**3. Rare earth elements and their influence on living organisms, including human health**

Kabata-Pendias [3] documented rare earth element influences on plant physiology, noting several studies, reporting that the REE stimulates seed germination, root growth, nutrient uptake, biological nitrogen fixation, chlorophyll synthesis, and photosynthesis. Kabata-Pendias was careful to note that further research is required for conformation and whether the rare earth elements are considered plant essential elements. The influence of rare earth elements, because of their production, processing, and usage on mammalian health, including human health, has not been widely investigated [12]. Of the elements comprising the lanthanide series and their influence on human health, the elements Ce, La, Gd, and Nd have received the most scrutiny [13]. Compounding rare earth element research is that many chemicals involved in rare earth element mining, recovery, primary and secondary processing, and recycling are involved; thus, it is difficult to isolate the influence of rare earth elements on human health.

Industry and occupational health research are limited because ore extraction and refining are localized in only a few nations [12, 13]. Bioaccumulation of rare earth elements appears to be restricted near mine and ore processing sites. There is growing evidence of the adverse effect of gadolinium (Gd) on skin conditions and nephrogenic systemic fibrosis because of Gd's use as an element in contrast agents used in magnetic resonance imaging [13]. Short-term exposure animal studies suggest rare earth element toxicity involves the liver, lungs, blood, and nervous systems. The global use of

#### *Rare Earth Elements - Emerging Advances, Technology Utilization, and Resource Procurement*


#### **Table 2.**

*Rare earth element usage in modern industries and technologies.*

cerium oxide nanoparticles as a catalytic additive in diesel fuel may be an air and soil pollutant. Conversely, rare earth elements may confer beneficial antioxidant activity. In an extensive review, Rim [12] noted that the rare earth elements high redox potential supported oxidative stress, which may enhance diabetes, atherosclerosis, inflammatory conditions, high blood pressure, neurodegenerative diseases, and cancer. Rim [12] further noted that selective chemicals used for rare earth element ore extraction, processing, and manufacturing may contribute to the environmental impact. The combined toxicities of the rare earth elements may influence soil pH and influence the human toxic response.

Many soil studies have been conducted to determine if soil rare earth element concentrations may have sufficient soil variability to influence environmental responses. In Brazil, Landim et al. [14] established soil rare earth element quality references and assessed their spatial distributions. The mean background concentrations in soils followed the abundance of the earth's upper crust: Ce > La > Nd > Pr > Sm > Dy > Gd > Er > Yb > Eu > Tb > Lu. In the Piaui state in Brazil, the ∑REEs across the mesoregions were (i) southeast (263 mg kg−1), (ii) north and central-north (90 mg kg−1), and (iii) southwest (40 mg kg−1) [14].

The effects of rare earth elements on aquatic biota are largely unknown [15, 16]. Gonzalez et al. [15] researched the sensitivity of aquatic organisms to REE's. Lanthanide series toxicity increased with atomic number for *Aliivibrio fischeri* and *Pseudokirchneriella subcapitata*, whereas the lanthanide series sensitivity of *Daphnia magna*, *Heterocypris incongruens*, *Brachionus calyciflorus,* and *Hydra attenuata* were effectively equal across atomic number [15]. Comparison of environmental risk

#### *Evaluation of Rare Earth Element Mine Sites for Environmental Impact DOI: http://dx.doi.org/10.5772/intechopen.109161*

indexes indicated that lanthanide concentrations immediately downstream of wastewater treatment plants are most problematic. Malhotra et al. [16] reviewed previous studies to understand the bioavailability, accumulation, interaction, and toxicity criteria of rare earth elements with aquatic organisms. Previous studies demonstrated that rare earth elements frequently provide a stimulatory influence at low dosage, whereas adverse influences are observed at higher dosages.

In Canada, the exposure-response relationships of three native plant species (*Asclepias syriaca*, *Desmodium canadense*, and *Panicum virgatum*) and two commonly used crop species (*Raphanus sativus*, and *Solanum lycopersicum* L.) to lanthanum, yttrium, and cerium were evaluated [17]. Germination was influenced by Ce at lower pH values. All species showed growth inhibition with Ce addition. Growth inhibition was evident for *A. syriaca* and *D. canadense* with rare earth element addition [17].

Li, et al. [18] assessed the toxicity of lanthanum, after 3 to 4 weeks of exposure, to five representative soil invertebrates. Toxicity was related to (i) total lanthanum, (ii) 0.01 M CaCl2-extractable lanthanum, and (iii) porewater lanthanum concentrations. Reduced growth of Isopod (*Porcellio scaber*) showed the most sensitive response. Reproduction issues involving earthworms (*Eisenia andrei*), enchytraeids (*Enchytraeus crypticus*), springtails (*Folsomia candida*), and oribatid mites (*Oppia nitens*) were observed at various elevated soil La concentrations. This study suggested that La may affect soil ecosystems at La concentrations slightly above natural background levels (6.6–50 mg La kg−1).

In China, Zhou et al. [19] performed experiments involving dry grass landfilling, chicken manure broadcasting, and plant cultivation to reclaim a rare earth element mine. After 2 years of restoration, soil organic matter, available potassium, available phosphorus, and acid phosphatase activity were improved. Soil physical properties (bulk density, water holding capacity, pH, and electrical conductivity), nutrient availabilities, and enzyme activities after 5 years were either similar or less impacted than soil not impacted by rare earth mining activities.
