Synthetic nanomaterials form part of a gigantic emerging market world-wide with expected growth rates of about 23 percent. Only a few years ago, nanomaterials were viewed as barely out of science fiction, with highly promising applications but also novel risks. To date, no labeling requirements exist that would alert consumers to potential near- or long term hazards to the environment, even though the European Union has a directive on cosmetic labeling that will enter into force in July 2013. Some nanomaterials cannot be degraded naturally or filtered and recycled by waste processing plants; some involve risks similar to asbestos, and others may facilitate development of bacterial resistance against their very antibacterial proprieties currently used in hospitals.
Absent mandatory labeling and registration, consumers cannot determine today whether a product contains nanomaterials. While nanoparticle applications feature them typically bound in other compounds, those are hardly problematic and almost never pose health hazards. But the same cannot be said about production processes and waste disposal. Nanoparticles can be suspended in air, breathed in, and can enter the bloodstream. They can also penetrate various sensitive areas of the environment. Little is known about the dispersion, behavior, and chemical qualities of aging and disintegrating nanoparticles. The benefits of nanotechnology are seldom in dispute – but the question is how to assess and balance benefits and risks appropriately, so that the hygienic, protective, energy, weight, or physical advantages are not offset by unacceptable long-term environmental hazards.
Not surprisingly, manufacturers lobby for a delay of labeling and registration requirements, arguing that the cost of regulation, approval, and labeling will be as dramatic as in the case of pharmaceutical products. They also warn that consumers may misinterpret labels, become exposed to irrational scares, or develop expectations that are not justified by existing knowledge about a substance. The lack of effectiveness of self-policing and self-regulating by industry has been demonstrated in too many instances to accept this line of argument at face value. It swings both ways: time and again new products are marketed as “nano,”despite the fact that nothing of the sort is among their ingredients. In other cases, well-known materials science applications are relabeled as “nano” to increase their attractiveness. Thus, manufacturers’ argument that the time for labeling has not come yet because no definitive consensus exists as to what is and is not a nanomaterial remains unpersuasive – not least because a definitive consensus may never be reached so long as it does not suit certain interests.
Silicon dioxide, for example, is one of the likely innocuous nanoparticles with advantageous mechanical properties useful in many areas: in precision polishing pastes, in plastics, tires, or as a gas barrier in PET bottles and packaging for foodstuffs. A principal component of sand, silicon dioxide may raise health concerns only if inhaled in large quantities.
Nanosilver is also hardly absorbed through the skin and its toxicity is therefore considered low, while its antimicrobial properties are highly valued in underwear, socks and exercise gear. However, if nanosilver were to enter the body, it could result in brain damage and allergies. Waste processing absorbs 90 percent of silver content. Besides its potential to disrupt the human immune system, the long-term characteristics of nano-scaled silver and the effects of chronic exposure to it remain unclear. Its cherished antimicrobial characteristics used increasingly in textiles and laundry machines imply the risk that bacteria may develop resistance to it and render its medical applications in hospitals ineffective.
Carbon nanotubes consist of pure carbon with a diameter of one to 50 nanometers and a length of up to several hundred nanometers. Because of their excellent conductivity they are used as mechanical stabilizers of compound materials widely employed in aircraft, automobiles and bikes. In their applications, carbon nanotubes are integrated in their compounds and therefore highly unlikely to be released – unless it happens through attrition, abrasion or decay of compounds. Such residuals could accumulate in nature since they can hardly be decomposed, except through incineration. If inhaled over extended periods of time, they could cause cancer through mechanisms very similar to asbestos.
Titanium dioxide has become a favorite UV filter in cosmetics, external paints, self-cleaning surfaces and textiles. It does not penetrate the healthy epidermis and is considered free of hazard in day-to-day applications. Again, though, inhalation may result in inflammations of the lung, and entry into the bloodstream may prove carcinogenic. The material enters the environment typically through ablution of sunscreen and through the decay of external paints or layered surfaces. Current water purification plants do not filter these particles in their entirety. Water insects and fish may be affected. Long-term effects of low dose exposure are also unclear.
Zinc oxide is used in textiles and paints as a transparent UV filter, anti-scratch covering layer and antimicrobial agent, as well as in semiconductors including flat screens. Its toxicity is associated with inhalation, and various studies have focused on zinc oxide’s cytotoxicity. Nanoparticles exposed to liquids emit zinc ions that cause cell damage and in this way burden the ecosystem. There is a paucity of data on long-term performance of zinc oxides and its remnants following disposal.
Although research into risks and hazards has been intensified in recent years, substantial white spots continue to exist on our map of knowledge about nanomaterials, not least because studies are done primarily on freshly produced materials straight out of manufacture. Little is known about what happens when these are exposed to the elements, to weather, attrition, abrasion, decay, and other perfectly natural and foreseeable influences of material fatigue and aging that are part of the long-term aspects of materials science.