Triphenylphosphine oxide (TPPO) is a neurotoxic very stable polar compound present in waste organic solutions from the chemical and pharmaceutical industry. The acute toxicity of TPPO LC50=12.2µg/mL, LC90=29.5µg/mL is higher than triphenyltin acetate so that a correct management in the relationship with sustainable chemistry is strongly required. TPPO was identified as a selective and potent inhibitor of transient receptor potential melastatin-5 (TRPM5), but at the same moment, it had no effect (up to 100 μM) on the membrane potential responses of TRPA1, TRPV1, or TRPM4b.