Potential of Phytoremediation to clean up uranium-contaminated soil with Acacia species

Abstract

Pollution by depleted uranium (DU) is considered one of the major problems faced by many countries, where this by-product is considered as a major  source of radiotoxic and chemotoxic heavy metal soil pollution. An experiment was designed for uranium uptake from sandy soil treated with different concentration of uranium  by using two species of Acacia  (Acacia albida and A. nelotica ). Results showed there is a difference in the ability of the Acacia seedlings tested to absorb different concentrations of uranium through their roots. Acacia nilotica registered the highest levels of absorption and accumulation of uranium in dry weight of roots in different concentrations (202, 339, 1175, and 1477 µg.g^-1 ) respectively of  the concentrations (50, 100, 200, and 500 mgkg^-1). Compared to the root of Acacia albida, the absorption of uranium was (60, 54, 133, and 526 µg.g^-1) in the concentrations of the same samples. The ability of A. nilotica is better than that of A. albida to uptake uranium from the soil, where 80-90% of the uranium is absorbed by the seedlings, compared to 44-85% in  A. albida. In the case of low concentrations  of uranium (50 and 100 mgkg-1)  A. nilotica seedlings absorbed  about 80-90%  of the original concentration, whereast A. albida absorbed only 44-70% of the same treatment.  In high concentrations (500mgkg-1), we found  that the A. nilotica uptake of 90% of uranium was higher compared to that of  A. albida whose average uptake was about  77%. Also, we found a difference between species and treatment in the remainder of the uranium in the soil. The uranium remaining in the soil at the end of the period of uranium application showed a difference between species and treatments. The uptake of uranium by A. albida was 14-41% while in A. nilotica it it was 58-67%, based upon the concentration in soil solution. In low concentrations (100mg.kg-1) A. albida absorbed only 16%, while A. nilotica absorbed about 67% from the uranium in soil solution. In high concentrations (2000mg.kg-1) of uranium, 23%  was found in A. albida and 66% in A. nilotica. This shows that A. nilotica can uptake uranium from soil solution three times more than A. albida.

The  biomass results, the shoot height of  A.nilotica plants decreased with the progression of time during the treatment with high concentrations of uranium, but in low and moderate concentrations (50,100, and 200mg.kg-1) it was less affected than high concentrations (500mg.kg-1). A. albida height was reduced  when treated with (200mg.kg-1)   in all the growth periods, whereas the growth of seedlings gave values less than when treated with the height concentration of uranium (500mg.kg-1) for the two species.

Keywords: Phytoremediation,  Depleted Uranium, Acacia albida,  A. Nilotica.