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Ecotoxicology of nanoparticles to algae, bacteria and biofilms

Bacteria and algae occur together in ecological communities as so-called periphyton - biofilms composed of tens to hundreds of species of algae, bacteria and grazing organisms that establish themselves on submerged solid surfaces such as sediments, stones and reeds.

So far we have no idea on the effects of manufactured nanoparticles on this system with its tightly interwoven ecological interactions (figure 1 below), which is a major gap in our understanding of the ecotoxicology of manufactured nanoparticles. In fact, most of our current knowledge on the toxicity of nanoparticles to microorganisms stems from investigations with isolated single species and with environmentally unrealistic high concentrations (mg/L) of NPs. Such studies confirm the principal high biological activity of the NPs, but do not allow estimating effects in the real environment.


Figure 1

In order to fill in these knowledge gaps, we aim to

  1. provide ecologically highly realistic toxicity data for natural microbial communities for high production volume NPs, and
  2. identify particularly vulnerable groups of species and sensitive endpoints.

These results will inform whether current chemical risk assessment methodologies as they are laid out in REACH and which are based on generic assessment factors, can also be applied to manufactured NPs in the environment. Furthermore, by testing a set of particles with different size, shape and surface functionalization, we will provide information on nanoparticle characteristics that drive ecotoxicological effects (besides the elementary composition). This will help in the development of ecotoxicity modeling approaches such e.g. QSARs.

The picture to the left illustrates post-doctoral fellow Marianne Matzke in the process of collecting field samples.
 

 

 

 

 

References

Matzke M., Arning J., Köser J., Scheiber I., Köhler I., Arndt D., Ivanov O., Kolesnikov D., Knauer A., Köhler M., Hartwig A., Bäumer M., Dringen R. & Filser F.: Particle characteristics only partly explain the varying toxicity of silver nanoparticles in an ecotoxicological test battery - submitted

Tests with single-species (algae, diatoms, and bacteria)

For the single species tests we focus on (a) growth inhibition assays according to modified OECD guidelines, and (b) mechanistic studies using a series of fluorescent dyes and flow cytometry.

Tested individual species (including some examples of microscopic photos):

Pseudokirchneriella subcapitata (Green algae)
Chlamydomonas reinhardtii (Green algae)
Cyclotella meninghiana (Diatom)


Containers used for the exposure of the single species in the lab.

Tests with natural biofilm communities

For tests with biofilm communities, we use the so-called SWIFT-assay following the strategy outline by Porsbring and colleagues (2007).

Natural periphyton communities are employed that were sampled on substrata directly in the environment and are subsequently exposed under semi-static conditions in the lab. This strategy combines a high ecological relevance of the biological material with controlled exposure conditions and a high test capacity that provides sufficient statistical power for reliably describing also low effects. The semi-static exposure conditions limit the amount of needed NPs during the test. After the exposure a range of different endpoints can be analyzed, both analyzing physiological effects as well as integrating ecological effects.

Some pictures of the tested biofilms

Effects on biodiversity of exposed communities are recorded in the form of direct microscopic species counts (algae), community pigment fingerprinting (algae), and catabolic profiles of the bacteria (see figure below). Effects on the community's genetic diversity will be evaluated using temperature gradient gel electrophoresis (TGGE).

The physiological status of the community is determined by standard physiological methods such as the incorporation of radiolabelled Leucin (biosynthetic activity of the bacteria), the uptake of radiolabelled carbon and PAM-measurements (Pulse modulated chlorophyll fluorescence) for analyzing the potential primary production of the algae (photosynthetic activity).

Characterisation of the bacterial community via ECOLOG plates: determination of changes in the ability of exposed communities to metabolise various carbon sources.

 

Contact person

Thomas Backhaus

Page Manager: Robert Karlsson|Last update: 11/17/2014
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