Barium oxide, obtained by calcining witherite

Endpoint summary

Description of key information

rapid absorption after instillation into the airways, accumulation in bone tissue in long-term studies

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

The information on resorption of barium is limited and contradicting. Animals studies showed absorption efficiencies between 0.7 and 85%, probably dependent on study duration, animal species used and age of the experimental animals. One study analyzed gastrointestinal absorption of barium in different species and found that it was around 50% in beagle dogs (treated with barium chloride), and 30% in rats and mice (administered barium sulfate). A second study found that adult beagle dogs only absorbed 0.7 -1.5% of administered barium (IPCS Concise International Chemical Assessment Document No. 33 on Barium and Barium Compounds).

McCauley et al. (1983) showed that barium is rapidly resorbed and appears in the blood stream after instillation into the airways, independent of the barium salt which was administered. Resorption was faster in fasted than in fed rats and decreased slowly after reaching the peak levels. 24 hours after treatment, blood barium levels were still significantly increased over baseline. In the tissues analyzed, barium concentration was greatest in the heart, however since bone tissue had not been studied, the results of this investigation are difficult to correlate with other data existing on barium accumulation.

Tardiff et al. (1980) showed accumulation of barium in the bone in a 13-week drinking water study. Bone barium levels were significantly increased already at 4 weeks after treatment initiation, the earliest time point checked in the study. At 8 and 13 weeks, the barium concentration remained steady, thus increasing treatment time did not result in increasing accumulation of barium in the bone. However, the substance concentration in drinking water positively correlated with the amount of barium accumulated in the bone tissue. In line with these findings, a study sponsored by NTP (1994) also found accumulation of barium in bone tissue after a 15-month drinking water administration period. Concurrently, calcium and phosphorus levels in bone tissue remained unchanged and bone density was not impacted by barium accumulation. Additionally, plasma barium levels were increased slightly but significantly in a dose-dependent manner.

Barium is excreted mainly in the feces, but also in the urine, two studies in humans showed that of the daily consumed barium amounts (in food and drinking water), 90-98% were excreted in the feces, most of the remaining barium was found in urine. Overall, these studies showed that only small amounts of barium are absorbed, the majority is excreted in feces or urine.

Thus, barium does show bioaccumulation potential, mainly in osseous tissue, in a dose- but probably not time-related manner.

However, also in the absence of chemical barium exposure, low levels of barium are taken up from the environment and are stored in osseous tissue. Since direct structural and toxic effects on the bones could not be found in rats receiving high doses of barium for up to 2 years (NTP 1994), the biological relevance of barium accumulation in osseous tissue is questionable.