Effect of the dose on the toxicokinetics of a quaternary mixture of rare earth elements administered to rats.

Large human biomonitoring studies are starting to assess exposure to rare earth elements (REEs). Yet, there is a paucity of data on the toxicokinetics of these substances to help interpret biomonitoring data. The objective of the study was to document the effect of the administered dose on the toxicokinetics of REEs. Male Sprague-Dawley rats were injected intravenously with 0.3, 1 or 10 mg/kg body weight (bw) of praseodynium chloride (PrCl3), cerium chloride (CeCl3), neodymium chloride (NdCl3) and yttrium chloride (YCl3) administered together as a mixture. Serial blood samples were withdrawn up to 72 h following injection, and urine and feces were collected at predefined time intervals up to 7 days post-dosing. The REEs were measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). For a given REE dose, the time courses in blood, urine and feces were similar for all four REEs. However, the REE dose administered significantly impacted their kinetics, as lower cumulative excretion in urine and feces was associated with higher REE doses. The fraction of REE remaining in rat tissues at the terminal necropsy on post-dosing day 7 also increased with the dose administered, most notably in the lungs and spleen at the 10 mg/kg bw dose. The toxicokinetic parameters calculated from the blood concentration-time profiles further showed significant increases in the mean residence time (MRTIV) for all four REEs at the 10 mg/kg bw dose. The shift in the REE kinetics at high dose may be explained by a higher retention in lysosomes, the main organelle responsible for accumulation of these REEs in different tissues.

Comparison of the effects of lanthanum, cerium and praseodymium on rumen fermentation, nutrient digestion and plasma biochemical parameters in beef cattle.

The objectives of the trial were to compare the effects of supplementing rare earth elements (REE) lanthanum (La), cerium (Ce) and praseodymium (Pr) on rumen fermentation, nutrient digestion, methane (CH4) production, nitrogen (N) balance and plasma biochemical parameters in beef cattle. Four Simmental male cattle, aged 12 months, with initial average liveweight of 333 ± 9 kg and fitted with rumen cannulas, were fed with a basal ration composed of concentrate mixture and maize silage. Animals received a basal ration without adding REE (Control) or three treatments, i.e. supplementing LaCl3, CeCl3 or PrCl3 at 204 mg/kg DM to the basal ration, respectively, which were allocated in a 4 × 4 Latin square design. Each experimental period lasted 15 d, consisting of 12 d for pre-treatment and three subsequent days for sampling. Results showed that all tested levels of REE tended to increase neutral detergent fibre digestibility (p = 0.064) and tended to decrease rumen CH4 production (p = 0.056). Supplementing LaCl3 and CeCl3 decreased total N excretion and urinary N excretion, increased N retention (p < 0.05), tended to increase total urinary purine derivatives (PD) (p = 0.053) and microbial N flow (p = 0.095), whereas supplementing PrCl3 did not affect N retention, urinary PD and microbial N flow. No differences were found in the effects of nutrient digestibility, CH4 production and plasma biochemical parameters among LaCl3, CeCl3 and PrCl3. Further trials using graded levels of LaCl3, CeCl3 and PrCl3 in a wide range are needed to obtain more pronounced results for comparing effects of La, Ce and Pr on rumen fermentation and nutrient digestion in beef cattle.

Weaning pig performance and faecal microbiota with and without in-feed addition of rare earth elements.

Two 6-week feeding trials were conducted on a total of 112 newly weaned piglets to examine the recently reported growth promoting effects of dietary rare earth elements (REE) in European pig production. Rare earth element-diets were supplemented with a REE-citrate premix of lanthanum and the light lanthanoides cerium, praseodymium and neodymium at 200 mg/kg for 6 weeks after weaning. Overall for both trials, growth performance of REE-citrate and control fed piglets did not differ significantly (p > 0.05). An early enhancive tendency for REE-citrate in trial 1 (feed conversion ratio, FCR -3%, p = 0.15) proved irreproducible in trial 2. In the late period of trial 1, in-feed addition of REE-citrate significantly impaired piglet performance (FCR + 8%, p = 0.01). A cultivation-independent molecular approach, polymerase chain reaction-denaturing gradient gel electrophoresis was further applied to assess REE induced alterations in the predominant faecal microbiota from weaning pigs. Calculation of various ecological characteristics does not indicate (p > 0.05) an often discussed selective effect on local microbial composition of dietary REE.