Bioaccumulation Of Rare Earth Elements Research Articles

Effect of nutrient uptake by plant roots on the fate of REEs in soil

Concentrations of rare earth elements (REEs) and major ions in soil solutions were observed under different growth stages of soybean in order to evaluate the effect of nutrient uptake by plant roots on the mobility of REEs in soil–plant systems. Soybean plants were grown in pots, which were kept in a greenhouse for 84 days. The concentrations of major nutrient cations (K and Ca) in the soil solution decreased with the soybean growth. On the other hand, the concentrations of Al, Y, La, Ce, Nd, Gd, Dy, Er and Yb increased. Although no decrease of pH was observed, it was assumed that the REEs and Al were dissolved from the soil solid phase due to H + release from the plant roots for K + and Ca 2+ uptake. Subsequently, the bioaccumulation of REEs in the soybean roots was observed in the maturing stage of the soybean. These results showed that the soybean roots could enhance the dissolution of REEs from the soil solid phase and they could also accumulate REEs through plant growth.

Effects of fulvic acid on the bioavailability of rare earth elements and GOT enzyme activity in wheat ( Triticum aestivum)

Fulvic acid (FA) was extracted and purified from natural soil and the effects of such FA on the bioaccumulation of rare earth elements (REEs, La 3+, Gd 3+ and Y 3+) in wheat seedling were investigated. The results indicated that low concentration of FA (<0.4 mg C/l to root, <0.7 mg C/l to tops (stem and leaves)) could increase the bioaccumulation values of REEs in wheat, but when the concentration of FA was high (>0.4 mg C/l to root, >1.5 mg C/l to tops) the bioaccumulation values were decreased. Kinetic experimental results suggested that bioaccumulation values of REEs in roots for 30 days were correlated with the kinetic linear growth equation, and correlation coefficients were higher than 0.861. The kinetic bioaccumulation pattern of REEs in tops was different from that in root. The bioaccumulation values of REEs in wheat root were much higher than in wheat tops. Variations of glutamic oxaloacetic transaminase (GOT) enzyme activities in wheat root and tops were determined. A good correlation existed between the bioaccumulation values of REEs and GOT enzyme activities, and the correlation coefficients were higher than 0.922. GOT is an important parameter influencing the bioavailability of REEs.

The influence of rare earth element fertilizer application on the distribution and bioaccumulation of rare earth elements in plants under field conditions

This field study describes the distribution and bioaccumulation of rare earth elements (REEs) in wheat, rice and vegetables grown in Jiangxi, Anhui, Beijing and Heilongjiang provinces, located in southern and northern China after application of REE fertilizer at different levels. The results indicate that accumulation of REEs in different parts of plants follows the order: root>leaf>stem>grain. The concentrations of REEs in root, leaf and stem increase remarkably when the REE fertilizers were applied. However, no significant accumulation was observed in cereal grains except for those grown at the Jiangxi site. A significant accumulation of REEs in the edible parts of vegetables was observed, therefore, fertilizers containing REEs are not recommended. The exogenous REEs in the fertilized soil were extracted by a three-stage sequential extraction procedure into three fractions: (1) water soluble, exchangeable and carbonate bound (B1), (2) Fe–Mn oxide bound (B2) and (3) organic matter and sulfide bound (B3). The results demonstrated that all of the exogenous REEs were present in the fractions B1, B2 and B3 with ranges of 1.49–13.91%, 35.23–70.34% and 19.14–60.78% of total, respectively. No exogenous REEs entered the residual form within the field study period. However, the chemical forms of exogenous REEs in the fertilized soil and their bioavailability are dependent on the physicochemical properties of soil and plant species. It seems that REEs present in fraction B1 are more easily available to plants.

Effects of humic acid on speciation and bioavailability to wheat of rare earth elements in soil

Humic acid (HA) was extracted from an organic-rich soil in Heilongjian Province of China by 0.5 mol L-1 NaOH. The effects of HA on the distribution of rare earth elements (REEs) in Red Soil, a major soil type in the south of China, were investigated. The speciation of REEs in soil was analyzed by a sequential extraction technique. The bioavailabity of REEs in the same soil was investigated by the use of wheat seedling. The results showed that organic fraction of REEs is highly related to the concentration of HA, whereas the exchangeable fraction and carbonate fraction decreased as more HA was added. This was possibly related to the cation exchange capacity (CEC), because HA and CEC had a significant linear relationship. The REEs in wheat pooled in the roots. Low concentration of HA(<0.2 g kg-1) promoted the bioaccumulation of REEs in wheat root, while high concentration (>0.2 g kg-1) decreased the REE concentrations. The REE concentration in roots was negatively correlated to the HA concentration.

