Characterization of selected organo-nitrogen herbicides in South Florida canals: exposure and risk assessments.
Much uncertainty exists regarding the discharge characteristics of terrestrial-use herbicides into aquatic systems. This study evaluated the temporal distribution and concentrations of five commonly used herbicides (atrazine, bromacil, metolachlor, norflurazon, and simazine) in a typical South Florida watershed. Surface water samples were collected weekly over a 3-yr period from four canals and Ten Mile Creek. These systems received drainage water from a variety of land-uses, including residential, pastures, and citrus production. Herbicides were extracted and analyzed by GC-MS/SIM. Atrazine was most frequently detected (87% of samples) in the canal serving the residentially developed sub-basin, with median and maximum concentrations of 0.43 and 6.67 μg L(-1), respectively. Norflurazon was most frequently detected (90-95% of samples) in the systems serving agricultural production areas, with median and maximum concentrations ranging from 0.37-0.63 μg L(-1) and 1.98-6.97 μg L(-1), respectively. Bromacil was detected in 14-36% of samples with median and maximum concentrations ranging from 0.50-0.67 μg L(-1) and 2.31-4.96 μg L(-1), respectively. Metolachlor was detected in 1.8-10% of the samples, with median and maximum concentrations ranging from 0.16-0.2 μgL(-1) and 0.17-1.55 μg L(-1), respectively. Simazine was detected in 10-35% of the samples, with median and maximum concentrations ranging from 0.18-0.28 μg L(-1) and 0.37-1.35 μg L(-1), respectively. Bromacil+norflurazon was the most commonly detected (240 samples of 1060 total) binary combination of herbicides; whereas bromacil+norflurazon+simazine was the most frequently detected tertiary combination (58 samples). While detectable concentrations were present for significant periods of time, risks of acute toxicity were relatively low; affecting <1% of the potentially affected fraction (PAF) of plant species based on 90th centile exposure concentrations and 10th centile effects concentrations from species sensitivity distributions.
University of Florida/IFAS Indian River Research and Education Center (Soil and Water Science Department), 2199 South Rock Road, Fort Pierce, FL 34945, USA. pcwilson@ufl.edu
P Chris
PC
Wilson
Brian J
BJ
Boman
D059001:Aquatic Organisms / Q000187:drug effects*; D004784:Environmental Monitoring / Q000379:methods*; D005431:Florida; D005618:Fresh Water / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry; D006540:Herbicides / Q000032:analysis / Q000633:toxicity*; D010944:Plants / Q000187:drug effects; D018570:Risk Assessment; D012621:Seasons; D012680:Sensitivity and Specificity; D013045:Species Specificity; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000633:toxicity*
D006540:Herbicides; D014874:Water Pollutants, Chemical