Engineering professor Norma Alcantar answers a question from NPR’s Scott Simon on how cactus internal organs may filter water. Her grandmother, who was aware of its exceptional cleansing capabilities, gave her the inspiration.
HOST: SCOTT SIMON
Cacti don’t require a lot of water to survive. However, adding some cacti to the water can greatly improve its quality. Or more specifically, the gooey substance found inside cacti can function as a filter to remove microorganisms or heavy metals from contaminated water. Norma Alcantar’s research focuses on this purifying quality of cacti. She joins us from the WUSF studios where she teaches chemical and biomedical engineering at the University of South Florida. We really appreciate you being here.
SIMON: Practically speaking, though, you must be in a desert with cacti if you come across any tainted water (laughing).
ALCANTAR: We have a method whereby we take the sticky portion of the cactus and turn it into a powder. The water can then be separated by adding this powder to the water.
Simson agreed. I assume you have therefore worked in Haiti, for instance, both before and after the BP oil catastrophe.
Yes, Alcantar. Our research in Haiti focused on heavy metals and bacteria in the vicinity of the area where a greater quantity of metals actually leached into the groundwater. Therefore, we discovered that interacting with the cactus could be employed in an emergency response scenario.
ALCANTAR: Well, it’s a very good tale (laughs) because my grandmother is actually involved. She was raised in a remote area of Mexico in the early 1900s.
She once inquired about my day when I visited her after high school. And I informed her that we were using this chemical in my chemistry lab that day. Surfactants are typically present in soaps and detergents. And they’re employed in the cleaning of filthy dishes and water. She was fully aware of it.
I therefore ask, “Oh, how did you know about this?” She says, “Well, you know, I used to bring water from the river or the retention pond depending on the season when I was little.” Additionally, some contaminants like sediments and debris will be present in the water. As a result, they will roast the cactus at that time and use some of the water they collect as a result to purify water. The rest, as you know, is history.
SIMON: So your grandmother recognized something that you end up cultivating, and that is assisting people all over the world, when she was growing up in rural Mexico in the early 20th century (laughs).
Yes, Alcantar. For me, that was incredibly special. In 2008, she passed away. But I was able to inform her that we were conducting research and that it actually worked once we obtained our first funding from the National Science Foundation. She informed me that she was confident in its success.
SIMON: University of South Florida professor Norma Alcantar works there. We appreciate you being here.
Cacti filter water in what ways?
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Mexicali City A common edible cactus’ ability to purify water has been discovered by scientists, opening the door for its application in underdeveloped nations.
Opuntia ficus-indica, sometimes known as the nopal or prickly pear cactus, is a native of the United States and is also widely cultivated in Mexico, Africa, and other developing nations. According to the experts, it may now be used as an economical and long-lasting water filtration technique in rural areas of developing nations.
Although scientists were aware that prickly pears may purify water, they had little grasp of how.
Two varieties of mucilage, a gelatinous byproduct of the cactusin-contaminated water, were investigated. By aggregating dirt and bacteria into tiny “flocs,” or clusters of floating particles that could readily be filtered out, the cactus eradicated 98% of bacteria in 15 minutes.
According to the researchers, these results pave the door for recommendations on the quantity of cacti needed to cleanse water. Another natural water purifier, the moringa seed, also has rules in place (see Poor miss out on moringa seeds’ water-purifying benefits).
People in the rural town where she tested the cactus in Mexico were “all open to the concept of using the cactus,” she said.
The Mexican Institute of Water Technology’s (IMTA) Alejandra Martn, who oversees the program for water stabilization, says that teaching people about the value of water purification is the biggest issue.
Currently, Alcantar’s team is collaborating with colleges and nonprofit organizations in Mexico on educational initiatives. She anticipates beginning a similar effort in June to assist with the water issues brought on by the recent earthquake in Haiti (see Geologists survey Haiti quake aftermath).
More thorough research on natural polymers for water purification is welcome, according to Adrian Rennie, a materials physicist at Uppsala University in Sweden whose work on water purification by moringa seeds. Different environments are better suited for certain bio-polymers.
Is cactus water safe to drink?
There are five places to look, three places not to look, and one reason to disregard it all.
Water balloon fights and, of course, the desert are two areas where you don’t want to be caught without water. But occasionally things don’t turn out as expected. Perhaps you miscalculated how far you’d be hiking, got lost in Zion’s backcountry, or, worse, your water bottle spilled. You’re currently outside in one of the hottest, driest, and most oppressive settings in the nation without a drop to drink. For advice on where to look for water in the desert, we turned to Tony Nester, a survivalist and the proprietor of the outdoor survival school Ancient Pathways in Flagstaff, Arizona.
