The accumulated particles in the sediments contain at least 10,000 times more natural nanoparticles than artificial ones. This result emerged from a model study conducted by researchers at Wageningen University in the Netherlands, Duke University in the USA and Empa in St. Gallen, Switzerland.
Carbon-based nanoparticles are increasingly used in products, but are also present in nature, often as miniscule soot particles originating from forest fires and from human activities such as traffic and industrial processes. Until now, it was unclear how many of the nanoparticles encountered in the environment originated from natural sources and how many originated from consumer products. Knowledge about this situation is important in order to estimate the relative risk of nanoparticles, especially now that nanoparticles are being used for more and more applications, such as anti-fungal and antibacterial agents in sunblock creams.
The research team, comprising Prof. Bart Koelmans of Wageningen University and colleagues from Duke University and the Swiss Federal Laboratories for Materials Testing and Research (Empa), collected previous calculations about the emissions of nanoparticles and their concentrations in surface water in order to predict the sedimentation in lakes. Based on this information, they calculated the concentration in the sediment.
The concentrations of soot in lake and river beds were already known. In an article in the March issue of the leading journal Environmental Pollution, the researchers showed that the number of artificial carbon-based nanoparticles in sediment was more than 10,000 times smaller than the concentration of already present 'natural' soot nanoparticles. These predictions were based on a worst-case scenario; the actual differences are probably even greater. With a more realistic scenario, the proportion would be 1:10 million. "This would mean that the artificial carbon-based nanoparticles pose virtually no additional risk in comparison to the proportion of nanoparticles that are already present in sediments", explains Prof. Koelmans.
Nanoparticles of natural and artificial origin that enter the environment are washed away by precipitation and ultimately sink into lake or river beds, where they end up in the sediment. They also pass unaffected through water purification installations. Once in the sediment, they can bind to toxic substances and can build up in organisms, such as aquatic sowbugs or water fleas. The risks of these particles depends, among other things, on their concentration. The tiny particles are capable of passing through the cell walls in the body, resulting in cellular damage, also due to the toxic substances bound to the particles.
The model calculations that were used always have a degree of uncertainty. Therefore, additional experimental support and a more detailed approach are very important. In the Netherlands, a major research programme in the area of nanotechnology (FES-High Tech Systems and Materials) is in preparation. The programme also focuses attention on the possible negative effects of nanoparticles on people and the environment.