Rotenone is the most commonly used compound for treating lakes. It has been used in numerous lakes and reservoirs in Oregon with great success to remove unwanted fish species and restore traditional fisheries. Diamond Lake was treated in 1954 with rotenone and treatment was 100 percent successful. Biologists believe the treatment can be repeated to restore this highly productive fishery.
Rotenone treatments are not without risks, however, and membersof the public have expressed concerns about how safe rotenone treatment is, how long residues remain and what the effects are on other wildlife in the area. In planning for the Diamond Lake treatment, many steps will be taken to isolate the treated water and minimize the risk of potential impacts to other waters and wildlife.
The following material was excerpted from the Sport Fish Restoration publication, "Better Fishing Through Management: How Rotenone is Used to Help Manage Our Fishery Resources More Effectively"
Today the public has a high awareness of the potential dangers of chemicals in the environment. The mere mention of the word "chemical" to some is often associated with "danger. Therefore, it is important to clearly define the properties of any chemical being used in our environment.
A question that might be raised by concerned citizens could be "Has rotenone been adequately tested to assure our personal safety and to protect the environment?" For answers to such questions, we must turn to the scientists who know the chemical best.
In recent years, we have heard a great deal about synthetic pesticides that were designed and produced in chemical laboratories. Some of these are so unique or unusual that they are not readily broken down by normal biological systems. Such synthetic compounds may persist for long periods in the environment. Where does rotenone fall in the gamut of modern pesticides?
Rotenone is a natural substance derived from several tropical and sub-tropical plants. Natives in Central and South America have used the juices of these plants for centuries to help them collect fish for food.
In developed countries, scientists have learned that dried roots of rotenone producing plants can be ground into a powder that is useful as a garden insecticide. For many years, it was also a widely used agricultural insecticide applied to crops and livestock to control insect pests. Unfortunately, because rotenone producing plants grow only in the wild, the supply is dependent on natives who locate, dig, and dry theroots for sale to wholesalers. In recent years, agricultural uses of rotenone have declined in the face of new synthetic pesticides that can be mass produced but fishery needs have continued.
This publication discusses how rotenone is used in fishery resource management, describes the testing that has been done, and lists the precautions that have been taken to assure the safety of rotenone to people and to the environment. Its purpose is to provide information based on research findings that will help you better understand fishery uses of rotenone as a fish control agent.
Q. What is rotenone?
A. Rotenone is a natural substance contained in the stems and roots of certain tropical plants, such as the Jewel Vine or Flame tree (Derris Spp.), Lacepod (Lonchocarpus spp.), or hoary pea (Tephrosia spp.).
Q. Does rotenone have other names?
A. Many products are sold that contain rotenone. Brand names include Chem Fish, Cube', Derrin, Derris root, Fish Tox, Nicoulins, Nusyn Nox fish, Prentox, Noxfish, rotenone dust, and Timbo powder.
Q. What other uses are there for rotenone?
A. Rotenone is used as a garden insecticide to control chewing insects, has been used as a dust on cattle, and is used as a dog and sheep dip, in addition to its use as a fish control agent.
Q. How does it work?
A. Rotenone does not "suffocate" fish as was long believed. Instead, it inhibits a biochemical process at the cellular level making it impossible for fish to use oxygen in the release of energy needed for body processes.
Q. Is rotenone a selective pesticide?
A. Although rotenone has some toxicity to all oxygen breathing animals, it is selective to fish at the concentrations used by fishery biologists. In general, most common aquatic invertebrates are less sensitive than fish to rotenone but some of the zooplankton are equally sensitive. Snails and clams are quite tolerant. With respect to fish, trout and salmon are the most sensitive, sunfish are less sensitive and catfish are the most resistant.
Q. Why is rotenone so selective?
A. Fish, insects, birds and mammals have natural enzymes that will detoxify sub-lethal amounts of rotenone. Fish are highly susceptible because rotenone is readily absorbed through their gills, and they cannot escape exposure to it.
