Emerging environmental substances are not necessarily new chemicals. They are substances that have often long been present in the environment but whose presence and significance are only now being elucidated. Data for emerging substances are often scarce and measurement methods are often at the research and development stage or have not yet been harmonised at the European level. This makes it difficult to interpret and compare the results and represents a major difficulty for regulatory bodies in their decision-making.

A distinction has, however, to be made between "emerging substances" and "emerging pollutants" – see .

can be defined as substances that have been detected in the environment, but which are currently not included in routine monitoring programmes at EU level and whose fate, behaviour and (eco)toxicological effects are not well understood.

can be defined as pollutants that are currently not included in routine monitoring programmes at the European level and which may be candidates for future regulation, depending on research on their (eco)toxicity, potential health effects and public perception and on monitoring data regarding their occurrence in the various environmental compartments.

NORMAN has identified a today. Examples of this list are surfactants, pharmaceuticals and personal care products, methyl tert-butyl ether (MTBE) and other related petrol additives and their degradation products, polar pesticides and their degradation products and various proven or suspected endocrine disrupting compounds (EDCs). Another example is nanoparticles, which behave aerodynamically like gas molecules and have a large surface area per unit mass.