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United States Department of Agriculture

Agricultural Research Service

Research Project: CONSERVATION EFFECTS ASSESSMENT IN THE SOUTH GEORGIA LITTLE RIVER Title: Atrazine fate and transport within the coastal zone in southeastern Puerto Rico

Authors
item Potter, Thomas
item Bosch, David
item Dieppa, Angel -
item Whitall, David -
item Strickland, Timothy

Submitted to: Marine Pollution Bulletin
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 2012
Publication Date: February 27, 2013
Citation: Potter, T.L., Bosch, D.D., Dieppa, A., Whitall, D.R., Strickland, T.C. 2013. Atrazine fate and transport within the coastal zone in southeastern Puerto Rico. Marine Pollution Bulletin. 67:36-44.

Interpretive Summary: Agriculture is a primary land-use in the Jobos Bay National Estuarine Research Reserve (JBNERR) watershed located on Puerto Rico’s southeast coast. Crop production in near-shore areas depends on pesticides for weed, disease and insect control. There are continuing concerns about their potential for adverse impacts on the Bay and bordering wetland habitats. We evaluated pesticide fate and transport from a farm field adjacent to JBNERR’s Mar Negro mangrove forest region. Active ingredients and selected degradates of products used for silage production were monitored in shallow groundwater, drainage ditches, and estuarine waters. Residues, levels detected and their timing indicated that surface water drainage associated with tropical storm events is a primary pathway for pesticide residue transport. Companion studies showed that loading of a frequently used product, atrazine, to Mar Negro and the Bay was likely reduced due to very rapid degradation in cropland soil. We conclude that mitigation measures including storm water detention and treatment, and improved pest management practices are needed to protect Mar Negro and other critical JBNERR habitats.

Technical Abstract: Herbicide transport from crop-land to coastal waters may adversely impact water quality. This work examined potential atrazine impact from use on a farm field adjacent to the Jobos Bay National Estuarine Research Reserve on Puerto Rico’s southeastern coast. Atrazine application was linked to residue detection in shallow groundwater. Findings also indicated that residues moved with prevailing groundwater gradients toward the estuary. However, the quantity of atrazine transported via this pathway appeared small. Relatively high atrazine concentration was detected in one near-shore estuary water sample. This was likely due to farm field runoff during a tropical storm that passed through the area 3 days after atrazine was applied. After subsequent runoff events, atrazine and its two dealkylated degradates (DIA and DEA) were near or below detection limits in estuary samples. Contributing factors were the timing of runoff events relative to atrazine application and very rapid atrazine dissipation (DT50=1-3 days) in field soil. Soil dissipation studies indicated that adapted degradation conditions had developed in the field due to repeated atrazine treatments. To improve weed management in the field, atrazine replacement with other herbicide(s) is recommended. If active ingredient(s) selected have greater soil persistence runoff risks may be increased.

Last Modified: 10/19/2014
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