189
(UO 2 ) 3 (OH) 5
+
, and UO 2 (OH) 3
−
in cultivation solution on the uptake of U by variant
Sedum alfredii were studied by Du et al. (2016). They found three different uranium
species would all have significant effect on the uranium bioaccumulation. The bioaccumulation amount in the roots of Sedum alfredii reached the highest, which was
3.7 × 10
4
mg kg
−1
, when the main species in the solution was (UO 2 ) 3 (OH) 5
+
(Du
et al. 2016). The results reported by Laurette et al. (2012b) and Du et al. (2016) were
consistent with our research results.
The minimum bioaccumulation amount and bioaccumulation factor of five different uranium species by Azolla-Anabaena reached 122 and 61 mg kg
−1
, respectively, when the main species of uranium in the solutions was UO 2 (OH) 3
−
. The
bioaccumulation amount and bioaccumulation factor of UO 2 (CO 3 ) 3
4−
by AzollaAnabaena were also very low, which were 622 and 311 mg kg
−1
, respectively. The
results indicated that the bioaccumulation ability of Azolla-Anabaena for uranium
was inhibited when the main species of uranium were UO 2 (OH) 3 and UO 2 (CO 3 ) 3
4−
.
This is because UO 2 (OH) 3
−
and UO 2 (CO 3 ) 3
4−
were both metal anions which cannot
easily be absorbed by Azolla-Anabaena. The results agreed with those by Du et al.
(2016) who found that UO 2 (OH) 3
−
and UO 2 (CO 3 ) 3
4−
in the solution could inhabit
the ability of bioaccumulation of uranium by variant Sedum alfredii (Du et al. 2016).
The bioaccumulation amount and bioaccumulation factor of Azolla-Anabaena
for UO 2 PO 4
−
were only 132 and 66 mg kg
−1
, respectively, when the main species of
uranium in the solutions was UO 2 PO 4
−
. The results indicated that the bioaccumulation ability of Azolla-Anabaena for uranium was also greatly inhibited when the
main species of uranium was UO 2 PO 4
−
. The reasons for these results are that phosphate and uranium could form an insoluble complex, and the species of UO 2 PO 4
−
was anionic, which cannot easily be absorbed by Azolla-Anabaena. Misson et al.
(2009) and Mkandawire et al. (2007) also reported that phosphate could inhibit the
ability of plants to accumulate uranium. Thus, in order to increase the removal rate
and bioaccumulation amount of uranium by Azolla-Anabaena, the main species of
uranium in solution should be regulated to UO 2
2+
or (UO 2 ) 3 (OH) 5
+
, and the concentration of carbonate and phosphate in solution should be reduced.
4 Conclusions
1. The growth inhibition rates on Azolla-Anabaena by the five uranium species
were significantly different. (UO 2 ) 3 (OH) 5
+
, UO 2 (OH) 3
−
, and UO 2 (CO 3 ) 3
4−
had
high growth inhibition, UO 2
2+
had higher growth inhibition, and UO 2 PO 4
−
had
high growth promotion.
2. The accumulation efficiencies of UO 2
2+
and (UO 2 ) 3 (OH) 5
+
by Azolla-Anabaena
were relatively high; the bioaccumulation amount and bioaccumulation factor of
UO 2
2+
by Azolla-Anabaena reached 3831 and 1916 mg kg
−1
, respectively; and its
bioaccumulation amount and bioaccumulation factor for (UO 2 ) 3 (OH) 5
+
were
3057 and 1529 mg kg
−1
, respectively.
Influence of Uranium Speciation on Plant Uptake
(UO 2 ) 3 (OH) 5
+
, and UO 2 (OH) 3
−
in cultivation solution on the uptake of U by variant
Sedum alfredii were studied by Du et al. (2016). They found three different uranium
species would all have significant effect on the uranium bioaccumulation. The bioaccumulation amount in the roots of Sedum alfredii reached the highest, which was
3.7 × 10
4
mg kg
−1
, when the main species in the solution was (UO 2 ) 3 (OH) 5
+
(Du
et al. 2016). The results reported by Laurette et al. (2012b) and Du et al. (2016) were
consistent with our research results.
The minimum bioaccumulation amount and bioaccumulation factor of five different uranium species by Azolla-Anabaena reached 122 and 61 mg kg
−1
, respectively, when the main species of uranium in the solutions was UO 2 (OH) 3
−
. The
bioaccumulation amount and bioaccumulation factor of UO 2 (CO 3 ) 3
4−
by AzollaAnabaena were also very low, which were 622 and 311 mg kg
−1
, respectively. The
results indicated that the bioaccumulation ability of Azolla-Anabaena for uranium
was inhibited when the main species of uranium were UO 2 (OH) 3 and UO 2 (CO 3 ) 3
4−
.
This is because UO 2 (OH) 3
−
and UO 2 (CO 3 ) 3
4−
were both metal anions which cannot
easily be absorbed by Azolla-Anabaena. The results agreed with those by Du et al.
(2016) who found that UO 2 (OH) 3
−
and UO 2 (CO 3 ) 3
4−
in the solution could inhabit
the ability of bioaccumulation of uranium by variant Sedum alfredii (Du et al. 2016).
The bioaccumulation amount and bioaccumulation factor of Azolla-Anabaena
for UO 2 PO 4
−
were only 132 and 66 mg kg
−1
, respectively, when the main species of
uranium in the solutions was UO 2 PO 4
−
. The results indicated that the bioaccumulation ability of Azolla-Anabaena for uranium was also greatly inhibited when the
main species of uranium was UO 2 PO 4
−
. The reasons for these results are that phosphate and uranium could form an insoluble complex, and the species of UO 2 PO 4
−
was anionic, which cannot easily be absorbed by Azolla-Anabaena. Misson et al.
(2009) and Mkandawire et al. (2007) also reported that phosphate could inhibit the
ability of plants to accumulate uranium. Thus, in order to increase the removal rate
and bioaccumulation amount of uranium by Azolla-Anabaena, the main species of
uranium in solution should be regulated to UO 2
2+
or (UO 2 ) 3 (OH) 5
+
, and the concentration of carbonate and phosphate in solution should be reduced.
4 Conclusions
1. The growth inhibition rates on Azolla-Anabaena by the five uranium species
were significantly different. (UO 2 ) 3 (OH) 5
+
, UO 2 (OH) 3
−
, and UO 2 (CO 3 ) 3
4−
had
high growth inhibition, UO 2
2+
had higher growth inhibition, and UO 2 PO 4
−
had
high growth promotion.
2. The accumulation efficiencies of UO 2
2+
and (UO 2 ) 3 (OH) 5
+
by Azolla-Anabaena
were relatively high; the bioaccumulation amount and bioaccumulation factor of
UO 2
2+
by Azolla-Anabaena reached 3831 and 1916 mg kg
−1
, respectively; and its
bioaccumulation amount and bioaccumulation factor for (UO 2 ) 3 (OH) 5
+
were
3057 and 1529 mg kg
−1
, respectively.
Influence of Uranium Speciation on Plant Uptake