Monitoring of β-D-galactosidase activity as a surrogate parameter for rapid detection of sewage contamination in urban recreational water

Abstract

Simple, automated methods are required for rapid detection of wastewater contamination in urban recreational water. The activity of the enzyme β-D-galactosidase (GAL) can rapidly (<2 h) be measured by field instruments, or a fully automated instrument, and was evaluated as a potential surrogate parameter for estimating the level of fecal contamination in urban waters. The GAL-activity in rivers, affected by combined sewer overflows, increased significantly during heavy rainfall, and the increase in GAL-activity correlated well with the increase in fecal indicator bacteria. The GAL activity in human feces (n = 14) was high (mean activity 7 × 107 ppb MU/hour) and stable (1 LOG10 variation), while the numbers of Escherichia coli and intestinal enterococci varied by >5 LOG10. Furthermore, the GAL-activity per gram feces from birds, sheep and cattle was 2-3 LOG10 lower than the activity from human feces, indicating that high GAL-activity in water may reflect human fecal pollution more than the total fecal pollution. The rapid method can only be used to quantify high levels of human fecal pollution, corresponding to about 0.1 mg human feces/liter (or 103 E. coli/100 mL), since below this limit GAL-activity from non-fecal environmental sources may interfere.