Effects of ultrasonic irradiation and direct heating on extraction of priority pesticides from marine sediments

Abstract

Priority pesticides (alachlor, aldrin, γ-chlordane, chlorfenvinphos, chlorpyrifos, dieldrin, 4,4′-DDT, 4,4′-DDD, 4,4′-DDE, α-endosulfan, β-endosulfan, endosulfan sulphate, endrin, α-HCH, β-HCH, γ-HCH, δ-HCH, HCB, HCBD, heptachlor, heptachlor epoxide, isodrin, methoxychlor, mirex, quintozene, terbuthylazine and trifluralin) are a group of toxic substances that are known by their persistency in the aquatic environment. Their screening in marine sediments may provide information on the sources and distribution in the water mass of fresh-transitional and coastal waters. This work proposes a rapid and reliable method to extract multi-residues of priority pesticides by ultrasounds irradiation from marine sediments. Multiple variables have been optimised: ultrasound frequency, sonication intensity, signal operation mode, time of extraction and water bath temperature. After sample clean-up and pre-concentration of the pesticides by stir bar sorptive extraction, the compounds were analysed by gas chromatography-mass spectrometry (GC-MS) using the selective ion monitoring acquisition mode (SIM). Better performance was found for ultrasonic-assisted extractions (UAE) at frequency of 35 kHz and an output intensity of 60% in a sweep mode of operation. An increase of water bath temperature to 80°C had a significant effect on the extraction of pesticides with high octanol-water partitioning coefficients (K_ow). Under optimal conditions, method detection limits (MDLs) and method quantification limits (MQLs) ranged from 0.3 to 4.4 ng g⁻¹ and from 0.8 to 14 ng g⁻¹, respectively. Recoveries between 70 and 111%, at high precision levels, were found at different types of marine sediments with a single extraction cycle. Method performance was in good agreement with quality control guidelines.

Keywords:

• gas chromatography-mass spectrometry (GC-MS)
• marine sediments
• multi-frequency ultrasonic baths
• priority pesticides
• ultrasound-assisted extraction (UAE)

Acknowledgements

The authors are grateful to Fundação para a Ciência e Tecnologia (Ministério do Ensino Superior e Ciência e Tecnologia) for the PhD fellowship to M. Isabel Pinto (grant no. SFRH/BD/76547/2011). Authors are also grateful to Professor Mário Diniz for his scientific and technical support in this work.

This work was first presented at the 7th European Conference on Pesticides and Related Organic Micropollutants in the Environment and 13th Symposium on Chemistry and Fate of Modern Pesticides, 7–10 October 2012, Porto, Portugal.