Comprehensive Analysis of the Great Lakes Top Predator Fish for Novel Halogenated Organic Contaminants by GC×GC-HR-ToF Mass Spectrometry

Abstract

The U.S. Environmental Protection Agency's Great Lakes Fish Monitoring and Surveillance Program (GLFMSP) has traced the fate and transport of anthropogenic chemicals in the Great Lakes region for decades. Isolating and identifying halogenated species in fish is a major challenge due to the complexity of the biological matrix. A nontargeted screening methodology was developed and applied to lake trout using a 2-dimensional gas chromatograph coupled to a high resolution time-of-flight mass spectrometer (GC×GC-HR-ToF MS). Halogenated chemicals were identified using a combination of authentic standards and library spectral matching, with molecular formula estimations provided by exact mass spectral interpretation. In addition to the halogenated chemicals currently being targeted by the GLFMSP, more than 60 nontargeted halogenated species were identified. Most appear to be metabolites or breakdown products of larger halogenated organics. The most abundant compound class was halomethoxyphenols accounting for more than 60% of the total concentration of halogenated compounds in top predator fish from all five Great Lakes illustrating the need and utility of nontargeted halogenated screening of aquatic systems using this platform.

Automated Isotopic Profile Deconvolution for High Resolution Mass Spectrometric Data (APGC-QToF) from Biological Matrices

“…29 Ten grams of whole fish homogenate was extracted with 120 mL of dichloromethane using an Accelerated Solvent Extractor (ASE, Dionex) followed by size exclusion chromatography. Silica gel activated with ethylenediamine-N-propy bonding solid phase extraction cartridges purchased from Supelco were then used for fatty acid removal prior to concentrating the extracts to 100 μL using the method of Fernando et al 1 An injection standard, PCB-65 (100 ng), was then added immediately prior to the injection into the APGC/Q-TOF system.…”

“…A previous NTS experiment in our lab was performed using lake trout from Lake Michigan collected in 2014. 1,29 The sample processing was consistent with the current extract but analyzed using a two-dimensional gas chromatograph coupled to a high resolution time-of-flight mass spectrometer (GC×GC-HRT, LECO, St. Joseph, MI). 1 The GC×GC-HRT utilizes a standard EI source that may not preserve molecular ions but has a secondary chromatographic separation dimension to reduce coeluting interferences.…”

“…1,29 The sample processing was consistent with the current extract but analyzed using a two-dimensional gas chromatograph coupled to a high resolution time-of-flight mass spectrometer (GC×GC-HRT, LECO, St. Joseph, MI). 1 The GC×GC-HRT utilizes a standard EI source that may not preserve molecular ions but has a secondary chromatographic separation dimension to reduce coeluting interferences. The one-dimensional chromatography APGC-QToF operated with an atmospheric pressure chemical ionization (APCI) source provides softer ionization relative to EI, resulting in less fragmentation, and potentially increases the instrument sensitivity by providing a larger molecular ion signal.…”

“…A large number of organohalogenated compounds have long half-lives and persist in the environment for decades. − Chlorinated and brominated contaminants are of particular concern due to their persistent, bioaccumulative, and/or toxic (PBT) tendencies . Many undiscovered chlorinated and brominated compounds may be formed from the breakdown of legacy contaminants. , In addition, recently deployed alternative commercial products with PBT properties may also bioaccumulate in biota .…”

“…Therefore, these patterns can be used to isolate spectral features (components) that contain Br and/or Cl. A number of commercial software packages such as ChromaTOF v1.90.60 (LECO instrument software) , and ACD/Spectrus Processor have used this profile to isolate Br/Cl containing compounds in complex HRMS data. However, the majority of screening software packages may not adequately detect trace level contaminants in more complex biological matrices (e.g., fish).…”