Brouziotis, Antonios Apostolos (2023) Toxicity of Rare Earth Elements on human and environmental health. [Tesi di dottorato]

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Abstract

The Rare Earth Elements (REEs) are a group of metals consisting of the 15 lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) generally along with Sc and Y. These metals have similar ionic radii and physicochemical properties. Their continuous application in sectors like agriculture and medicine, as well as their necessary utilization for the production of electronic devices, have increased concerns over the last years for both human and environmental health. Previous studies on animal models showed that REEs could cause several types of toxicity. Therefore, this PhD project investigated the potential hazardness of REEs on three different levels: i) on human toxicity, through the biomonitoring of the REE levels on human matrices; ii) on environmental toxicity, through elaborating ecotoxicity trials with several organisms; and on environmental chemistry, through determing the REE levels on abandoned mining sites. A literature review concerning the toxicity of REEs exclusively on human health was elaborated. Ce is the most studied REE, cytotoxicity the most studied field, while hair, blood and blood serum are the most studied human matrices. Human exposure to REEs can happen via many ways, such as environmental exposure, exposure through the food web or due to the lifestyle. REEs have been associated with several dieases, like neural tube defects, anemia and endomyordical fibrosis. GBCAs could be accumulated in kidney or muscles causing renal failure and fibromyalgia. The mining of REEs does not affect only the mining workers, but also residents near the mining areas. REEs have been shown to affect a number of metabolic pathways. They could activate metabolic pathways resulting to ROS production, DNA damage and apoptosis. However, they could be potential anticancer agents, since they are more cytotoxic on cancer compared to normal cells. Due to the implementation of REEs in diesel fuels as additives, concerns have increased about the potential human exposure to them through the car exhausts. For that reason, urine and scalp hair samples of car mechanics were collected from two different types of workshops. The car mechanics in the workshops of Avellino are lacking the use of means of protection, while those of Como are using them properly. Before the analysis of REEs on the human matries, it was essential to determine the LOD and LOQ values of REEs on ICP-MS, as well as validating the methods of preparation before analysis by ICP-MS. For determining the LOD and LOQ values, the REE content in 10 blank samples containing only HNO3 2% (v/v) was determined. LOD values ranged from 0.001 to 0.004 μg/L, while LOQ values ranged from 0.005 to 0.013 μg/L. Due to the lack of certified reference materials for REEs on human urine and hair, only the two methods for preparing human urines were validated following a method of spiking. Both methods showed adequate precision of repeatability and intra-laboratory reproducibility. The CVr% values of repeatability ranged from 1.5 to 12% for the DIL and from 8.4 to 16% for the MIN method. The CVr% values of reproducibility ranged from 6.2–23% for the DIL and from 8.6 to 24% for the MIN method. REE recoveries for both methods were very close to 100%. Therefore, both methods proved to be effective for the determination of REE levels in human urine matrices. Proceeding with the human matrices, the levels of REEs were determined in urines and hair. In addition, the levels of creatinine and 1-OHP were determined in urines. Our results showed significantly elevated levels of La, Ce, Gd, Tb and Total REEs in the urines of the exposed group, as well as levels of creatinine and 1-OHP. No REE or Total REEs were significantly different in the scalp hair between the two groups. Statistical analysis revealed that levels of La and Ce were significantly higher in the scalp hair of smokers when the use of hair dye does not affect the levels of any REE. These results indicate a highly possible occupational exposure of car mechanics to REEs due to car exhausts and a direct excretion through urines. There are also indications that smoking affects the levels and bioaccumulation of La and Ce. Several models were used in the lab for investigating the environmental toxicity of REEs. The real concentration of REEs in the samples prepared for elaborating the ecotoxicity trials was determined by ICP-MS with respect to the nominal concentration. The effect of Ce, Gd, La, and Nd was investigated in a simulated AMD at pH 4 and 6 considering a number of photosynthetic organisms (R. subcapitata, L. sativum, and V. faba) according to a multipleendpoint approach (growth inhibition, germination index, and mutagenicity). Gd was the most toxic element at pH 4, followed by La, Nd, and Ce. At pH 6, their effects significantly decreased, and Nd evidenced the highest toxicity. Gd, La and Nd evidenced at pH 4 their potential mutagenicity, that was not present at pH 6. These results indicate that the toxicity of REEs is increased in acidic environments, while the increase of the pH could mitigate their toxic effects. The microalagae R. subcapitata was exposed to La and Ce for 3 days (short-term exposure) to derive the EC10 values that were consequently used for the long-term exposure (21 days) to observe growth inhibition, biomarkers of stress, and bioconcentration. La and Ce increased the growth inhibition and were bioconcentrated. La increased also the ROS production. These results indicate that even low concentrations of La and Ce could be toxic to R. subcapitata with the potential to be bioaccumulated and transferred through the food web. The toxicity of eight REEs (La, Ce Nd, Sm, Eu, Gd, Dy, and Er) to the microalga Phaeodactylum tricornutum Bohlin was investigated. The EC50 values ranged from 0.98 mg/L to 13.21 mg/L and the elements were ranked according to their toxicity as follows: Gd > Ce > Er > La > Eu > Nd > Dy > Sm. Based these results, the presence of REEs in the marine environment does not seem to represent a widespread environmental risk except at some hotspots which may become more severe with the increase of REE application. Ce, La and their combination were tested across a concentration range for their effects on the sperm of S. granularis. A significantly decreased fertilization rate and increased developmental defects were noticed in higher concentrations, while an increased fertilization rate and decreased developmental defects were observed in lower concentrations. These results indicate that REEs could have a hormetic effect on several models. REEs can be used as catalysts on Advanced Oxidation Processes for the enhancement of the degradation of organic pollutants from aqueous solutions, including pharmaceuticals, dyes, and other molecules such as alkaloids, herbicides, and phenols. Ce and La are the most studied REEs on this field, and their mechanism of action is based on the oxygen vacancies and REE ion concentration in the catalysts. Metal oxide surfaces improve the decomposition of hydrogen peroxide to form hydroxide species, which degrade the organics. The REE content was analyzed in environmental samples collected from three abandoned mining sites in the region of Puglia (Gargano, Otranto and Spinazzola). After the digestion, the REE content was determined by TXRF and ICP-MS. TXRF performed much higher LOD levels than ICP-MS. Only by ICP-MS, could all REEs be traced in the samples. Ce seems to be the most abundant REE in all sites, while Spinazzola seems to be the site containing the highest amount of these elements, making it the most interesting among all for a possible REE extraction. According to the calculation of BCF, REEs are not bioaccumulative. All in all, this project has shown that REEs are potentially hazardous for both human and environmental health. They have been associated with several diseases, they could be bioaccumulated in human matrices and they are toxic for a number of living organisms. In the future, other research projects should consider of investigating the safety of these elements as well, since their human utilization and environmental concentration is increasing overtime.

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