Tag Archives: mesocosms

This Oct. 1, 2014 news item on ScienceDaily about carbon nanotubes accumulating in the wetlands is carefully worded,

A Duke University team has found that nanoparticles called single-walled carbon nanotubes accumulate quickly in the bottom sediments of an experimental wetland setting, an action they say could indirectly damage the aquatic food chain. [emphasis mine]

The results indicate little risk to humans ingesting the particles through drinking water, say scientists at Duke’s Center for the Environmental Implications of Nanotechnology (CEINT). But the researchers warn that, based on their previous research, the tendency for the nanotubes to accumulate in sediment could indirectly damage the aquatic food chain in the long term if the nanoparticles provide “Trojan horse” piggyback rides to other harmful molecules. [emphases mine]

There’s a lot of hedging (could, if) in the way this research is being described. I imagine the researchers are indicating they have concerns but have no wish to stimulate panic and worry.

An Oct. 1, 2014 Duke University news release (also on EurekAlert), which originated the news item, goes on to explain the interest in carbon nanotubes specifically,

Carbon nanotubes are rapidly becoming more common because of their usefulness in nanoelectric devices, composite materials and biomedicine.

The Duke study was done using small-scale replications of a wetland environment, called “mesocosms,” that include soil, sediments, microbes, insects, plants and fish. These ecosystems-in-a-box are “semi-closed,” meaning they get fresh air and rainwater but don’t drain to their surroundings. While not perfect representations of a natural environment, mesocosms provide a reasonable compromise between the laboratory and the real world.

“The wetland mesocosms we used are a much closer approximation of the natural processes constantly churning in the environment,” said Lee Ferguson, associate professor of civil and environmental engineering at Duke. “Although it’s impossible to know if our results are fully accurate to natural ecosystems, it is clear that the processes we’ve seen should be considered by regulators and manufacturers.”

Ferguson and his colleagues dosed the mesocosms with single-walled carbon nanotubes and measured their concentrations in the water, soil and living organisms during the course of a year. They found that the vast majority of the nanoparticles quickly accumulated in the sediment on the “pond” floor. However, they found no sign of nanoparticle buildup in any plants, insects or fish living in the mesocosms.

That sounds marvelous and then the researchers provide a few facts about carbon nanotubes,

While this is good news for humans or other animals drinking water after a potential spill or other contamination event, the accumulation in sediment does pose concerns for both sediment-dwelling organisms and the animals that eat them. Previous research has shown that carbon nanotubes take a long time to degrade through natural processes — if they do at all — and any chemical that binds to them cannot easily be degraded either.

“These nanoparticles are really good at latching onto other molecules, including many known organic contaminants,” said Ferguson. “Coupled with their quick accumulation in sediment, this may allow problematic chemicals to linger instead of degrading. The nanoparticle-pollutant package could then be eaten by sediment-dwelling organisms in a sort of ‘Trojan horse’ effect, allowing the adsorbed contaminants to accumulate up the food chain.

“The big question is whether or not these pollutants can be stripped away from the carbon nanotubes by these animals’ digestive systems after being ingested,” continued Ferguson. “That’s a question we’re working to answer now.”

It’s good to see this research is being followed up so quickly. I will keep an eye out for it and, in the meantime, wonder how the followup research will be conducted and what animals will be used for the tests.

Here’s a link to and a citation for the researchers’ most recent paper on possible ‘Trojan’ carbon nanotubes,

Fate of single walled carbon nanotubes in wetland ecosystems by Ariette Schierz, Benjamin Espinasse, Mark R. Wiesner, Joseph H. Bisesi, Tara Sabo-Attwood, and P. Lee Ferguson. Environ. Sci.: Nano, 2014, Advance Article DOI: 10.1039/C4EN00063C First published online 03 Sep 2014

This is an open access paper.

