Environmental Sampling of Per- and Polyfluoroalkyl Substances in the Middle Chickahominy River Watershed, Virginia, 2021-2022 (ver. 2.0, September 2023)

These data were collected to understand the occurrence of Per- and Polyfluoroalkyl Substances (PFAS) in the middle Chickahominy River watershed. Specifically, this effort was initiated to:

1. Determine concentrations of PFAS in surface water at select locations in the middle Chickahominy River watershed;
2. Determine concentrations of PFAS in edible portions of fish at select locations in the middle Chickahominy River watershed;
3. Determine concentrations of PFAS in bed sediment at select locations in the middle Chickahominy River watershed; and
4. Quality Assure all data collected in accordance with USGS policies and publicly release those data as a citable USGS Data Series.

Description of Available Datasets:

These data are available in four Excel (.xlsx) files that contain water-quality and quality-assurance results. The Excel files are duplicated as tab-delimited text files to increase accessibility to nonproprietary formats. The files titled Middle_Chickahominy_Fish_Tissue_Results contain analytical results for PFAS in tissue samples collected from various fish species at different locations. The files titled Middle_Chickahominy_Sediment_Results contain analytical results for PFAS in sediments collected at four locations in the watershed. The files titled Middle_Chickahominy_Surface_Water_Results contain analytical results for PFAS in surface water collected at eleven locations in the watershed.
These files also contain associated field blanks, lab blanks, and replicates used for quality control. Lab blanks are used to assess contamination imparted by the analytical process. Field blanks were collected using certified analyte-free water at the sampling point and used to assess possible cross contamination from sampling materials and sampling technique in the field. Field replicates were collected concurrently with the environmental sample and used to understand the variability of results.  
The attached XML file titled Middle_Chickahominy_Metadata contains metadata explaining the provenance of the data and should be thoroughly read to understand data structure and limitations. The files titled Data_Dictionary may be used as a reference to explain codes, terms, and abbreviations used in these datasets. The files titled Ongoing_Precision_and_Recovery contain quality assurance samples reported by the lab which establishes additional confidence in results over time.

Data Validation and Quality Assurance:

U.S. Environmental Protection Agency (EPA) Draft Method 1633 (U.S. Environmental Protection Agency, 2021) was used to determine PFAS concentrations in all three media types (surface water, sediment, tissue). Samples were analyzed at SGS AXYS in British Columbia, Canada, which is accredited by the U.S. Department of Defense Environmental Laboratory Accreditation Program for analysis of PFAS using Draft Method 1633. Reporting and detection levels for PFAS results are specific to the analyte, sample matrix, instrumentation, and laboratory performance. Results throughout this dataset that are reported with a “<” (less than) qualifier represent values that were not detected above the reporting level for that sample and specific analyte. The reporting levels show in this dataset are synonymous with the minimum level of quantitation as defined by U.S. Environmental Protection Agency (2021).       
 A combination of field blanks, laboratory method blanks, isotopically labeled compound recoveries, and ongoing precision and recovery samples were used to assess field techniques and validity of the reported results. Surface water results met all quality assurance criteria, and no additional qualification was required. Likewise, sediment results met all quality assurance criteria, and no additional qualification was required.
Tissue results contain three analytes [6:2 fluorotelomersulfonate (6:2 FTS), N-Methylperfluorooctanesulfonamidoethanol (N-MeFOSE), N-Ethylperfluorooctanesulfonamidoethanol (N-EtFOSE)], that did not meet quality assurance criteria. Ongoing precision and recovery spikes for 6:2 FTS and N-EtFOSE were higher than 130 percent. 6:2 FTS was detected in every tissue sample, but all values were less than five times the concentration detected in the associated laboratory blank. Isotopically labeled compound recoveries for N-MeFOSE and N-EtFOSE were close to, or lower than, 10 percent in most samples. According to a review of EPA Draft Method 1633 by EPA and U.S. Department of Defense (Willey and others, 2021), analyses of N-MeFOSE and N-EtFOSE in tissue using Draft Method 1633 have been shown to be inaccurate. For these reasons, analytical results for 6:2 FTS, N-MeFOSE, and N-EtFOSE were rejected and are represented in the tissue dataset with an “R” qualifier.   

References:

U.S. Environmental Protection Agency, 2021, Draft Method 1633 - Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS/MS: U.S. Environmental Protection Agency Document EPA 821-D-21-001, 65 p., accessed July 14, 2022, at https://www.epa.gov/system/files/documents/2021-09/method_1633_draft_au….
 
Willey, J., Anderson, R., Hanley, A., Mills, M., Hamilton, C., Thompson, T., and Leeson, A., 2021,
Report on the Single-Laboratory Validation of PFAS by Isotope Dilution LC-MS/MS: Strategic
Environmental Research and Development Program (SERDP), Project ER19-1409, 571 p., accessed July 14, 2022, at https://apps.dtic.mil/sti/pdfs/AD1157957.pdf.