Genetically Pinpointing Pollution Sources
Tracing the source of contamination in surface water can be complicated. When high numbers of “indicator” bacteria, such as E. coli, are detected in a water sample, scientists diagnose fecal contamination. But where are the feces from?
Fecal contamination can come from any number of sources—septic tanks percolating into the groundwater, overflow from wastewater treatment plants, and runoff from livestock feeding operations are the usual suspects. Even deer and elk droppings or waste from dogs and cats have been blamed for water pollution problems. How can a community take action against contamination and prevent a problem from happening again unless sources of the problem are located?
“Traditional water quality testing tells you that you have contamination, but not where the contamination comes from,” explained Katharine Field, a microbiologist with OSU’s Agricultural Experiment Station. Field developed a molecular test to determine the source of fecal contamination in water, detection that is both faster and far more specific than traditional standard fecal coliform tests.
Field developed a method that detects bacteria other than the usual indicators for feces, choosing a group of anaerobic bacteria (they grow without oxygen) that are associated with feces. “These bacteria are both more common and more diverse than coliforms, and there are more genetic markers,” she explained. “But anaerobic bacteria are a pain to grow, because they can’t be exposed to oxygen or they die.”
Her solution was to use molecular methods to avoid having to grow the bacteria. “We use gene amplification to detect the presence of gene sequences, called markers, that are unique to particular strains of bacteria found in just one host species.”
Field and her colleagues have developed techniques to assay polluted water samples directly for the presence of marker genes, revealing the source of the fecal contamination. Their technique has been able to detect the difference between fecal bacteria from many species, including humans, cows, dogs, pigs, horses, and elk. Knowing the source helps managers focus on fixing the problem.
Field’s methods are currently in use in many parts of the United States and the world. With a patent pending, she continues to standardize the procedure so that a simple kit can contain everything needed to perform the test.