Assessment of the bioavailability of rare earth elements in soils by chemical fractionation and multiple regression analysis

The bioavailability of rare earth elements (REEs) in soils was evaluated, based on the combination of chemical fractionation and multiple regression analysis. REEs in soils were partitioned by a sequential extraction procedure into water soluble (F(ws)), exchangeable (F(ec)), bound to carbonates (F(cb)), bound to organic matter (F(om)), bound to Fe–Mn oxides (F(fm)) and residual (F(rd)) fractions. Alfalfa ( Medicago Staiva Linn.) had been grown on the soils in a pot-culture experiment under greenhouse conditions for 35 days. The concentrations of REEs in fractions and plant were determined by inductively coupled plasma-mass spectrometry (ICP-MS). Chemical fractionation showed that (F(ws)) fraction of REEs was less than 0.1% and residual (F(rd)) was the dominant form, more than 60% in soils. Bioaccumulation of REEs was observed in Alfalfa. REE availability to the plant was evaluated by multiple regression analysis. F(ws), F(ec), F(cb) and F(om) fractions were significantly correlated with REE uptake by alfalfa. But the exchangeable Pr(F(ec)) was significantly correlated with Pr concentration in alfalfa. F(ec), F(cb) and F(om) greatly contributed to La and Nd bioavailability; F(ec) and F(om) to Ce, Gd and Dy; F(ec) and F(cb) to Yb; and F(ws), F(ec) and F(om) to total REEs. This meant that the bioavailability of different species of REEs varied with individual REE. The results of this study indicated that the sequential extraction procedure, in conjunction with multiple regression analysis, may be useful for the prediction of plant uptake of REEs from soils.

Bioaccumulation of rare earth elements in cultured HeLa cells.

HeLa S-3 cells were grown in minimal essential medium supplemented with 10% calf serum and 1 mM L-glutamine without adding any rare earth elements (REEs). Exponentially growing cells were collected, and dried materials were used to analyze their REE content by inductively coupled plasma-mass spectrometry. The results showed that the cells accumulated REEs in individually different manners; namely the accumulation ratio was higher in the lighter REEs than in the heavier REEs. To deduce the implication of the accumulation of REEs in HeLa cells, the accumulation ratios for REEs were compared with those of other biologically important elements. It was seen that the accumulation ratios obtained for REEs (from 31.8 [Ce] to 14.7 [Lu]) were intermediate among those of many bioelements: Fe (124), Mg (54.5), K (38.8), Cr (12.7), Na (11.8), Mn (11.3), Zn (10.7), Ca (8.8), and V (6.7).

The effect of EDTA on rare earth elements bioavailability in soil ecosystem

In this paper, the effects of the organic ligand EDTA on the bioaccumulation of rare earth elements(REEs) by wheat seedlings growing in two types of soils were investigated. The results indicate that the bioaccumulation values of REEs in wheat roots were much higher than those in the tops (stems and leaves) for both types of soils. Adding the organic ligand (EDTA) promoted the REEs bioavailability of wheat by increasing the REEs desorption from soils. Not only bioaccumulation of REEs in roots and tops of wheat but also the REEs desorption amount from soil had good correlation with the concentration of EDTA in the soils. Also, a good correlation existed between the REEs desorption amount and their contents in wheat seedlings for the same EDTA concentration. The REEs bioaccumulation values of wheat seedlings in Yellow-brown soil were a little higher than that in Black soil.

The effects of chemical species on bioaccumulation of rare earth elements in rice grown in nutrient solution

In this study, the effects of the complexing agent ethylenediamine tetraacetic acid (EDTA) on the species of Rare Earth Elements (REE) Lanthanum, Gadolinium and Yttrium in nutrient solution and bioaccumulation of REEs in rice seedling were investigated. The results showed that addition of EDTA can reduce the bioaccumulation values in the rice root, on the other hand, the bioaccumulation values in the aboveground parts (stem and leaves) increased. Considering the different parts of rice, root had higher bioaccumulation ability than that in aboveground parts of rice. During the experimental concentration range, for different species REEs, the bioaccumulation processes on rice's root were almost controlled by adsorption and because of the effects of adding EDTA, ionic and complexed species REEs showed two different patterns during the bioaccumulation process. All these indicated that EDTA had strong effects on the bioavail‐abilities of REEs through controlling their species in nutrient solution.

Bio-accumulation of environmental residues of rare earth elements in aquatic flora Eichhornia crassipes (Mart.) Solms in Guangdong Province of China

Scattering and bio-accumulation of rare earth elements (REEs), including the inner transition series, in the aquatic environment in southern China have resulted from increased industrial and agricultural applications. Environmental residues of REEs entered into aquatic flora, namely Eichhornia crassipes, commonly known as water hyacinth, via the root system in contaminated substrate water and could distribute to various parts of the plant. REEs could also bio-accumulate and concentrate in the leaves at a concentration ratio of approx. 3 times regardless of initial REE concentration in the substrate water. REEs could also enter into the plant via the leaves that are exposed to atmospheric contaminants. While officially permitted residual concentrations of mixed REE nitrates in foodstuffs or animal feedstocks are not available, high REE concentrations in the substrate water in which water hyacinth grew could possibly enter the human food chain and lead to adverse public health problems.

The effects of chemical species on bioaccumulation of rare earth elements in wheat grown in nutrient solution

In this study, the effects the of complexing agent ethylenediamine tetraacetic acid (EDTA) on the species of Rare Earth Elements Lanthanum Gadolinium and Yttrium in nutrient solution and bioaccumulation of REEs in wheat seedling were investigated. The results showed that addition of EDTA can reduce the bioaccumulation values in the root, on the other hand, the bioaccumulation values in the aboveground part (stem and leaves) increased. Considering the different parts of wheat, root had higher bioaccumulation ability than that in the aboveground part of wheat. During the range of experiment concentrations (0–4 mg L −1), both ionic and complexed species REEs in nutrient solution had positive linear correlation with their concentrations in root. All these indicated that EDTA had strong effects on the bioavailabilities of REEs through controlling their species in nutrient solution and transportation processes from root to aboveground part of wheat.