Influence of Soluble Organic Matter on Cryptosporidium Parvum Oocyst Mobility in Variable Charge Soils
07/15/06 – 07/14/09
Cryptosporidia are pathogenic protozoa that are present in the digestive tracts of a wide range of vertebrates. Runoff water can carry Cryptosporidium oocysts (a tough dormant form) from manure to source waters (such as rivers and lakes). If this water is not properly treated before drinking, the pathogen can be ingested by humans and cause diarrhea and a variety of other gastrointestinal problems. In 1993, a massive outbreak of gastrointestinal illness in Milwaukee, Wisconsin was attributed to poor performance of a drinking water treatment plant and large numbers of protozoa in runoff waters. More than 400,000 cases of stomach illness, and about 120 deaths (primarily among individuals with compromised immune systems) were recorded.
Recent US Environmental Protection Agency regulations require surface water treatment plants to remove 99.99% of Cryptosporidium oocysts through sand filtration. This high degree of removal is often not achievable. Therefore watershed management practices to reduce the numbers of Cryptosporidia in runoff waters are needed to prevent their getting into the drinking water source water in the first place.
Goal and Design of Study:
Although there have been several studies on the fate and transport of Cryptosporidium oocysts in temperate soils, this had not been addressed in tropical soils. The charge of most soils on the US mainland (temperate) does not change with solution pH. However, soil charge varies with pH in tropical soils.
This research examined how soil pH, organic compounds (such as compost, sludge, wastewater), and the salinity of soil pore water affect the attachment of Cryptosporidium oocysts to tropical soils. The study findings clarified if Cryptosporidium oocysts are a major problem in tropical as they are in temperate soils.
Dr. Chittaranjan Ray
Water Resources Research Center
University of Hawaii at Manoa