I have written about Duke University and its nanoparticle research in mesocosms before. Most recently, there was a Feb. 28, 2013 posting about work on silver nanoparticles which mentions research in the ‘mesocosm’ (scroll down about 50% of the way). There’s also an Aug. 15, 2011 posting which describes the ‘mesocosm’ project at some length.

For anyone unfamiliar with the Trojan horse story (from its Wikipedia entry; Note: Links have been removed),

The Trojan Horse is a tale from the Trojan War about the subterfuge that the Greeks used to enter the city of Troy and win the war. In the canonical version, after a fruitless 10-year siege, the Greeks constructed a huge wooden horse, and hid a select force of men inside. The Greeks pretended to sail away, and the Trojans pulled the horse into their city as a victory trophy. That night the Greek force crept out of the horse and opened the gates for the rest of the Greek army, which had sailed back under cover of night. The Greeks entered and destroyed the city of Troy, decisively ending the war.

Silver nanoparticles, water, the environment, and toxicity

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I am contrasting two very different studies on silver nanoparticles in water and their effect on the environment to highlight the complex nature of determining the risks and environmental effects associated with nanoparticles in general. One piece of research suggests that silver nanoparticles are less dangerous than other commonly used forms of silver while the other piece raises some serious concerns.

A Feb. 28, 2013 news item on Nanowerk features research about the effects that silver nanoparticles have on aquatic ecosystems (Note: A link has been removed),

According to Finnish-Estonian joint research with data obtained on two crustacean species, there is apparently no reason to consider silver nanoparticles more dangerous for aquatic ecosystems than silver ions.

The results were reported in the journal Environmental Science and Pollution Research late last year (“Toxicity of two types of silver nanoparticles to aquatic crustaceans Daphnia magna and Thamnocephalus platyurus”). Jukka Niskanen has utilised the same polymerisation and coupling reactions in his doctoral dissertation studying several hybrid nanomaterials, i.e. combinations of synthetic polymers and inorganic (gold, silver and montmorillonite) nanoparticles. Niskanen will defend his doctoral thesis at the University of Helsinki in April.

The University of Helsikinki Feb. 28, 2013 press release written by Minna Merilainen and which originated the new item provides details about the research,

“Due to the fact that silver in nanoparticle form is bactericidal and also fungicidal and also prevents the reproduction of those organisms, it is now used in various consumer goods ranging from wound dressing products to sportswear,” says Jukka Niskanen from the Laboratory of Polymer Chemistry at the University of Helsinki, Finland.A joint study from the University of Helsinki and the National Institute of Chemical Physics and Biophysics (Tallinn, Estonia), Toxicity of two types of silver nanoparticles to aquatic crustaceans Daphnia magna and Thamnocephalus platyurus, shows that silver nanoparticles are apparently no more hazardous to aquatic ecosystems than a water-soluble silver salt. The study compared the ecotoxicity of silver nanoparticles and a water-soluble silver salt.

“Our conclusion was that the environmental risks caused by silver nanoparticles are seemingly not higher than those caused by a silver salt. However, more research is required to reach a clear understanding of the safety of silver-containing particles,” Niskanen says.

Indeed, silver nanoparticles were found to be ten times less toxic than the soluble silver nitrate - a soluble silver salt used for the comparison.

The bioavailability of silver varies in different test media

To explain this phenomenon, the researchers refer to the variance in the bioavailability of silver to crustaceans in different tested media.

University lecturer Olli-Pekka Penttinen from the Department of Environmental Sciences of the University of Helsinki goes on to note that the inorganic and organic compounds dissolved in natural waters (such as humus), water hardness and sulfides have a definite impact on the bioavailability of silver. Due to this, the toxicity of both types of tested nanoparticles and the silver nitrate measured in the course of the study was lower in natural water than in artificial fresh water.

