How is a PECQ value calculated?

The Probable Effect Concentration Quotient (PECQ) is calculated using the formula that involves dividing the concentration of a contaminant measured in the environment (often referred to as the observed concentration, or OC) by the Probable Effect Concentration (PEC) of that contaminant. This approach allows for the evaluation of the potential ecological risk associated with the observed level of a contaminant compared to a standard level known to cause effects in 50% of the species tested in the environment.

When the PECQ is calculated, a value greater than 1 indicates that the observed concentration exceeds the PEC, suggesting a potentially detrimental ecological impact, whereas a value less than 1 may suggest a lower risk. This quotient is vital for assessing the likelihood of harmful effects on aquatic life and helps inform environmental management decisions.

In this context, the division used in the calculation reflects the relationship between what is being observed in the environment and the established thresholds for ecological risk, making the choice of division the correct method to assess the potential impact of contaminants.