Environmental monitoring of metolachlor and atrazine herbicides in water samples has been reported recently with the use of the “bubblein-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 the residues of these herbicides from the water and sediment samples obtained in the streams running into the
Caledon River in the eastern Free State – South Africa. 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 > R
2 > 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 (R
2 =
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.
Key words: bubble-in-drop micro-extraction, hot-water extraction, herbicides monitoring, sediments, farming area, Lesotho
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