Author
 |
Bouwer, Herman |
|
Submitted to: Journal of Environmental Health
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/1/2000 Publication Date: N/A Citation: N/A Interpretive Summary: Sewage effluent is being used widely for agricultural/urban irrigation, but pathogens have been the main health concern and complete removal of viruses, bacteria, and protozoa and other parasites is required before the effluent can be used to irrigate fruits/vegetables consumed raw or brought raw into the kitchen, or parks, playgrounds and other areas with free public access. Long-term effects of such irrigation on underlying ground- water usually focus on dissolved salts and nitrate, but other chemicals must also be considered, especially since chemical concentrations in deep percolation water below irrigated areas are much higher than effluent itself (five times if the irrigation efficiency is 80% and rainfall is negligible). They include disinfection byproducts, pharmaceutically active chemicals and DBP precursors like humic and fulvic acids formed by decomposition of plant material (biomass). These precursors form a whole new suite of DBPs when groundwater is pumped up and chlorinated for potabl use. Many of these chemicals are suspected carcinogens or toxic. While sewage irrigation looks good on the surface, a more extensive look reveals a potential for serious contamination of groundwater. Municipalities and other entities responsible for irrigation with sewage effluent should do a groundwater impact analysis to develop management protocols and be prepared for liability actions. Those who benefit are local and state institutions in water resources, environmental quality protection, public health, consultants and operators of effluent irrigation projects. Technical Abstract: Using municipal wastewater for agricultural/urban irrigation is considered a safe practice if effluent is treated to reduce virus, bacteria, and parasite concentrations to acceptable levels (zero where there is a chance for human ingestion/close contact). Effects on underlying groundwater usually are not considered, but since chemicals in the effluent are leached dout of the root zone with much less water than was applied for irrigation, their concentrations in deep leaching or percolation water are much higher than in the effluent, especially where rainfall is low. These chemicals not only consist of salts and nitrate, but can also include disinfection byproducts (DBPs) that were first formed by chlorination of the drinking water and again by chlorination disinfection of the effluent, hormone and medical drug residues (pharmaceutically active chemicals or PACHs), and humic and fulvic acids and other organic compounds formed by decomposition of plant parts (biomass) in the soil. Since deep percolation water continues to move downward, the groundwater below effluent irrigation areas becomes contaminated with these chemicals. This is undesirable where groundwater is used for drinking, since DBPs can be carcinogenic, PACHs may disrupt hormone production and weaken immune systems, and humic and fulvic acids form a whole new suite of DBPs when the groundwater is chlorinated. Municipalities planning to use effluent for irrigation should do a ground- water impact analysis, and be prepared for long-term effects on groundwater and possible liability for groundwater pollution. |