Q. Can the toxic effects of rotenone be neutralized?
A. If biologists want to neutralize the effects of rotenone in lakes or rivers, potassium permanganate or chlorine can be used. These are added to the water at a 1:1 ratio with the concentration of rotenone applied plus sufficient additional compound to satisfy the chemical oxidation demand caused by organic matter that may be present in the treated water.
The toxicity can be reversed by placing affected fish in a water solution of methylene blue. If fish are captured early during a treatment, they may also be revived by placing them in untreated water. Success can be enhanced if the water is highly oxygenated or contains an oxidizing agent to detoxify any residual rotenone that may be on the gills or body surface.
Q. What happens to rotenone after it has been applied?
A. Rotenone is an unstable compound that breaks down when exposed to light, heat, oxygen and alkaline water. The breakdown process is very rapid. Scientists have been able to identify about 20 degradation products, most of which spontaneously break down to lesser non toxic substances. Ultimately, rotenone breaks down into carbon dioxide and water; two common substances.
Q. How long does it last?
A. How fast rotenone breaks down is affected by temperature, light, oxygen and alkalinity. Generally, most treatments are made during summer months. At 80° F, treated water will detoxify naturally in less than four days. As water cools, biological and chemical processes slow down and the breakdown of rotenone also slows. At 45° F, the toxicity to fish may last for 33 days. Detoxification may take longer in acid waters, in very soft water, or in deep stratified bodies of water. Generally, most lakes treated with rotenone completely detoxify within five weeks of treatment.
Rotenone is unstable and will degrade rapidly with exposure to light, heat, oxygen and alkaline water. In natural waters, other factors that influence the degradation rate and therefore reduce the toxic effect include the presence of organic debris, turbidity, lake shape and depth, dilution by inlets and runoff and the dosage used. The presence of ice and snow cover may prolong the toxic effect.
If desired or necessary, a treatment can be ended or toxicity can be removed by adding oxidizing chemicals, such as potassium permanganate or chlorine, to accelerate the natural breakdown of rotenone.
Q. Is rotenone likely to enter ground water and pollute water supplies?
A. The mobility of rotenone in soil is low to slight. The expected leaching distance of rotenone in soils would be only two cm (less than one inch) in most types of soils. An exception would be in sandy soils where the expected leaching distance is about eight cm (sightly more than three inches). Rotenone is strongly bound to organic matter in soil, so it is unlikely that it would enter ground water, even if it had not degraded.
Because of its rapid breakdown, rotenone leaves only temporary residues that would not persist as pollutants of ground water supplies.
Q. Why use a chemical fish control agent?
A. Fishery resource managers have tried many ways to manipulate fish populations. Although some approaches are useful in special circumstances, most are only partially effective. Others take several years before the outcome is evident, and some apply only to one or two species.
Use of a fish toxicant enables managers to establish a definite population at a specific time and makes it possible to clearly follow growth and abundance of the re-stocked species.
Q. Why not harvest the problem species?
A. Generally, the problem species are gizzard shad, carp, and bullheads. These are fish that have very high reproduction rates and that are very tolerant of declining water quality. If predator populations are over fished, so many young of the problem species survive that they soon may represent over 90 percent of the fish present. When this occurs, the lake or stream becomes filled with small, stunted fish. Gizzard shad cannot be caught on hook and line and they have no food or market value. Although some large carp and bullheads may be taken by anglers or commercial fishermen, they are generally not very popular species. The commercial value of these fish is also quite low. Commercial fishing will remove the largest fish but the space provided by their removal is usually filled by even more young carp, shad, or bullheads.
Q. How is rotenone applied?
A. It is applied as a wettable paste/powder or an emulsifiable spray concentrate that contains about 5 percent rotenone. It is usually diluted and applied through drip stations, or sprayers, or pumped through a hose into the propeller wash of a power boat. Aerial applications are sometimes made.
