Environmental
by Joe Anacleto
Detecting Trace-Level Pyrethroid Insecticides in Sewage and Ocean Sediments With GC-MS/MS
s the use of pyrethroid insecticides continues to increase in the United States, it is becoming increasingly im- portant to monitor levels of the compounds in environmental waters, river and ocean sediment and wastewater effluent. Pyrethroids are lethal to mayflies, gadflies and other in- vertebrates at extremely low levels, and are toxic to fish and other aquatic organisms. The insecticides have been found to be unaffected by secondary treatment systems at municipal wastewater treatment facilities, appearing in the effluent. Effective pyrethroid detection techniques are vital for environmental moni- toring and for understanding the impact of the compounds in the environment, even at lower nonlethal levels.
A
Any method for pyrethroid detection must be able to discriminate effectively against complex matrices and provide trace-level de- tection. This article details the use of GC-MS/ MS to screen a group of pyrethroid insecticides at low concentrations in complex matrices of sewage outfall and ocean sediments. Electron and negative chemical ionization techniques are also compared to examine which delivers the best results in these complex matrices.
Introduction Pyrethroids are synthetic insecticides based on
the structure of pyrethrins, which are derived from chrysanthemum flowers. The compounds are used in a range of household insecticides and repellents because they are stable, toxic and effective against a wide range of pests. Pyrethroids work by altering nerve function, which causes paralysis in target insect pests, eventually resulting in death.1
Pyrethroids that
have entered the environment through agri- cultural and domestic use have proved to be lethal to many invertebrates and toxic to fish and other aquatic organisms.
Ion source
The stability and highly hydrophobic nature of pyrethroids means they remain in sediment and have been identified in influent, effluent and biosolids from sewage treatment plants in Europe and the United States. Pyrethroids have also been found in secondary-treated munici- pal wastewater in California at concentration levels above the LC50
the test system organism, Hyalella azteca.2
(lethal concentration) for To
address this, the California Department of Food and Agriculture has implemented monitoring programs requiring low to sub-parts-per-billion reporting limits in soil and water samples.
Since the use of pyrethroids continues to increase in both urban and agricultural set- tings, it is important to have robust, sensitive methods that are capable of measuring these compounds at the limits required in both water and sediment. Such methods will also help scientists understand pyrethroid behav- ior in the environment.3
In pesticide monitoring, discrimination against matrix components arising from wastewater outfall (sewage) and sediment extracts is critical to the success of any method. Gas chromatography-coupled triple quadrupole
tandem mass spectrometry (GC-MS/MS) is an ideal technique to analyze pyrethroids because it can discriminate effectively against matrices and provide trace-level detection. Recent ad- vances in GC-MS/MS systems, such as the axial ion source and lens-free design of the Bruker SCION TQ (Bruker Daltonics, Billerica, Mass.), result in robust operation and high sensitivity for the pyrethroid insecticides.
Case study To determine the best method of analysis, a group of pyrethroids was analyzed using GC-MS/MS. Electron ionization (EI) and nega- tive chemical ionization (NCI) techniques were optimized and compared in terms of calibra- tion range, method detection limits and precision. The SCION TQ triple quadrupole mass spectrometer coupled to a Bruker 456 GC and CP-8400 liquid autosampler (Agilent Technologies, Santa Clara, Calif.) was used with a standard hot splitless injection, which reduced instrument matrix load compared to often-used large-volume programmed tem- perature vaporization (PTV). The instrument parameters are shown in Table 1.
Table 1 – Instrument parameters for pesticide quantification using SCION TQ GC-MS/MS coupled to a 456 gas chromatograph
Column
Carrier gas Oven
Injection
BR-5ms, 15 M × 0.25 mm i.d. × 0.25 µm Helium at 1.0 mL/min
60 °C (2 min), at 50 °C/min to 150 °C (1 min), at 5 °C/min to 320 °C (hold 3 min)
2 µL pulsed splitless at 28 °C with 4.0-mm-i.d. fritted liner EI at 250 °C; NCI at 150 °C
NCI reagent gas Ammonia at 20 psi
AMERICAN LABORATORY • 24 • MARCH 2015
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