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NATIONAL WATER-QUALITY ASSESSMENT PROGRAM FIPRONIL AND DEGRADATION PRODUCTS IN THE RICE-PRODUCING AREAS OF THE MERMENTAU RIVER BASIN, LOUISIANA, FEBRUARY- SEPTEMBER 2000 Significant Findings Maximum fipronil concentrations in water ranged from 0.829 to 5.29 µg/L (micrograms per liter) during March through April, corresponding to the release of ricefield tailwater. Fipronil degradation products in water were detected from February through June 2000. Aero- bic degradation products desulfinylfipronil and fipronil sulfone were detected at maximum con- centrations in March and April, similarly to the parent compound. Maximum concentrations of the anaerobic degradation product fipronil sulfide were detected in June. Concentrations of fipronil and degradation products in suspended sediment ranged from 1 to 10 percent of the concentrations in water. The parent compound fipronil is not accumulating in bed sediment. The anaerobic reduction degradation product fipronil sulfide was the predominant degradation product detected in bed sediment, and concentrations ranged from 0.636 to 24.8 µg/kg (micro- grams per kilogram). The degradation products desulfinylfipronil and fipronil sulfone also were frequently detected in bed sediment. INTRODUCTION cially-produced crawfish populations in the The banks generally are steep in the tributaries Mermentau River Basin. Traditional rice-cul- with cypress-water tupelo extending into the The Mermentau River Basin is a unique tivation practices include releases of ricefield stream. Along the lower reaches, banks often agricultural area located in southwestern water in the spring months. The effects of are not discernible as the water extends into a Louisiana. Historically, the area was a ricefield drainage on receiving waters and bottomland hardwood flood plain. The flood tallgrass prairie similar in many ways to the biota are not well understood. plain may abruptly end as it meets a ricefield tallgrass prairie in the midwestern United This report presents a study of the analy- levee system or roadway. Water velocities are States (Allain and others, 2000). The area typically less than 1 ft/s (foot per second). also is called coastal prairie or wet prairie ses of fipronil and three of its degradation products in water, suspended sediment, and Isolated flow reversals can occur in the tribu- (Brown, 1972). The distinctive prairie char- taries and canals draining into the river during acteristics of the basin are a result of an bed sediment. Samples were collected from 17 sites in the rice-producing areas of the Mer- periods of heavy pumping for rice irrigation. impermeable clay layer underlying the shal- The streambed substrate in the tributaries and low soils. Five major tributaries divide the mentau River Basin from February to Septem- ber 2000 collected as part of the U.S. main channel is silt and clay. The substrate in basin into a series of broad, flat areas ideal for the loops of the main stem and smaller tribu- agriculture. The areas are separated by bot- Geological Survey National Water-Quality Assessment (NAWQA) Program. This insecti- taries can also be a soft flocculent muck rich tomland hardwood riparian corridors that in organic matter. vary in width from only a hundred feet to sev- cide and its degradation products--desulfi- Total rice acreage in the seven parishes eral miles. Thus, the basin is characterized by nylfipronil, fipronil sulfide, and fipronil (Acadia, Allen, Evangeline, Jefferson Davis, a dendritic river system, low gradient, and a sulfone--were selected for discussion because Lafayette, St. Landry, and Vermilion) of the heavy clay soil. little information currently exists on the occur- rence and partitioning of this new insecticide Mermentau River Basin was almost 400,000 Most of the Mermentau River Basin has in the environment. acres in 1998 and about 340,000 acres in 2000 been altered for growing rice, sugarcane, for- (Louisiana Cooperative Extension Service, age, grain crops, crawfish production, and The Mermentau River Basin has a drain- 2 1998, 2000). The primary cause of the cattle grazing. Rice, however, is the most age area of about 3,800 mi (square miles) (Sloss, 1971). Land-surface elevations are less decrease in rice acreage was a drought in important agricultural crop produced in the south Louisiana which began in the spring of basin. Crawfish farming also occurs in rice- than 100 feet in most of the basin and range from 20 to 30 feet above the National Geodec- 1999 and lasted well into the summer and fall fields. The insecticide fipronil was licensed of 2000. Rice cultivation in this basin utilizes in 1996 (U.S. Environmental Protection tic Vertical Datum of 1929 along the Mermen- tau River main stem (Garrison, 1997). both ground and surface water (fig. 1) (B.P. Agency, 1996a), and the insecticide was Sargent, U.S. Geological Survey, written com- widely used on rice seed to control the rice Vegetation in the upper basin consists of mixed pine-hardwoods, but as the land flattens veg- mun., 2002). The decreased availability of water weevil beginning