Toxicity of Rhodium Complexes

There are no data on rhodium involvement in either human or animal biochemical systems. Studies of the 105RhCl3 metabolism in rats administered via the oral, intravenous and intramuscular routes revealed that rhodium was poorly absorbed. Initial rapid elimination occurred in the urine and later via the gastrointestinal tract. Rhodium was mainly accumulated in kidney and liver, but minor fractions were found in many soft tissues. The biological half-life of 105Rh varied between 4.3 and 16.5 days. The few studies on rhodium toxicity indicate that Rh salts are slightly toxic by oral ingestion and are mild skin irritants.108 112 The rhodium trichloride fed to mice at 5ppm in drinking water produced tumors: adenocarcinoma and lymphoma-leukemia. Thus, RhCl3 at these dosage levels is slightly carcinogenic. The oral LD50 values for rats are 500-2000mg/kg for RhCl3 and Na3[RhCl6], >5000mg/kg for RhI3,

>500 mg/kg for [Rh(NH3)5Cl]Cl2 and [RhCl(PPh3)3], and >2000mg/kg for Rh(acac)3. An examination of the frequencies of the positive prick test and patch test reactions to the chlorinated complexes of platinum-group metals revealed that the present concentration of these metals in the environment does not increase the incidence of reactions to these salts in patients with dermatitis and/or urticaria.112 Rhodium complexes show relatively low mutagenicity. The Ames tests indicate that the [Rh2(RCOO)2(N-N)2(H2O)2](RCOO)2 complexes (R = H, Me, Et, Ph; N-N = bpy, phen, dmpq) at MIC (minimal inhibitory concentration) do not show any mutagenic activity.45 Rhodium trichloride, at a concentration 300 mM, induced mutations in V-79 cells.113 Apart from the test of Ames, the bacterial SOS chromotest is used for the assessment of genotox-icity. The latter is a rapid test giving results within hours. In this assay, the lacZ gene of the tester strain E. coli PQ37 is fused to the bacterial sfiA SOS operon and lacZ is concomitantly expressed in the case of bacterial SOS response. Investigations of the mutagenicity of K2[RhCl5] and (NH4)3[RhCl6] in the SOS chromotest have shown that their activity is lower than that of cisplatin.114,115 Mutagenicity strongly depends on the structure and properties of the complexes. The complexes with 2,2'-biquinoline (biq) and 2-(2'-pyridyl)quinoline (pq), cis-[RhCl2(biq)2]Cl and cis-[RhBr2(pq)2]Br are highly mutagenic, cis-[RhCl2(pq)2]Cl and cis-[RhBr2(biq)2]Br are moderately mutagenic, while fac-and mer-[RhCl3(pq)(H2O)], as well as cis-[RhCl2(pq)2][RhCl2(CO)2]-H2O, are slightly mutagenic.116 Concentration of rhodium and other platinum group elements (PGE) in the earth crust is very low. However, the increasing uses of PGE in industry (mainly in catalytic processes), in vehicle exhaust catalysts, in jewelry and in medicine cause their anthropogenic emission and increase of their concentration in the environment.117 The metallic form of the PGE is generally considered to be inert as regards biochemical processes. However, the platinum metals in the environment are partly transformed into soluble compounds. In water at pH values between 5 and 8 the transformation in the model samples prepared from a milled catalytic vehicle converter is low and nearly constant: 0.01 0.025% for Pt and 0.05% for Rh. However, it was demonstrated that even 2 10% of the total PGE present in traffic dust was soluble. The bioaccumulation of PGE is low. The transfer coefficient (TC) (the ratio of the metal concentration in the plant to that in the soil) decreases in the order Pd > Pt > Rh. The TC values of Pt for cabbage were found to be in the range of 0.004 0.008. However, the PGE can be accumulated by some plants and animals very efficiently. In the case of the hydroponically grown cucumbers the TC values for roots ranged from 1700 to 2100. Water hyacinth is capable of recovering PGE even from diluted solutions (5 ppm) according to the order: Pt(II) > Pd(II) > Os(IV)« Ru(III) > Ir(III)« Rh(III). The toxicity at the 10 ppm level decreases in the same order. The Pt(II) compounds at this concentration are toxic, in contrast to the Na3[RhCl6], causing increase of the biomass of hyacinths some 6.7%. The exposure of the freshwater isopod Asellus aquaticus to PGE standard solutions for 24 h yielded the TC values equal to 150, 85 and 7 for Pd, Pt and Rh, respectively. The PGE are also biologically available for earthworms, rats, zebra mussels, barbels and European eels.

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