Rotenone is a naturally occurring compound that can be used as a broad spectrum insecticide, piscicide, and pesticide. Used in fish management programs, Rotenone is used in a variety of ways: to study fish populations, to control the spread of invasive fish species, and to control the spread of fish diseases by killing infected fish. The ultimate goal of using Rotenone in fisheries management is to restore native (or desirable) fish and to return the natural aquatic environment to a healthy state.
The use of Rotenone dates back centuries to indigenous populations of South America that used Rotenone extracted from the roots and stems of plants. These cultures used Rotenone as a fishing tool. Rotenone would kill the fish, which could then be eaten. In the United States, Rotenone has been used as a fisheries management tool for over 50 years, and currently over 30 states use Rotenone as a fisheries management tool(1). Even though Rotenone has been used extensively in the United States since the 1930s, its misuse has lead to an increase in awareness of possible unwanted ancillary effects, and the need for environmental impact studies.
Rotenone is a nonspecific piscicide that not only kills unwanted fish, but all fish in an aquatic system. If used improperly, Rotenone can also have harmful effects on aquatic life other than fish, such as macroinvertebrates, zooplankton, and phytoplankton(2).
Therefore, Rotenone should be used carefully after a full risk assessment and its concentration in the environment should be monitored during and after its use(3). State agencies that use Rotenone, including the California Department of Fish and Game, the Washington Department of Game and Wildlife, and the Michigan Department of Natural Resources, have prepared extensive environmental studies of Rotenone use in fisheries management(4).
Because Rotenone is not soluble in water, emulsifying agents are added to most commercially used formulas, as well as synergists like piperonyl butoxide and a variety of chemical stabilizers and solvents. Piperonyl butoxide is a cytochrome P450 inhibitor, which is a group of enzymes that is one of the primary detoxification pathways for Rotenone in fish, and therefore, inhibiting P450 allows Rotenone to remain in fish for a longer period of time and thus, increase its efficacy. The final concentration of Rotenone needed to achieve various control objectives can be as high as 250 ppb, but concentrations as low as 5 ppb have been found to have piscicidal activity(5). As a result, initial concentrations of Rotenone need to be determined, as well as the concentration at different time intervals post application, to ensure the efficacy of the treatment and that Rotenone has dissipated to nontoxic levels. Also, aquatic systems to which these Rotenone formulations have been applied should be tested for any synergists, as well as any chemical emulsifiers, carriers, and solvents(3).
The half life of Rotenone in the environment is a function of a variety of factors and ranges from several hours to several weeks. These factors include pH, temperature, and exposure to light. Therefore, samples taken from the surfaces of lakes and streams are likely to have different concentrations of Rotenone than samples taken at greater depths.
The degradation of Rotenone has been found to be dependent on temperature, with a half life of 23 hours at a water temperature of 5 degrees C, but a half life of only 10.6 hours at a water temperature of 25 degrees C(4). Temperature dissipation rates for Rotenone were even more pronounced in water containing sediments and ranged from 20 days in cold water pond sediment to only 1.5 days in warmer pond sediment(6).
Rotenone degradation has also been found to be dependent on the pH of the water in which it is placed. Studies have shown that at a pH of 5, Rotenone had a half life of only
12.6 days(7). At a pH of 7, Rotenone had a half life of 3.2 days, and at a pH of 9, Rotenone had a half life of 2.0 days(7).
One of the most critical factors affecting Rotenone degradation in aquatic systems is exposure to light. Rotenone has been shown to be extremely sensitive to photolysis, with a half life of only 21 hours in the top 1 cm of water exposed to light, but with a half life of up to 191 days in 2 meters of water(8).
Because of all of these factors, aquatic systems treated with Rotenone cannot be labeled as nontoxic until the systems have been analyzed for Rotenone and its degradation products, as well as other chemicals found in various Rotenone formulations. The analytical methods used to determine the levels of Rotenone (and other chemicals) must be sensitive enough to detect these compounds in the low ppb levels and specific enough to ensure identification of each compound.
Nonspecific methods of detecting Rotenone include ultraviolet and infrared analysis. However, these methods can lead to an overestimation of Rotenone content due to interferences by other rotenoid compounds and Rotenone degradation products(9).
Although 20 degradation products of Rotenone have been found, only Rotenelone has been found to be toxic(10). Therefore, liquid chromatography has been used to separate individual rotenoid compounds, and ultraviolet detection is used for quantification.
However, many regulatory agencies now require analytical methods to provide specificity by using diode array detection in order to obtain a complete ultraviolet profile or mass spectrometry to obtain mass identification of the compounds of interest.
The analytical methodology employed at the Hauser Division of Microbac Laboratories, Inc. utilizes the separating power of high performance liquid chromatography coupled with diode array detection/identification and mass spectrometry identification/quantification. Please contact Microbac at microbac_info@microbac.com for determination of Rotenone by HPLC/MS.
REFERENCES
McClay, W., 2000. Rotenone Use In North America (1988-1997), Fisheries Management, Vol. 25, No. 5, 15-21.
Bradbury, A., 1986. Rotenone and Trout Stocking. n.p.: Washington Department of Game, fisheries management division.
EPA, 1992. Framework for Ecological Risk Assessment, EPA/630/R-92/001, updated in the Guidelines for Ecological Risk Assessment (1998).
4. WDG 1986. MDNR 1990, WDW 1992, CDFG 1994.
Kinney, E., 1965. Rotenone in Fish Pond Management. USDI, Washington, D.C. Leaflet FL-576.
Gilderhus, P., V. Dawson V, and J. Allen. 1986. Persistence of Rotenone in Aquatic Environments at Different Temperatures. Report No. Rot 83-988-02. National Fishery Research Laboratory, U.S. Fish and Wildlife Service.
Thomas, R., 1983, Final Report: Hydrolysis of [6-[Carbon-14]] Rotenone: Project No. 0301A, Borriston Laboratories, Inc. Temple Hills, MD for the U.S. Fish and Wildlife Service (MRID 00141409).
EPA, 2006, Environmental Fate and Ecological Risk Assessment for the Reregistration of Rotenone [Phase IV (final) EFED chapter], Docket # EPA-HQ-OPP-2005-0494-0035.
Delfel, N. E., 1976. Ultraviolet and Infrared Analysis of Rotenone: Effect of Other Rotenoids, Journal of the AOAC, Vol. 59, No. 3, 703-707.
Cheng, H.-M., I. Yamamoto, and J. E. Casida, 1972. Rotenone Photodecomposition,
J. Agric. Food Chem., Vol. 20, No. 4, 850-856.
Authored by: Peter Perrone – Microbac Laboratories, Inc
