Tiny water fleas could play a big role in filtering out drugs, pesticides and industrial chemicals from wastewater to make it safe, according to scientists.
“We’ve developed our bioequivalent of a Dyson vacuum cleaner for wastewater, which is very, very exciting,” said study co-author Karl Dearn, a professor of mechanical engineering at the University of Birmingham.
Treatment plants do not remove all of the persistent chemical pollutants in wastewater from industry, so they often end up in rivers, streams and irrigation systems. This harms the biodiversity of these ecosystems and pollutes our food and water, but many of the current options for water filtering are expensive, carbon-costly and can be polluting themselves.
So the scientists turned to a natural filter that they say is eco-friendly, low-cost and scaleable – water fleas.
Members of the genus Daphnia are not actually fleas but a group of more than 450 species of tiny crustaceans that filter feed, ingesting any small particles of detritus, algae or bacteria in their path.
“I had my ‘A-ha!’ moment and I thought, ‘Wait a second, they can absorb chemicals’,” said Luisa Orsini, an environment professor at the University of Birmingham and co-author of the study published in the journal Science of the Total Environment.
The scientists selected four types of water flea that consume some of the pollutants that worry public health professionals the most: the pharmaceutical compound diclofenac, the pesticide atrazine, the heavy metal arsenic and the industrial chemical PFOS, which is often used to make clothes waterproof.
To find the fleas that would be best suited to tackle these pollutants Orsini resurrected some dormant embryos stuck in sediment at the bottom of rivers. Their embryos are encapsulated in a case that sinks to the bottom of lakes and waits for better conditions to hatch – but if that time does not come they can lie dormant for centuries.
She selected embryos from times when these pollutants were most rampant, or not present at all – selecting strains from 1900, 1960, 1980 and 2015. “Either the naive or the very experienced ones were doing a better job at filtering chemicals,” said Orsini.
Once in the lab, they grew the flea populations by cloning and tested their genetic makeup and survival skills. Orsini’s team then tested their vacuuming abilities, first in an aquarium, then in 100 litres of water, and are now using them in a real treatment facility with more than 2,000 litres of water. The next step will be to move up to 21m litres.
In the lab the water fleas sucked up 90% of the diclofenac, 60% of the arsenic, 59% of the atrazine and 50% of the PFOS. In an outdoor environment with conditions similar to a wastewater treatment plant, they performed similarly.
“Removing 50% of PFOS is excellent compared to whatever exists now because nothing removes or metabolises PFOS like this,” said Orsini. “And [other approaches are] extremely costly, producing a lot of toxic byproducts.”
The fleas are self-sustaining as they reproduce by cloning and they self-regulate, growing or decreasing in population according to the nutrients available.
Given the adaptability of these crustaceans to many different habitats, it should be possible to adapt this system to a large variety of environmental conditions and needs, according to Joseph R Shaw, an environmental toxicologist from Indiana University who was not involved in the study.
Since it is cheap and carbon-neutral, this solution could be used in sophisticated water treatment plants and in developing countries with less infrastructure, he said.
“This system is poised to be a gamechanger,” said Shaw. Adding technologies such as gene editing could even lead to developing “super-Daphnia” to target specific chemicals of interest and to improve the efficiency of collection.
“I’m a big fan of Daphnia. The sky’s the limit,” he said.