Austempered ductile iron (ADI) is an advanced type of heat treated ductile iron, with excellent combination of mechanical properties, which are comparable to forged steels. However, in recent publications it was established that in contact with water the ductility of ADI decrease. Despite notable scientific attention, the cause of this phenomenon remains unclear. Some authors suggested that a small atom chemisorption causes the weakening of the surface atomic bonds. To test proposed hypothesis, two different types of ADI materials were tensile tested in various environments, such as: argon, helium, hydrogen gas and water. It was discovered that only the hydrogen gas and water gave a statistically significant decrease in mechanical properties, i.e. cause embrittlement. Thus, the primary deteriorating effect on the ADI material tensile properties comes from hydrogen atoms. The morphology of the embrittled zone indicates that the brittle zone may be caused by cyclic local-chemisorption, micro-embrittlement and local-fracture.