Q. Is it cost effective?
A. A Washington State researcher estimated that for each dollar spent on rotenone and stocked trout, anglers gained between $32 to $105 worth of fishing. On non treated trout lakes, the gain from fish stocking alone was between $10 to $15.
Q. When is the most effective time to treat with rotenone?
A. For most fish, the toxicity is greatest between 50ï and 75ï F. Rotenone persists for only a short time at high temperatures. Consequently, biologists usually try to treat during warm months when the waters will quickly detoxify and can be restocked at a time when hatchery raised fish are available. However, applications made in the fall and winter are also quite effective.
Q. How much is used?
A. Treatments range from 0.5 parts per million (ppm) to 5.0 ppm of the commercial products (5 percent formulations). The most typical treatment rate is 2 ppm. The actual amount of rotenone involved in a 0.5 ppm treatment would be 25 parts per billion (ppb) active ingredient; at 5 ppm, it would be 250 ppb.
Q. How do biologists determine when it is safe to restock?
The simplest test used by most fishery specialists is to put several fish in a cage and hold them in the treated water for several days. If they survive, the water is safe for restocking. Analytical techniques can also be used to determine how much rotenone is still present.
How often are treatments made?
A. Although treatments are usually 99 to 100 percent effective, rotenone rarely kills every fish. Occasionally, some areas cannot be effectively treated. In general, the benefits from treatments will last for five to 15 years; most are good for about 10 years.
Q. How soon can we expect fishing to improve after a rotenone treatment?
A. Fish stocking can begin as soon as biologists determine that it is safe to re-introduce fish. Generally, small fish are stocked because they are cheaper. This means more can be stocked but a longer time will be required for them to grow to catchable size. Depending on the growing season, most waters will have good fishing within two to three years after treatment. As a general rule, aquatic invertebrate populations return to pre treatment levels within several months to one year.
Q. What about residue levels in dead fish or those that survive?
A. Rotenone in dead, dying or surviving fish degrades at about the same rate as that in the water. Surviving fish quickly eliminate rotenone residues from their bodies. The maximum residue in fish flesh expected from a rotenone treatment of 5.0 ppm at 74ï F would be about 0.15 ppm.
Mammals and birds that ingest rotenone by drinking treated water or by eating dead fish would simply digest it without any toxic effect. Most warm blooded animals also have effective natural enzymes that would destroy small amounts entering the blood stream. However, hogs are uniquely sensitive and should not be treated with rotenone.
Q. Is it safe to eat fish killed by rotenone?
Calculations that address a worst case situation indicate that a 132 pound person would have to consume 535 pounds of raw fish containing 100 ppb rotenone to acquire a toxic dose. Cooking destroys rotenone so there would be a further loss of any residues during cooking. However, because no tolerance (acceptable residue level permitted in fish flesh) has been set by EPA, the consumption of rotenone killed fish cannot be recommended.
Q. Do some fish build up resistance to rotenone?
A. Some insects are becoming more tolerant of modern pesticides. Since rotenone is not persistent in the environment and because fish reproduce at a much slower rate than insects, acquired resistance has not been a problem.
Q. Are fish eggs affected by rotenone?
A. Research indicates that fish eggs are much more resistant to rotenone treatments than larval or adult stages. For example, newly fertilized rainbow trout eggs were 41 to 106 times more resistant; salmon eggs are 10 times more resistant than the fish and carp eggs are 50 times more resistant.
Q. How does rotenone affect the environment?
A. Rotenone is non-persistent so there is no accumulation in the water, soil, plants, or surviving animals. Because it breaks down so rapidly, its environmental significance does not extend beyond one year. For example, populations of aquatic invertebrates that have been reduced may take from several months to one year to recover to their former numbers. Surviving organisms will grow and reproduce at an accelerated rate due to reduced competition. While adult frogs and other amphibians would not be seriously affected, tadpoles and juvenile salamanders probably would be killed. For these species, it would be the next breeding season before more animals would be produced and the populations would be slower to recover.
