Studies to distinguish between human and animal faecal pollution using F-RNA coliphages and faecal sterols

Abstract

Human enteric viral infections are considered to be predominantly associated with human wastes, as opposed to animal wastes, and a distinction between these has benefits for water quality control and risk assessment. A variety of techniques have been described to distinguish between human and animal faecal pollution of water. F-RNA (male-specific) coliphages have been classified into four sero-groups and evidence has been presented that two of these sero-groups are specific for human excreta and the other two for animal excreta. Certain chemical compounds such as the faecal sterols cholesterol and coprostanol yielded valuable results in attempts to distinguish between faecal pollution of human and animal origin.
In this study the application of F-RNA coliphages and faecal sterols to distinction between human and animal excreta has been investigated. Faecal sterols were extracted from water and analysed by gas chromatography using published methods that were adapted for the detection and quantification of cholesterol and coprostanol. Wastewater containing predominantly animal excreta was collected from cattle, pig and chicken feedlots. Wastewater containing predominantly human excreta was collected from hospitals.
Results revealed that F-RNA coliphages isolated from wastewater from four different hospitals consisted almost exclusively of genotypes 2 and 3. Only F-RNA coliphage genotypes 1 and 4 were detected in all three wastewater samples from cattle feedlots, while F-RNA coliphage genotypes 1, 3 and 4 were detected in all three chicken feedlot wastewater samples. Five wastewater samples from pig feedlots contained typically F-RNA coliphage genotypes 3 and 4.
Cholesterol and coprostanol were detected in ranges of 28 to 1 013 ƒÊg/. and 19 to 1 441 ƒÊg/. in wastewater, respectively. Coprostanol concentrations were more than double the cholesterol concentration in wastewaters from hospitals and pig feedlots in the five samples analysed. The opposite applied to wastewater from cattle and chicken feedlots, where cholesterol concentrations in all seven samples were higher than coprostanol concentrations. Analysis of wastewater from a poultry feedlot yielded a high cholesterol:coprostanol ratio and the presence of predominantly F-RNA coliphage genotype 4, confirming the specificity of these determinants for animal wastes.
The results of this study confirmed earlier reports on the specificity of F-RNA coliphage genotypes 1 and 4 for animal wastes, and genotypes 2 and 3 for human excreta, in a part of the world where investigations using these methods are limited. The same applies to the higher ratio of coprostanol: cholesterol in human excreta, and the higher ratio of cholesterol: coprostanol in animal excreta. The observations suggested that further optimisation of applying these indicators in combination may lead to the development of procedures for the meaningful distinction between faecal pollution of human and animal origin in quantitative terms.