Scientists were recently taken aback by the discovery that zooplankton — tiny aquatic creatures known for consuming bacteria — present in both freshwater and saltwater do not effectively purify water tainted with fecal microorganisms.
Scientists at The University of Texas at El Paso and Stanford University were recently taken aback by the discovery that zooplankton, which are tiny aquatic organisms that feed on bacteria, in both freshwater and saltwater, do not effectively purify water contaminated with fecal microorganisms.
This research, published today in the biology journal mSphere, highlights the limitations of zooplankton in cleaning water bodies polluted with fecal organisms, according to the research team. A 2017 assessment of water quality in the U.S. found that more than 50% of rivers, bays, and estuaries were unsafe for at least one use, often due to fecal pollution.
“When sewage is released into clean water and people come into contact with it, it can result in health issues,” stated Lauren Kennedy, Ph.D., assistant professor of civil engineering at UTEP and the lead author of the study. “Our research aims to identify the factors that can stop pathogens from infecting humans. Essentially, we want to know how long it takes for water to become safe for recreational use without any external help.”
Kennedy noted that water from sewage systems and septic tanks can unintentionally enter freshwater sources due to spills, insufficient treatment, or deteriorated infrastructure.
The research team proposed that the zooplankton found in water might consume microorganisms from fecal contamination, thus inactivating them and effectively “cleansing” the water.
To investigate this hypothesis, the researchers introduced a virus called MS2 and the bacteria E. coli to water samples collected from both freshwater and saltwater in the San Francisco Bay area of California. According to Kennedy, MS2 and E. coli are valuable for scientific studies because they are found in high numbers in sewage and their presence frequently signals fecal contamination in the environment. The water samples naturally contained both “large” particles like zooplankton, sand, and dirt, as well as “small” particles or dissolved substances like salt.
The findings revealed that the larger particles, which include zooplankton, did not significantly influence the inactivation of the pathogen proxies. In contrast, the smaller particles appeared to have more impact. For instance, the pathogens were inactivated more effectively in saline water, particularly ocean water sourced from San Pedro Beach.
“I am delighted that we could offer a new perspective for surface water remediation strategies,” Kennedy expressed.
She also mentioned that this research is a crucial step in grasping the limitations of zooplankton as natural “cleaners” for polluted water. Future research phases will investigate how salinity affects pathogen survival in contaminated waters.
“I am proud to see this significant work emerging from our team,” remarked Carlos Ferregut, Ph.D., chair of the Department of Civil Engineering. “The research conducted by Dr. Kennedy and her team provides crucial insights into the difficulties associated with pathogen inactivation, particularly in regions where wastewater poses a risk to human health.”
