We tested the toxicity of pesticides to shrimp and phytoplankton to better understand the environmental risks of these chemicals. We found that pesticide toxicity can change with temperature and salinity. These results are being used to improve the ways that pesticides are applied in coastal areas.
Why We Care
Estuarine systems are considered especially sensitive to climate change, as they are already subject to considerable stress from pollution, dredging, habitat loss, and other human disturbances. Pesticides may enter estuarine waters from runoff of agricultural, golf course, and residential lawn treatments, and spray drift from mosquito control applications. Ecological risk assessments of pesticides use data from toxicity tests conducted under standard exposure conditions. Variation in water temperature and salinity may impact the toxicity of pollutants, both because of altered chemical fate and transport, and because of changes in physiological response. Thus standard toxicity bioassays may not provide enough information to assess the risks of pesticides in aquatic systems.
What We Did
We studied the effects of increased temperature and salinity, two potential impacts of global climate change, on the toxicity of pesticides to the estuarine grass shrimp, Palaemonetes pugio. P. pugio is an abundant crustacean inhabiting tidal marsh habitats along the U.S. Atlantic and Gulf of Mexico coastlines. It is important to energy flow in the coastal ecosystem because it accelerates the breakdown of plants and serves as a prey item for many important recreational fish species. It is sensitive to numerous pesticides, making it an excellent species to test for toxic effects.
We exposed larval and adult grass shrimp to two commonly used pesticides in the coastal zone (the fungicide chlorothalonil and the insecticide Scourge). In the southeastern United States, chlorothalonil is used primarily on home lawns and golf courses, whereas Scourge is used primarily for mosquito control.
We exposed the grass shrimp under:
- Standard toxicity test conditions
- An increase in temperature
- An increase in salinity
- A combined increased temperature and salinity exposure.
Similarly, we tested the effect of increased temperature and increased salinity on the toxicity of four common weed killers, or herbicides (atrazine, irgarol, diuron, and ametryn) to the phytoplankton, Dunaliella tertiolecta. Phytoplankton are important primary producers that serve as the base of aquatic food webs. Phytoplankton can serve as an early warning system of ecosystem stress.
What We Found
We found that toxicity of the fungicide chlorothalonil to shrimp increased with increasing temperature and salinity. The toxicity of the insecticide Scourge also increased with temperature, while increased salinity reduced Scourge toxicity, but only in adult shrimp. We found that herbicide effects on growth rate, cell density, and starch content of the phytoplankton Dunaliella tertiolecta were more pronounced under elevated salinity and temperature conditions. Therefore, changes in temperature and salinity may alter the toxicity of certain pesticides, and the nature of the effect will depend on both the organism’s life stage and the chemical contaminant.
Since temperature was the most significant factor affecting pesticide toxicity in the estuarine organisms we have examined thus far, we will focus our future research on temperature effects. Temperature is known to influence organism growth and activity. We plan to study how temperature changes affect sublethal biomarkers of pesticide toxicity, such as enzyme function, in grass shrimp. We also plan to expand the study to include other water quality variables such as pH and dissolved oxygen content.