通过指示生物进行水质分析

Monitoring water samples for each unique pathogen associated with fecal pollution is not feasible due to extensive labor, time, and costs. Indicator organisms provide a simple, rapid, and cost-effective way to detect fecal contamination. Their presence correlates with pathogen presence, allowing water safety assessment without testing for every individual disease-causing microorganism.

Indicator organisms must be detectable when pathogens are present and absent when pathogens are absent. Their numbers must correspond with pathogen levels. They should persist longer in the environment than pathogens and be tougher. Finally, detection must be easy, safe, inexpensive, and effective across all water types.

Total coliforms are found in mammalian guts but also occur naturally in soil and surface water. Fecal coliforms, typically E. coli, reside entirely within gastrointestinal tracts of mammals and birds and are continuously shed in feces. Because fecal coliforms are exclusively from fecal sources, they serve as more specific indicators of fecal contamination than total coliforms.

For total coliforms, added ONPG is converted to nitrophenol, turning the water yellow. For fecal coliforms, E. coli converts MUG to methyl-umbelliferone product that fluoresces blue-green under ultraviolet light. These color changes and fluorescence signals confirm the presence of indicator organisms in the water sample.

After incubating a sample-reagent mixture in a partitioned tray, positive wells are counted and categorized by size. The number of small positive wells is located on the chart's top axis, and large positive wells on the left axis. The intersection provides the Most Probable Number, representing the estimated organisms per 100 milliliters of water sample.

US drinking water supplies must contain zero total coliforms per 100 milliliters to be deemed safe for human consumption. Treated wastewater must also achieve zero detectable indicator bacteria before release into the environment or repurposing for human use. These strict standards protect public health by ensuring pathogenic contamination is minimized.

Sodium thiosulfate is a powdered reagent included in sample bottles to neutralize chlorine that might be present in water samples. This neutralization is essential because residual chlorine can interfere with indicator organism detection and compromise test accuracy, ensuring reliable results for water quality analysis.