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J.Health Sci., 49(6), 429-435, 2003
Use of Paramecium Species in Bioassays for Environmental Risk Management: Determination of IC50 Values for Water Pollutants
Norikazu Miyoshi,a Tomonori Kawano,b, 1 Miho Tanaka,b, 2 Takashi Kadono,b, 1
Toshikazu Kosaka,b Manabu Kunimoto,c, 3 Tadao Takahashi,a and Hiroshi Hosoya*, b
aBiological Laboratory, Nishikyushu University, 4490-9 Ozaki, Kanzaki, Saga 842-8585, Japan, bDepartment of Biological Science, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan, and cEnvironmental Health Science Division, The National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan
Effect of chemical water pollutants on the growth of two Paramecium species (Paramecium caudatum and Paramecium trichium) were examined. The chemicals used as model chemical pollutants include organic solvents, potential carcinogens, mutagens, metabolic modulators, herbicides, insecticides, fungicides, antimicrobials, heavy metals, and heavy metal-containing chemicals. In this study, the IC50 values indicating the concentration of substances inhibiting the proliferation of Paramecium cells by 50% were used instead of the LD50 value, which indicates the dose of substances killing half the population of organisms, since the former is a more sensitive parameter for assessing the toxicity of substances at lower concentrations. Among 25 chemicals examined, di-(2-ethylhexyl)phthalate, potassium dichromate, 2,4-dichlorophenoxy acetic acid, and paraquat stimulated the growth of paramecia depending on the concentrations used. Dimethyl sulfoxide and formaldehyde were shown to be inert to paramecia in the range of concentrations (up to 1%, v/v) used here. Other chemicals were shown to inhibit the growth of the paramecia and thus the IC50 values for those chemicals were determined. Our data presented here may be a useful reference for assessing the impact of water pollutants on aqueous microecosystems consisting of various microorganisms including protozoa.
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