Which of the following is a limitation of using PECQs?

The limitation of using Probable Effect Concentration Quotients (PECQs) is primarily due to their potential not to account for synergistic effects of multiple substances. PECQ assessments generally consider individual contaminants and their concentrations in isolation when evaluating their impacts on ecosystems. However, in real-world scenarios, contaminants often exist in mixtures, and their combined effects can be greater than what would be expected from their individual effects alone.

This means that understanding the safety and environmental impacts requires evaluating not just single chemicals, but also how they interact with one another. The failure to consider these synergistic effects can lead to an underestimation of toxicity and ecological risk, resulting in decisions that may not adequately protect the environment.

In contrast, the other options either misrepresent the function of PECQs or introduce criteria that do not necessarily limit their application, such as requiring laboratory analysis for every substance or stating that they provide absolute safety evaluations. These elements do not correctly define the fundamental limitations of PECQs within ecological risk assessments.