To evaluate the toxicity of environmental chemicals to invertebrates, a static bioassay was developed in the laboratory using the Caenorhabditis elegans (C. elegans). First, reproducibility of this aquatic acute toxicity test system was confirmed. In order to estimate chemical toxicities in C. elegans, worms were subsequently exposed to eleven different xenobiotics. Mortality after 24 hr was adopted as the endpoint of toxicity. We found that benzo[a]pyrene, nonylphenol, benzophenone, bisphenol A and cadmium chloride affected viability of C. elegans. These data suggest that C. elegans is a suitable toxicity test organism for environmental xenobiotic chemicals, and that lethality can be used as a testing endpoint.

Recently, a number of studies have been performed worldwide to examine endocrine-disrupting chemicals (EDCs) and their interactions with the development and function of various systems in animals and humans.1-3) Among these EDCs, alkylphenol polyethoxylate non-ionic surfactants are used in the manufacture of cleaning agents, cosmetics and food products, as well as in plastic polymerization processes. Nonylphenol ethoxylates have predominantly been used, amounting to about 80% of the production of alkylphenol surfactants. In a recent study, nonylphenol (NP) had significant effects on the reproductive potential of medaka (Oryzias latipes) at concentrations as low as 17.7 mg/l, 4) and 50% of the male fish in the 50 mg/l treatment and 86% of the males in the 100 mg/l treatment developed testis-ova, an intersex condition characterized by both testicular and ovarian tissue in the gonad. 5) On the other hand, triclosan (TCS, 2,4,4Ј-trichloro-2Ј-hydroxydiphenyl ether) is widely used as an antibacterial agent in liquid toothpaste, soap, shampoo, and cosmetics, and is frequency found in wastewater effluent. Water samples collected near the outfall of a wastewater treatment plant in Rhode Island, U.S.A., showed 10-20 mg/l of TCS in the effluent and 80-100 mg/g of TCS in the sediment.6,7) Our previous study suggests that TCS has high toxicity on the early life stages of medaka, and that the metabolite of TCS may be a weak estrogenic compound in male medaka but with no adverse effect on reproductive success (such as fecundity and fertility) and offspring. 8) Moreover, Hanioka et al. 9,10) reported that 7-benzyloxyresorufin Odebenzylase (BROD) and 7-pentoxyresorufin O-depentylase (PROD) activities, which are associated with CYP2B1 activity, were remarkably induced by all doses of TCS in rats. Their results suggested that TCS induces the P450 isoforms of the CYP2B subfamily in the rat liver, and that the induced P450 isozymes were closely related to the toxicity of TCS or its chlorinated derivatives. However, there is no information about the effects of these chemicals on the hormonally responses of amphibian. 11)The South African clawed frog (Xenopus laevis) is sensitive to environmental chemicals as it spends all the life stages (egg, larva, and adulthood) in water. Hayes et al. 12) examined the effects of atrazine on sexual development in X. laevis, and reported that atrazine (Ͼ or ϭ0.1 mg/l) induced hermaphroditism and demasculinized the larynx of exposed males (Ͼ or ϭ1.0 mg/l), and male X. laevis suffered a 10-fold decrease in testosterone levels when exposed to 25 mg/l atrazine. Therefore, in the present study, we used X. laevis as a test organism, and investigated the effects of NP and TCS on production of plasma vitellogenin (Vg, egg yolk protein precursor), steroid hormone testosterone (T) synthesis, and hepatic CYP1A and CYP2B, as measured by the ethoxyresorufin O-deethylase (EROD) or PROD activities in male X. laevis. To our knowledge, this is first study on the effect of TCS in male X. laevis. MATERIALS AND MET...

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The free-living nematode, Caenorhabditis elegans (C. elegans) was adopted as a multicellular biosensor of biological toxicity from alkylphenols and organotin compounds. Alkylphenols were found to affect reproduction at lower doses than indicated by the acute toxicity assay. In particular, nonylphenol altered the reproduction rate of C. elegans at a dose 10-to 100-fold lower than the 50% lethal concentration (LC 50 ). A comparison of the number of viable worms and eggs suggested that alkylphenols and organotin compounds possess hatching toxicity. A 0.1 µM dose of organotin compounds caused a significant decrease, in the order of 20-50%, in reproduction of the worms, and an abnormal male: hermaphrodite ratio was observed. C. elegans therefore appears to represent a potent and sensitive organism with which to evaluate the biological effects of chemicals. In particular, the sensitivity of reproduction as an endpoint is highly useful for assessing the sublethal effects of chemicals.

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