Currently, the method of evaluating the ecological impact of wastewater through biological responses is being utilized as a self-management technique by businesses. While previous research by the authors has clarified the ecological impact of algae due to effluent from Tandoku-syori and Gappei-syori Johkasou including grey water, there has been no case where the toxic substances responsible for these impacts have been identified, particularly for effluent from Tandoku-syori and Gappei-syori Johkasou including grey water. Therefore, in this study, the toxic substances were investigated through toxicity identification evaluation (TIE) from samples that exhibited harmful effects on algae growth. The study focused on 8 cases of Gappei-syori Johkasou effluent, 13 cases of Tandoku-syori Johkasou effluent, and 12 cases of grey water. As a result, it was estimated that oxidizing agents and non-polar organic substances were the inhibitory factors in the Gappei-syori Johkasou effluent, while PO₄-P, NH₃-N, and non-polar organic substances were the inhibitory factors in the Tandoku-syori Johkasou effluent. Regarding grey water, it was estimated that the toxic substances varied depending on the active ingredients in the detergents used in each household, and that metal components, possibly originating from water pipes, were causing inhibitory effects.