National Water-Quality Assessment (NAWQA) Program
Michael S. Majewski, U.S. Geological Survey, Sacramento, California, William T. Foreman and Donald A. Goolsby, U.S. Geological Survey, Denver, Colorado.
Beginning 31 May, 1994, a 20 day research cruise up the Mississippi River from New Orleans, Louisiana to St. Paul, Minnesota, was conducted on the Research Vessel Acadiana. One objective was to determine the occurrence, concentration, and geographical distribution of agricultural pesticides in air over the Mississippi River. The vessel traveled at a continuous speed of about 10 knots and averaged about 300 km per day. It stopped only to refuel and when locking through dams. Air samples were collected by pulling air through polyurethane foam (PUF) plugs at 100 liters per minute for 24 hours. Each air sample consisted of a primary and a secondary PUF plug. The secondary PUF was analyzed separately in selected samples to check for analyte breakthrough. Each sample was analyzed for 45 pesticides using gas chromatography with selected-ion mass spectrometry or flame-photometric detection. Twenty three pesticides were detected at ng/m3 concentrations. Among those detected were fourteen herbicides including atrazine, metribuzin, and trifluralin, six insecticides including chlorpyrifos, diazinon, and methyl parathion, and three pesticide degradation products, 2, 6-diethylanaline, deethyl atrazine, and p, p'-DDE. Eight pesticides were detected in 80% or more of the samples. The observed pesticide concentrations were compared to agricultural use by state along the river, and by use per hectare of crop land within a 40 km radius of the river. For example, molinate was detected only in the lower part of the river near the rice growing areas of Louisiana, Mississippi, and Arkansas, whereas EPTC, a corn herbicide, was detected only in the upper half of the river. These results show that pesticides can become airborne and their concentration in air can be correlated to local use.