Researcher monitors pathogen levels in Rio Grande water
By Jenna Smith
For more information regarding this subject, contact:
George DiGiovanni
(915) 859-9111
gdigiovanni@ag.tamu.edu
Although the Rio Grande is a major source of drinking and irrigation water for counties in the El Paso area, limited research on waterborne pathogens has been performed.
For the first time, George Di Giovanni, associate professor of environmental microbiology at the Texas A&M Agricultural Research and Extension Center in El Paso, is monitoring Cryptosporidium and Giardia pathogen levels in Rio Grande water from El Paso to Fabens, using new molecular methods and a recently developed United States Environmental Protection Agency (USEPA) method.
Cryptosporidium and Giardia are two microorganisms responsible for numerous waterborne and foodborne disease outbreaks.
The water quality in the study area may be affected by several different sources, including agricultural return flows, urban runoff, waterfowl and effluents from local wastewater treatment plants. These potential sources are upstream from the American Diversion Dam and the head of the American Canal. Water diverted into the American Canal is used for irrigation and drinking water during the irrigation season, which typically runs March through October.
“We want to evaluate the levels of Cryptosporidium and Giardia in our water supply, because high levels of these pathogens may pose a risk to drinking water and safe agriculture,” he said. “Under the recently proposed USEPA Long Term 2 Enhanced Surface Water Treatment Rule (LT2), drinking water treatment plants using surface water must adhere to treatment requirements based on levels of Cryptosporidium in their supply water.”
Although Di Giovanni reports that Giardia is found at higher levels, Cryptosporidium is the focus of the USEPA LT2.
“Cryptosporidium is more difficult to disinfect with conventional treatment methods than Giardia,” he said. “Also, because it is much smaller than Giardia, filtration procedures at treatment plants don’t remove as much Cryptosporidium. Under LT2, if average Cryptosporidium levels in surface supply waters are found to be higher than 0.075 per liter, additional treatment beyond current conventional treatment will be required.”
According to Di Giovanni, chlorination used in conventional wastewater treatment easily kills indicator organisms such as fecal coliform bacteria but not Cryptosporidium and Giardia. Effluent may be negative for indicators but still contain high levels of potentially infectious Cryptosporidium and Giardia.
Di Giovanni’s research has revealed large seasonal differences in levels of Cryptosporidium and Giardia in Rio Grande water. Pathogen levels are much higher during the non-irrigation season than during the irrigation season.
Fortunately, during the non-irrigation season, drinking water plants use groundwater instead of Rio Grande water due to the low river flow and salinity, Di Giovanni said. During the irrigation season, releases from Elephant Butte reservoir and return flows increase the volume of river water, and lead to a 20-fold or greater decrease in levels of Cryptosporidium and Giardia.
“Our goal for this project is to determine the levels, animal and human sources, and health risks posed by Giardia and Cryptosporidium in river water,” he said. “Not all species and strains of Cryptosporidium and Giardia from animals can cause disease in humans.”
Di Giovanni believes that in the near future, upgrading conventional wastewater treatment plants with technologies such as ultraviolet treatment and advanced filtration methods could help further decrease pathogens in wastewater effluents.
“Hopefully, we will have feasible routine pathogen monitoring methods for treatment plants,” he said.
“Water quality regulations are still trying to catch up with science on the occurrence of waterborne pathogens and protection of our water resources. Significant advances have been made in drinking water treatment, but additional preventive measures are needed at wastewater treatment plants to protect water quality.”
