Rotenone - Frequently Asked Questions
Rotenone is a naturally derived organic compound found in the roots of bean plants in South America and the Pacific. Traditionally used by Indigenous communities to catch fish for consumption, rotenone has been officially registered for fishery uses in the United States since 1947. Today it is the most common method used for controlling invasive fish species worldwide. Health Canada's Pest Management Regulatory Agency has reviewed and approved products containing rotenone for use in waterways in Canada. The following Frequently Asked Questions are borrowed from the American Fisheries Society's rotenone stewardship program. To view the source material, and other rotenone related information please visit: rotenone.fisheries.org
Q. How does rotenone work?
A. The toxicity of rotenone stems from its specific effect on cellular aerobic respiration (i.e., phosphorylation
inhibitor). This suspends utilization of oxygen for energy production at the cellular level, eventually leading to cardiac and neurological failure at the organ level. Rotenone is highly toxic to fish due to the rapid uptake across the gill surface. Waterfowl and other birds as well as mammals are comparably resistant.
Q. How and when is rotenone applied?
A. Rotenone liquid is typically packaged in 1-, 5-, 30- and 50-gallon containers and powder is typically in 50- and 200-pound containers. Applications are generally made with boats in lakes, reservoirs and ponds, with direct metering into moving water such as streams, and with hand-held equipment such as backpack sprayers in difficult to reach areas. Rotenone may be applied at any time of year, but most applications typically occur during warm months when the compound is more effective and degrades more rapidly. Rotenone is usually applied during low water conditions to limit amount of area treated and piscicide needed.
Q. How much rotenone is used?
A. The concentration of active rotenone used to eradicate fish varies with the target species and environmental conditions from 12.5 to 200 parts per billion; 12.5 to 200 parts of rotenone in 1,000,000,000 parts of water (equivalent to 0.07 to 1.1 pounds of rotenone in an Olympic-size swimming pool of 666,430 gallons).
Q. When is it appropriate to use rotenone?
A. It is appropriate to use rotenone in aquatic management situations where eradication (e.g. complete removal and elimination) of a target population of fish is required to prevent severe problems to a native ecosystem and reduction in biodiversity. Other fish management techniques such as physical removal and explosives only control, but do not eliminate, the IAS fish population.
Q. How safe is rotenone to the public and applicators?
Although rotenone is toxic to the nervous system of insects and fish, commercial rotenone products have presented little hazard to humans over many decades of use and are not considered a cause of Parkinson's disease. Millions of dollars have been spent on research in testing laboratories and environmental monitoring studies to determine the safety of rotenone prior to registration in the U.S. by the EPA and in Canada by the Pest Management Regulatory Agency. Extensive acute (short-term) and chronic (long-term) tests on rotenone have been conducted. Rotenone is not considered a carcinogen (capable of causing cancer), mutagen (capable of causing genetic mutation), teratogen (interferes with normal embryonic development), or reproductive toxin (affects reproductive capabilities). The public will be excluded from treatment areas until rotenone residues have dissipated to safe levels, and applicators wear safety gear to minimize rotenone exposure.
Q. Does rotenone use in fisheries management cause Parkinson's disease (PD)?
A. No. While there is little doubt that rotenone and other chemicals that directly inhibit the mitochondrial energy chain can, under certain laboratory exposure conditions, reproduce features of PD in animal models, studies that have shown these results involved the use of intravenous (directly into the vein), subcutaneous (below the skin) or intragastric (stomach tube) routes of exposure with the rotenone dissolved in solvents and stabilizers to enhance tissue penetration. The purpose of these studies was often to document possible PD models, not in finding the cause(s) of PD. These laboratory exposures limit their applicability to humans because these avoid the normal protective measures of the human body through dermal and oral exposure. For example, a two-year long study where rotenone was mixed in the food of rats, using much higher dosages of rotenone, did not produce PD pathology.
Q. What are the dangers from consuming fish from rotenone treated water?
A. Fish killed by rotenone should not be consumed by humans because of concern for salmonella and other bacteriological poisoning that may occur from consuming fish that have been dead for a period of time. The rotenone residues in dead fish carcasses are quickly broken down by physical and biological reactions.
