Dissolved pollutants are contaminants that are fully solubilized in water at the molecular or ionic level, meaning they are not present as visible particles and cannot be removed by simple settling or basic filtration. In stormwater management, dissolved pollutants are a major concern because they move readily with flowing water and are more difficult to capture and treat than particulate-bound pollutants.
These pollutants exist in true solution, where individual molecules or ions are uniformly distributed throughout the water. Common examples include nutrients such as nitrogen, often in the form of nitrate, and phosphorus in dissolved forms, as well as metals like copper and zinc when present as ions. Other dissolved pollutants can include salts from road deicing, hydrocarbons in soluble fractions, and certain organic compounds such as pesticides or solvents.
Dissolved pollutants typically originate from a variety of sources in urban and developed environments. Fertilizers applied to lawns and agricultural land contribute dissolved nutrients. Road salts used for winter maintenance introduce chloride and sodium into runoff. Atmospheric deposition can add dissolved nitrogen compounds, while industrial and commercial activities may release soluble metals and chemicals. As stormwater flows over impervious and pervious surfaces, it can pick up and transport these substances directly into drainage systems and receiving waters.
In the context of stormwater systems, dissolved pollutants behave differently from suspended solids. Because they do not settle out, they are not effectively removed by sedimentation-based practices such as sediment basins or forebays. Instead, their treatment relies on processes such as adsorption to soil particles, biological uptake by plants and microorganisms, chemical transformation, and infiltration through soil media where these mechanisms can occur.
Dissolved pollutants are particularly important from a water quality perspective because they are immediately bioavailable, meaning they can be readily taken up by aquatic organisms. This can lead to issues such as eutrophication, toxicity to aquatic life, and degradation of drinking water sources. As a result, managing dissolved pollutants often requires carefully designed green infrastructure and soil-based treatment systems that maximize contact time and promote physical, chemical, and biological removal processes.