Small quantities of which pollutants are likely to pass through a POTW without treatment?

The most suitable choice highlights that ketones and soluble heavy metals can pass through a Publicly Owned Treatment Works (POTW) without undergoing significant treatment. This occurs primarily due to their chemical properties and the typical treatment processes employed at POTWs.

Ketones are organic compounds characterized by the presence of a carbonyl group, which makes them relatively volatile and less likely to be effectively removed during standard wastewater treatment processes that may not specifically target such substances. Soluble heavy metals, on the other hand, can be dissolved in water and are not always effectively precipitated or removed during the conventional treatment process, especially if they exist in forms that do not aggregate or settle easily.

In a POTW, the treatment processes are often designed to address bulk organic matter and suspended solids. As a result, certain pollutants, particularly those that remain dissolved or are in low concentrations, may not be adequately filtered, settled out, or chemically treated. This capability to bypass treatment highlights the need for more targeted approaches to manage these specific pollutants effectively, ensuring that they do not compromise water quality in the receiving environment.