Researchers at The University of Texas at El Paso and Stanford University have made a surprising discovery – the natural community of zooplankton, known for grazing on bacteria, does not effectively clean water contaminated with fecal microorganisms. This research, published in the biology journal mSphere, offers important insights into the limitations of using zooplankton as a natural solution to treat bodies of water polluted with fecal matter. The study’s findings suggest that other factors, such as salinity, may play a more significant role in inactivating these harmful pathogens. Zooplankton and fecal contamination are key topics explored in this research.
Zooplankton, It Turns Out, Have Their Limits
Scientists at The University of Texas at El Paso and Stanford University found that the natural water-craving zooplankton – tiny, aquatic animals known to eat bacteria —resident in freshwater and saltwater fail to sufficiently clean water that has been compromised by fecal microorganisms. The work, published in the journal of biology mSphere — and led by researchers at Rutgers University–provides critical understanding on the challenges of using zooplankton as an ecosystem-based method for treating bodies of water polluted with fecal organisms.
According to a 2017 U.S. water quality inventory, over half of rivers, bays and estuaries were unsafe for one or more uses (often because of fecal contamination). Sewage discharged into clean bodies of water from illegal pipes or illicit lines and exposure of humans to sewage released in these bodies of water can make people sick, added Lauren Kennedy, Ph. Bijay K. Panthi, Ph.D., an assistant professor in civil engineering at UTEP and corresponding author on the study. Our work was done in an attempt to identify features that would make pathogens no longer able to infect humans. Put differently, to how long will an unprotected body of water return to a condition where it is safe for recreation?
Zooplankton Fail to Save the Day
To investigate the idea that potential microorganism grazers — in this case, existing zooplankton from water sources — would eat fecal contamination-borne microorganisms, and thereby “clean” the water, investigators put a nonpathogenic virus (MS2) and the bacterium E. coli into saltwater and freshwater samples gathered from various locations in California’s San Francisco Bay area. Kennedy said that MS2 and E.coli have been targeted by researchers as useful surrogates for scientific research, because they are highly concentrated in sewage and their presence often indicates the presence of fecal pollution in the environment.
The water samples already had both “large” particles (zooplankton, sand, dirt) and “small” or dissolved particles (like salt). The researchers discovered that the bigger particles, which contained zooplankton, had a negligible impact on the inactivation of those pathogen proxies. More, however, seemed to be due to the smaller particles. For instance, the pathogen proxies were effectively deactivated more readily in high salinity water such as ocean water from San Pedro Beach.
Insight for Better Water Remediation
Kennedy said, “I am glad that we were able to offer an alternative for surface water remediation. This represents a significant contribution to our knowledge of the constraints on zooplankton as natural “biocleansers” in contaminated waters, she said. In the next part of the study, researchers will be examining the effectiveness of salinity on pathogen inactivation in contaminated waters.
Carlos Ferregut, Ph. D., chair of the Department of Civil Engineering. Dr. Kennedy: Our research identifies the significant factors at play in pathogen inactivation, particularly in regions where wastewater can be a human health concern. The results of their research are an important part of the puzzle in exploring what helps to deactivate harmful pathogens and how we can develop better strategies for water remediation that will protect public health.
