Rotenone is a naturally occurring chemical compound derived from the roots and stems of certain tropical and subtropical plants. Its primary function is as a broad-spectrum pesticide and piscicide, a substance that is toxic to fish. While it is a natural product, it is also highly toxic, leading to its use being both controversial and subject to strict regulation in many regions.
Sources and Applications
Rotenone is extracted from the roots and stems of specific leguminous plants, most notably those belonging to the Derris genus in Southeast Asia and the Lonchocarpus genus, also known as cubé root, in South America. The compound is obtained by drying and grinding the plant material into a fine powder, which is then subjected to a solvent extraction process to isolate the rotenone. This substance has been used for centuries by indigenous peoples to harvest fish and has been utilized commercially as an insecticide for over 150 years.
The applications of rotenone are primarily twofold. It has been used as a botanical insecticide in gardens and for some agricultural purposes, controlling a wide variety of pests like aphids and spider mites. However, its use as an insecticide has been banned in many places, including the United States and the European Union, due to its toxicity.
A more common application today is its use as a piscicide in fisheries and water resource management. Resource managers use rotenone to eradicate invasive fish species that threaten native ecosystems. By eliminating dominant, non-native fish, managers can restore a waterway and help native populations recover. It is used to remove aggressive species illegally introduced into lakes and rivers, which can outcompete or prey on native fauna.
Mechanism of Action
Rotenone’s toxicity stems from its ability to disrupt cellular energy production. It functions as a mitochondrial poison, targeting the process of cellular respiration. This process can be imagined as an assembly line where electrons are passed along protein complexes to produce adenosine triphosphate (ATP), the cell’s main energy currency.
Rotenone halts this process by inhibiting the function of a protein cluster known as Complex I, the first step in the electron transport chain. This binding action prevents electrons from being passed along, effectively shutting down the production of ATP.
This blockage of ATP synthesis leads to cell death and, on a large scale, the death of the organism. The mechanism is effective in fish because the lipophilic (fat-loving) nature of rotenone allows it to be absorbed efficiently through the gills. This direct interference with a fundamental cellular process explains its broad-spectrum toxicity.
Toxicity and Human Health Concerns
Exposure to rotenone can occur through inhalation of dust or spray, ingestion, and direct skin contact. Acute poisoning in humans is rare, partly because the compound is irritating and often induces vomiting if ingested, which can expel the substance before a fatal dose is absorbed. Symptoms of acute exposure can include respiratory irritation, nausea, and muscle tremors.
A significant concern is the link between rotenone exposure and Parkinson’s-like symptoms. Studies on laboratory animals show that rotenone can induce the selective damage to dopamine-producing neurons in the brain that is characteristic of Parkinson’s disease.
The risk is highest for those who handle the substance regularly, such as agricultural workers, pesticide applicators, and researchers. While a definitive causal link in humans is still under investigation, the evidence from animal models has prompted regulatory agencies to restrict its use and emphasize protective measures for handlers. One study noted that exposure during fetal development may impede proper brain development.
Environmental Fate and Ecological Effects
The high toxicity of rotenone to fish and aquatic invertebrates makes it an effective tool for fisheries management, as it is lethal to gilled organisms at very low concentrations. In contrast, its acute toxicity to birds and mammals is substantially lower, providing a margin of safety for non-target terrestrial animals during application.
Rotenone breaks down relatively quickly in the environment, a process accelerated by exposure to sunlight, heat, and oxygen. In warm water, its half-life—the time it takes for half of the substance to degrade—can be as short as a few days. This degradation transforms rotenone into less toxic, water-soluble components.
This rapid breakdown is a primary reason it is still considered a viable management tool. The potent effects are temporary, allowing a treated body of water to be detoxified naturally and eventually restocked with native fish species. While the initial application impacts the local aquatic ecosystem, including invertebrates and zooplankton, studies show that many ecosystems can recover as the chemical dissipates.