The toxicity of silver nanoparticles and silver ions was studied using two aquatic crustaceans, a water flea (Daphnia magna) and a fairy shrimp ( Thamnocephalus platyurus). Commercially available protein-stabilised particles and particles coated with a water-soluble, non-toxic polymer, specifically synthesised for the purpose, were used in the study. First, the polymers were produced utilising a controlled radical polymerization method. Synthetic polymer-grafted silver particles were then produced by attaching the water-soluble polymer to the surface of the silver with a sulfur bond.

Jukka Niskanen has utilised such polymerisation and coupling reactions in his doctoral dissertation. Polymeric and hybrid materials: polymers on particle surfaces and air-water interfaces, studying several hybrid nanomaterials , i.e., combinations of synthetic polymers and inorganic (gold, silver and montmorillonite) nanoparticles....

It was previously known from other studies and research results that silver changes the functioning of proteins and enzymes. It has also been shown that silver ions can prevent the replication of DNA. Concerning silver nanoparticles, tests conducted on various species of bacteria and fungi have indicated that their toxicity varies. For example, gram-negative bacteria such as Escherichia coli are more sensitive to silver nanoparticles than gram-positive ones (such as Staphylococcus aureus). The difference in sensitivity is caused by the structural differences of the cell membranes of the bacteria. The cellular toxicity of silver nanoparticles in mammals has been studied as well. It has been suggested that silver nanoparticles enter cells via endocytosis and then function in the same manner as in bacterial cells, damaging DNA and hindering cell respiration. Electron microscope studies have shown that human skin is permeable to silver nanoparticles and that the permeability of damaged skin is up to four times higher than that of healthy skin.

While this Finnish-Estonian study suggests that silver nanoparticles do not have a negative impact on the tested crustaceans in an aquatic environment, there’s a study from Duke University suggests that silver nanoparticles in wastewater which is later put to agricultural use may cause problems. From the Feb. 27, 2013 news release on EurekAlert,

In experiments mimicking a natural environment, Duke University researchers have demonstrated that the silver nanoparticles used in many consumer products can have an adverse effect on plants and microorganisms.

…

The main route by which these particles enter the environment is as a by-product of water and sewage treatment plants. [emphasis] The nanoparticles are too small to be filtered out, so they and other materials end up in the resulting “sludge,” which is then spread on the land surface as a fertilizer.

…

The researchers found that one of the plants studied, a common annual grass known as Microstegium vimeneum, had 32 percent less biomass in the mesocosms treated with the nanoparticles. Microbes were also affected by the nanoparticles, Colman [Benjamin Colman, a post-doctoral fellow in Duke’s biology department and a member of the Center for the Environmental Implications of Nanotechnology (CEINT)] said. One enzyme associated with helping microbes deal with external stresses was 52 percent less active, while another enzyme that helps regulate processes within the cell was 27 percent less active. The overall biomass of the microbes was also 35 percent lower, he said.

“Our field studies show adverse responses of plants and microorganisms following a single low dose of silver nanoparticles applied by a sewage biosolid,” Colman said. “An estimated 60 percent of the average 5.6 million tons of biosolids produced each year is applied to the land for various reasons, and this practice represents an important and understudied route of exposure of natural ecosystems to engineered nanoparticles.”

“Our results show that silver nanoparticles in the biosolids, added at concentrations that would be expected, caused ecosystem-level impacts,” Colman said. “Specifically, the nanoparticles led to an increase in nitrous oxide fluxes, changes in microbial community composition, biomass, and extracellular enzyme activity, as well as species-specific effects on the above-ground vegetation.”

As previously noted, these two studies show just how complex the questions of risk and nanoparticles can become. You can find out more about the Finish-Estonian study,

Toxicity of two types of silver nanoparticles to aquatic crustaceans Daphnia magna and Thamnocephalus platyurus by Irina Blinova, Jukka Niskanen, Paula Kajankari, Liina Kanarbik, Aleksandr Käkinen, Heikki Tenhu, Olli-Pekka Penttinen, and Anne Kahru. Environmental Science and Pollution Research published November 11, 2012 online

The publisher offers an interesting option for this article. While it is behind a paywall, access is permitted through a temporary window if you want to preview a portion of the article that lies beyond the abstract.

