Bioassay
Bioassay
A bioassay is the use of a living organism to test for the presence of a compound or to determine the amount of the compound that is present in a sample. The organism used is sensitive to the compound for which the test is conducted. Thus, the effect observed is typically the death or deteriorated health of the test organism. Depending on the test organism, soil, air, or liquid samples can be assayed.
The classic historical example of a bioassay was the use of canaries by miners in past centuries. Because canaries are more sensitive than humans to noxious gases like methane, they reacted quickly to even small amounts of the gas. This would give the miners time to escape.
Today’s bioassays are more sophisticated than the canary. The ASTM (formerly known as the American Society for the Testing of Materials) has catalogued over 70 different bioassays. These are used to analyze soil, freshwater, and the sediment at the bottom of watercourses like streams and rivers, saltwater, and air.
Plants can be used as indicators of the presence of toxic compounds in the soil. In this bioassay, seeds or the mature plant is introduced into the soil of a site that is suspected of being contaminated. Failure of the seeds to germinate, or failure of the mature plant to thrive, can be evidence of contamination. If the assay is done in a controlled manner with the use of standards to provide reference points, then the geographical area of contamination can be determined.
Some species of plants can also be used to accomplish bioassays in the water. More commonly, however, the test organisms are single-celled organisms such as algae, water fleas (in particular a species called Daphnia magna, or fish (in particular the fathead minnow).
Bacteria can be used in bioassays. For example, the use of bacteria to detect and determine the amount of antibiotics or compounds that might be carcinogens in a sample has been practiced for decades. Another particularly useful bacterial bioassay involves the use of bacteria that have been designed to fluoresce (to emit light). If the bacteria are harmed by a toxic compound in the test sample, they fail to fluoresce. The decrease in fluorescence of bacterial populations is measured in a device called a spectrophotometer. The degree of decrease can be compared to standards in order to determine the concentration of the toxic compound.
With the wide variety of bioassays available, the investigator must choose the assay with care. The test organism used needs to be appropriate for the task, and must provide a result that is readily apparent. Being able to determine the level of the toxic agent (in other words being able to quantify the agent) can be very useful.
Bioassays continue to be developed. For example, bioassays can now detect the presence of some human hormones in the environment, the growth and metabolic activity of cells, and the potential therapeutic action of compounds.
Resources
BOOKS
Rahman, Atta-ur, M.Iqbal. Choudhary, and William J. Thomsen. Bioassay Techniques for Drug Development. Boca Raton: CRC, 2001.
PERIODICALS
DeMartini, David M., Lance R. Brooks, Sarah H. Warren, Takahiro Kobayashi, M. Ian Gilmour, and Pramila Singh. “Bioassay-directed fractionation and Salmonella mutagenicity of automobile and forklift diesel exhaust particles.” Environmental Health Perspectives. 112 (2004): 814-820.
Suszkiw, Jan. “Easy-to-use bioassay spots Varroa resistance.” Agricultural Research. 53 (2005): 19-20.
Brian Hoyle
Bioassay
Bioassay
A bioassay is the use of a living organism to test for the presence of a compound or to determine the amount of the compound that is present in a sample . The organism used is sensitive to the compound for which the test is conducted. Thus, the effect observed is typically the death or deteriorated health of the test organism. Depending on the test organism, soil , air, or liquid samples can be assayed.
The classic historical example of a bioassay was the use of canaries by miners in past centuries. Because canaries are more sensitive than humans to noxious gases like methane, they reacted quickly to even small amounts of the gas. This would give the miners time to escape.
Today's bioassays are more sophisticated than the canary. The ASTM (formerly known as the American Society for the Testing of Materials) has catalogued over 70 different bioassays. These are used to analyze soil, freshwater , and the sediment at the bottom of watercourses like streams and rivers , saltwater , and air.
Plants can be used as indicators of the presence of toxic compounds in the soil. In this bioassay, seeds or the mature plant is introduced into the soil of a site that is suspected of being contaminated. Failure of the seeds to germinate, or failure of the mature plant to thrive, can be evidence of contamination . If the assay is done in a controlled manner with the use of standards to provide reference points, then the geographical area of contamination can be determined.
Some species of plants can also be used to accomplish bioassays in the water . More commonly, however, the test organisms are single-celled organisms such as algae , water fleas (in particular a species called Daphnia magna, or fish (in particular the fathead minnow).