Q. How safe is rotenone to people?
A. In 1973, a Spanish investigator claimed that rotenone fed to six rats resulted in mammary tumors in three of the animals. Many investigators have since tested rotenone on large numbers of animals; some using the very same approach as the Spanish study. None has observed any tumor-inducing effects. EPA has ruled that the Spanish study was not valid and that the allegations are not supported by sound scientific evidence.
Q. Just how well was rotenone studied before EPA reached its conclusion that it does not cause cancer?
A. Rotenone was fed daily to rats, mice and dogs in studies that ranged from six months to two years. In two studies, high levels were fed daily through three generations with no evidence of significant adverse effects. No tumor induction was observed, even when 75 ppm was fed daily to rats or when 1,200 ppm was fed to mice. In the tests with both males and females of each species, there was no firm evidence that rotenone caused any increase in the incidence of tumors. In some lots, treated animals had significantly fewer tumors than untreated groups.
Q. Might rotenone affect fertility or the ability to have offspring?
A. Extensive testing using levels up to 75 ppm in the daily diet of rats through two generations showed no effects on sexual performance, fertility, pregnancy, fetal development, or on the ability to sire or to produce normal offspring. Slightly reduced weights were observed at birth, but high doses of rotenone have a bitter taste so the test animals consume less feed.
Q. Does rotenone cause birth defects?
A. Studies have shown that daily oral doses up to 15 mg/kg per day in pregnant mice and up to six mg/kg/day in pregnant rats caused no abnormalities among developing young.
Q. Is rotenone likely to cause inherited or genetic disorders?
A. Results of studies using DNA repair, cytogenic analysis of bone marrow cells, embryonic mouse cells, eukaryotic microbial tests, and DNA synthesis tests showed no evidence that rotenone causes mutations or chromosome damage.
Q. Does rotenone cause muscle, kidney, liver or other physiological problems?
A. Rotenone is highly toxic to insects and fish but represents little risk to people or other mammals. This characteristic makes it a useful pesticide. However, rotenone does affect living cells. See the question about how rotenone works for information on its mode of action.
If a massive dose is administered or received, warm blooded animals will exhibit reduced pulse, reduced heart contractions, and a drop in blood pressure. The rate and depth of breathing increases but peristalsis in the gut is reduced. Levels of sodium, potassium, chlorides, and glucose in the urine increase. All of these effects are temporary and they cease as soon as the exposure ends.
Acute poisoning (as might be caused by the swallowing of extremely high doses) causes nausea, vomiting, gastric pain, muscle tremors, incoordination, convulsions and stupor. Death may result. No human deaths due to rotenone poisoning have been reported in published literature.
Q. What is the danger associated with accidentally drinking rotenone treated water?
A. The hazard associated with such an event is very low because of the low concentration of active ingredients used in treatments and the rapid breakdown of rotenone. Estimates of oral toxicity to humans are 300 to 500 mg rotenone per kg of body weight. Thus, a 132 pound person would have to drink over 60,000 liters (15,790 gallons) of treated water at one sitting to receive a lethal dose. When a 1,000 X safety factor is included, a person could drink 14 liters of treated water per day and still be well below the most conservative safe intake level.
Q. What can people or municipalities who draw their water from a lake or stream that is to be treated do to avoid drinking rotenone treated water?
A. Normal treatment of water drawn from a lake or stream should remove or destroy any traces of rotenone. Charcoal filtration and chlorination would both protect users from exposure to any rotenone that might temporarily occur. Potassium permanganate could also be added to destroy any rotenone that might be present.
Q. How soon can people enter the treated water?
A. In 1981, EPA concluded "that there was no reason to restrict the use of rotenone in waters intended for irrigation, livestock consumption, and recreational swimming uses". Even though there is no health risk, as a precaution, swimmers should consider waiting for four hours before entering a treated pond or lake.