Study: Nanomaterials may create algae outbreaks, kill off waterways
Thursday, June 28, 2018
We’ve been here before. Nanoparticles getting onto the environment and fouling things up. In previous reporting here, it was plastic in the oceans. This time, though, we’re talking about something potentially more dangerous: chemicals.
According to a new study by Duke University, during the last decade there has been a surge in the use of tiny substances — nanomaterials — in agrochemicals like pesticides and fungicides. The idea is to provide more disease protection and better yields for crops, but decrease the toxins sprayed on agricultural fields.
However, when combined with nutrient runoff from fertilized cropland and manure-filled pastures, these nanopesticides could also mean more "toxic algae outbreaks for nearby streams, lakes and wetlands."
These particles are obviously too small to see, except with the most powerful microscopes. The engineered nanomaterials are substances manufactured to be less than 100 nanometers in diameter, many times smaller than a hair's breadth. Since the chemicals are so small, they are able to spread more quickly across a great area.
Because of the ability for these chemicals to spread easily, "they could intensify harmful algal blooms in wetlands," according to experiments led by Marie Simonin, a postdoctoral associate under biology professor Emily Bernhardt at Duke University.
Tiny carbon nanotubes and miniscule particles of silver, titanium dioxide and other metals are added to hundreds of commercial products to "make everything from faster, lighter electronics, self-cleaning fabrics, and smarter food packaging that can monitor food for spoilage." These same materials, the Duke researchers said, are also used on farms for slow- or controlled-release plant fertilizers and pesticides for more targeted delivery.
The outcome after 10 years of comprehensive use? Possibly harmful algae blooms in wetlands, Simonin and Duke biology professor Emily Bernhardt found.
The research team’s findings appear in the June 25 issue of the journal Ecological Applications.
The potential risks to human health or the environment aren't fully understood, Simonin said. However, these blooms can reduce oxygen levels to the point where fish and other organisms can't survive. If these blooms become toxic they may and can make pets and people who swallow them sick.
This is important research for a number of reasons, especially because the 260,000 to 309,000 metric tons of nanomaterials produced worldwide each year are disposed in landfills. Up to 80,000 metric tons per year are released into soils, and up to 29,200 metric tons end up in natural bodies of water.
"And these emerging contaminants don't end up in water bodies alone," Simonin said. "They probably co-occur with nutrient runoff. There are likely multiple stressors interacting." Nitrogen and phosphorus pollution makes its way into wetlands and waterways in the form of agricultural runoff and untreated wastewater.
"The excessive nutrients cause algae to grow out of control, creating a thick mat of green scum or slime on the surface of the water that blocks sunlight from reaching other plants."
During the tests, researchers set up 18 separate 250-liter tanks with sandy sloped bottoms to mimic small wetlands and each open-air tank was filled with water, soil and a variety of wetland plants and animals, such as waterweed and mosquitofish.
The experiments took place across nine months. Some tanks received a weekly dose of algae-promoting nitrates and phosphates like those found in fertilizers, some tanks got nanoparticles, and some tanks got both.
"The results were surprising," Simonin said. "The nanoparticles had tiny effects individually, but when added together with nutrients, even low concentrations of gold and copper nanoparticles used in fungicides and other products turned the once-clear water a murky pea soup color, its surface covered with bright green smelly mats of floating algae."
Across the experiments, the blooms were more than three times more frequent and more persistent in tanks where nanoparticles and nutrients were added together than where nutrients were added alone.
The bloom overgrowths reduced dissolved oxygen in the water, too. The results also suggest that nanoparticles and other "metal-based synthetic chemicals may be playing an under-appreciated role in the global trends of increasing eutrophication," the researchers said.
Eutrophication is the excessive richness of nutrients in a lake or other body of water, frequently from the runoff from the land, which causes a dense growth of plant life and death of animal life from lack of oxygen.
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