Which organisms are commonly used to derive Probable Effect Concentration values?

Probable Effect Concentration (PEC) values are primarily derived from studies that assess the effects of various substances on aquatic ecosystems. Aquatic organisms such as fish, invertebrates, and algae are critical in this context because they represent the primary components of freshwater and marine habitats. The effects of pollutants or chemicals on these organisms can indicate the potential ecological risks associated with exposure to those substances.

The use of fish and invertebrates allows for the assessment of different levels of biological complexity and ecological interactions. Algae serve as primary producers in aquatic environments and are integral to the food web. By determining the concentrations at which these organisms show harmful effects, researchers can set PEC values that help in evaluating environmental risk and in making regulatory decisions for chemical discharges.

The other categories, such as terrestrial mammals, birds, microorganisms, and plants, are valuable in their own right but do not align with the primary focus of PEC values. Terrestrial organisms are generally assessed using different models and criteria, while microorganisms and plants serve distinct roles that differ from the immediate effects sought in PEC assessments for aquatic systems. Thus, the correct answer reflects the specific focus on aquatic organisms integral to deriving PEC values.