Several studies demonstrated clearly that quantum dots (QDs) distribute all over the body after their uptake and may accumulate in specific organs or tissues. Comparable to their toxicity (see section “exposure - in vitro”) the uptake, the distribution, the possible metabolism and the excretion of QD is determined by their size, surface charge, amount, stability and coating [1].

 

The distribution of various quantum dots (QDs) in the body of animals has been tested by intravenous injection into mice and rats and has been analysed after different time points of treatment [2-7]. Some examples will be discussed below in more detail.

After the injection into the tail vein of mice all QDs distribute rapidly within the blood circulation even though various coatings have been used. Within one hour nearly all QDs had left the blood stream and could be detected depending on their coatings within the liver, skin or the bone marrow [3,7]. Only one very specific coating could prevent the fast elimination from the blood. Even after 133 days of observation the QDs could still be detected due to their strong fluorescence within the bodies of the animals. The stable high fluorescence signal indicates no degradation of the QDs within the organisms. Moreover, during the whole period of the experiment no cell death or acute toxicity could be detected in the surrounding tissues [7]. Changing the coating may result in degradation of the QDs as has been shown in other experiments in which a loss of luminance could be observed [2,7,8]. Probably coatings with larger molecules (high molecular weight) protect much better against degradation as compared to smaller molecules with a low molecular weight [7].

Within a 10-days short term study in rats it could be demonstrated that QDs depending on their coating could be detected within the liver and the spleen and to a lesser extent within the lung tissue and the kidneys [4]. During the whole observation time the QDs were stable (no degradation) and were not excreted via urine or faeces. It has been discussed that the used QDs are too large to be excreted via the kidneys [4,7].

In agreement with this a longer study (28 days) showed in mice that QD accumulate in liver, spleen and kidneys without being excreted [6]. Treatment and observation of mice over a period of two years (!) after injection of QD resulted in the following data: shortly after injection the QD could be detected in liver, spleen, lymph and the bone marrow. The fluorescence signal weakened within 5 days in the liver but stayed constant for 6 months within the bone marrow before decreasing there as well. Overall the signal could be detected over the whole period of 2 years within the lymph, no degradation took place and also no toxicity could be detected after this time of treatment [7,9].

 

 

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