Lanthanide compounds toxicity

Recently, Kobayashi has disclosed significant advances regarding rare-earth and lanthanide triflates as catalysts for Mannich-type reactions [65-68] and there are several reviews available on catalytic Mannich-type reactions [69-73]. High catalytic activity, low toxicity, and low tolerance to moisture and air make lanthanide triflates valuable catalysts. However, the high cost of these catalysts restricts their use. Bismuth compounds are of interest as lower toxicity and cheaper alternatives to such catalysts. 

A compound that is able to influence the relaxation times of water protons has to be paramagnetic. In the Periodic System paramagnetic ions are to be found amongst the transition metals and the rare earth metals (lanthanides). However, it was well known, that the free ions of heavy metals are toxic. Lanthanide ions form soluble complexes with ligands such as phospholipids, amino acids and proteins that are present in plasma. The liver and the skeleton are the major sites of accumulation of free metal ions. Uptake in the liver is mediated by the hepa-tocytes [2]. 

Biological indicator species such as fresh water sponges, clams, mussels, insect larvae that sorb water-borne pollutants are difficult to assess over time periods of years. The lanthanides may be used as indicator species utilizing the adventitious roots of stream-side trees [204-206]. The ability of tree roots to sorb both chelated and non-chelated lanthanides from water indicate that aquatic roots accumulate, concentrate and retain lanthanides to such an extent that the roots can be used as indicators of aquatic pollution, and that lanthanides can be studied as analogues of toxic elements and compounds. 

Thus, the synthesis of triphenylscandium is a salt-elimination reaction (or metathesis) whilst the route for the lanthanide phenyls involves a redox reaction. The former has the problem of producing LiCl, which is often significantly soluble in organic solvents and contaminates the desired product, whilst the latter involves disposal of mercury waste, as well as handling toxic organomercury compounds. 

The lanthanide series of metals includes the 15 elements with atomic numbers 57-71, plus yttrium (atomic number 39). The lanthanides occur in the earth s crust at concentrations exceeding some commonly used industrial elements making the term rare earths something of a misnomer. For example, yttrium, cerium, lanthanum, and neodymium are present in the earth s crust at higher concentrations than lead. Of the 15 lanthanides, only promethium does not occur in nature - it is a man-made element. All of the lanthanides have similar physical and chemical properties. Because of similarities in their chemistry and toxicity, the characteristics of the lanthanides are often described as a group. Within the lanthanide group, however, there are differences between the toxicity of the individual lanthanide elements and their compounds. 

Different forms of lanthanide differ in their toxicity. There are three forms of lanthanides soluble (chlorides, nitrates, acetates), insoluble (oxides, carbonates), and chelated compounds (DTPA). Most of the available information on lanthanide absorption and toxicity comes from the soluble lanthanide salts. In one study, rats given DTPA (chelating agent) 1 or 2 days after oral administration of cerium chloride were found to have significantly reduced whole body retention of soluble cerium (from 40% to 2%). 

GdClj has been used to study the mechanisms of chemical-induced hepatotoxicity (Badger et al. 1997, Sauer et al. 1997). Since lanthanides have an affinity for reticuloendothelial cells, GdClj injection selectively destroys Kupffer cells (the resident macrophage cell in the liver), and this results in protection of the liver from a number of toxicants hence, a role is suggested for these cells in chemical-mediated hepatotoxicity. The role of Kupffer cells in hepatotoxicity was implicated for those compounds required to undergo biotransformation before eliciting their toxicity (e.g., 1,2-dichlorobenzene and carbon tetrachloride), as well as those chemicals which do not (e.g., cadmium chloride). 

Bulman RA (1988) Yttrium and lanthanides. In Seiler HG, Sigel H, and Sigel A, eds. Handbook on toxicity of inorganic compounds, pp. 769-785. Marcel Dekker, New York. 

Bulman R (1988) Yttrium and the Lanthanides. In Seiler H, Sigl H and Sigl A, eds. Handbook on the Toxicity of Inorganic Compounds, pp. 769— 785. Marcel Dekker Inc, New York. 

EXPLOSION and FIRE CONCERNS dangerous fire hazard NFPA rating Health 2, Flammability 3, Reactivity 0 explosive reaction with lanthanide perchlorates and nitrogen-fluorine compounds reacts with water, steam, and acids to produce toxic and flammable vapors incompatible with chlorosulfonic acid, nitric acid, sulfur trioxide use foam, carbon dioxide, or dry chemical for firefighting purposes. 

Speciation and reactivity of actinide compounds comprise an important area for quantum chemical research. Even more so than in the case of lanthanides, f-type atomic orbitals of actinides can affect the chemistry of these elements [185,186] the more diffuse 5f-orbitals [187] lead to a larger number of accessible oxidation states and to a richer chemistry [188]. The obvious importance of relativistic effects for a proper description of actinides is often stressed [189-192]. A major differences in chemical behavior predicted by relativistic models in comparison to nonrelativistic models are bond contraction and changes in valency. The relativistic contribution to the actinide contraction [189,190] is more pronounced than in the case of the lanthanides [191,192]. For the 5f elements, the stabilization of valence s and p orbitals and the destabilization of d and f orbitals due to relativity as well as the spin-orbit interaction are directly reflected in the different chemical properties of this family of elements as compared with their lighter 4f congeners. Aside from a fundamental interest, radioactivity and toxicity of actinide compounds as well as associated experimental difficulties motivate theoretical studies as an independent or complementary tool, capable of providing useful chemical information. 

Another important aspect of the lanthanides is their substantial absence of toxicity, as can be concluded from the specialized literature. For example, some Ln compounds are under investigation for use in pharmacology and medicine (1). This low toxicity is an important pre-requisite for their large-scale application. 

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