Meanwhile here’s the article by the Duke researchers,

Low Concentrations of Silver Nanoparticles in Biosolids Cause Adverse Ecosystem Responses under Realistic Field Scenario by Benjamin P. Colman, Christina L. Arnaout, Sarah Anciaux, Claudia K. Gunsch, Michael F. Hochella Jr, Bojeong Kim, Gregory V. Lowry, Bonnie M. McGill, Brian C. Reinsch, Curtis J. Richardson, Jason M. Unrine, Justin P. Wright, Liyan Yin, and Emily S. Bernhardt. PLoS ONE 2013; 8 (2): e57189 DOI: 10.1371/journal.pone.0057189

This article is open access as are all articles published by the Public Library of Science (PLoS) journals.

For anyone interested in the Duke University/CEINT mesocosm project, I made mention of it in an Aug. 15, 2011 posting.

Nature of Things’ series: The Nano Revolution (Episode 3); Will Nano Save the Planet?

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I’m never thrilled with titles of this ilk, Will Nano Save the Planet? Refreshingly, this episode featured some work being done by Canadian scientists (two of them) although the average Canadian could be forgiven for thinking that it’s the only nanotechnology research taking place in Canada.

It’s a little puzzling that they chose this final episode for a description of the term nanoscale. David Suzuki, the host, mentioned the ridges of skin on your fingers and noted that a nanoparticle is 80,000 times smaller than the distance between the ridges. (If you want a really good description of scale, I recommend listening to Professor Ravi Silva’s audio interview with Alok Jha on the (UK) Guardian’s Oct. 14, 2011 Science Weekly podcast.)

In general, I found the descriptions of the science in this episode were not of the same standard as the previous two, which were very good.

The vignettes, as always, were problematic largely since they were internal monologues of some character who’s grappling with ethical issues and other social impacts of these technologies. Interestingly, men starred in the vignettes where the ‘big’ issues are covered: ethics of health care; longer life; access to energy sources; pollution from nanotechnology-enabled products; etc. The woman who starred in the vignettes from episode one (as I noted in my review) was concerned with cleanliness, tidiness, shopping, and privacy. I guess things don’t change that much in our future, especially in 2050 where nanotechnology protestors are putting up banners, spraypainting, and leafletting (almost as if it were 1968) to express their opposition (in episode three).

There was some interesting work being covered. They profiled Professor Ted Sargent, based at the University of Toronto, who’s doing some exciting work with solar cells (he wants to make them flexible and, even, paintable). His latest breakthrough is mentioned in my Sept. 20, 2011 posting.

Professor Vicki Colvin, Rice University in Texas, is working to purify water. The project is in Mexico and highlights the difficulties when water supplies are contaminated, in this case, with arsenic. (Here in the Pacific Northwest we tend to forget that access to fresh clean water is not easy in many parts of the world.) Colvin and her colleagues are working on a simple solution that can be implemented with some sand, gravel, a tube, and active nanoparticles. (Her work with the Environmental Nanoscience Initiative; a UK/US collaboration was mentioned in my Jan. 28, 2011 posting.)

The third project was focussed on soil remediation and a team from the University of Western Ontario headed by Professor Dennis O’Carroll. I have not come across O’Carroll’s work previously so this was a find for me. As you may or may not know, there are many sites with contaminated soil throughout North America and elsewhere. If successful, O’Carroll’s technique promises to remediate (rehabiltate) the soil without having to move massive amounts of soil and use big equipment.

This episode featured more discussion about the risks and uncertainties associated with nanotechnology and its use. Unfortunately, I did not recognize the names and (one of my major pet peeves with this series) they either didn’t write out the names on screen or they flashed them briefly which meant that unless I recognized the names it was difficult to find out more about the experts.

