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Pesticide Affects Phytoplankton, Aquatic Food Chain

(Beyond Pesticides, January 25, 2007) The commonly used herbicide atrazine has been found to have negative biological effects on phytoplankton-free-floating algae that forms the base of the food chain for aquatic animals. The study, published in the January 2007 issue of the journal Pesticide-Biochemistry and Physiology, indicates that protein levels in phytoplankton significantly decrease as a result of atrazine exposure, possibly having a negative affect on the nutritional levels of all aquatic species.

The National Oceanic and Atmospheric Administration (NOAA) National Centers for Coastal Ocean Science researchers exposed five algal species to atrazine levels within the range of concentrations measured in the estuarine environment. In the majority of the species tested, the amount of energy converted into protein from photosynthesis, the process by which green plants convert water and carbon dioxide into organic materials using solar energy, significantly decreased with increased exposure.

Atrazine is one of the most heavily used herbicides in the United States, applied to a wide variety of crops including corn, sorghum, sugarcane, pineapple, and Christmas trees, as well as turf. It acts as an inhibitor of photosynthesis by preventing the transfer of energy in certain plant species. NOAA researchers observed significant decreases in the size of phytoplankton species exposed to atrazine, decreasing its nutritional value for those species for whom phytoplankton are a crucial food source.

“Many aquatic animals such as clams and oysters rely on phytoplankton as a food source,” said Marie DeLorenzo, Ph.D., NOAA research ecologist. “Disruption to the cellular composition of phytoplankton species may negatively affect nutritional levels of the plant, resulting in decreased growth rates for those animals that consume phytoplankton.”

“The use of atrazine as a growth inhibitor in broadleaf and grassy weeds is an accepted practice,” said Mike Fulton, Ph.D., a NOAA research fishery biologist. “But it is equally important to gain an understanding of the potential effects of this herbicide on non-target aquatic plant species.”

This finding adds to a growing body of literature documenting the widespread presence and subsequent danger of pesticides on water quality and aquatic organisms. For more information, see Beyond Pesticides’ new report Threatened Waters: Turning the Tide on Pesticide Contamination.


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