Rotenone is an organic compound that has been described as "by far the most important rotenoid." It is an odorless, colorless, crystalline isoflavone. It occurs naturally in the seeds and stems of several plants, such as the jicama vine, and in the roots of several other members of the Fabaceae. It was the first-described member of the family of chemical compounds known as rotenoids. Rotenone is approved for use as a piscicide to remove alien fish species, see Uses. It has also been used as a broad-spectrum insecticide, but its use as an insecticide has been banned in many countries.
Discovery The earliest written record of the now-known rotenone-containing plants used for killing leaf-eating caterpillars was in 1848; for centuries, these same plants had been used to poison fish. The active chemical component was first isolated in 1895 by a French botanist, Emmanuel Geoffroy, who called it nicouline, from a specimen of Robinia nicou, now called Deguelia utilis, while traveling in French Guiana. He wrote about this research in his thesis, published in 1895 after his death from a parasitic disease. In 1902 Kazuo Nagai, Japanese chemical engineer of the Government-General of Taiwan, isolated a pure crystalline compound from Derris elliptica which he called rotenone, after the Taiwanese name of the plant 蘆藤 (Min Nan Chinese: lôo-tîn) translated into Japanese rōten (ローテン). By 1930, nicouline and rotenone were established to be chemically the same.
Uses
Use as piscicide in fisheries management Rotenone is used as a nonselective piscicide (fish killer). Rotenone has historically been used by Indigenous peoples to catch fish. Typically, rotenone-containing plants in the legume family, Fabaceae, are crushed and introduced into a body of water, and as rotenone interferes with cellular respiration, the affected fish rise to the surface, where they are more easily caught. In modern times it is frequently used as a tool to remove alien fish species, as it has a relatively short half-life (days) and is gone from rivers in the course of days and from lakes within a few months, depending on (seasonal) stirring, organic content, availability of sunlight and temperature. Rotenone has been used by government agencies to kill fish in rivers and lakes in the United States since 1952, and in Canada and Norway since the 1980s. It is less frequently used in EU countries, due to strict regulations, but has seen some use in selected countries such as the UK (Topmouth gudgeon), Sweden (Pike, marsh frog, goldfish and pumpkinseed), Spain (Topmouth gudgeon, Gambusia) and Hungary (Prussian carp). Rotenone has also seen some use in other field studies in the marine environment needing only small quantities. Small-scale sampling with rotenone is used by fish researchers studying the biodiversity of marine fishes to collect cryptic, or hidden, fishes, which represent an important component of shoreline fish communities, since it has only minor, local and transient environmental side effects.
Rotenone degradation and ecosystem impact Rotenone primarily affects gilled organisms such as fish and aquatic invertebrates. Terrestrial animals such as birds, mammals, and amphibians (except tadpoles/larvae) are much less affected by rotenone. When applied in freshwater systems, the treatment dose kills the target fish and usually other gilled species like tadpoles and zooplankton are affected, depending on dosage. However, timing treatments in the fall or winter, when many species are less active, can reduce these impacts. Some taxa may also recover through natural life cycles, such as resting eggs. Its use is more benign for the environment (as compared to drying ponds, or using other piscicides), and studies show that most ecosystems naturally recover within one or two years after rotenone application- with aquatic invertebrates repopulating affected areas, thus restoring initial local biodiversity to its status prior to the introduction of the invasive species. Rotenone decays through metabolites and its final product is reduced to water and carbon dioxide. It oxidizes to rotenolone, which is about an order of magnitude less toxic than rotenone. In water, the rate of decomposition depends upon several factors, including temperature, pH, water hardness and sunlight. The half-life of rotenone in a pond of 1.1 mean depth ranged from half a day at 24 °C to 3.5 days at 0 °C, but in deeper oligotrophic systems (thus less degradation due to sunlight and organic content) the half-life may be considerably longer.
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