by Andrew Curry
A freshman at Colorado College, Andrew Curry learned to overcome hardship at the early age of five, when both his parents were killed in an automobile accident. A dedicated student and athlete, he was recognized as Scholar-Athlete of the Year in 1997 by Mount Miguel High School in San Diego, CA. He plans to pursue a career in medicine or international business. The following article describes his studies of the effects of Malathion on phytoplankton productivity, which received the PPNF award of Second Place in Environmental Sciences at the 1997 Greater San Diego County Science Fair.
In a large community with a variety of environmental features such as lakes, streams, and small stagnant ponds, insects can thrive. These insects can pose a hazard to plants and crops, carry diseases and be a nuisance to everyone. The most common method for removing these “pests” from the environment is by using an insecticide or pesticide such as Malathion. Malathion, probably today’s most widely used organophosphorus insecticide, is sold as a general purpose insecticide for household, home garden, vegetable and fruit insect control, and for controlling mosquitoes and flies. In addition, Malathion is often applied to crops through aerial spraying or crop dusting.
Malathion is a potential hazard to the environment both directly and indirectly. The possibility of this product seeping through the ground and into freshwater lakes as runoff is likely. In these lakes reside oxygen-producing plants called phytoplankton. My studies show that although Malathion is designed to target animals and not plants, when introduced into a lake it has a deleterious effect on phytoplankton.
Phytoplankton are the most photosynthetic members of the plankton community. Their most important function is the conversion of solar energy and CO2 to oxygen during photosynthesis. The phytoplankton converts the carbon dioxide produced by fish and other aquatic life into usable dissolved oxygen.
We can measure the “biological health” of phytoplankton by its productivity, that is, by the amount of dissolved oxygen it produces. With a decline in phytoplankton in a particular lake, the lake loses its oxygen supplier and becomes anoxic (without oxygen), and therefore animal life cannot survive.
Measuring the productivity of phytoplankton can be accomplished by measuring of the amount of dissolved oxygen in a sample of water. I took phytoplankton culture samples “in-situ,” with a range of concentrations of Malathion similar to those thought to occur as the result of urban runoff. The samples were allowed to culture for 72 hours. They were then removed, transported to the lab, and tested for dissolved oxygen content using a dissolved oxygen meter.
The results of the trials showed that the pesticide Malathion does have a significant negative effect on phytoplankton productivity. In other words, the higher the concentration of Malathion in the water, the lower the level of phytoplankton productivity. This means that high concentrations of Malathion in our lakes can reduce the populations of fish and other aquatic life.
In order to better understand the effects of Malathion, a long term study would be necessary. In such a study, it is recommended that more cultures be run simultaneously in various positions around the lake. This would eliminate any variance caused by changing weather conditions and other variables. Also, the cultures could be allowed to culture “in-situ” for longer periods to determine long-term effects on the phytoplankton and to allow for the presence of representative seasonal variations in the amount of dissolved oxygen. Also, research could be conducted to learn more about the effect the depletion of phytoplankton communities might have on animals higher up on the food chain. Knowledge of the effect of Malathion on the environment should encourage researchers to look for less environmentally-impacting substances to reduce nuisance insects.
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