Groundwater problems caused by irrigation with sewage effluent

Abstract

Increasingly, sewage effluent will be used for urban and agricultural irrigation. The main concern is the potential for infectious diseases in farm workers and city dwellers exposed to the effluent, as well as in people who consume crops irrigated with effluent, especially when those crops are eaten raw or brought raw into the kitchen. Prevention requires adequate disinfection of the effluent. The effluent also must meet normal irrigation water requirements for parameters such as salt content, sodium adsorption ratio, trace elements, and so forth. Unfortunately, little or no attention is paid to long-term effects of sewage irrigation on underlying groundwater. Since most of the water applied for irrigation in dry climates evaporates, the concentrations of non-biodegradable chemicals in the drainage or deep-percolation water going down to the groundwater can be much higher than in the effluent itself (about five times higher for an irrigation efficiency of 80 percent). These chemicals comprise not only the salts, nitrates, and possible pesticide residues normally expected in irrigated agriculture, but also "sewage chemicals" like synthetic organic compounds, disinfection by-products, pharmaceuticals and pharmaceutically active chemicals like endocrine disrupters, and fulvic and humic acids. These acids are known precursors of disinfection by-products that are formed when the drainage water ends up in drinking-water supplies that are then chlorinated. Thus, groundwater below sewage-irrigated areas eventually may become unfit for drinking, which raises questions of liability. More research on long-term effects of sewage irrigation on groundwater is urgently needed.