Determination of organochlorine pesticides in river water samples by liquid-liquid-liquid extraction combined with dispersive liquid-liquid microextraction

Abstract

Aldrin and dieldrin are insecticides of organochlorine pesticides (OCPs), widely used to kill pest and known to be highly persistent and exhibit slow degradation. Leaching from agricultural runoff causes them to enter nearby water bodies, which can pose a threat to humans and aquatic organism. Determination of OCPs in Sungai Skudai is crucial because the river serves as the raw water source for part of Johor drinking water. A new extraction technique termed liquid-liquid-liquid extraction (LLLE) combined with dispersive liquid-liquid microextraction (DLLME) followed by gas chromatograph-microelectron capture detector (GC-µECD) was applied to determine aldrin and dieldrin in river water samples of Sungai Skudai. LLLE-DLLME involves three phases which are water sample, acetonitrile (ACN) and n-hexane (clean-up solvent). Targeted pesticides with medium polarity were extracted into the ACN phase, non-polar interference into n-hexane, and polar compound remained in the sample. The ACN phase is separated from aqueous phase using sodium sulfate as a phase separating agent. Calibration curves for aldrin and dieldrin were linear in the range of 2-20 µg/L with a good coefficient of determination, r² of 0.9995 and 0.9985, respectively. The percentage recovery obtained for aldrin and dieldrin were 39% and 76% with relative standard deviation (RSD) of 15.97 and 9.81%, respectively. Analysis on Sungai Skudai river water samples revealed that aldrin was present at concentration of 0.27 µg/L while dieldrin at 0.089 µg/L. Both pesticide concentrations were above the standard set for raw water quality by Ministry of Health Malaysia and World Health Organization (WHO) for drinking water purpose which is 0.03 µg/L for combined aldrin and dieldrin. In summary, the LLLE-DLLME method is simple, inexpensive and allows extraction of samples without the need of filtration to remove suspended solids.