Cultured human-cell-based bioassay for environmental risk management.

Among bioassays for evaluating various impacts of chemicals on humans and ecosystems, those based on cultured mammalian-cells can best predict acute lethal toxicity to humans. We expect them to be employed in the future in environmental risk management alongside mutagenicity tests and endocrine-disrupting activity tests. We recently developed a disposable bioassay device that immobilizes human hepatocarcinoma cells in a small micropipette tip. This enables very quick (within 2 h) evaluation of acute lethal toxicity to humans. For bioassay-based environmental management, 2 promising approaches have been demonstrated by the US-EPA: toxicity identification evaluation (TIE) and toxicity reduction evaluation (TRE). The Japanese Ministry of Environment has been supporting a multi-center validation project, aimed at assembling a bioassay database. To make full use of these resources, we present a numerical model that describes contribution of individual chemical to observed toxicity. This will allow the selection of the most effective countermeasure to reduce the toxicity. Bioassay-based environmental risk management works retrospectively, whereas impact assessment using substance flow models and toxicity databases works prospective. We expect that these 2 approaches will exchange information, act complementarily, and work effectively in keeping our environment healthy in the 21 st century.