Hazardous waste refers to waste that has at least one of the following properties:
Properties of wastes which render them hazardous 
|Symbol||Type of operation|
|H1||‘Explosive’: substances and preparations which may explode under the effect of flame or which are more sensitive to shocks or friction than dinitrobenzene.|
|H2||„’Oxidizing’: substances and preparations which exhibit highly exothermic reactions when in contact with other substances, particularly flammable substances.|
|H-3A||‘Highly flammable’: liquid substances and preparations having a flash point: below 21°C (including extremely flammable liquids), or – substances and preparations which may become hot and finally catch fire in contact with air at ambient temperature without any application of energy, or – solid substances and preparations which may readily catch fire after brief contact with a source of ignition and which continue to burn or to be consumed after removal of the source of ignition, or – gaseous substances and preparations which are flammable in air at normal pressure, or – substances and preparations which, in contact with water or damp air, evolve highly flammable gases in dangerous quantities.|
|H3-B||‘Flammable’: liquid substances and preparations having a flash point equal to or greater than 21°C and less than or equal to 55°C.|
|H4||‘Irritant’: non-corrosive substances and preparations which, through immediate, prolonged or repeated contact with the skin or mucous membrane, can cause inflammation.|
|H5||‘Harmful’: substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may involve limited health risks.|
|H6||‘Toxic’: substances and preparations (including very toxic substances and preparations) which, if they are inhaled or ingested or if they penetrate the skin, may involve serious, acute or chronic health risks and even death.|
|H7||‘Carcinogenic’: substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may induce cancer or increase its incidence.|
|H8||‘Corrosive’: substances and preparations which may destroy living tissue on contacts.|
|H9||‘Infectious’: substances containing viable micro-organisms or their toxins which are known or reliably believed to cause disease in man or other living organisms.|
|H10||Teratogenic’: substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may induce non-hereditary congenital malformations or increase their incidence.|
|H11||‘Mutagenic’: substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may induce hereditary genetic defects or increase their incidence.|
|H12||Substances and preparations which release toxic or very toxic gases in contact with water, air or an acid.|
|H13||Substances and preparations capable by any means, after disposal, of yielding another substance, e.g. a leachate, which possesses any of the characteristics listed above.|
|H14||Substances and preparations capable by any means, after disposal, of yielding another substance, e.g. a leachate, which possesses any of the characteristics listed above.|
Examples of hazardous waste: clinical waste, pharmaceuticals, medicines and veterinary compounds, biocide, solvents, halogenated organic substances employed as solvents, cyanides, hydrocarbon/water emulsions, substances containing PCBs and/or PCTs, polychlorinated dibenzofurans, dibenzo-para-dioxine policlorurate, tarry materials, dyes, resins, plasticizers, glues, unidentified chemical substances whose effects on man and/or the environment are not known (e.g. laboratory residues), explosive materials, etc. All these are indexed in specific lists. This type of waste can only be processed and treated by economic agents that meet the necessary criteria and under strict regulation, based on an authorisation.
Storage of hazardous waste requires special landfills. Before such landfills became operational, Romania was granted a transition period from January 1st 2007 to December 31st 2009 for temporarily storing hazardous industrial waste, in compliance with all environmental and health protection requirements. It was also granted a transition period for the ban on liquid waste storage, and on the storage of waste with certain properties (corrosive and oxidizing), and for landfill water infiltration prevention (only surface water) until December 31st 2013 for 23 landfills of the energy, chemical and metallurgical industries, and until December 31st 2011 for 5 landfills of the mining industry, which had to either comply or suspend their activity.
Warning symbol for radioactive substances.
Radioactive waste is a special category of hazardous waste. They cannot be destroyed; they can only be stored. In order to address this issue, Romania needs two landfills for storing the radioactive waste generated by the Cernavoda Nuclear Plant.