Sulfonamides in the environment as veterinary drugs.

SAs, a structurally related group of antibiotics containing a similar 4-aminobenzene sulfonamide backbone, are used in agriculture, aquaculture, animal husbandry, and also as human medicines. Competing with p-aminobenzoic acid in the enzymatic synthesis of dihydrofolic acid, SAs inhibit the growth and reproduction of bacteria. Once released to the environment, SAs distribute themselves among different environmental compartments, along with their degradation products, and are transported to surface water and groundwater. The physicochemical properties, the dosage applied and the nature of the environmental components with which they interact, govern the whole process. SAs, as a class, are less sorptive, impersistent, and leachable. They cannot be characterized as readily biodegradable. Their adsorption to soil increases with the aromaticity and electronegativity of functional groups attached to the sulfonyl phenyl amine core. Preferential flow in clay soils has been identified as a mechanism responsible for surface water contamination by SAs.