos, G. S.; Witt, K. L.; Melnick, R. L.; Abdo, K. M.; Malarkey, D. E.; Hooth, M. J. Environmental Health Perspectives 2008, 117(5), 716–722.
[2]Sutton, R. Chromium-6 in U.S. Tap Water https://www.ewg.org/research/chromium6-in-tap-water (accessed Jun 26, 2018).
[3]Lead poisoning and health http://www.who.int/news-room/fact-sheets/detail/lead-poisoning-and-health (accessed Jun 26, 2018).
[4]Ingraham, C. This is how toxic Flint's water really is https://www.washingtonpost.com/news/wonk/wp/2016/01/15/this-is-how-toxic-flints-water-really-is/?noredirect=on&utm_term=.b9580495d997 (accessed Jun 26, 2018).
[5]Centers for Disease Control and Prevention. Lead https://www.cdc.gov/nceh/lead/ (accessed Jun 26, 2018).
[6]Enhanced Monitoring for Hexavalent Chromium (Chromium-6). Dept. of Water Management, City of Chicago.
[7](2018, May 14) Occurrence Data for the Unregulated Contaminant Monitoring Rule. EPA. Environmental Protection Agency.
[8]Hawthorne, M. (2018, April 3) U.S. Steel to pay nearly $900,000 to settle lawsuit over chromium spill into Lake Michigan. Chicagotribune.com.
[9]Chicago Water Quality . Know your Water http://www.chicagowaterquality.org/ (accessed Jun 26, 2018).
[10]Barteczko, U., Buchholz, L., Drews, G., Dreyer, A., Grawe, A., Ho, U. L., Jackowski, M., Kracht, M., Luders, J., and Vornholt, T. (2015) iGEM Bielefeld 2015 Project. iGEM Bielefeld 2015 Wiki. iGEM.