Q. How are the effects of rotenone kept restricted to the treatment site?
A. Potassium permanganate, through a chemical reaction called oxidation, deactivates rotenone. Potassium permanganate can be injected into the flowing water stream at the point where the effects of rotenone are no longer desired. Potassium permanganate is used worldwide in treatment plants to purify drinking water.
Q. What happens to rotenone after it is applied to the water?
A. Rotenone is a compound that breaks down very rapidly in the environment. Rotenone degrades quickly through physical (hydrolysis and photolysis) processes and biological mechanisms. An increase in temperature or sunlight increases the breakdown rate.
Q. What is a safe level of rotenone exposure?
A. The EPA has suggested a safe level for rotenone in drinking water of 40 parts per billion and a safe level for water contact (e.g. swimming) of 90 parts per billion. These safe levels assume a conservative worst-case lifetime exposure to rotenone. These are conservative levels since most treatments result in rotenone residues persisting for no longer than a few weeks to a few months.
Q. Can rotenone-treated water be used for irrigation of crops?
A. As an additional precaution, water containing residues of rotenone cannot be used on crops. This does not mean that doing this is actually unsafe, it is just not allowed because a tolerance (rotenone residue level legally allowed on crops) has not been established.
Q. When can the public access the water after treatment?
A. The public will not be allowed in contact with the treated water until rotenone residues have dissipated below 90 parts per billion. Many treatments will occur at rotenone levels less than 90 parts per billion and contact can commence immediately after the treatment process has been completed.
Q. How long does rotenone persist in water and sediment?
A. Numerous monitoring studies have shown that rotenone residues typically disappear within about one week to one month, depending on environmental conditions. The half-life (time required for 1⁄2 of material to breakdown) for rotenone varies from about 12 hours to 7.5 days, and is inversely related to temperature. Rotenone is typically applied when water temperatures are warm to optimize effect on the fish and the breakdown rate in the environment. If necessary, potassium permanganate can be used to speed-up (within 30 minutes) the breakdown of rotenone.
Q. What are the dangers of contaminating ground water?
A. The ability of rotenone to move through soil is low. Rotenone is strongly bound to organic matter in soil so it is unlikely that rotenone would even enter ground water. Monitoring studies in ground waters adjacent to treatment areas have found no contamination associated with rotenone treatments.
Fish and Wildlife
Q. How does rotenone affect aquatic animals?
A. Because rotenone is selectively toxic to gill breathing animals, fish are the most sensitive, followed by aquatic invertebrates and gill breathing forms of amphibians. Benthic invertebrates appear less sensitive than planktonic invertebrates, smaller invertebrates typically appear more sensitive than their larger counterparts, and aquatic invertebrates that use gills appear more sensitive than those that acquire oxygen through the skin, or that use respiratory pigments or breathe atmospheric oxygen. Studies have shown that amphibians and invertebrates will repopulate an area after rotenone breaks down.
Q. Will wildlife be affected from consuming water or food containing rotenone?
A. Birds and mammals are tolerant of rotenone having natural enzymes in the digestive tract that neutralize rotenone. Birds and mammals that eat dead fish and drink treated water will not be affected. Rotenone does not concentrate in fish tissue, rotenone residues are broken down quickly in the environment, and rotenone is not readily absorbed through the gut of an animal eating the fish or drinking the water. Most fish quickly sink to the bottom of treated water and rapidly decompose making the likelihood of extended exposure through the diet of terrestrial animals very low. This difference in toxicity between fish and birds and mammals coupled with its lack of environmental persistence makes rotenone an ideal fish management substance.
Q. Will wildlife be affected by the loss of their food supply following a rotenone treatment?
A. During rotenone treatments, fish-eating birds and mammals can be found foraging on dying and recently dead fish for up to several days after treatment. Following this abundance of dead fish, a temporary reduction in food supplies may result until fish and invertebrates have been restored. However, most of the affected species are mobile and will seek alternate food sources or forage in other areas. In unique situations like the fledging of young raptors, dead fish may be brought into the treated water body for extended periods of time to provide for an uninterrupted food supply or the timing of the treatments can avoid periods of time when raptors are raising their young.