Nanoparticles - toxic or harmless?

When nanotechnology emerged as a fledgling technology in the 1990s it had great potential, but were the disadvantages overlooked? Here Maria Anguita gets to grips with the hazards of nanoparticles

SINTEF scientists both exploit the benefits of nanotechnology, and try to discover if nanoparticles behave hazardously in nature. Andy Booth, SINTEF scientist and environmental chemist, is interested in what nanotechnology is doing to the marine environment and is leading a project called “The environmental fate and effects of SINTEF-produced nanoparticles.”

The scientists will study both how the particles behave and how they affect organisms when they are released into the marine environment. One of the goals of the project is to find out whether nanoparticles are toxic to marine organisms such as small crustaceans and animal plankton. Further down the road, the ability of cod larvae and other large organisms to tolerate nanoparticles will also be studied. “Our experiments will tell us whether these tiny particles will be excreted or remain inside organisms, and if they do, how they will behave there,” explains Booth.

Booth points out that not all nanoparticles are necessarily dangerous. Many occur naturally in the environment, and have existed ever since the Earth was formed, like ash.

“What is new is that we are now capable of designing nanoparticles with a wide range of different properties. Such particles can be different from those that already occur in nature, and they are intended to perform specific tasks at our command, so we do not know how they will behave in nature. This could potentially – and I say “potentially” because this topic is so new to science – indicate that these particles could be toxic under certain conditions. However, this depends on a number of factors, including their concentration and the combination of particles,” emphasises Booth.

But has industry got tests to ensure that the nanoproducts that it releases in the market are safe enough?

“In the field of chemical analysis, we have standard tests that tell us whether or not a material is toxic. Today, there are no such tests of nanoparticles that are 100% accurate, so this is something that scientists are currently working on at international level,” says Booth, adding that he believes that it is extremely difficult to put products that are a danger to health on the market.

The nanoparticle concept is general, and includes many more than one type. There are millions of potential variants, Today, it is impossible to obtain an overview of how many there actually are - and some of them will be toxic, while others are harmless - just like other chemicals.

This is why Booth and his 12-strong team at SINTEF have just launched their painstaking efforts. One of the biggest challenges they have faced so far is that of identifying scientific methods that will enable them to discover how these tiny particles behave in nature, and how they might affect natural processes.

Booth’s colleague, Christian Simon and his research department at SINTEF Materials and Chemistry, has recently made an important industrial breakthrough in nanoparticle technology - and it looks as though nanosubstances could be environmentally friendly alternatives to chemicals.

One of Norway’s leading manufacturers of powders and paints is about to start production of a new type of paint containing nanoparticles, which has been developed by SINTEF. The particles possess fluid characteristics that make the paint easy to apply, meaning that a higher proportion of dry matter can be used, with correspondingly less solvent. Furthermore, the paint will dry rapidly and be more wear-resistant than normal paint.

“We have already signed licensing agreements for certain applications, and are currently in the upscaling phase. The product will be delivered in the autumn, but there are still a few things to be tested,” says Simon.

There is a worry that when materials painted with nanoparticles are demolished, the hazardous components will escape into the environment.  “The particles have been produced in such a way that they create chemical bonds to the other components of the paint. When the paint is fully cured, the nanoparticles no longer exist, so they cannot separate from the polymer matrix when whatever has been painted is torn down, chopped up or burnt,” answers Simon.

“The emerging environmental problems related to nanotechnology are probably due to the size and shape of the particles, rather than to the nature of the materials themselves,” says Liv Furuberg, who works at MiNaLab, the laboratory for microsystems and nanotechnology. The laboratory is squeezed into a building in Gaustadbekkdalen in Oslo, and it is owned by SINTEF and the University of Oslo.

Several of SINTEF’s research groups are collaborating on the task of shrinking the large analytical laboratories that we are familiar with down to miniature versions the size of a credit card.  The tiny diagnostic system can automatically perform advanced analyses of blood, urine and other bodily fluids. The card/chip is engraved with microscopic channels and capillary structures. In the walls of these channels, the scientists use molecule-thick layers that ensure that the chip operates as a biological system.

“We build up individual layers of molecules in order to obtain surfaces with sensitive areas. These can react with and thus measure individual molecules that act as markers of specific diseases, for instance in blood,” says Furuberg.

Could these chips lead to new types of environmental problems?  “No. This technology utilises functional thin films as the surface of large chips. We are working at the nanometre level, but there are no nanoparticles involved, only nanostructured surfaces, and the chemical compounds these employ are exactly the same as those used in normal laboratories,” answers Furuberg. “Analysis performed on microchips actually produces much less waste than conventional diagnostic systems. In our case, no particles are involved, only thin films.”

