Transplacental uptake of 127m Tellurium studies by whole-body autoradiography

Toxicity of tellurium and its compounds

Tellurium (Te) is widely used in industry because of its unique physicochemical properties. In the general population, foodstuff like meat, dairy products, and cereals is the major source of tellurium exposure. In the occupational environment, inhalational exposure predominates. Due to its exceptional properties as a metalloid, Te is broadly used in the industry. For example, Te is used as an alloy for solar panels, phase change optical magnetic disks, and Peltier devices. Recently, alloys of Te with cadmium, zinc, and other metals are used for nanomaterials, such as quantum dots. Thus, it is suggested that there is an existence of risk of exposure to Te in everyday life. Commercial Te is mostly obtained from slimes of electrolytic copper refineries. Te concentration in the slimes can extend up to 10% or more. Slight levels of its organic compounds may also be absorbed via skin. Not much information is available to prove Te as carcinogenic but its toxicity is well established. The present paper will review the toxicity of Te and its compounds.

Distribution of artificial radionuclides in abandoned cattle in the evacuation zone of the Fukushima Daiichi nuclear power plant

The Fukushima Daiichi Nuclear Power Plant (FNPP) accident released large amounts of radioactive substances into the environment. In order to provide basic information for biokinetics of radionuclides and for dose assessment of internal exposure brought by the FNPP accident, we determined the activity concentration of radionuclides in the organs of 79 cattle within a 20-km radius around the FNPP. In all the specimens examined, deposition of Cesium-134 (¹³⁴Cs, half-life: 2.065 y) and ¹³⁷Cs (30.07 y) was observed. Furthermore, organ-specific deposition of radionuclides with relatively short half-lives was detected, such as silver-110m (^110mAg, 249.8 d) in the liver and tellurium-129m (^129mTe, 33.6 d) in the kidney. Regression analysis showed a linear correlation between the radiocesium activity concentration in whole peripheral blood (PB) and that in each organ. The resulting slopes were organ dependent with the maximum value of 21.3 being obtained for skeletal muscles (R² = 0.83, standard error (SE) = 0.76). Thus, the activity concentration of ¹³⁴ Cs and ¹³⁷Cs in an organ can be estimated from that in PB. The level of radioactive cesium in the organs of fetus and infants were 1.19-fold (R² = 0.62, SE = 0.12), and 1.51-fold (R² = 0.70, SE = 0.09) higher than that of the corresponding maternal organ, respectively. Furthermore, radiocesium activity concentration in organs was found to be dependent on the feeding conditions and the geographic location of the cattle. This study is the first to reveal the detailed systemic distribution of radionuclides in cattle attributed to the FNPP accident.

Toxicology of choroid plexus: special reference to metal-induced neurotoxicities

The chemical stability in the brain underlies normal human thinking, learning, and behavior. Compelling evidence demonstrates a definite capacity of the choroid plexus in sequestering toxic heavy metal and metalloid ions. As the integrity of blood-brain and blood-CSF barriers, both structurally and functionally, is essential to brain chemical stability, the role of the choroid plexus in metal-induced neurotoxicities has become an important, yet under-investigated research area in neurotoxicology. Metals acting on the choroid plexus can be categorized into three major groups. A general choroid plexus toxicant can directly damage the choroid plexus structure such as mercury and cadmium. A selective choroid plexus toxicant may impair specific plexus regulatory pathways that are critical to brain development and function, rather than induce massive pathological alteration. The typical examples in this category include lead-induced alteration in transthyretin production and secretion as well as manganese interaction with iron in the choroid plexus. Furthermore, a sequestered choroid plexus toxicant, such as iron, silver, or gold, may be sequestered by the choroid plexus as an essential CNS defense mechanism. Our current knowledge on the toxicological aspect of choroid plexus research is still incomplete. Thus, the future research needs have been suggested to focus on the role of choroid plexus in early CNS development as affected by metal sequestration in this tissue, to explore how metal accumulation alters the capacity of the choroid plexus in regulation of certain essential elements involved in the etiology of neurodegenerative diseases, and to better understand the blood-CSF barrier as a defense mechanism in overall CNS function.

