What does 'Probable Effect Concentration' represent?

Probable Effect Concentration (PEC) is designed to identify the concentration of a substance in the environment, particularly in aquatic ecosystems, where it is likely to cause adverse effects on organisms. It serves as a critical threshold indicating potential harm to fish and other aquatic life. This measure is based on empirical data that reflect the relationship between concentration levels and observed adverse effects, thus allowing researchers and environmental managers to gauge risk levels associated with chemical exposure in water bodies.

The other choices do not accurately capture the essence of what PEC represents. For instance, the highest concentration that can be measured refers to a measurement limit rather than biological impact. The threshold for safe drinking water pertains to human health standards rather than ecological effects. Lastly, the average concentration of contaminants does not specifically relate to identifying risk levels for adverse ecological outcomes, thus diverging from the core purpose of PEC.