Nickel release and surface characteristics of fine powders of nickel metal and nickel oxide in media of relevance for inhalation and dermal contact

► Powders of nickel metal and NiO may have different surface properties. ► Significantly more nickel released from nickel metal powders compared with NiO. ► The release of nickel increases with increasing complexation capacity of the fluid. ► Released nickel and particle/surface characteristics are strongly correlated. ► Bioaccessibility and particle/surface characteristics essential for risk assessment.