An Measured Environmental Concentration (MEC) relates to a chemical substance found in an environmental sample. The concentration of the compound may result from direct contamination, transformation and/or metabolization of an different chemical contaminant, natural origin or a combination of these sources.

MEC is to be used as a reference in the context of Chemical Safety Assessment

Chemical safety assessment

According to REACH legislation, a chemical safety assessment "has to be performed by registrants for substances manufactured and imported in quantities starting at 10 tonnes per year and by downstream users if their uses are not addressed by their supplier."The CSA includes the evaluation of all...

s (CSA) and should be compared with the respective Predicted Environmental Concentration

Predicted environmental concentration

Calculated value of a chemical in the environment on the basis of exposure models such as the European Union System for the Evaluation of Substances . Used in the context of Chemical Safety Assessments and referenced in Chemical Safety Reports ....

 (PEC) and Predicted No-Effect Concentration (PNEC) in order to decide weather exposure model is valid and the compound related risk is controlled.