Environmental impact of Fipronil to the Louisiana crawfish industry

The Mermentau River Basin, located in southwestern Louisiana, is an agriculturally vital region. The 3,800-square-mile basin is a chief producer of rice and crawfish, which are grown in rotation on the same fields. The rice farmers face a constant problem in controlling rice water weevils (Lissorhoptrus oryzophilus), which feed on their rice crops. In 1998, the EPA banned the use of Furadan, which had been used to combat the rice water weevil nervous system. Furadan, also known by its chemical name carbofuran, weakens the nervous system by inhibiting cholinesterase and restricting the degradation of acetylcholine. The replacement for Furadan, issued in 1999, was Fipronil, sold under the brand name of Icon (TM). Fipronil is an arthropod-selective gamma-aminobutyric acid receptor antagonist. A low crawfish production in 2000 appeared to be correlated with the use of Fipronil on rice crops during the previous year. Fipronil and its degradation products strongly sorb to soils during the rice planting process, causing runoff from fields that have been seeded with Fipronil-laden rice to contaminate the surface water system. Fipronil-laden water that is pumped onto previously uncontaminated fields will kill crawfish within days of application. Fipronil degradates will persist in rice- and crawfish-producing fields, and will continue to worsen commercial crawfish-production for several proceeding years. This article details the findings and conclusions of studies performed on behalf of the affected farmers, as well as a review of studies on Fipronil conducted by Louisiana State University (LSU) Agricultural Center and their recommendations.