Down to earth: Nanotechnology turns the worm

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  • Published: Jul 15, 2011
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Down to earth: Nanotechnology turns the worm

The upshot of uptake

Inductively coupled plasma atomic emission spectroscopy (ICP-AES) has been used in the testing of uptake and toxicity of titania nanoparticles in earthworms as a marker of potential ecological harm.

Emilie Bigorgne of the Université Paul Verlaine - Metz and colleagues suggest that the increasing production of nanomaterials will in turn increase the release of nanosized by-products to the environment. Whether or not these particles will accumulate or be degraded and whether or not they pose an ecological risk depends on the chemical and physical properties of the individual types and classes of nanoparticles rather than "nano" representing any intrinsic hazard. With this in mind the team hoped to assess the behaviour, uptake and ecotoxicity of titania nanoparticles and by-products in the earthworm Eisenia fetida. Earthworms play a critical role in the activity of fertile soil and as such have been used extensively in ecotoxicity studies for heavy metals and organic pollutants. This ubiquitous species might thus act as a marker for risk on exposure to the common titania nanoparticles.

Titania nanoparticles are now commonly used as UV filters in cosmetics and sun screen, in self-cleaning glass, food packaging, paint, waste-water treatment and elsewhere. Titania in cosmetics and sun screen is frequently rinsed into the sewerage system. Any organic shell or coating is degraded whereas aluminium hydroxide shells are more resistant.

Preliminary concerns

The team has carried out preliminary experiments in which they exposed worms to suspensions containing 0.1, 1 and 10 milligrams per litre of titania by-products for 24 hours; this, they explain represents a perhaps unrealistic "worst-case" exposure scenario. Laser diffraction studies revealed that titania-containing aggregates could form at sizes up to 700 micrometres. However, it was only those worms exposed at 10 milligrams per litre that showed bioaccumulation of titanium, as revealed by ICP-AES.

Given the photocatalytic properties of titania nanoparticles one might assume that the particles induce oxidative stress. Indeed, the researchers observed increasing expression of metallothionein (MT) and superoxide dismutase (SOD) mRNA, demonstrated via real-time polymerase chain reaction (PCR) experiments. Antioxidant systems, such as SOD, catalase (CAT), glutathione S-transferases and MT protect living things from harmful reactive oxygen species and the level of mRNA expression of these proteins correlates well with toxicity exposure. Apostain and TUNEL assays showed that programmed cell death, apoptosis, was also initiated. Interestingly, titania by-porudcts did not induce cytotoxicity but did lead to a significant reduction in immune system phagocytosis even at concentrations of 0.1 milligrams per litre.

The main conclusion made by the researchers is that bioaccumulation of titania by-products and the formation of reactive oxygen species might be responsible for the alteration of the antioxidant system in worms.

 

     

Photo credit: Creative Commons image via flickr user http://www.flickr.com/photos/merydith/4509559094/ Inductively coupled plasma atomic emission spectroscopy (ICP-AES) has been used in the testing of uptake and toxicity of titania nanoparticles in earthworms as a marker of potential ecological harm.

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