A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

TOXICOLOGYIn general all the lanthanides are considered as having a low toxicity rating[1][2] and this isespecially so when they are present in material with a low aqueous solubility. When orallyadministered poor absorption from the gastro-intestinal tract tends to result in the lanthanideshaving little effect. (Solubility is a critical aspect of the oral bioavailability of a material and thenature of the anion is often the important determinant of a material's toxicity.) For comparison theoral toxicity of lanthanide oxides is apparently comparable to that of common table salt[3] and thislow toxicity of the Ln's has led to their use as markers in nutritional studies.The inhalation toxicology of lanthanides has been studied but often using specificnon-natural radio-active species in order to investigate effects that would arise fromnuclear-fall-out. In addition the past use of monazite, a thorium-containing mineral as the majorresource led to confusion regarding the relation between radio-activity and the lanthanides;inadequate separations in the past produced Th- contaminated Ln- products. Current processingtechnology for mineral recovery and for lanthanide separation results in products that meet allregulatory requirements."The very few human studies [regarding inhalation] that showed any medically significanteffects were the result of essentially unmitigated chronic exposures over long periods of time.These studies were further confounded by other factors (e.g. smoking and exposure to other toxicsubstances)." [4] "It is also obvious from epiderniologic data that, when compared to otherwell-documented fibrogenic dusts such as quartz and silica, rare earths display only mildpathogenic potential."[5] These two quotes from recent publications summarize the acceptedmedical view. Material safety data sheets for lanthanide products, as regards inhalation exposure,tend to recommend for TLV-TWA (Threshold limit value-Time weighted average) values thewidely used nuisance-dust limits.[1] Pharmacology and Toxicology of the Rare Earth Elements, T.J.Haley, J.Pharm-Sc, 1965, 54, 663 : Toxicity,T.J.Haley, in "Handbook on the Physics and Chemistry of Rare Earths", ed. K.A.Gschneidner and L.Eyring,publ. North-Holland, 1979, vol.4, Ch. 40: Rare Earths in Biological Systems, P.H.Brown et al., ibid, 1991,vol.13 : Toxicity of Rare Earths, P.Arvela, Prog. Pharmacology, 1979, 2(3), 69[2] Institut Francais de Toxicologie, Oxyde de Cerium : Essais de Toxicite Aigue par Vois Orale et Percutanéechez le Rat, Rapport 301229, 1/1983; Oxyde de Cerium : Essais de Toxicite Aigue par Vois Respiratoire chezle Rat, Rapport 302217, 2/1983; Oxyde de Cerium : Tests de Tolerance Locale chez le Lapin, Rapport, 302314[3] DHHS-NI0SH, Registry of Toxic Effects of Chemical Substances, DHHS-NI0SH Publication 86-103, 1986[4] A Review of the Literature on the Toxicity of Rare-Earth Metals as it pertains to the EngineeringDemonstration System Surrogate Testing, P.H.Wald and V.A.Mode., publ. Lawrence Livermore NationalLaboratory, January 1990, UCID-21823 Rev. 1 (avail. NTIS)[5] Pulmonary Toxicity of Stable and Radio-active Lanthanides, P.J.Haley, Health Physics, 1991, 61(6), 80950