Bioassays
Bioassays are experimental tests that utilize biological organisms to detect the presence of specific chemical substances or to assess the biological activity of known compounds in particular environments. They play a vital role in environmental science, particularly in evaluating the effects of pesticides and the resistance of plants to pests. Bioassays can be employed when scientists suspect the presence of a chemical but lack the necessary equipment for direct measurement or when no established protocol exists for detection.
A well-designed bioassay meets two essential criteria: specificity, ensuring that it measures the intended physiological response, and accuracy, reflecting responses observed in natural settings. Common applications include determining the median lethal dose (LD50), which identifies the concentration of a substance that kills half of a tested organism population, and assessing plant resistance to insect pests to reduce reliance on chemical insecticides. The ongoing need for innovative and improved bioassay methods highlights their significance in advancing our understanding of ecological interactions and fostering sustainable agricultural practices.
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Bioassays
DEFINITION: Tests that use biological organisms to detect the presence of given chemical substances or determine the biological activity of known substances in particular environments
Bioassays enable environmental scientists to evaluate the effects of the chemicals used in pesticides as well as the resistance of plants to particular pests.
In many instances, a scientist may suspect that a certain chemical is present in a given but may not have access to a specific piece of equipment designed to measure the presence of the chemical. In some cases, an experimental protocol for the detection of the chemical may not exist. In either of these cases, the scientist may be able to detect the presence of the chemical by using a biological that responds in a specific manner when exposed to that particular chemical agent. At other times, a scientist may know that a certain chemical is present but not know how a particular organism will respond when exposed to the agent. In this case, the scientist will expose the test organism to the chemical and measure a particular physiological response.
Bioassays are utilized in many different areas of the biological sciences, including environmental studies. Some methods work better than others. A good bioassay meets two basic criteria. First, it is specific for a given physiological response. For example, if a given chemical is responsible for inhibiting the feeding response of a particular insect, then the bioassay for that chemical should measure only the inhibition of feeding of that insect and not some other physiological response to the chemical. Second, a good bioassay measures the same response in the laboratory that is observed in the field. Again, if a particular chemical inhibits the feeding response in the field, then the laboratory bioassay for that chemical should also inhibit feeding. An ongoing need exists for the development of accurate bioassay methods as well as the improvement of existing techniques.
Many different bioassays are used in environmental studies. One of the most common is the measure of the median lethal dose (LD50)—the or dose of a chemical that will result in the deaths of one-half of a of organisms—of a new on species of and nonpest organisms. To conduct this bioassay, the test species is exposed to a wide range of different concentrations of the chemical. The concentration of the pesticide that kills one-half of the test organisms represents the LD50.
Another common environmental bioassay is the measure of of plants to a particular insect pest. In order to reduce the dependence on chemical insecticides, plant breeders are continually trying to develop insect-resistant plants, either through traditional breeding programs or by using to transfer resistance genes to susceptible crop strains. Bioassays are used to measure the degree of success of these attempts. In these bioassays, the same numbers of susceptible and resistant plants are subjected to infestation by equal numbers of the insect pest for which the breeder is trying to develop resistance. The two groups of plants are observed, and the degree of resistance, if any, is recorded.
Bibliography
Ohkawa, H., H. Miyagawa, and P. W. Lee, eds. Pesticide Chemistry: Crop Protection, Public Health, Environmental Safety. New York: Wiley-VCH, 2007.
Rand, Gary M., ed. Fundamentals of Aquatic Toxicology: Effects, Environmental Fate, and Risk Assessment. 3d ed. Boca Raton, Fla.: CRC Press, 2008.
Viegas, Cristina A. "Microbial Bioassays in Environmental Toxicity Testing." Advances in Applied Microbiology, vol. 115, 2021, pp. 115–158, doi.org/10.1016/bs.aambs.2021.03.002. Accessed 12 July 2024.