This work shows a paradoxical fact: a highly plasticized PVC sample containing the maximum amount of the plasticizer di(2-ethylhexyl) phthalate (DEHP) compared to medium- and low-plasticized polymers turned out to be the least toxic. This was confirmed in express bioassays for the pre-lethal reactions of Paramecium caudatum Ehrenber and Escherichia coli M-17 when determining the acute toxicity for mortality of Daphnia magna Straus and Ceriodaphnia affinis Lilljeborg, as well as in chronic tests for D. magna. The migration of DEHP from the tested PVC samples into water was confirmed by the mass spectrometry method. It was shown that the contact of PVC materials with hot water (70℃) led to a significant increase in the toxicity of the extracts compared to cold extraction (20℃). The search for safe composition of PVC materials must be carried out in the direction of the optimal ratio of PVC-polymer, plasticizer and heat stabilizer, as well as replacing the components of the composition with safe substances.