Summary update of the Brookhaven tritium toxicity program with emphasis on recent cytogenetic and lifetime-shortening studies

A number of years ago a multiparameter program to evaluate the toxicity of tritiated water (HTO) was undertaken in the Medical Department at Brookhaven National Laboratory. The results of most of these studies have been published and will receive brief attention. Emphasis will be placed on the unpublished studies involving the induction of sister chromatid exchanges (SCE's) in bone marrow of mice, new biochemical information, and preliminary results on lifetime-shortening and carcinogenesis. In brief, male Hale-Stoner Brookhaven (HSB) mice maintained on HTO concentrations ranging from 3.0 to 30.0 ..mu..Ci/ml exhibited essentially the same number of SCE's per cell throughout their lifetime. Control mice showed a decrease in number of SCE's with age. The lack of a dose-response effect and the constant level of SCE's in HTO mice as compared to controls will be discussed. In the carcinogenesis study C57BL/6J male mice received various x-ray or HTO regimens. Mortality data from these and other studies in which CBA/Ca/BNL mice received single x-ray exposures or equivalent integrated dose exposures by single HTO injections will be discussed. 25 refs., 4 figs

Comparative evaluation of effects of gamma-rays and heavy metals on mobility of the water flea Daphnia magna

The authors comparatively studied effects of gamma-ray and some heavy metal treatments on mobility of water flea Daphnia magna according to the OECD Guideline for Testing of Chemicals, which is generally used for ecotoxicity evaluation of chemicals. The 50 % effect dose at 24 hours after gamma-irradiation (ED50/24h) was 1600 Gy. The 50 % effect concentrations following 24 hour exposure for manganese, nickel and copper (EC50/24h) were 990, 180 and 3.3 uM, respectively. The Gy-equivalent factors (=ED50/24h /EC50/24h) were therefore caluculated as 1.6, 8.9 and 480 for manganese, nickel and copper, respectively. These factors indicated that toxicity of these metals to D. magna could be ranked in an order of Mn<Ni<Cu. This toxicity rank showed a similar trend to that evaluated previously in the experimental model ecosystem (microcosm) consisting of three species of aquatic microorganisms. However, there was a noteworthy difference in the toxicity ranks obtained from the D. magna immobilization test and the microcosm test, suggesting that ecotoxicity ranking should be carried out by integrated evaluation on the basis of various ecotoxicity tests

Characterization of Simple Aquatic Microcosm for Ecotoxicity Screening

This study aimed at characterization of a simple aquatic microcosm consisting of algae Euglena gracilis as a producer, ciliate protozoa Tetrahymena thermophila as a consumer and bacteria Escherichia coli as a decomposer. The authors investigated changes in the cell densities, photosynthesis and respiration rates in the microcosm and its pure-culture systems when exposed or unexposed to copper. The following characteristics were deduced from the results. (1) The microcosm mimicked essential processes in natural aquatic microbial communities. That is, development of the microcosm could be regarded as a combination model of heterotrophic and autotrophic development in natural aquatic microbial communities. After such development, the microcosm reached a mature stage, in which the photosynthesis rate was balanced with the respiration rate. (2) The microcosm could evaluate not only direct effects of toxic agents but also community-level effects due to interspecies interactions or interactions between organisms and toxic agents. (3) The microcosm would have almost the same sensitivity to toxic agents as some other microcosms consisting of more diverse microbes. These three characteristics indicated that the microcosm studied was useful for community-level ecotoxicity screening for aquatic microbial communities

Ecological effects of various toxic agents on the aquatic microcosm in comparison with acute ionizing radiation

The purpose of this study was an evaluation of the effect levels of various toxic agents compared with ionizing radiation for the experimental model ecosystem, i.e., microcosm mimicking aquatic microbial communities. For this purpose, the authors used the microcosm consisting of populations of the flagellate alga Euglena gracilis as a producer, the ciliate protozoan Tetrahymena thermophila as a consumer and the bacterium Escherichia coli as a decomposer. Effects of aluminum and copper on the microcosm were investigated in this study, while effects of g-rays, ultraviolet radiation, acidification, manganese, nickel and gadolinium were reported in the previous studies, respectively. The microcosm could detect not only the direct effects of these agents but also the community-level effects due to the interspecies interactions or the interactions between organisms and toxic agents. The authors evaluated doses or concentrations of each toxic agent which had the following effects on the microcosm: (1) no effects; (2) recognizable effects, i.e., decrease or increase in the cell densities of at least one species; (3) severe effects, i.e., extinction of one or two species; and (4) destructive effects, i.e., extinction of all species. The resulting effects data will contribute to an ecological risk assessment of the toxic agents compared with ionizing radiation