Never leave your house without it. He used the occasion to remind us that the best course of action is to be ready and bring adequate water in the first place, waving a (friendly) finger in our faces. The most crucial thing to keep in mind is that, because there isn’t much water out here, the most dependable water supply is the tap at home or in your hotel room before you go.
Look within canyons that face north “Try looking for north-facing canyons if you have a topo map or if you can see them off the land from a ridgeline. Because they don’t have southern exposure and are shielded from sunlight for a considerable portion of the day when they fill up with snowmelt or rainfall, they have a tendency to retain water in large amounts, sometimes for months at a time. We’ve discovered pour-offs in canyons that face north and have practically more water in them than a Jacuzzi. Even if the water is sluggish, muddy, and likely home to pollywogs, it is still preferable to the alternative.”
Look for trees with large leaves that enjoy water.”
If you’re in the Mojave Desert, Africa, or the Middle East, look for the bright green foliage of cottonwoods, willows, aspens, or palm palms. You’re searching for broad-leaved, vibrant green foliage, which is very different from evergreens. When I take kids on a vacation, if we see a cottonwood, sycamore, or willow from a distance and it jumps out as a green assault on your eyes because it’s the only thing nearby that isn’t sand- or rock-colored, we frequently stake some time on walking to those. At the absolute least, you can dig a hole down to the roots underground and it will fill with water. They either have water on the surface in the form of a spring, have a water hole nearby, or both.”
Look for insects and birds “Look for insects and birds. Over the years, we’ve had a lot of luck in places like the Grand Canyon and the Sonoran Desert, where we’ll be hiking for five or six miles through an incredibly remote and desolate area when all of a sudden, we come around a bend and see a hummingbird, followed by a wasp, and then perhaps a butterfly. It’s crucial to pay attention to when life suddenly appears after several hours of nothingness. That’s how we’ve found water holes. Situational awareness will aid you in noticing this kind of thing because those animals are there for a reason.”
Get to a higher location “Getting to a vantage point is the final item that can truly assist. It doesn’t entail scaling a ridgeline or anything, but if you can stand a little higher on the trail and gaze around, you may occasionally catch a glimpse of the cottonwood and willow trees as well as reflections in the water. I always have a small pair of 8×24 binoculars with me. They are a vital element of my desert equipment because they allow me to focus on a water source that is trustworthy rather than worrying about something I see in the distance and using a lot of energy to get there.”
Never take a sip from a cactus.”
Solar stills are useless. Cacti cannot be made to produce water. These are the two myths that recur frequently in books and television. Cactus does not provide “water,” only a stomachache and vomiting. In movies, you may have seen a cowboy cut off the top of a large, barrel-shaped cactus—also known as a beach ball cactus—dip his ladle in, and take a sip of water. But that’s not water. It is a poisonous fluid with a high alkalinity level. That’s an issue because if you add any of that material to your body while you’re already experiencing heat exhaustion or heat stress, you’ll put more strain on your kidneys and put yourself in danger of developing heat stroke. In essence, you’re consuming something that your body must metabolize, which is not advised. Only one of the five varieties of barrel cactus—the fishhook barrel—is non-toxic, yet you can drink from them.”
Don’t rely on the cactus fruit, but do eat it “There are many cactus fruits that can be eaten, like prickly pears. In the summer, we’ll gather those in large quantities on our courses. To remove the tiny hairs and spines, you roast them in the coals for 30 seconds before eating them. But it won’t make up for the massive amounts of fluid you’ll need in the heat—the 2 or 3 liters of water.”
Don’t follow this advice. “The bottom line is that research from the Grand Canyon and search-and-rescue operations out here demonstrates that a person who is lost and runs out of waterin the summer, with triple-digit heatcan live up to 48 hours if they are wise with their own sweat. We’re talking about this person in a situation where they run out of water. So, adopt a cowboy mentality and wait for rescuers by hiding out in the shade, remaining hidden, and avoiding the wind. However, if you choose to continue looking for water in the heat of the day without doing that, you run the risk of suffering from heat stroke and passing out within three hours simply from overworking your “engine.” So, if you’ve told someone about your hiking intentions, be patient and wait for assistance.”
Through his Ancient Pathwaysschool, Tony Nester has been instructing outdoor survival courses throughout the arid southwest and Rocky Mountains for more than 20 years.