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Analytical Methods

Pathogens and Chemicals. July 2014 

Pathogens and ChemicalsIdentifying the presence of specific pathogens can help understand sources of fecal contamination. Because viruses are often species-specific, monitoring for human-specific viruses (enteric viruses), such as adenovirus and enterovirus, can provide direct evidence of a human source. Two of the most common methods for examining water for enteric viruses are cell culture and quantitative polymerase chain reaction (qPCR). The cell culture method provides information on the infectivity of the viruses, but it is expensive and time consuming, requiring several weeks for confirmed positive results. The qPCR method is semi-quantitative, more rapid, and less expensive than the cell culture method; however qPCR is a molecular method that detects both infective and noninfective viruses. Monitoring for bacterial and protozoan pathogens provides less information than viruses on the source of contamination, but still provides information on human health risk. Many bacterial and protozoan pathogens are zoonotic, meaning that they could be transferred from animals to humans and cause disease in humans. These include E. coli O157:H7 and specific types of Cryptosporidium, Salmonella, or Campylobacter. However, Shigella spp. are exclusively transferred from humans to humans.

Chemicals found in human wastewater can be used to discriminate between human and animal fecal sources. For a suite of 78 wastewater chemicals detected in a national study (Glassmeyer and others, 2005), there was a higher frequency of detection in wastewater effluents than in water samples collected upstream. Chemical concentrations decreased downstream as distance from the outfall increased. Specifically, the distinct changes in concentrations of the fragrance chemicals ethyl citrate, galaxolide, and tonalide between the upstream, effluent, and two downstream sites suggest that they may be good indicator chemicals for human wastewater discharge.