Determination and correlation of herbicide residues in water and sediments from the streams flowing into the Caledon River in the eastern Free State using the bubble-in-drop single drop micro-extraction method

Mosotho Joseph George


Environmental monitoring of metolachlor and atrazine herbicides in water samples has been reported recently with the use of the recently reported “bubble-in-drop single drop micro-extraction” (BID-SDME) method. This study reports the application of this method coupled with the hot-water extraction for the analysis of these herbicides residues from the water and sediment samples obtained in the streams running into the Caledon River in the eastern Free State – South Africa using the hot-water extraction (for the sediments) coupled to BID-SDME. The method was validated for several figures of merit before application to the real samples: it showed sufficient robustness (%RSD < 7% repeatability and reproducibility); sufficient linearity with 0.9991 > R2 > 0.9978, accuracy of 98% using 5 ng mL-1 atraton CRM in water. The results demonstrated that both these herbicides are widely used in the farms as all the streams had detectable levels of at least one herbicide with concentrations ranging from 5 ng mL-1 to about 30 ng mL-1 for water samples and 1 ng mL-1 to 35 ng mL -1 in the sediment samples with some positive correlation between the abundance in the two media (R2 = 0.8267 for atrazine and 0.9012 for metolachlor). The analyte recoveries from the samples relative to HPLC grade water solutions were higher than 90% demonstrating sufficient recovery. Some related compounds (simazine, terbutylazine and acetochlor) were also detected in some of these samples, although not quantified for lack of appropriate standards.

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