Fullerenes and fish brains: nanomaterials cause oxidative stress.

As interest increases in the production and use of nanomaterials in consumer products such as sunscreens and cosmetics, pharmaceuticals, and industrial applications, so do concerns about human and environmental health effects as the tiny particles inevitably reach the soil, water, and air, and are eventually taken up by living organisms. Further direct human exposure will occur through workplace exposure during manufacture. Although there have been few studies to date on the potential toxicity of nanomaterials, research activity is growing. Now biologist Eva Oberdorster of the Duke University Marine Laboratory in Beaufort, North Carolina, and Southern Methodist University in Dallas, Texas, shows for the first time that one of the most popular nanomaterials, carbon-based particles known as fullerenes, can have adverse physiologic impacts on aquatic organisms [EHP 112:1058-1062]. Oberdorster shows significant evidence of oxidative stress in the brains and gills of juvenile largemouth bass exposed for 48 hours to water laced with fullerenes at concentrations that may likely be found in the aquatic environment.

Nanomaterials are defined as manufactured substances where one dimension measures 1-100 nanometers. Within the last few years, large-scale industrial production of tons of fullerenes has begun for a diverse and growing range of commercial applications, including sunscreens, coatings for bowling balls, and fuel cell membranes. Previous research with ambient nano-scale particles such as ultrafine particulate matter has demonstrated that some of these particles tend to migrate into cell membranes and mitochondria, and that a selective pathway transports them into the brain in mammals. Oberdorster hypothesized that fullerenes might follow similar pathways, and that because they are reactive with oxygen and attracted to lipids--both of which are components of oxidative reactions--they could cause oxidative damage in the brains of fish.

Fullerenes are typically coated during the manufacturing process to reduce potential toxicity, and it is unknown how long the coating will persist when the molecules are exposed to the environment. However, cell culture experiments have suggested that the coating may break down quickly upon exposure to air or ultraviolet radiation. Therefore, Oberdorster used uncoated fullerenes in her tests, at concentrations of 0.5 and 1.0 parts per million, comparable to typical concentrations of other lipophilic chemicals currently found in the aquatic environment, such as polycyclic aromatic hydrocarbons.

Oberdorster found that lipid peroxidation, a sign of free radical oxidative damage, was significantly elevated in the brains of several of the fish, though there was no clear dose response. The lipid-rich character of the brain lends credence to the suspicion of a selective lipid pathway, although the mechanism is still undetermined. Lipid peroxidation actually decreased in the animals' gills and liver. However, there was evidence in the gills of a depletion of the antioxidant compound glutathione, indicating that those tissues also were undergoing oxidative stress.

Interestingly, Oberdorster also observed that the water in the fullerene tanks was clearer than that in control tanks. She speculates that this may have been due to interference by the fullerenes with the growth of beneficial bacteria normally found in aquaria. Although the phenomenon has not been documented, she suggests that this potential risk of damage to the microbial community would be an important subject for future research.

Oberdorster writes that the effects she found in fish could be predictive of similar effects in humans. With fullerenes and other nanomaterials likely to be used widely in the near future, she stresses that research efforts should be intensified in order to prevent the possibility of damage to human health and the environment.