Carcinogenic risk assessment criteria associated with inhalation of airborne particulates containing chromium (VI/III).

Contaminated land sites and unused chromate production facilities raise the possibility that remediation operations could involve generation of airborne particles of respirable size containing both Cr(VI) and Cr(III) in soluble and insoluble forms. These airborne particles reaching human populations in the neighborhoods involved, can pose carcinogenic risks via Cr(VI)-containing material retained in the lungs. It is proposed that the risk assessment process for this inhalation exposure be governed by the following considerations. (i) Only the respirable fraction (0.2-10.0 microns diameters) of the inhaled particulates should be considered as contributing to delivered dosage of Cr(VI) to the lung. (ii) In accordance with the ICRP analysis of particulate retention in the lung for extended intervals, the airborne respirable particle intake should be multiplied by the factor 0.125 to generate an estimate of dosage of particles retained in the lung for extended intervals, leading to possible carcinogenesis from the Cr(VI) content. And (iii), the inhalation carcinogenic risk for Cr(VI) should only be modelled in increments above a daily total chromium intake of 100 micrograms per day, a current estimate of the required daily intake of this essential mineral.

Critical issues facing animal scientists.

An important series of issues confronts the animal research scientist involved in meeting world needs for food products from animal agriculture. The major issues stem from societal pressures for improved products, for prevention of chemical pollution of the biosphere, and for wise use of animal resources in toxicological testing and research. The following issues are among those treated in the present discussion: (1) There is a need to obtain reliable dosage vs response information for chronic effects produced in the human by food additive chemicals. (2) There is a need for toxicological research on combined hazard from multiple contaminants in animal food products. (3) There is a requirement for development of methodology for proper usage and (or) disposal of chemically contaminated animal food products. (4) The public must be educated with respect to the absolute necessity for use of intact animals in biological research, to supplement information from in vitro systems. (5) Animal scientists must characterize fully each animal species and strain employed in research and testing, to guarantee reproducibility of results. (6) Animal scientists must evolve a universal set of principles for translation of animal toxicity data into prediction of human hazard. (7) Animal scientists should develop universally uniform methodology for toxicological testing of foods and food chemical residues. (8) Animal scientists should rebut national regulatory philosophies that derive from unsound science. (9) The animal scientist should assist regulatory authorities in developing sound, practical "Good Laboratory Practice" guidelines.

Changes in rat respiratory behavior under varying PCO2 levels and argon content in hyperbaric Ar-O2-CO2 atmospheres.

An anesthetized rat preparation has been used for breathing studies in hyperbaric Ar-O2-CO2 atmospheres in which total saturation pressure was varied in the range 1-19.1 ATA and PCO2 was set at levels of 0.0, 0.05 or 0.10 ATA. The variables monitored were respiration rate and an isotonic measure of diaphragm-twitch amplitude during contracture/relaxation (twitch index). The results indicate that: (1) hyperbaric Ar-O2 atmospheres are able to maintain the animal in stable condition for several hours; (2) elevation in PCO2 level produces enhancements in respiration rate and twitch index that are markedly dependent on the PAr level; (3) successive increases in PAr are able to lower progressively the effects on both breathing parameters produced by either 0.05 or 0.10 ATA of CO2, with full abolition of both effects of inhaled CO2 in the PAr range 14-19 ATA; and (4) the intrinsic ability of hyperbaric argon to abolish respiratory enhancement by CO2 is greater than that of hyperbaric helium. These results have been discussed in terms of possible CNS loci at which hyperbaric argon (or helium) is able to antagonize centrally induced effects from dissolved molecular species derived from inspired CO2, and in relation to the broader task of control of excitatory/inhibitory centers of the CNS during diving by manipulation of the partial pressures of diluent components of breathing-gas mixtures.