title: Effects of chronic γ-irradiation on the aquatic microbial microcosm: equi-dosimetric comparison with effects of heavy metals.
abstract: Effects of chronic γ-irradiation were investigated in the aquatic microcosm consisting of flagellate algae Euglena gracilis as producers, ciliate protozoa Tetrahymena thermophila as consumers and bacteria Escherichia coli as decomposers. At 1.1 Gy day(-1), no effects were observed. At 5.1 Gy day(-1), cell densities of E. coli showed a tendency to be lower than those of controls. At 9.7 and 24.7 Gy day(-1), population decrease was observed in E. coli. E. gracilis and T. thermophila died out after temporal population decrease and subsequent population increase in T. thermophila. It is likely that this temporal population increase was an indirect effect due to interspecies interactions. Effect dose rates of γ-rays were compared with effect concentrations of some metals using the radiochemoecological conceptual model and the effect index for microcosm. Comparison of these community-level effects data with environmental exposure data suggests that ionising radiation, gadolinium and dysprosium have low risks to affect aquatic microbial communities while manganese, nickel and copper have considerable risks. Effects of chronic irradiation were smaller than those of acute irradiation, and an acute to chronic ratio was calculated to be 28 by dividing an acute dose by chronic daily dose rate at which the effect index was 10%. This ratio would be useful for community-level extrapolation from acute to chronic radiation effects.
authors.affiliation: Research Center for Radiation Protection, National Institute of Radiological Sciences, 4-9-1 Anagawa, Chiba 263-8555, Japan. fuma@nirs.go.jp
authors.forename: Shoichi
authors.initials: S
authors.lastname: Fuma
authors.forename: Isao
authors.initials: I
authors.lastname: Kawaguchi
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kubota
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yoshida
authors.forename: Zen'ichiro
authors.initials: Z
authors.lastname: Kawabata
authors.forename: Gennady G
authors.initials: GG
authors.lastname: Polikarpov
mesh_terms: D003300:Copper / Q000633:toxicity; D004419:Dysprosium / Q000633:toxicity; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development / Q000528:radiation effects*; D005056:Euglena gracilis / Q000187:drug effects / Q000528:radiation effects*; D005682:Gadolinium / Q000633:toxicity; D005720:Gamma Rays; D008345:Manganese / Q000633:toxicity; D019216:Metals, Heavy / Q000633:toxicity*; D009532:Nickel / Q000633:toxicity; D011839:Radiation, Ionizing; D011874:Radiometry / Q000379:methods*; D018570:Risk Assessment; D016808:Tetrahymena thermophila / Q000187:drug effects / Q000528:radiation effects*; D013997:Time Factors
chemical_list: D019216:Metals, Heavy; D004419:Dysprosium; D008345:Manganese; D003300:Copper; D009532:Nickel; D005682:Gadolinium