Carbon nanotubes (CNTs) add strength and design flexibility to many materials, from reinforcing adhesives and materials used in electronics to enhancing the design of carbon fiber composites for use in cars and aerospace applications. But there's been increasing evidence that they, along with other nanoscale materials, may pose risks to human health and the environment. In ongoing research efforts to determine just how toxic they actually are, researchers at Texas Tech University have come up with a new method for detecting CNTs in soils.
The university's environmental biologists built an apparatus that can quantify how much CNT is present in a given soil sample. That's not an easy task since they're so small: mean outer diameters of 13nm to 16nm are common in multi-walled tubes. The apparatus was developed as part of the researchers' ongoing work in locating CNTs in biological environments and examining how they to accumulate in soil, plants such as food crops, or other organisms.
Researchers at Texas Tech University have come up with a new method for detecting CNTs in soils, which will help determine their toxicity. CNTs are so small that mean outer diameters of 13nm to 16nm are common in multi-walled tubes, shown here as grains partially smeared on paper (scale in centimeters). (Source: Shaddack/Wikimedia Commons)
The testing apparatus works by exposing soil samples to microwaves, which can reveal even mere trace quantities of CNTs. That's because, in the presence of microwaves, CNTs produce very high quantities of heat, much higher than most materials. The effect is so extreme that, if you put CNTs in your kitchen microwave oven, the carbon will spontaneously ignite. The researchers used this fact to heat samples to different temperatures to determine different concentration levels. The method has also been used to determine the amount of CNT loading in plant samples and earthworms.
The news about CNTs' toxicity is more than a little unwelcome, since graphene, the tubes' constituent substance, is the hardest known substance. When layers of it are rolled up into tubes, the resulting CNTs constitute a fiber that is 100 times stronger than steel and weighs one-sixth as much. That combination, along with qualities such as mechanical strength and electrical and thermal conductivity, makes them highly unusual and ideal building blocks for industrial uses.
Earlier this year, a joint study by the University of Missouri and the US Geological Survey showed CNTs to be toxic to various species of invertebrate aquatic organisms that live in sediment, including mussels, worms, and crustaceans. These researchers note that CNTs, which may contain metals as well as carbon, tend to accumulate in sediment when released into water. Both the metals -- including nickel, chromium, and other metals used in manufacturing that may remain as impurities -- and the carbon in CNTs can reduce growth rates or even kill certain types of marine life. The degree of toxicity varied depending on the type and source of CNT, the species of test organism, whether the materials had been cleaned using acid, and what method was used for dispersing the materials.
Researchers of the joint study say one of the biggest potential contamination risks occurs during the manufacture of carbon composites, but careful waste management and handling procedures can reduce that risk. More information is also needed on what happens when the composites begin to break down.
"Burning stuff" is how nature does it. [I've been presented lake sediment data showing prehistoric fire events were quite periodic (every 25-27 years)]
It doesn't go away.
We evolved eating and breathing it. (we didn't evolve eating grains)
Great parallel. Burning "stuff" is a quick solution used too many places in the world. When the fire is out, the stuff is gone and out of mind. But what is out of mind oftimes becomes the stuff in the lungs, the bloodstream, the organs and cells.
As for the scented candles, hopefully the proliferation of LED "fake" candles on the store shelves this year lead to fewer scented candles that must be endured. A Christmas wish for 2013 and beyond?
""Its carbon, the thing that loves to react with oxygen... Light it up :) Let's find out how fast this material will decay or adhere to larger particles.""
I suggest reading up on the subject of Polycyclic Aromatic Hydrocarbons. "Lighting it up." is how this sort of stuff (including some actual fullerenes) is formed in nature. The primary example of PAH is soot, from which the earliest known carcinogens were recognized. The toxicities of PAHs in soot range from nontoxic to extremely toxic.
Carbon in this form is quite persistent in the environment. For an easy example, consider how long charcoal lasts in soil. Devoid of carbohydrate, it is not readily biodegradable (coal does not rot very fast ...)
Polycyclic aromatic hydrocarbons are naturally pervasive in the food supply. The natural source is grass and forest fire. The soot settles on leaves and soil and from there are absorbed into the plant oils. Environmentally released nanotubes and graphene would be able to participate in those same processes.
Now, given that PAH are both carcinogenic and pervasive, animals must have some means of tolerance of the toxicity. Healthy lungs should expel most air-borne PAH to the digestive track through mucus. Primary exposure to food-borne PAH is at the intestinal lining. Healthy intestinal walls continuously shed their surface cells, so, if PAH happens to trigger a cancerous change in a cell, the cell is sloughed off with all the rest. This suggests that anything that impairs intestinal lining health (e.g., gluten sensitivity, folate deficiency, folic acid supplements) should increase risks of intestinal cancers.
I am trying to imagine, though, an industrial life cycle "leak" of PAH or fullerenes comparable to a forest fire or a nation's population of scented candles.
Clint, I don 't know if those 2 are the scariest for me, also, but GMOs are certainly at the top of my list. I was really, really disappointed to find out how toxic CNTs appear to be. Thanks for the feedback on the "alarmist attitude" and AM radio--I'm not a listener so I didn't realize that might be the source of this puzzling attitude. That attitude also seems to apply to comments on some of the stories we've posted about alternative energy, implying that climate change either isn't occurring, or is nothing to worry about.
Ann, I don't know how I missed this article when it was first published, but I'm glad you wrote it. I have long said that the two things that scare me the most when it comes to the future of the human race are GMOs and notechnology/nanomaterials.
Though commenting on old articles rarely re-starts a discussion, I'd question why some of the commentors chose to use words like "hysteria" and "hysterical" when describing the voices that are preaching concern and safety. The "alarmist" accusation has become the standard strategy of AM talk radio hosts and neo-cons who feel that any limitations/regulations/restrictions on industry are automatically bad.
Such knee-jerk responses are not conducive to constructive conversation like those which take place after a good article like this one; rather they are designed to shut down the exchange of thoughts.
Unfortunately, Dave is right. A surprising number of polluting entities *did* know what they were doing and how dangerous it was, and spent a lot of time and energy and money covering it up. That's how the EPA came about in the first place.
@Cabe: Smoking is a good analogy, since companies made an effort to conceal the risks. Johns-Manville was aware of the dangers of asbestos as early as 1930. By that time, there were already multiple reports in the medical literature, since doctors were starting to see patients dying of asbestos-related diseases. But Johns-Manville made a conscious effort to cover this up, and pretty much succeeded in keeping the general public from finding out until the '70s. They kept producing it until the end of the '80s.
True, it is a bit of an exaggeration. I find the past ignorance to be troubling. I suppose they didn't know. Like smoking hazards became mainstream, only after centuries of oblivious use.
Exploitation of developing worlds has brought me to a similar frustration level. Labor practices in China being the most forefront. What can be done to prevent such travesties? Not buying from those countries? Perhaps some products are more ethical... perhaps better research is the key to change?
It's also important to keep in mind that the problem of pollution and contamination, intended or not, is much greater today than in earlier times simply because it's expanded along with the world's expanding population. Even if the rates of careless materials production and handling had stayed the same, the geometric population expansion of the last century means that the problem has gotten a lot, lot worse.
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