CLEMSON — A Clemson University graduate student is learning how environmental toxicants in freshwater systems affect aquatic organisms in the ecosystem, which can be used to determine water quality.
Namrata Sengupta, an environmental toxicology doctoral student, is determining how being exposed to the chemicals atrazine and triclosan affects starvation survival and reproduction of Daphnia magna, or water fleas.
Atrazine is an herbicide commonly used to control broadleaf and grassy weeds in corn, sorghum, sugarcane, pineapple, Christmas trees and other crops, as well as in conifer reforestation plantings. It also is used as a non-selective herbicide on non-cropped industrial lands and on fallow lands. Triclosan is an ingredient added to certain soaps, cosmetics, toothpastes, plastics and other materials to reduce or prevent bacterial contamination in the products. Sengupta’s study focused on how the Daphnia magna reacted after being exposed to these chemicals.
“One of the key things we are trying to understand from this research is what happens in a freshwater ecosystem, such as a river or pond, when these aquatic animals are exposed to multiple stressors at the same time,” Sengupta said. “A lot of research focusses on effect of individual stressors such as individual chemical contamination, temperature or drought. Our project looks at a mixture of chemical and dietary stressors to understand how animals respond differently to these different stressors.”
Daphnia magna is an invertebrate and low-to-middle on the food chain, but is still a very important indicator of what is going on in an aquatic ecosystem, Sengupta said. These organisms are being used because they are included in the Environmental Protection Agency’s aquatic toxicity test methods. Daphnia is an “excellent model organism” for ecology and toxicology research, she said.
“Studies using Daphnia magna can be translated to studies in other species or research that is done on higher species,” Sengupta said.
Key pieces of data involve treatment with the dietary fatty acid docosahexaenoic acid (DHA).
“When we did this work, if we treated with DHA, the animals lived longer,” said Bill Baldwin, a biology professor who also is Sengupta’s adviser. “And, to our surprise, they reproduced a little bit better.”
When triclosan was used, the organisms survived a little longer than when DHA was used, but their reproduction terminated when combined with dietary stress and they didn’t continue to develop.
“For some reason, when triclosan was used, the organisms were unable to continue to develop so they never entered in to an adolescent stage, never became adults and therefore never reproduced,” Baldwin said. “For some reason, triclosan blocked maturation.”
This is relevant because in a lot of instances it is difficult to get rid of triclosan.
“For example, wastewater treatment plants have problems getting rid of triclosan when it gets in their systems,” Sengupta said. “There are lot of pharmaceutical companies that are interested in triclosan research because it is put in a lot of products and eventually makes its way into water systems.”
The researchers also found that sphingomyelins built up in the triclosan group. Sphingomyelins are polar lipids found in animal cell membranes that help in maturation and development. They are associated with poor reproduction, and the researchers want to find out why they built up in the triclosan group, Baldwin said.
“The key thing that we’ve learned is that the sphingomyelins are higher in the triclosan group,” Baldwin said. “High sphingomyelins are not good, but high phosphatidylcholines are good and help with both the maturation and reproductive states.”
Phosphatidylcholine also is a polar lipid. Past research has shown phosphatidylcholine provides protection from toxicants.
The study is continuing to find out why the sphingomyelins increased and why they are not broken down.
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