Conducting phytoremediation procedures is important to recover potable water from water supplies that can be tapped within the Navajo Nation’s borders. At present, a significant portion of the already limited water within Navajo Nation’s borders is non potable due to pollution, especially heavy metal pollution from mines and industrial processes [1]. However, many of the Diné people have no other choice but to use this polluted water in their everyday lives due to lack of viable alternatives. Additionally, heavy metals are problematic as aquatic pollutants due to their ability to persist in the environment for generations and high potential to accumulate and reach toxic concentrations across the food chain [2]. As a result, crops and livestock grown with contaminated water ultimately will pass on concentrated toxins to the people that consume them. The primary heavy metals found in Navajo Nation include uranium and arsenic, according to EPA tests of unregulated wells [3]. Uranium is associated with kidney damage as a result of acute exposure and increased cancer risk due to radioactive decay [4]. Arsenic has been linked to a wide range of symptoms for both chronic and acute exposure [5]. Chronic exposure to arsenic has been known to cause hyperpigmentation, developmental effects, diabetes, pulmonary disease, and cardiovascular disease [5]. Acute arsenic exposure has been linked to vomiting, abdominal pain, diarrhea, numbness in the limbs, and death [5]. Continuous exposure to such toxic heavy metals has already had significant health impacts on the Diné people. Normally, the Diné have rates of cancer incidence lower than the average American. However, they are far more likely to pass away from certain types of cancers than a non-Hispanic white person living in the same state (7.2 times for gallbladder cancer, 4.4 times for stomach cancer, 2.1 times for kidney cancer, and 1.8 times for liver cancer), likely due to chronic exposure to heavy metals [1].
Figure 1: Distribution of wells, abandoned uranium mines, and major cities in the Navajo Nation.
Phytoremediation can help solve heavy metal contamination of the Diné water supply by making use of plants with the ability to absorb heavy metals from soil and water. First, the plants to be used must be selected based on the extent and type of pollution [6]. For example, surface level contamination can be treated with shallow-rooted plants, and subsurface and/or groundwater contamination would be best handled by deep-rooted plants [6]. The plants must also be able to effectively uptake the contaminant in question and grow to maturity despite the presence of toxins [6]. Additionally, the plants should be fast-growing to maximize plant turnover, especially considering that multiple rounds of phytoremediation (at least one per growing season) are usually needed over the span of 2-5 years [6][7].
Figure 2: A general overview of how phytoremediation works [7]
Once selected, these plants can be grown directly on the site of contamination (e.g. abandoned mines, contaminated wells) or grown in artificial environments with exposure to heavy metals [7]. They will uptake the heavy metal ions into their structures, removing the contaminants from the local environment [8]. Once the plants have fully matured, they are harvested and incinerated to prevent re-release of heavy metals into the environment [7][8]. Plants native to the area, such as prickly pear cactus, sunflowers, tobacco, and tumbleweed, can be used to prevent the risk of invasive species endangering ecosystems and ensure ecological compatibility during the growing season of the accumulator plants. [8][11][12][13][14][15].
For a classroom or project-based setting, students can learn how to select and grow different phytoremediation candidates. The plants can be grown in a variety of settings to show the concept of phytoremediation while tailoring to the school’s resources and the age of the students. The most advanced level would be allowing high school and college students to directly plant on sites with actual contaminated water and soil, and using water and soil quality tests to measure the changes in contamination levels over time. Conversely, for elementary school students, the concept can be simulated with colored water and potted plants, so the students can watch the changes in color as the “contaminant” is absorbed. Students can make use of trial and error to find the optimal plants and growing conditions that maximize removal of contaminants, enabling them to gain new skills in acquiring clean water for their own farms and families in the future.
