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Microbial community nano-ecotoxicology: interplay between effects on structure and the consequent effects on function.

Final Report Summary - MICRONANOTOX (Microbial community nano-ecotoxicology: interplay between effects on structure and the consequent effects on function.)

Nanotechnology is one of the most rapidly growing fields of science with a vast potential for industrial applications. It builds on the intentional and controlled generation of novel arrangements of atoms at the nanometer scale (1-100 nm). Many manufactured nanoparticles (NPs) display very special chemical properties because of their size, shape, composition and electronic structure. NPs are already widely used e.g. as antibacterial coatings, cosmetics or paints [1, 2]. Despite this wide array of applications and the resulting potential environmental exposure we sorely lack sound scientific knowledge on the ecological and ecotoxicological consequences of an exposure to man-made NPs [3, 4]. Sutherland and coworkers [5] have identified NPs as one of the major emerging, but as yet unquantifiable, risks for biodiversity in the UK and therefore a realistic hazard assessment in the environment is urgently needed because the same properties that lend NPs their functionality may also lead to toxic effects. The overall aim of this project was to integrate modern molecular biology and nano-ecotoxicology approaches for addressing the interplay between effects nanoparticles on microbial community structure and the consequent effects on their ecosystem function roles and vulnerability, following the exposure to engineered nanoparticles. This project contributed to an environmentally more realistic hazard and risk assessment of nanoparticles (NPs) for microbial communities revealing research gaps to be able to come to a more realistic and improved environmental hazard assessment for two of the commercially most important NPs these days namely: silver (Ag) and zinc oxide (ZnO) NPs. Attention was also given to the question how NPs fate and behaviour are influenced by their respective environmental matrix as well as crucial biotic and abiotic keyfactors (e.g the exudation of extrapolymeric substances, microbial key species, pH, organic matter etc.).
Major results can be summed up as follows: there was no evidence found for NP specific effects, most effects could be attributed to the dissolved particles, i.e. metal ions. And because this project was focused on working at environmentally relevant concentrations for the freshwater compartment, this made it impossible to follow the particles behaviour over the exposure time due to insufficient sensitivities of common analytical characterisation techniques such as NTA, DLS or TEM. For soils the high background of naturally occurring particles made it difficult to follow the particles fate and emphasis was on the determination of the metal concentration in the soil pore water.
The community finger-printing (T-RFLP) showed for both – terrestrial as well as aquatic microbial communities – that time has a bigger influence on the communities’ diversity development than the chemical stress at environmentally relevant concentrations. Therefore biodiversity seems to be not suitable for detecting NP caused stress in low concentrations as it is hard to distinguish these from the normal background during long-term exposures. Conclusions about ecological consequences cannot be drawn at this stage and this only shows the necessity to further investigate effects of nanoparticles on complex ecological systems because the potential for interactions with the NPs, recovery and shifts in community structure are still not fully understood.

In terms of a more realistic environmental hazard assessment for metal nanoparticles future research should focus on the fact that not only particles cause effects on microbes but microbes are also able to strongly influence the particles, e.g. by the exudation of so called extrapolymeric substances leading to the exchange of particle coating and the formation of so called eco-coronas. Current applicable standard ecotoxicological test systems do not allow for cross-reading or extrapolation for expected impacts of NPs on the environment because they do not consider the particles fate, their interactions in the environment and the influence of time.
1 Aitken RJ, et al. 2006. Occup Med-Oxford 56(5): 300-306. 2 D’Britto V, et al. 2011. Nanoscale 3 (7): 2957-2963. 3 Colvin VL. 2003. Nature Biotechnol 21(10): 1166-1170. 4 The Royal Society & The Royal Academy of Engineering. 2004. Report to UK Government. 5 Sutherland WJ, et al. 2008. Journal of Applied Ecology 45: 821–833.