Cerium toxicity

Cerium toxicity has been previously studied in its Ce form, and, more recently, a mechanism of cerium uptake by fibroblasts was proposed. Cerium oxide is indeed used in its nanometric form as an exhaust gas catalyst, and, when the nanoparticles are diluted, they form a dispersion of individual nanoparticles. To study the impact of nanoparticles through a water path and describes the interaction between a water dispersion of nanoparticles and a model bacteria. Thill et al. selected cerium oxide as the model nanoparticles, and E. coli was chosen as a widely used model organism. They found that (1) a large amount of Ce02 NPs can be adsorbed on the E. coli outer membrane (2) the speciation of the NPs is significantly modified after adsorption (3) the adsorption of the NPs and their reduction are associated with a significant bacterial cytotoxicity and (4) the toxicity of the NPs is prevented when they are put into contact with the bacteria in the presence of the growth medium. 

In general the lanthanides, including cerium, have a low toxicity rating (17), especially when they are present in material having low aqueous solubiUty. When orally adrninistered poor absorption from the gastrointestinal tract tends to result in the lanthanides generally having Httle effect. The anion is often an important deterrninant in toxicity. 

Fritz, T. E., Norris, W. P., Rehfeld, C. E. and Poole, C. M. (1967). Cerium-144-toxic manifestations in beagle dogs, page 260 in Biological and Research Division Annual Report 1967, Report No. ANL-7409 (Ar-gonne National Laboratory, Argonne, Illinois). 

A serious drawback is the large amount of CAN (up to 2.5 molar amounts) needed. Cerium salts are highly toxic pollutants and must be removed from industrial effluents and wastewaters. Cerium (III) solutions from penem pilot plant solutions containing up to 1.2 M Ce(III) were recycled in a two compartment Electro Syn Cell. Typical recycling conditions Nation diaphragm with coated Ti-anode, applied current densities = 50-150 A/em2 yield > 90% processed amount about 475 kg CAN [46,126,136,137], The simultaneous determination of Ce(III) and Ce(IV) in the pilot plant solution and in solid CAN can be performed polarographically. As little as 0.3% Ce(NH4)2(N03)5 can be determined in Ce(NH4)2(N03)6 [136]. 

Most of the compounds of cerium are toxic if ingested or if the fumes are inhaled. Cerium will ignite when heated. 

Two epidemiology studies have examined mortality among thorium workers neither found significant excess mortality. The standard mortality ratio (SMR) for all causes of death in a cohort of 3039 male workers in a thorium processing plant was 1.05 in comparison to United States white males (Polednak et al. 1983). The estimated radiation levels to the workers for inhalation intake ranged from 0.003-0.192 nCi/m (0.001-0.007 Bq/m ) for a period of 1-33 years. No evidence of overt industrial disease was found in a cohort of 84 workers at a thorium refinery exposed to <0.045-450 nCi/m (<0.002-0.02 Bq/m ) for <1-20 years (Albert et al. 1955). In both studies, the workers were exposed to other toxic compounds (uranium dust) as well as other radioactive materials (thoron, uranium daughters, thorium daughters, cerium). 

Cerium, Ce at wt 140.13,at No 58 one of the "rare earth elements gray, ductile, maleable metal which tarnishes in moist air d 6.78 mp 645°, bp 1400° sol in dil acids insol in cold w slowly oxidizes in hot w forms numerous alloys salts. It occurs in monazite sand which is an orthophosphate of thorium and rare earths. Ce-Fe pyrophoric alloys are used as sparking flints for lighters, tracer bullets for military signalling. Ce metal is used as component of some rocket proplnts and in alloys for jet engines. Toxicity, fire expln hazards of Ce are discussed in Ref 5- Ce alloy, called Misch Metal Ce 52, Nd 18, Pr 5, Sm 1 other substances(such as La, Ca, Al, C, Si Fe) 24%, has many applications. Mixt of Ce ... 

The effect on the central nervous system of the rare-earth metals following inhalation may preclude welding operations with these materials to any large extent. Cerium is stated to produce polycythemia but is useless in the treatment of anemia owing to its toxic effects. The salts of cerium increase the blood coagulation rate. See also RARE... 

SAFETY PROFILE Poison by intravenous, intraperitoneal, and subcutaneous routes. Moderately toxic by ingestion. See also CERIUM COMPOUNDS. When heated to decomposition it emits toxic fumes of Cl. ... 

