The above comment addresses a pressing problem going even beyond the outlined silver particles. Both industrial cleaning chemicals, antibiotics and silver containing, persistent materials are currently exposed to the environment and affect micro- or other aquatic organism. This obviously stays in contrast to the need, at certain point, to have sterile surfaces, e.g. in hospitals. We strongly agree with this comment that use of silver should not be too widespread. A way to reduce the exposure of products in the environment is to build more efficient products and to reduce the possible exposure by lower used concentration. The here presented silver containing polymer has a 1000 fold increased efficiency compared to commercial available silver containing products. This means that just 0.1% of the silver is required for the same effect.

The calcium phosphate nanoparticles are currently in a preclinical investigation as biomaterial for implants. Several in vivo studies have confirmed this material’s rapid dissolution in living tissue and its full biocompatibility. Since the silver/calcium phosphate particles are incorporated into the polymer and not adsorbed on the polymer, this minimizes the exposure of particles into the environment. Additionally, the carrier material (calcium phosphate) is degradable. We currently believe that dissolved silver ions will precipitate as silver chloride. In waste water streams, this mineral constituents has a high affinity for biomass (clearing sludge), it should therefore be removed efficiently unless present in such high concentration that it imparts the sludge’s viability.

One thing is sure, the future impacts of nanoparticulate applications have to be addressed prior to commercialization. Our research group has started to investigate possible impacts of nanomaterials as early as 2004. One of our studies was investigating the clearing efficiency of sewage treatment plants regarding the exposure of nanomaterials (ETH life Article).

We have also contributed to the precaution raster of the Federal Office of Public Health and the Federal Office for the Environment. This raster combines several risk factors of nanomaterials in order to prevent impacts on the environment and the public health. An honest discussion on benefits and possible impacts of nanomaterials has to be conducted. This includes that concerns are neither neglected nor hyped.

Wendelin Stark, Assistant Professor at the Institute for Chemical and Bioengineering of ETH Zurich - 29.01.09

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