TOXICOLOGICAL PROFILE FOR BARIUM AND COMPOUNDS ...

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2. HEALTH EFFECTS
(including a maximum tolerated dose) and complete histopathological
examinations are performed would provide useful information on the potential
carcinogenic effects of barium. A dermal tumor promotion/tumor initiation
study evaluating barium hydroxide and other barium compounds would be useful
to clear up concerns as to whether or not barium hydroxide is a tumor-promoting
agent.
Genotoxicity. The genotoxicity of barium has not been well
characterized. The available data relating to the genotoxic effects of barium
are derived from in vitro studies only (Korman et al. 1978; Nishioka 1975;
Sirover and Loeb 1976a, 1976b; Sora et al. 1986); there were no available data
regarding the genotoxicity of barium in vivo. A single recombination assay in
which Bacillus subtilis was exposed to barium was negative for mutagenicity
(Nishioka 1975). Results of a test evaluating the fidelity of DNA synthesis
in an avian myeloblastosis virus DNA polymerase system indicates that barium
did not affect the accuracy of DNA replication (Sirover and Loeb 1976a,
1976b). Results of a study with Micrococcus luteus suggested that DNA
polymerase activity was stimulated and inhibited at low and high barium
concentrations, respectively (Korman et al. 1978). In a study with
Saccharomyces cerevisiae, inhibition of sporulation and marginal increases in
recombination frequency and diploid clones were observed following barium
treatment (Sora et al. 1986). Additional studies evaluating the genotoxic
effects of barium in a variety of in vivo and in vitro systems would be useful
because there is limited evidence suggesting barium may affect DNA polymerase
activity in bacteria and sporulation, meiotic failures, and recombination
frequency in yeast. The limited genotoxicity database for barium supports the
need for additional genotoxic studies.
Reproductive Toxicity. The reproductive effects of barium have not been
thoroughly studied. There are no studies regarding reproductive effects in
humans following barium exposure. However, two animal studies have provided
limited information suggesting that humans exposed to barium may be at
increased risk for developing reproductive effects (Borzelleca et al. 1988;
Tarasenko et al. 1977). Decreased ovary weight and decreased ovary/brain
weight ratio have been noted in rats following acute oral exposure to barium
(Borzelleca et al. 1988). Intermediate inhalation exposure to barium has been
associated with disturbances in spermatogenesis, shortened estrous cycle, and
alterations in the morphological structure of the ovaries and testes in rats
(Tarasenko et al. 1977). Since limited animal evidence suggests a potential
for adverse reproductive effects, epidemiological or occupational studies with
humans and/or additional experimental studies with animals would be useful to
fully characterize the reproductive toxicity of barium. Experimental animal
studies evaluating a wide variety of reproductive parameters through
multigenerations would be particularly useful because of the limited number of
parameters evaluated in the available single-generation studies.