Environmental Quality Standards (EQS) or Limit Values are widely used to protect the environment and human health from substances released by human activity. They usually relate to doses or concentrations in the environment for specific chemicals, below which unacceptable effects are expected not to occur. Some standards are legally enforceable numerical limits, such as Quality Standards for Priority Substances under the Water Framework Directive. Others are not mandatory, but are contained in guidelines and codes of practice, as is the case for many soil and waste related limit values.

Limit values and environmental quality standards are expressed as numerical limits. There are numerous uses of such values including:

• Generic screening assessments
• Informing risk mitigation measures and permitting
• Discharge consents
• Possible legal regulatory enforcement.

Different jurisdictions use these values in different ways but generally all limits are based on reliable and relevant ecotoxicity data.