Testing PAHs in Shellfish

Analytical testing dots Testing PAHs in Shellfish (including shrimp)

Laboratory testing of PAHs and alkylated PAHs in shellfish is typically performed using Gas Chromatography/Mass Spectrometry (GC/MS) in the Selective Ion Monitoring (SIM) mode. PAH (Polycyclic Aromatic Hydrocarbons) and alkylated PAH levels can be determined for a variety of shellfish, including shrimp, prawn, lobster, crayfish, crabs, clams, mussels, oysters and scallops.

View the Core List of PAH and Alkylated PAHs by EPA 8270/SIM...

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Analytical Procedure for Testing PAHs in Shellfish

The key to the analytical procedure is proper sample preparation: shucking, compositing (as appropriate to the project plan), and homogenization via mechanical mixing. Preliminary preparation under clean laboratory conditions prevents contamination by common PAHs. Decontamination of sample preparation equipment is performed and monitored to assure clean conditions. The sample homogenate consists of homogenous slurry when prepared correctly. ALS Environmental has been inspected and approved by various organizations (e.g. EPA, private industry, private consultants, etc.) during homogenization activities prior to receiving clearance to proceed with selected projects with high public, private, and government visibility.

Muscles lab testingAfter homogenization, samples are solvent extracted and subjected to cleanups via silica gel to remove interfering matrix components. Again, careful control of laboratory conditions and equipment is critical to assuring valid results. The cleanups are essential to remove interfering background components that mask the target compounds. Insufficient cleanup results in potential false positive results and/or elevated detection limits that render the data useless in many cases.

The SIM mode is used to further improve selectivity but also increases sensitivity. Typical reporting limits for shellfish range from 0.5 ng/g (ppb) to 5 ng/g (ppb), depending on the data quality objectives outlined in the project plan. The associated Method Detection Limits (MDL) are on the order of five to ten times lower than the reporting limit. When performing the low range determinations, the reporting limit of 0.5 ng/g (ppb) is derived from the lowest standard in the calibration curve.

The inclusion of alkylated homologs is critical to the forensic aspect of the determinations, which provides the connection to the source of the PAHs. The ratios of the various PAHs with substituted low molecular weight alkyl groups provide unique chemical characteristics that relate to the source of the contamination.

ALS Environmental testing conforms with all requirements for production of a legally defensible data package. From receipt at the laboratory to final review of the report, every sample processing operation is recorded in the package, allowing the entire process to be re-created at a later time. Any anomalies associated with the analysis of the samples are discussed in narrative form. A standard deliverable includes full summaries of all quality assurance and quality control (QA/QC) operations associated with the analysis. Importantly, self-validating reporting software  performs QA/QC checks that automatically document any anomaly in the data. This ensures that an issue can be addressed prior to releasing final reports.

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