Biochemistry of tellurium

Tellurium (Te) demonstrates properties similar to those of elements known to be toxic to humans, and has applications in industrial processes, which are rapidly growing in importance and scale. It is relevant, therefore, to consider the tellurium physiology, toxicity, and methods for monitoring the element in biological and environmental specimens. Animal studies suggest that up to 25% of orally administered tellurium is absorbed in the gut. There is a biphasic elimination from the circulation with loss of about 50% within a short period, t1/2 = 0.81 d, and slower elimination of the residual Te, t1/2 = 12.9 d. Following a single ip, injection the largest proportion is in the kidney and bone, but with repeated oral administration, Te is found in the heart > > kidney, spleen, bone, and lung. Formation of dimethyl telluride is a characteristic feature of exposure, and gives a pungent garlic-like odor to breath, excreta, and the viscera. The main target sites for Te toxicity are the kidney, nervous system, skin, and the fetus (hydrocephalus). Te can be reliable measured in different specimens by several analytical techniques. Recent work has employed hydride generation atomic absorption spectrometry. Topics for further investigation are proposed.

Placental and blood-brain barrier transfer following prenatal and postnatal exposures to neuroactive drugs: relationship with partition coefficient and behavioral teratogenesis

In order to determine the neurotoxicity of prenatal and postnatal exposures to neuroactive drugs in developing rats, we examined placental and blood-brain barrier (BBB) transfers of these radiolabeled drugs when they were administered sc to pregnant rats on Day 19 of gestation, and to pups on Days 2, 7, and 14 after birth. The logarithms of partition coefficients (log Pcorr), used as indices of the lipid solubility of the drugs, decreased in the order propranolol greater than chlorpromazine greater than haloperidol greater than atropine greater than reserpine greater than dopamine greater than epinephrine greater than norepinephrine. The coefficients of correlation between log Pcorr and BBB transfer were statistically significant in all dams, fetuses, and pups. Propranolol, chlorpromazine, and haloperidol, having high lipid solubility, passed rapidly into fetuses. Behavioral teratogenesis occurred to a greater extent with postnatal than with prenatal exposures. All moderately and poorly lipophilic drugs transferred into fetuses, although at lower plasma concentrations than in dams. BBB transfer was low in dams, fetuses, and pups. The behavioral teratogenic potential of these drugs was relatively weaker than that of highly lipophilic drugs. Our results suggest that BBB transfer of drugs, which varies according to lipid solubility, is a major factor in behavioral teratogenesis. Highly lipid-soluble drugs were readily incorporated into developing rat brains, becoming strongly behaviorally teratogenetic by impairing postnatal functional maturation.

Teratogenicity of tellurium dioxide: prenatal assessment

The effects of multiple maternal subcutaneous injections of tellurium dioxide (TeO2) suspended in olive oil (0-1,000 mumol/kg) from day 15 to day 19 of gestation were evaluated in the Wistar rat. External and internal soft-tissue examinations were performed on day 20 fetuses. Multiple maternal injections, at doses higher than 10 mumol/kg, resulted in a dose-related appearance of hydrocephalus, edema, exophthalmia, ocular hemorrhage, umbilical hernia, undescended testis, and small kidneys in fetuses on day 20 of gestation. At 500 mumol/kg, reduction in maternal weight gain was also observed. At this level, the incidence of the above anomalies was 100%. The 100 mumol/kg dose of Te, which did not produce apparent maternal toxic responses, resulted in a 100% incidence of hydrocephalus and edema but no fetal mortality. Thus, tellurium can be teratogenic to the rat fetus without concomitant maternal toxicity. Also, the fetal period may be more sensitive than the organogenic period for the induction of hydrocephalus. Such evidence is consistent with the development of the choroid plexus and an effect of TeO2 on the production/resorption of cerebrospinal fluid.