Nanoparticles build up

Nanoparticles could accumulate in food chains Source: Michelle Bergkamp - Fotolia.com

Studies by groups working on two different types of nanoparticle - gold nanoparticles and cadmium selenide (CdSe) quantum dots - show that they can be transferred from species lower down in food chains to those that feed on them, concentrating at the higher level. Many pollutants are taken up by plants or bacteria at the bottom of food chains, but of particular concern are those that are ‘biomagnified’ at higher levels, meaning they accumulate in higher concentrations in organisms further up the food chain. The classic example is the pesticide DDT. Patricia Holden’s team at the University of California, Santa Barbara, US, and Paul Bertsch’s team at the University of Kentucky, US, tried to understand whether nanoparticles might behave in this way. In the Kentucky group’s study, caterpillars feeding on tobacco plants grown in solutions containing gold nanoparticles accumulated the nanoparticles at concentrations between 6-12 times higher than those measured in the plants. Bertsch says the results of his team’s work with gold nanoparticles were particularly surprising because metals - with very few exceptions - do not biomagnify. He notes that gold is a good starting point because it is stable and inert, whereas studies with silver nanoparticles present more of a challenge as silver has various chemical forms. Bertsch and other researchers say they are hopeful that manufacturers will be able to ‘design out’ the characteristics of nanoparticles that could make them unsafe, for instance, by adding coatings. Earlier work by Holden’s team suggests nanoparticle interactions that cause membrane damage through free radical formation might be involved in allowing particles to enter cells.3 Thus, coatings designed to reduce free radical formation might go a long way to making them safer, she says - it’s a fine balance between safety and application.