Russian researchers have developed a method for assessing biological accumulation of nanoparticles in planktonic organisms, and have demonstrated that algae and seed shrimps intensively accumulate titanium dioxide particles.

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It is known that nanoparticles can be transferred along food chains: a predator assimilates particles that were contained in the prey body. Majority of food chains in seas and lakes begin with plankton (microscopic organisms drifting in water mass), and therefore it is important to know how actively planktonic organisms accumulate nanoparticles when they get into water.

Yuri Morgalev and his colleagues at the Center “Biotest-Nano” of Tomsk University and Siberian State Medical University have investigated nanoparticles accumulation in chlorella and daphnids. Chlorella is the genus of unicellular algae, typical representatives of phytoplankton, and Daphnia is the genus of microscopic crustacea, widespread in zooplankton. Both organisms are often applied for water quality investigations.

The researchers dealt with titanium dioxide nanoparticles as these particles are already used now for production of paint, drugs, beauty aids and other products. It has become clear that titanium dioxide nanoparticles accumulate quickly and in large quantities in phyto- and zooplantkton. The work will be published in the next issue of the “Russian Nanotechnologies” journal.

The researchers obtained titanium dioxide particles (their size making 5 nm) via the electric explosion method. These particles were placed into water at concentrations from 10 mg/l through 1 g/l, and the researchers watched their behavior in aqueous environment. At high concentrations, nanoparticles coalesce and precipitate, stable nanoparticle suspension exists at the concentration lower than 2 mg/l. The experiment used dispersed solutions of titanium dioxide nanoparticles at the concentration of 1 mg/l.

Starting from the 5th day of chlorella cultivation in the presence of nanoparticles, the researchers estimated titanium presence in water and algae cells. The mass spectrometry method was used to this end. The biologists have proved that on the 5th day the titanium concentration in the cultivation environment decreased, and it made 246±12 mcg/g in chlorella cells. In a month, titanium concentration in chlorella increased, although insignificantly. To determine what part of titanium is firmly bound with chlorella, concentrate of its cells was exposed to sixfold washing. After the procedure, the titanium content reduced to 92.50±3.20 mcg/g – this particular quantity of titanium penetrated inside cells or was firmly bound with their surface. Titanium content in algae cells exceeded titanium content in the external environment by more than 200 times.

Daphnids biology peculiarities make it difficult to get an absolutely precise result because it is necessary to feed the animals and to clean up their aquarium, these processes bring some distortions in titanium concentration in water. Nevertheless, the researchers managed to prove that on the 5th day the seed shrimps concentrate contains 100±8 mcg/g of titanium, and after washing, its concentration reduces to 58±5 mcg/g – this particular quantity of the element gets bound with seed shrimps tissues. This is twice less than that of chlorella, but it is a hundred times more than titanium concentration in the environment.

So, experiments have proved that titanium nanoparticles are accumulated in aquatic tissues rather quickly (within 4-5 days) and in rather large quantities. They are accumulated both by algae – initial link of food chain - and by seed shrimps, which are at the nest stage. As zooplankton serves food for a lot of fish species, it can be expected that titanium nanoparticles will be transferred further along the food chain and appear in products of industrial fishery and aquaculture. Subsequent research will be required to assess if it is harmful and to what extent.

Source of information: Yu. N. Morgalev, N.S. Khoch, T.G. Morgaleva, E.S. Goulik, G.A. Borilo, U.A. Bulatova, S. Yu. Morgalev, E.V. Poniavina. “Biotesting of nanomaterials: about a possibility of nanoparticles translocation into food chains”. Russian Nanotechnologies, 2010, #11-12.

Further information: Morgalev Yuri Nikolayevich, Center “Biotest-Nano” of Tomsk State University.  Tel.: +7 (3822) 53-44-35, e-mail: morgalev@tsu.ru

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