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