I did recognize the mesocosm project at Duke University, which was featured here in my August 15, 2011 posting. The researchers are trying to understand what impact silver nanoparticles have on life. They spray silver nanoparticles in various mesocosms (they look like raised plant beds) and then track what happens to the plant, the soil, and the water supply as the silver nanoparticles cycle through.

There’s work in the UK examining air and the nanoparticles released through the use of internal combustion engines (cars/trucks) as well as our newly engineered nanoparticles. I’m glad to see this material in the episode, perhaps it will finally motivate some public discussion in Canada.

Mesocosms and nanoparticles at Duke University

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It’s that time of year when just about everybody seems to be on holidays and finding material to post about becomes harder than usual. Consequently, I dug through some of my backfiles to find this piece on mesocosms and Duke University from November 2010.

From the article, Ecosystem experiments to assess the environmental impact of nanoparticles, by Whitney J. Howell published November 25, 2010 on Nanowerk,

Deep inside Duke Forest, 32 alternate universes sit in quiet rows. They look identical – each with a puddle, some land, a few plants.

But wholly imperceptible to the naked eye, these plots have distinct and important differences.

The realms, known as mesocosms, house individual types of nanoparticles as part of a research effort conducted by the Center for the Environmental Implications of Nano Technology (CEINT) based at Duke University.

The mesocosms are (from the CEINT Mesocosm Construction page) “3ft x 12ft [constructed environments] where researchers can add nanoparticles [to study interactions] and effects on plants, fish, bacteria, and other elements within these contained systems.”

Mesocosm prototypes at Duke University (downloaded from Nanowerk)

According to Howell’s article (originally published in the Raleigh News & Observer), the mesocosm project at Duke should be winding up shortly,

To track where and at what levels the environment absorbs nanoparticles, CEINT began the yearlong mesocosm project in August [2011]. The findings will also reveal the effects of nanoparticle presence.

Each waist-high, 3-foot-by-12-foot box contains nanoparticles coated with a different substance, such as titanium dioxide or silver. By following the coating’s trail through the mesocosm, Wiesner said, researchers can pinpoint how the nanoparticles either positively or negatively alter their surroundings and at what levels they might become toxic.

For example, nanosilver has anti-microbial properties and could be a powerful disinfectant. But if high concentrations of the particles wipe out all surrounding bacteria and viruses – even those that may be benign or beneficial – the effects on plants and animals is unknown.

The Duke investigators are monitoring the mesocosm changes as nanosilver and other nanoparticle levels increase, hoping to identify which substances are most harmful to the environment and humans, and at what level they become worrisome.

CEINT’s external advisory board features Dr. Andrew Maynard, Director of the University of Michigan Risk Science Center (and mentioned here fairly frequently due to his longstanding expertise on nanotechnology [he was formerly the Chief Science Advisor for the Project on Emerging Nanotechnologies based in Washington, DC]).

They’ve been busy at the CEINT, here’s where you can find a list of publications by the staff, including blockbusters such as,

Shoults-Wilson, WA, Zhurbich OI, McNear DH, Tsyusko OV, Bertsch PM, Unrine JM. 2011. Evidence for avoidance of Ag [silver] nanoparticles by earthworms (Eisenia fetida). Ecotoxicology. 20:385-96. Abstract

And

Chae, SR, Hotze EM, Xiao Y, Rose J, Wiesner MR. 2010. Comparison of Methods for Fullerene Detection and Measurements of Reactive Oxygen Production in Cosmetic Products. Environmental Engineering Science. 27:797-804. Abstract

You can find more of Whitney Howell’s work here.

FrogHeart

Commentary about nanotech, science policy and communication, society, and the arts

Tag Archives: mesocosms

Investigating nanoparticles and their environmental impact for industry?

Carbon nanotube accumulation in Duke University’s (US) mesocosm

Silver nanoparticles, water, the environment, and toxicity

Nature of Things’ series: The Nano Revolution (Episode 3); Will Nano Save the Planet?

Mesocosms and nanoparticles at Duke University