Organisms associated with feces, known as “fecal indicator organisms,” are closely monitored to assess the potential for fecal contamination of surface water bodies in the United States. However, the impact of the complex mixtures of chemicals and the natural microbial community within surface water on fecal indicator organism persistence remains poorly understood.
Researchers from The University of Texas at El Paso and Stanford University were recently astonished to discover that the natural community of zooplankton, tiny aquatic animals that typically graze on bacteria, do not effectively clean water contaminated with fecal microorganisms. This groundbreaking research sheds light on the limitations of zooplankton in treating bodies of water contaminated with fecal organisms.
The findings are particularly significant in light of the 2017 U.S. water quality inventory, which revealed that over 50% of rivers, bays, and estuaries were unsafe for at least one use, largely due to fecal contamination.
“When sewage is released into clean bodies of water and humans are exposed to it, it can lead to illness in humans,” said Lauren Kennedy, Ph.D., assistant professor of civil engineering at UTEP, who is the corresponding author on the study. “Our research seeks to understand what factors can render pathogens unable to infect people. In other words, how long does it take for the water to become safe for recreation again without any forms of outside intervention?”
Kennedy explained that water from sewage and septic tanks can accidentally enter bodies of freshwater due to accidents, inadequate water treatment, or corroded infrastructure.
The authors hypothesized that zooplankton naturally present in water might graze on microorganisms from fecal contamination, inactivating the organisms and effectively “cleaning” the water.
To test this idea, the team added a virus called MS2 and the bacteria E.coli to samples of freshwater and saltwater taken from the San Francisco Bay area of California. MS2 and E.coli are considered useful proxies for scientific research, Kennedy said, because they are present at high concentrations in sewage, and their presence often indicates fecal contamination in the environment. The water samples naturally contained both “large” particles like zooplankton, sand, and dirt and “small” or dissolved particles like salt.
They found that the large particles, including zooplankton, did not have a significant effect on the inactivation of the pathogen proxies. The small particles, however, seemed to have a greater impact. The pathogen proxies were inactivated at higher rates in high-salinity water, such as ocean water taken from San Pedro Beach.
The research marks a significant leap in our understanding of the constraints on zooplankton as natural “cleaners” of polluted water. The upcoming stages of the study will delve into the effects of salinity on pathogen survival in contaminated waters.
“I am proud to see this important work coming from our team,” said Carlos Ferregut, Ph.D., chair of the Department of Civil Engineering. “The research by Dr. Kennedy and her team provides valuable insights into the challenges of pathogen inactivation, especially in areas where wastewater can compromise human health.”
Journal reference:
- Lauren C. Kennedy, Ava M. Mattis, Alexandria B. Boehm. You can bring plankton to fecal indicator organisms, but you cannot make the plankton graze: particle contribution to E. coli and MS2 inactivation in surface waters. mSphere, 2024; DOI: 10.1128/msphere.00656-24