#	Pagina
attuale pagina	/open-h2020/projects/201021/results.html

Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - NanoBioCar (Impacts of Nanoparticles on microphytobenthic Biofilms and consequences on the Carbon cycle)

Teaser

Summary

Nanoparticles are between 1 and 100 nanometres (billionth of metre) in size and due to their unique properties are being added to more and more consumer products, such as clothing and sunscreens. During their production and use nanoparticles are released in the aquatic environment, especially in coastal systems where they accumulate.
Coasts are important ecosystems for human populations: they produce oxygen that we breathe, they provide food for fishes and shells, they are used as recreational areasâ€¦ Coastal sediments host a large diversity of microorganisms that support several of these services, especially oxygen production, carbon trapping and recycling of nutrients that would otherwise pollute the water.
This project aims to investigate the impact of nanoparticles on coastal microorganisms, the consequences of these impacts for the functioning of coastal systems, and therefore for human populations.
We chose two types of nanoparticles: titanium oxide nanoparticles, that are the most produced nanoparticles, and one of the main components of sunscreens; and silver nanoparticles, which are the nanoparticles used in the wider range of products, such as clothing, medical material, food packaging, household appliancesâ€¦
Our aims were to determine:
- how nanoparticles influence coastal microorganisms in near-natural conditions;
- how nanoparticles influence oxygen, carbon and nutrient cycles in coastal zones;
- whether these effects are dependent on the type of nanoparticle considered and of the season.
We found that at current concentrations, these nanoparticles have limited impact on microorganisms and coastal ecosystem functions. However at higher concentrations, titanium oxide nanoparticles have the potential to limit the growth of microorganisms and alter their ability to produce oxygen and recycle nutrients. This toxicity appears after contact with the nanoparticles for several weeks, and is different between seasons.

Work performed

To assess the real environmental impact of nanoparticles, we designed tidal tanks to reproduce natural mudflats in more controlled laboratory conditions. The tanks were filled with coastal mud cores hosting natural assemblages of microorganisms, natural seawater, and left outside for natural light and temperature. We slowly dosed these tanks with nanoparticles for a month, at three different seasons. We then measured the growth of microorganisms and the production of molecules that form the matrix in which they live; we performed molecular analyses to characterise the composition of the assemblage of microorganisms in different conditions; we measured their photosynthetic ability, i.e. their ability to produce oxygen; and we assessed the fluxes of oxygen, carbon and nutrients between water and sediment.
In our experimental conditions, nanoparticles had little impact on any of these variables at low nanoparticle concentration (current estimated concentrations). But after one month of contact with titanium oxide nanoparticles, microalgae were less present in sediment, they produced less matrix, and the recycling of nutrients was altered. This effect was visible in summer and winter but not in spring. These results have been presented in 3 conferences, and have provided data for 2 scientific articles (one submitted, one in preparation).
To ensure that our results were relevant for assessing the environmental impact of nanoparticles, we then performed a field experiment, in winter, with only low concentrations of nanoparticles. We daily added nanoparticles to enclosed sediment in a natural mudflat, and performed the same analyses as before. Our results were consistent with the results of the tidal tanks experiments, in showing limited toxic effect of the nanoparticles at low concentrations. However, the composition of the microbial assemblages shifted slightly, so toxicity may appear on a longer time-scale. The results of this experiment will be presented in an article that is currently in preparation.

Final results

Most literature available on the toxicity of nanoparticles is based on short-term (a few days) laboratory experiments in controlled conditions, far from the natural coastal environment. This project provides an assessment of the true environmental impact of nanoparticles in coastal areas, in environmentally relevant conditions. It showed that titanium oxide nanoparticles are potentially concerning for coastal environments due to their high production rate and high level of use, which means that nanoparticle concentrations will quickly increase in these systems. Our experiment also demonstrated that the impact of nanoparticles is only apparent after several weeks, and dependent on the season, which could not have been known from short-term experiment in controlled conditions. Finally, effects on microbial biomass and effects on ecosystem functioning (carbon and nutrient cycling) were not happening at the same time, so a direct measurement of these process is necessary if we are to understand the impact of nanoparticles for human populations.
Our results will help guide decision-making regarding the release of nanoparticles in the water, and hopefully stimulate further research in near natural or natural conditions to assess the true impact of pollutants on coastal systems.