When used in glass compositions (at a low weight percentages) along with comparable amounts of titanium oxide, cerium oxide produces a deep yellow coloration [26]. RarC earth sulfides, among them also cerium are used in glass and ceramics as colorants to replace toxic CdS [27]. 

Compounds of cerium and the other rare-earth elements are basically of low toxicity [39], see Table L2. 

Tabtc 1.2. Acute Toxicity data of Cerium compounds... 

The aqueous colloidal solutions of activated lanthanide orthophosphate nanocrystals stable for more than 3 months have been prepared and optimal activator concentration for such systems has been determined. It is 15 mol.% of terbium in CeP04 Tb, 20 mol.% of europium for LaP04 .Eu and 35 mol.% of cerium for LaP04 Ce. Non-toxicity within the limits of working concentrations allows such colloidal solutions to be proposed as new multifunctional luminophores for biological applications. 

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%). 

Fe2(CO)g and CeClj—SnClj the latter present some advantages like lower toxicity, lower temperature and homogeneous reaction conditions. The first step in the reaction ofa,a -dibromoketone 56 with CeClj—SnClj (equation 10) involves a single debromina-tion in analogy with a Reformatsky reaction to afford a cerium a-bromo enolate 57, This intermediate suffers from further elimination of bromide via ionization to oxyallyl cation 58 which undergoes the [3 + 2] cycloaddition to the enamine. The aminocyclo-pentanonc 59 obtained was easily deaminated to cyclopentenone 60. 

The CerOx process avoided some of the difficulties of the Ag(II) process in that cerium is much cheaper and less toxic than silver. However, the most serious disadvantage for the CerOx process, at least at the time of the report (NRC, 2001a), was that it was found to not be as mature a technology as the Ag(II) process, and it had never been tested with any neutralents. As with the Ag(II) process, it also uses large amounts of nitric acid and thus rated poorly in terms of pollution prevention criteria. 

The use of electricity in reactions is clean and, at least in some cases, can produce no waste. Toxic heavy metal ions need not be involved in the reaction. Hazardous or expensive reagents, if needed, can be generated in situ where contact with them will not occur. The actual oxidant is used in catalytic amounts, with its reduced form being reoxidized continuously by the electricity. In this way, 1 mol% of ruthenium(III) chloride can be used in aqueous sodium chloride to oxidize benzyl alcohol to benzaldehyde at 25°C in 80% yield. The benzaldehyde can, in turn, be oxidized to benzoic acid by the same system in 90% yield.289 The actual oxidant is ruthenium tetroxide. Naphthalene can be oxidized to naphthoquinone with 98% selectivity using a small amount of cerium salt in aqueous methanesulfonic acid when the cerium(III) that forms is reoxidized to cerium(IV) electrically.290 Substituted aromatic compounds can be oxidized to the corresponding phenols electrically with a platinum electrode in trifluoroacetic acid, tri-ethylamine, and methylene chloride.291 With ethyl benzoate, the product is a mixture of 44 34 22 o/m/fhhy-... 

OTHER COMMENTS alpha-Naphthylamine is an extremely toxic chemical in any of its physical forms, such as flake, dust, liquid, or vapor may be fatal if absorbed through skin, if inhaled, or swallowed personnel should be completely protected against physical contact with this chemical this chemical has been used in the manufacture of dyes and toning prints made with cerium salts the hydrochloride with sulfanilic acid is a reagent for nitrate. 

Some inorganic metal salts have also been used that lead to the formation of heteropolar, electrophihc iodine species. Among them (Ag, Th, Ce ), cerium salts have the advantage of high chemoselectivity. They are nonetheless limited by their strong oxidation potential and high toxicity, which requires careful purification for the labeled products to be used in vivo. 

Handling, Storage, and Precautions solid used as supplied. No toxicity data available, but cerium is reputed to be of low toxicity. 

Handling, Storage, and Precautions while relatively insensitive to impact, the solid can decompose explosively above its melting point. It forms highly explosive azides with metals such as Cu, Pb, Hg, Ag, Au, their alloys and compounds, and reacts with acids to form hydrazoic acid (HN3) which is a toxic, spontaneously explosive gas. Explosive gem-diazides can be formed in CH2CI2 or other chlorinated solvents and shock or heat sensitive metal azidothioformates in CS2. All work with NaNs and other azides should be conducted on a very small scale behind a shield, in a fume hood. Excess NaNs on flasks, paper, etc. can be destroyed in a fume hood by soaking with acidifled Sodium Nitrite or by oxidation with Cerium(IV) Ammonium Nitrated... 

---