Cationic exchange capacity (CEC) is an indicator of the capability of the soil, [[filter media]] or [[green roof media]], to retain dissolved, positively charged elements such as [[heavy metals|metals]], which are a common pollutant in stormwater runoff. Soil has the ability to retain dissolved metals due to the negative charge of clay and [[organic matter]](OM). | Cationic exchange capacity (CEC) is an indicator of the capability of the soil, [[filter media]] or [[green roof media]], to retain dissolved, positively charged elements such as [[heavy metals|metals]], which are a common pollutant in stormwater runoff. Soil has the ability to retain dissolved metals due to the negative charge of clay and [[organic matter]](OM). |