188
was UO 2 PO 4
−
. The uranium concentration was reduced to the lowest level at the
third day because of the precipitation of phosphate and uranium. After that, the
reason for uranium concentration increase may be that Azolla-Anabaena secreted
organic acids (Rauser 1999; Bertin et al. 2003; Huang et al. 2016) in its roots during
growth, and the complexes formed by phosphate and uranium were dissolved in
solution again. Thus, in order to increase bioaccumulation amounts of uranium in
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 concentrations of carbonate and phosphate in
medium should be reduced.
3.3 Bioaccumulation Amount and Bioaccumulation Factor
of Azolla-Anabaena for Uranium in Different Hydroponic
Solutions
The bioaccumulation amount and bioaccumulation factor of Azolla-Anabaena for
uranium in different hydroponic solutions were calculated (Table 1). As shown in
Table 1, the maximum bioaccumulation amount and bioaccumulation factor of five
different uranium species by Azolla-Anabaena reached 3831 and 1916 mg kg
−1
,
respectively, when the main species of uranium in the solutions was UO 2
2+
. The
results indicated that the bioaccumulation ability of Azolla-Anabaena for UO 2
2+
was
the highest among five different uranium species in the hydroponic experiments.
The bioaccumulation amount and bioaccumulation factor of Azolla-Anabaena for
(UO 2 ) 3 (OH) 5
+
were 3057 and 1529 mg kg
−1
, respectively. The bioaccumulation
amount and bioaccumulation factor for (UO 2 ) 3 (OH) 5
+
were nearly the same as for
UO 2
2+
, which indicated that Azolla-Anabaena also had high ability to accumulate
(UO 2 ) 3 (OH) 5
+
. The reason was that UO 2
2+
and (UO 2 ) 3 (OH) 5
+
were both metal cations
which can easily be absorbed by Azolla-Anabaena. The influences of uranium speciation on the accumulation and translocation in oilseed rape, sunflower, and wheat
were studied by Laurette et al. (2012b). They found that bioaccumulation amounts
in the roots of oilseed rape, sunflower, and wheat were all very high when the main
species in the solution was UO 2
2+
(Laurette et al. 2012b). The effects of UO 2
2+
,
Table 1 Bioaccumulation amount and bioaccumulation factor of Azolla-Anabaena for uranium in
different hydroponic solutions
Initial uranium concentration
(mg L
−1
)
Condition
Bioaccumulation amount
(mg kg
−1 )
Bioaccumulation
factor
pH = 4
3831 ± 326
*
1916
pH = 6.5
3057 ± 213
*
1529
2.0
pH = 10.5
122 ± 10
*
61
Carbonate
622 ± 31
*
311
Phosphate
132 ± 8
*
66
*
p < 0.05
N. Hu et al.
was UO 2 PO 4
−
. The uranium concentration was reduced to the lowest level at the
third day because of the precipitation of phosphate and uranium. After that, the
reason for uranium concentration increase may be that Azolla-Anabaena secreted
organic acids (Rauser 1999; Bertin et al. 2003; Huang et al. 2016) in its roots during
growth, and the complexes formed by phosphate and uranium were dissolved in
solution again. Thus, in order to increase bioaccumulation amounts of uranium in
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 concentrations of carbonate and phosphate in
medium should be reduced.
3.3 Bioaccumulation Amount and Bioaccumulation Factor
of Azolla-Anabaena for Uranium in Different Hydroponic
Solutions
The bioaccumulation amount and bioaccumulation factor of Azolla-Anabaena for
uranium in different hydroponic solutions were calculated (Table 1). As shown in
Table 1, the maximum bioaccumulation amount and bioaccumulation factor of five
different uranium species by Azolla-Anabaena reached 3831 and 1916 mg kg
−1
,
respectively, when the main species of uranium in the solutions was UO 2
2+
. The
results indicated that the bioaccumulation ability of Azolla-Anabaena for UO 2
2+
was
the highest among five different uranium species in the hydroponic experiments.
The bioaccumulation amount and bioaccumulation factor of Azolla-Anabaena for
(UO 2 ) 3 (OH) 5
+
were 3057 and 1529 mg kg
−1
, respectively. The bioaccumulation
amount and bioaccumulation factor for (UO 2 ) 3 (OH) 5
+
were nearly the same as for
UO 2
2+
, which indicated that Azolla-Anabaena also had high ability to accumulate
(UO 2 ) 3 (OH) 5
+
. The reason was that UO 2
2+
and (UO 2 ) 3 (OH) 5
+
were both metal cations
which can easily be absorbed by Azolla-Anabaena. The influences of uranium speciation on the accumulation and translocation in oilseed rape, sunflower, and wheat
were studied by Laurette et al. (2012b). They found that bioaccumulation amounts
in the roots of oilseed rape, sunflower, and wheat were all very high when the main
species in the solution was UO 2
2+
(Laurette et al. 2012b). The effects of UO 2
2+
,
Table 1 Bioaccumulation amount and bioaccumulation factor of Azolla-Anabaena for uranium in
different hydroponic solutions
Initial uranium concentration
(mg L
−1
)
Condition
Bioaccumulation amount
(mg kg
−1 )
Bioaccumulation
factor
pH = 4
3831 ± 326
*
1916
pH = 6.5
3057 ± 213
*
1529
2.0
pH = 10.5
122 ± 10
*
61
Carbonate
622 ± 31
*
311
Phosphate
132 ± 8
*
66
*
p < 0.05
N. Hu et al.