Agricultural pesticides and selected degradation products in five tidal regions and the main stem of Chesapeake Bay, USA

Abstract

Nutrients, sediment, and toxics from water sources and the surrounding airshed are major problems contributing to poor water quality in many regions of the Chesapeake Bay, an important estuary located in the mid-Atlantic region of the United States. During the early spring of 2000, surface water samples were collected for pesticide analysis from 18 stations spanning the Chesapeake Bay. In a separate effort from July to September of 2004, 61 stations within several tidal regions were characterized with respect to 21 pesticides and 11 of their degradation products. Three regions were located on the agricultural Delmarva Peninsula: The Chester, Nanticoke, and Pocomoke Rivers. Two regions were located on the more urban western shore: The Rhode and South Rivers and the Lower Mobjack Bay, including the Back and Poquoson Rivers. In both studies, herbicides and their degradation products were the most frequently detected chemicals. In 2000, atrazine and metolachlor were found at all 18 stations. In 2004, the highest parent herbicide concentrations were found in the upstream region of Chester River. The highest concentration for any analyte in these studies was for the ethane sulfonic acid of metolachlor (MESA) at 2,900 ng/L in the Nanticoke River. The degradation product MESA also had the greatest concentration of any analyte in the Pocomoke River (2,100 ng/L) and in the Chester River (1,200 ng/L). In the agricultural tributaries, herbicide degradation product concentrations were more strongly correlated with salinity than the parent herbicides. In the two nonagricultural watersheds on the western shore, no gradient in herbicide concentrations was observed, indicating the pesticide source to these areas was water from the Bay main stem.

Metolachlor metabolite (MESA) reveals agricultural nitrate-N fate and transport in Choptank River watershed

“…In addition, the resulting stream water attenuated nitrate-N concentration relative to the groundwater without evidence for MESA diminishment (data not shown). These observations in conjunction with previous studies (Denver et al, 2010;Phillips et al, 1999;Steele et al, 2008;McConnell et al, 2007) indicate that 1) MESA is stable even in anaerobic …”

“…As shown above and elsewhere (Denver et al, 2010;McConnell et al, 2007;Phillips et al, 1999;Steele et al, 2008), MESA is a stable, soluble indicator for agricultural waters and has a long half-life in surface waters (Huntscha et al, 2008). The residence time of waters in the Choptank River estuary has been estimated to be 19 days (Bricker et al, 2007).…”

“…The limit of quantitation for nitrate-N was 0.01 mg N/L. MESA was analyzed using procedures published previously (McConnell et al, 2007). Briefly, samples were filtered through 0.7 μm GF/F filter paper (Whatman, Inc., Florham Park, NJ) prior to processing.…”

Comparison of marine sampling methods for organic contaminants: Passive samplers, water extractions, and live oyster deployment

“…The concentrations of atrazine found in the Housatonic River are also higher than those found by Garabedian et al (Garabedian et al, 1998) but comparable to those detected by Whitall et al (Whitall et al, 2010) in a Chesapeake Bay tributary and McConnell et al (McConnell et al, 2007) in the Chester River. Garabedian et al (Garabedian et al, 1998) analyzed samples collected in 1992, over 20 years ago.…”

Investigation of the Potential of Near Infrared Spectroscopy for the Detection and Quantification of Pesticides in Aqueous Solution

“…Due to the low solubility of the selected pesticides in water, working stock solutions at 100 mg·L -1 were prepared by direct dilution in a solvent of 1:1 methanol/ water (v/v) using deionized water from a Milli-Q water purification system (Millipore, Molsheim, France) [10]. Further dilutions were made by serial dilution in this solvent to create a series with the following concentrations: 50, 20, 10, 5, 2.5, 1 mg·L -1 (ppm).…”