Bacteria can be used in bioassays. For example, the use of bacteria to detect and determine the amount of antibiotics or compounds that might be carcinogens in a sample has been practiced for decades. Another particularly useful bacterial bioassay involves the use of bacteria that have been designed to fluoresce (to emit light ). If the bacteria are harmed by a toxic compound in the test sample, then they fail to fluoresce. The decrease in fluorescence of bacterial populations is measured in a device called a spectrophotometer. The degree of decrease can be compared to standards in order to determine the concentration of the toxic compound.
With the wide variety of bioassays available, the investigator must choose the assay with care. The test organism used needs to be appropriate for the task, and must provide a result that is readily apparent. Being able to determine the level of the toxic agent (in other words being able to quantify the agent) can be very useful.
Bioassays continue to be developed. For example, in the mid-1990s, a bioassay was introduced to detect the presence of some human hormones in the environment.
See also Ames test; Bioluminescence; Ecological monitoring; Poisons and toxins.
Resources
books
Haynes, K., and J. Millar. Methods in Chemical Ecology, Volume II: Bioassay Methods. New York: Kluwer Academic Publishers, 1998.
periodicals
Pauwels, A., et al. "Comparison of Chemical-Activated Luciferase Gene Expression Bioassay and Gas Chromatography for PCB Determination in Human Serum and Follicular Fluid." Environmental Health Perspective 108 (June 2000): 553–557.
Traunspurger, W., et al. "Ecotoxicological Assessment of Aquatic Sediments with Caenorhabditis elegans (nematoda)—A Method for Testing in Liquid Medium and Whole Sediment Samples." Environmental Toxicology and Chemistry 16 (1997): 245–250.
Brian Hoyle
Bioassay
Bioassay
Bioassay refers to an evaluation of the toxicity of an effluent or other material on living organisms such as fish, rats, insects, bacteria, or other life forms. The bioassay may be used for many purposes, including the determination of: 1) permissible wastewater discharge rates; 2) the relative sensitivities of various animals; 3) the effects of physicochemical parameters on toxicity; 4) the compliance of discharges with effluent guidelines; 5) the suitability of a drug;
6) the safety of an environment ; and 7) possible synergistic or antagonistic effects.
There are those who wish to reserve the term simply for the evaluation of the potency of substances such as drugs and vitamins, but the term is commonly used as described above. Of course, there are times when it is inappropriate to use bioassay and evaluation of toxicity synonymously, as when the goal of the assay is not to evaluate toxicity.
Bioassays are conducted as static, renewal, or continuous-flow experiments. In static tests, the medium (air or water) about the test organisms is not changed, in renewal tests the medium is changed periodically, and in continuous-flow experiments the medium is renewed continuously. When testing chemicals or wastewaters that are unstable, continuous-flow testing is preferable. Examples of instability include the rapid degradation of a chemical, significant losses in dissolved oxygen , problems with volatility, and precipitation.
Bioassays are also classified on the basis of duration. The tests may be short-term or acute, intermediate-term, or long-term, also referred to as chronic. In addition, aquatic toxicologists speak of partial- or complete-life-cycle assessments. The experimental design of a bioassay is in part reflected in such labels as range-finding, which is used for preliminary tests to approximate toxicity; screening for tests to determine if toxicity is likely by using one concentration and several replicates; and definitive, for tests to establish a particular end point with several concentrations and replicates).
The results of bioassays are reported in a number of ways. Early aquatic toxicity data were reported in terms of tolerance limits (TL). The term has been superseded by other terms such as effective concentration (EC), inhibiting concentration (IC), and lethal concentration (LC). The results of tests in which an animal is dosed (fed or injected) are reported in terms of effective dosage (ED) or lethal dosage (LD). When the potency of a drug is being studied, a therapeutic index (TI) is sometimes reported, which is the dose needed to cause a certain desirable effect (ED) divided by the lethal dose (LD) or some other ED. Median doses, the amount needed to affect 50% of the test population, are not always used. Needless to say, an evaluation of the response of a control population of organisms not exposed to a test agent or solution during the course of an experiment is very important.
Quality assurance and quality control procedures have become a very important part of bioassay methods. For example, the U.S. Environmental Protection Agency (EPA) has very specifically outlined how various aquatic bioassay procedures are to be performed and standardized to enhance reliability, precision , and accuracy . Other agencies in the United States and around the world have also worked very hard in recent years to standardize and improve quality assurance and control guidelines for the various bioassay techniques.
[Gregory D. Boardman ]
RESOURCES
BOOKS
Manahan, S. E. Toxicological Chemistry. 2nd ed. Ann Arbor, MI: Lewis, 1992.
Rand, G. M., and Petrocelli, S. R. Fundamentals of Aquatic Toxicology Methods and Applications. Washington, DC: Hemisphere, 1985.