Human Biokinetic Data And A New Compartmental Model Of Zirconium — A Tracer Study With Enriched Stable Isotopes

摘要

Biokinetic models describing the uptake, distribution and excretion of trace elements are an essential tool innutrition, toxicology, or internal dosimetry of radionuclides. Zirconium, especially its radioisotope 95Zr, isrelevant to radiation protection due to its production in uranium fission and neutron activation of nuclear fuelcladding material. We present a comprehensive set of human data from a tracer study with stable isotopes ofzirconium. The data are used to refine a biokinetic model of zirconium.Six female and seven male healthy adult volunteers participated in the study. It includes 16 complete doubletracer investigations with oral ingestion and intravenous injection, and seven supplemental investigations.Tracer concentrations were measured in blood plasma and urine collected up to 100 d after traceradministration. The four data sets (two chemical tracer forms in plasma and urine) each encompass 105-240measured concentration values above detection limits.Total fractional absorption of ingested zirconium was found to be 0.001 for zirconium in citrate-buffereddrinking solution and 0.007 for zirconium oxalate solution.Biokinetic models were developed based on the linear first-order kinetic compartmental model approachused by the International Commission on Radiological Protection (ICRP). The main differences of theoptimized systemic model of zirconium to the current ICRP model are (1) recycling into the transfercompartment made necessary by the observed tracer clearance from plasma, (2) different parameters relatedto fractional absorption for each form of the ingested tracer, and (3) a physiologically based excretionpathway to urine.The study considerably expands the knowledge on the biokinetics of zirconium, which was until nowdominated by data from animal studies. The proposed systemic model improves the existing ICRP model, yetis based on the same principles and fits well into the ICRP radiation protection approach.