in 1999. In the sum- fresh surface water during the drought in the mer of 1999, public concern in Louisiana etation rapidly changes. The Mermentau River Basin in the mid-to-lower reaches is bordered southern part of the basin, especially Vermil- arose over the use of fipronil-coated rice seed ion Parish, resulted in less rice planted in 2000 and the apparent negative effects on commer- by a cypress-water tupelo riparian zone that is typically flooded for a large part of the year. than in 1998. U.S. Department of the Interior 1 USGS Fact Sheet FS-010-03 U.S. Geological Survey March 2003 young seedling to become anchored, about Bayou Queue de Tortue (table 1). One site 3 to 5 days. The field is then re-flooded until was located near the headwaters of each major the rice nears maturity. Releases of ricefield tributary and 1 to 2 sites were located mid- water (called tailwater) into drainage ditches reach or downstream. Two sites were located and streams result in high turbidities during on the Mermentau River main stem: Mermen- March through May. tau at Mermentau and Mermentau at Lake The flooding of fields also functions to Arthur. Mermentau at Mermentau is a long- suppress red rice, a wild variety with no com- term USGS water-quality site. Downstream mercial value (Linscombe and others, 1999), from Mermentau at Lake Arthur, tidal effects and to make ricefields easily adaptable for and the Gulf Intracoastal Waterway greatly crawfish farming. Most crawfish farming complicate data analysis and were excluded occurs in ricefields, either double-cropped with from this study of fipronil and three of its deg- rice or utilizing ricefields that are not in rice radation products. The sites were sampled production that year. There are more than monthly February to June 2000. Bed sedi- 80,000 acres of farm-raised crawfish in south- ment samples were collected from August 28 ern Louisiana, including about 40,000 acres in to September 6, 2000. the Mermentau River Basin in 2000. Sample Collection and Laboratory Study Design Analysis Prior to the public concern about fipronil, USGS personnel conducted extensive dis- an assessment of agricultural practices on cussions with the following organizations stream quality and aquatic invertebrates in the before sampling for fipronil and its degrada- Mermentau River Basin was designed as part tion products: Louisiana Department of Agri- of the NAWQA Program. The purpose of the culture and Forestry, Louisiana State assessment is to integrate surface- and ground- University Agriculture Center, including their water-quality data with information about Aquaculture Research Station and Rice aquatic invertebrate community structure to Research Station, and Bayer CropScience, the gain a more complete understanding of the fac- manufacturers of fipronil. tors, both natural and human-induced, that Water column samples were collected affect water quality in the Mermentau River according to methods described in Fishman Basin. The community structure of aquatic and Friedman (1989) and Shelton (1994). In invertebrates in this area is of interest because, those streams where water velocities were less in addition to their value as indicators of the than 1.5 ft/s, a weighted bottle sampler was overall health of the system, the ricefields of used to collect a depth-integrated sample. southwestern Louisiana are an internationally Samples were processed on site in a USGS important stopover site for invertebrate-eating mobile laboratory. For analysis of fipronil and Figure 1. Ground- and surface-water with- shorebirds during their spring migration. About degradation products on suspended sediment, drawals in the Mermentau River Basin, Loui- 2 siana, 2000. (Data from: B.P. Sargent, U.S. 3,200 mi of the Mermentau Basin are assessed the volume of water passing through a baked Geological Survey, written commun., 2002.) by NAWQA. Three major components of the glass-fiber filter was measured, and the glass- assessment have been completed, as follows: fiber filter was retained and frozen until Aerial application of seed onto flooded • 2000: Surface-water quality--Occurrence and analysis. Fipronil and degradation products fields is the predominant method of rice distribution of major inorganic ions, nutri- were analyzed at the USGS National Water seeding in southwestern Louisiana. After ents, and pesticides in water; also fipronil Quality Laboratory in Lakewood, Colorado. aerial rice seeding, the water is retained for and degradation products in water, sus- These compounds were not part of any about 1 to 2 days and released. The field is pended sediment, and bed sediment. standard USGS analyses prior to this study. allowed to drain only long enough for the • 2000: Ground-water quality--Occurrence and Personnel at the USGS laboratory developed a distribution of major inorganic ions, nutri- custom method for these analyses in filtered ents, trace elements, and pesticides including water. This method was a modification of an fipronil and degradates in shallow ground approved analytical method (Zaugg and water.

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