The behavior and effects of nanoparticles in the environment.

The behavior and effects of nanoparticles in the environment have up to now been a field where the research was done based on a precautionary approach: what would happen if nanoparticles get into the environment? What would they do there and how would they affect organisms? The occurrence of engineered nanoparticles in the environment has been assumed because ‘‘given the increasing production of nanomaterials of all types, the potential for their release in the environment and subsequent effects on ecosystem health is becoming an increasing concern’’ (Klaine et al., 2008). This assumption, albeit well-based on the experience obtained with other pollutants (Kohler and Som, 2008), has governed the field of environmental effects of nanoparticles. However, this has changed now: the first report about the detection of an engineered nanoparticle in the environment is nowavailable: Kaegi et al. (2008) have shown that nano-TiO2 is leached out of house facades to which nano-TiO2 containing paint has been applied. They traced the particles from the house facades into receiving waters and found concentrations in the range of a few mg/L titanium in a small stream. These concentrations lie within the range of nano-TiO2 predicted by Mueller and Nowack (2008) in their exposure modeling of engineered nanoparticles for the water compartment. These authors have used the available knowledge about nanoparticle production and use in different products and information on the product life cycles to model the environmental concentrations of nanoparticles in water, air and soil. The two studies by Kaegi et al. (2008) and Mueller and Nowack (2008) have lifted the discussion about nanoparticles and the environment onto a new and much more quantitative level. For the first time we can be absolutely sure that at least some nanoparticles actually end up in the environment and we also have first ideas about the expected concentrations. These recent results make it clear that the investigation of the behavior and effects of nanoparticles in the environment is no longer in its infancy. Our knowledge on this subject is increasing almost exponentially, caused by a massive interest of the scientific community and increased funding. However, the field is by far from mature, and many investigations still have explorative character and raise more new questions than they answer. It is also noteworthy that despite the infancy of the field, a large number of reviews are already available that focus on environmental behavior and ecotoxicity (Lead and Wilkinson, 2006; Nowack and Bucheli, 2007; Baun et al., 2008; Handy et al., 2008a,b; JuNam and Lead, 2008; Klaine et al., 2008; Navarro et al., 2008). These reviews try to combine the available knowledge and to estimate the behavior and effects of nanoparticles based on the rudimentary information that we already have. The 18 papers in this