While the lab-on-a-chip technology is still in its infancy, nanoparticles and nanocapsules have gradually become a gilt-edged field of research for Christian Simon and his SINTEF colleagues. One technology after another has been patented. The opportunity to create a new industry beckons from afar.

“What is new is that we combine inorganic, tough, hard materials with organic, flexible, and formable materials when we create our nanoparticles. This gives us a new class of materials with improved properties; what are known as hybrid solutions. For example, we can make polymers with improved light stability that will also withstand scratches,” says Simon.

When a hollow nanoparticle is created, it is called a nanocapsule. The cavity can be filled with another material for subsequent release for any of a wide range of purposes. The SINTEF scientists have not come as far with nanocapsules as they have with nanoparticles, but they have developed a technology that can be used in several applications and they can produce nanocapsules on a large scale.

“For example, we can improve the durability of coatings for aircraft, ships and cars,” says Simon. “The components consist of substances that can close up cracks and scratches. Just think of vehicle bodywork. When gravel hits its surface, the enamel cracks and gets damaged. But simultaneously, the capsules inside the enamel burst and the material they contain will repair the damage.

Hollow nanocapsules can also be used in medical treatments with almost “surgical” effects. They can be sent directly into the sick cells. Ruth Baumberger Schmidt and her team are working on this topic.

The scientists fill nanocapsules with medication, and steer them to wherever they want their contents to end up. They do this by binding special molecules to the coating. The capsule’s shell is broken when its immediate environment is right in terms of the selected trigger, such as temperature or acidity. According to how the capsule has been concocted, its contents can be allowed to leak out gradually over time, or at a higher rate at first and gradually less as time goes by.

At the moment, Schmidt and a group of SINTEF chemists are concentrating on medicines to fight cancer, a long-term project that offers important challenges. The use of nanocapsules inside the body makes serious demands of the materials used. The particles that are being developed for medical purposes must be non-toxic and need to be broken down into non-hazardous components that the body can excrete, for example via the urine. The capsules also need to head for the right site of action and to liberate their contents, without being discovered by “watchdogs” such as T cells and natural killer cells.

“In this case these capsules are a plus because here we want the capsules to pass through the cell membrane and do their work locally. Other types of nanoparticles can pass the membrane and become a danger to the body. The risk of nanotechnology is that sometimes they are not supposed to pass, or that they accumulate in large quantities over a period of time, instead of disappearing, said Schmidt. "We don’t use nanotubes or nanofibres, because we believe that they are less safe than particles. But a lot of research is being done in this field.”

Among those who are concerned about the potential effects of nanotechnology on the human body are Tore Syvertsen and his team at the Department of Neuromedicine in NTNU. They have tested how rat brain cells react to a range of carbon-based nanomaterials such as nanofibres and nanotubes.

Nanomaterials of this sort have many applications, and little is known about their potential effects on health. For this reason, the scientists have been studying a number of carbon-based nanomaterials by placing the fibres in cell cultures extracted from the brains of rats. This has revealed how the cells react with each type of nanoparticle. And they were not unaffected: most of the cells turned out to be fairly sensitive to these substances, whose thickness and length was very important even when their chemical make-up was identical.

“This shows that there are good reasons for studying where the boundary between hazardous and non-hazardous nanotubes lies,” says Syvertsen. “Other studies of similar carbon fibres have shown that they can cause a type of lung cancer that is otherwise best known for being due to exposure to asbestos. Since this type of cancer takes a long time to develop it is essential to test such materials before they come into widespread use.”

So there is great potential, but also a high degree of uncertainty, is the conclusion. Can it be that nanotechnology was oversold when the subject emerged during the nineties? Were we simply blinded by its potential, with the result that we forgot to look out for its potential disadvantages?

Booth and his colleagues carry on tirelessly with their experiments.

“When nanoparticles are released into rivers and lakes, it is a rather complicated matter to study how they will behave. Chemistry is different at nanometre level, and nanoparticles do not behave like normal particles,” says Booth.

As an example, he mentions silver, which is a metal much used in jewellery that comes into intimate contact with the skin, without being in any way hazardous. But silver nanoparticles have quite different properties, as we know. They are bactericidal, just like antibiotics.

“These particles also behave differently in fresh- and salt-water. Finding methods that will enable us to study their behaviour is essential,” he says. “We can add a fluorescent marker to the particles - when we test the sample in a spectroscopic camera, the marker will light up and distinguish such particles from other particles.”

Nanoparticles can also aggregate and become so heavy that they sink into the sediment, which makes them less likely to affect organisms that live in the water column itself, and instead impact those that live in the river-bed.

“The big question now is to find out how high concentrations we need to test in order to be on the safe side. It is not worth taking chances with nature,” concludes Booth.