Nanoparticle accumulation in the food chain

Plants and microbes can absorb nano-sized synthetic particles that increase in concentration within predators up the food chain, according to two studies.

Getting into food chain

Nanoparticles are used in hundreds of consumer products ranging from transparent sunscreens to odor free socks. From there when they get washed down the drains, ultimately end up in the sewage sludge of wastewater treatment plants. Sice several million tons of dried-out sludge is subsequently mixed into agricultural soil each year, there is possibility of nanoparticles to go into the food chain in this way.

Nanoparticles

Synthetic nanoparticles made of silver, titanium dioxide, zinc oxide and other substances due to their small size and stability; they can nullify odors, prevent food spoilage and absorb harmful ultraviolet radiation, among other feats. But knowledge about their impacts to the environment is still in a state of infancy.

Experiments

To explore nanoparticle absorption in the food chain, researchers at University of Kentucky raised tobacco plants in a hydroponics greenhouse. While the plants grew, the researchers added super-stable gold nanoparticles to the water to mimic consumer nanoparticles in wastewater sludge. Gold nanoparticles built up in tobacco leaf tissue, and tobacco hornworms that ate the plants accumulated concentrations of the nanomaterials about 6 to 12 times higher than in the plant.

Predatory microbes in a separate study also built up concentrated levels of cadmium selenide nanoparticles after eating smaller microbes that ingested them.

Researchers at the University of Delaware have provided an experimental evidence that plants can take up nanoparticles and accumulate them in their tissues. The laboratory study, which involved pumpkin plants, indicates a possible pathway for nanoparticles to enter the food chain. The research also reveals a new experimental approach for studying nanoparticles and their potential impacts. The researchers chose pumpkins for the study because they take in a lot of water and are easy to grow. The plants were grown hydroponically in an aqueous medium to which nanoparticles of iron oxide, or magnetite, a magnetic form of iron ore, were added. After 20 days of growth, the plants were cut into pieces and dried in a vacuum dessicator. A magnetometer was then used to detect if any of the particles had been absorbed by the plant. The magnetometer subjected the dried pumpkin plants to a low-frequency monotone to vibrate them. The vibration revealed each tiny particle of magnetite's unique magnetic signal and, thus, exact location inside the plant.Thus magnetic nanoparticles can be taken up, translocated and accumulated in pumpkin plants.

Regulation

At least five government agencies (EPA, FDA, NIH, NIOSH and NIST) host efforts to investigate nanotechnology’s risks to health and the environment, and their funding is increasing each year. And while heavy metals and other toxins in sludge are federally regulated, manmade nanoparticles are not. That may cause concern as farms increasingly mix sludge into their soils, where nanoparticles may build up over time.There is some evidence that nanoparticles are toxic under lab-controlled conditions, but realistically assessing risks to health and the environment demands more advanced research efforts.