Method development and application: solid phase extraction (SPE), ultrasonic extraction (UE) and soxhlet extraction (SE) for the analysis of pesticides in water, soil, sediment and sludge.

Abstract

Ultrasonic extraction (UE), Soxhlet extraction (SE) and solid phase extraction (SPE) have been developed and applied for the simultaneous determination of the five most commonly used triazine pesticides. The extraction parameters that affect the recovery of the analytes for SPE, SE and UE methods were optimized before the application of the methods. The SPE optimized parameters were conditioning solvent and sample volume. The UE optimized parameters were: extraction solvent, the volume of extraction solvent and extraction time. The SE optimized parameters were extraction solvent and sample wetting. The analyses were conducted using a high-performance liquid chromatography-diode array detector (HPLC-DAD) which was also optimized to improve the limit of quantification and detection. The methods validation was performed using the mixture of triazine pesticides spiked distilled water and soil samples. The recoveries obtained were 107 - 111 %, 75 - 100% and 71 – 87% for SPE, UE, and SE respectively. The limits of detection (LOD) and limits of quantification (LOQ) obtained ranged between 0.67 –1.2 μg/L and 2.0 – 3.5 μg/L for SPE respectively. For UE, they ranged from 1.0-2.0 μg/kg and 3.2 – 6.1 μg/kg and for SE, they ranged from 0.092-0.22 μg/kg and 0.28 – 0.69 μg/kg respectively. A good precision with a relative standard (RSD) less than 20% in all compounds was achieved for all methods. The developed and validated methods were then applied to river water, wastewater, sludge, soil and sediment samples from around KwaZulu-Natal. The concentrations obtained were 3.0 - 65 μg/L in river water, 2.5 - 49 μg/L in wastewater, 8.4 -2820 μg/kg in liquid sludge, 17 - 1017 μg/kg in soil and 1.1 – 123 g /kg in sediment samples. The most dominant triazine was found to be simazine. In Gilboa Farm soil samples, simazine was found to be above the Maximum Residual Limits (MRLs). In Darvill sludge samples, simazine, atrazine, and ametryn were above MRLs. In Amanzimtoti wastewater samples, atrazine was above MRLs. In Bishopstowe river water samples, simazine was above MRLs.