Comparison of actual phytoremediation candidates already in Navajo Nation: [16][17][18][19][20][21][22][23][24][25][26][27][28]
| Name: | Depth of Remediation | Compatible heavy metals | Potential Effectiveness | Other considerations |
| Opuntia phaeacantha
Navajo Name: Common Name: Prickly Pear Cactus |
Very shallow, has shallow root system to soak up any runoff before it dries | Lead
Copper Manganese Cadmium Zinc Nickel Copper Chromium |
Moderate as a plant, has more explored potential when harvested | May be sharp, hazard for children
Excellent for dry climates |
| Helianthus sp.
Navajo Name: Hoshniteelí Common Name: Sunflower |
Deep, taproot reaches 4 feet | Radioactive Uranium
Arsenic Lead Mercury Cadmium |
Low to high, variable with soil conditions (ideally moist and well-drained with pH 6) | Will need more water to germinate but otherwise drought-hardy |
| Rumex crispus
Navajo Name: Dziłnát’oh Common Name: Navajo Tobacco |
Shallow depths due to shallow root system with mostly lateral spread | Arsenic
Uranium Cadmium Lead Zinc Copper Iron Manganese Magnesium |
High | Considered a weed
Toxic to animals Not suitable for small children |
| Salsola tragus
Navajo Name: Ch’ildeeníní Common Name: Tumbleweed |
Very deep, with main taproot reaching 6 feet | Arsenic
Uranium Chromium Copper Nickel Zinc |
High | Considered a weed
May be sharp, hazard for small children |
Phytoremediation shows promise as a method to acquire clean water that can be taught to and used by the future generation of the Diné people, helping promote greater water stability and agricultural productivity for future generations.
Works Cited:
[1] Ingram, J. C., Jones, L., Credo, J., & Rock, T. (2020, May). Uranium and arsenic unregulated water issues on Navajo Lands. Journal of vacuum science & technology. Retrieved November 30, 2022, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7083651/
[2] Lenntech. (2020). Heavy Metals. Lenntech Water treatment & purification. Retrieved November 30, 2022, from https://www.lenntech.com/processes/heavy/heavy-metals/heavy-metals.htm
[3] Environmental Protection Agency. (2022). Water sources table with MCLS. Navajo Nation Contaminated Unregulated Water Sources. Retrieved November 30, 2022, from https://www.epa.gov/sites/default/files/2016-06/documents/watersourcestable-with-mcls.pdf
[4] Depleted UF6 Management Program. (2022). Uranium Health Effects. Uranium health effects. Retrieved November 30, 2022, from https://web.evs.anl.gov/uranium/guide/ucompound/health/index.cfm
[5] World Health Organization. (2018, February 15). Arsenic. World Health Organization. Retrieved November 30, 2022, from https://www.who.int/news-room/fact-sheets/detail/arsenic
[6] Chirakkara, R. A., & Reddy, K. R. (2015). Plant Species Identification for Phytoremediation of Mixed Contaminated Soils. University of Illinois Chicago . Retrieved November 30, 2022, from https://cemmlab.webhost.uic.edu/2153-5515-0000282.pdf
[7] Environmental Protection Agency. (2012, September). A Citizen's Guide to Phytoremediation. United States Environmental Protection Agency . Retrieved November 30, 2022, from https://www.epa.gov/sites/default/files/2015-04/documents/a_citizens_guide_to_phytoremediation.pdf
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[11] New Mexico State University. (2018). Selected plants of navajo rangelands. NMSU. Retrieved November 30, 2022, from https://navajorange.nmsu.edu/perform_search.php?name=&genus=&species=&plantType=0&growingSeason=0&flowerColor=0
[12] The University of Georgia, National Park Service, Invasive Plant Atlas of New England, Invasive Plant Control Inc., USDA Forest Service, USDA NRCS PLANTS Database, Lady Bird Johnson Wildflower Center, National Association of Exotic Pest Plant Councils, Plant Conservation Alliance, & Biota of North America Program. (2018, October). The Common Sunflower. Invasive Plant Atlas. Retrieved November 30, 2022, from https://www.invasiveplantatlas.org/subject.html?sub=5688
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