Non-Target Screening and Identification of Organic Contaminants in Surface Waters Surrounding Drilling Mud Sumps in the Mackenzie River Delta, Northwest Territories, Canada

Overview These datasets accompany the publication Bischoff et al. (in prep.). Water samples were collected in August 2024 (pre-investigation) and August 2025 during field campaigns of the project “Thawing industrial legacies in the ArctIc - a threat to permafrost ecosystems (ThinIce)”. The four visited drilling mud sumps along the Inuvik-Tuktoyaktuk Highway in the Northwest Territories, Canada, are named Nuna A-32, Tuk E-20, Tuk H-30 and Tuk L-09. This dataset contains two .csv files. water_nontarget_metadata.csv, where lat_N and long_W are sampling coordinates reported in decimal degrees (°N and °W). The dataset uses EPSG:4326 (WGS 84) coordinates. field_EC_microS_cm-1 and lab_EC_microS_cm-1 are the electrical conductivities in µS cm-1 determined at given Temperature in °C (T_C) using a GMH 3430 series conductivity measuring device (Greisinger) in the field and an inoLab Cond Level 2 P (WTW) in the laboratory. lab_pH is the pH determined using an inoLab Cond 720 Conductivity Meter (WTW). Avg_DOC_mg_L-1 is the dissolved organic carbon content in mg L-1 determined using a LiquiTOC (Elementar Analysensysteme). Avg_TDN_mg_L-1 is the total dissolved nitrogen content in mg L-1 determined using a LiquiTOC (Elementar Analysensysteme). water_nontarget_concentrations.csv, where max_match is the maximum match of the mass spectrum with the NIST26 mass spectral library for each compound across the 23 samples. columns F-AC report the detection (d) of individual compounds in the 23 water samples. If analyte standards were available, compounds were quantified. Concentrations in ng L-1 were calculated as: C_A = ( A_A / ( A_std * (C_{std,RF} / C_{std,S}) ) ) * RF * V_std / V_S where: CA is the concentration of the Analyte in the sample [ng L-1] AA is the peak area of the Analyte [dimensionless] Astd is the peak area of the Standard [dimensionless] Cstd,RF is the concentration of Surrogate Standard d34-hexadecane [ng μL-1], here: 6.0 ng μL-1 Cstd,S is the concentration of Surrogate Standard d34-hexadecane in mixes of analyte standard, solvent and Surrogate Standard d34-hexadecane used for RF determination [ng μL-1], here: 3.0 ng μL-1 RF Response Factor [dimensionless], slope of analyte standard concentration [ng µL-1] vs. peak-area ratio, units of [ng µL-1] Vstd Volume of Surrogate Standard d34-hexadecane added to water sample [µL] VS Volume of sample [L] Sampling and instrumental analysis Water samples collected in 2025 were taken without headspace in 1.2 L pre-cleaned aluminum bottles, transported and stored refrigerated until analysis. The sampling setup of the pre-investigation in 2024 was not ideal, using HDPE bottles of only 250 ml volume, stored frozen until analysis. Excerpt from Bischoff et al. (in prep.): GC-MS analysis was carried out using a Trace 1610 gas chromatograph (Thermo Scientific, Waltham, MA, USA) equipped with a ZB-5 silica capillary column (Phenomenex, Torrance, CA, USA; 30 m length, 0.25 mm inner diameter, 0.25 µm film thickness) coupled to an ISQ 7610 single quadrupole mass spectrometer (Thermo Scientific, Waltham, MA, USA). Aliquots of 0.2 to 1 μL were injected in splitless mode at an injector temperature of 270 °C, and a splitless time of 60 s. The GC oven was set to a start temperature of 60 °C held for 3 min, followed by a temperature ramp of 3 °C min-1 to 310 °C and a final isothermal time of 20 min. Hydrogen served as the carrier gas at a constant flow rate of 1.5 mL min-1. Ionization was accomplished using electron ionization (EI+) with an ionization energy of 70 eV, at full-scan mode ranging from m/z 50 to m/z 650. Non-target Screening workflow Excerpt from Bischoff et al. (in prep.): The non-target screening workflow included manual peak picking followed by removal of observations that were less than 10 times higher than those detected in procedural blanks. The limit of detection (LOD) was defined by a signal-to-noise ratio (S/N) of 3, the limit of quantification (LOQ) was defined as S/N of 10 for compounds that were not detected in the blank. Identification of compounds was performed using Xcalibur software with the NIST26 mass spectral library. The workflow aimed to identify compounds with the greatest possible confidence, based on the nomenclature introduced by Schymanski et al. (2015). Based on diagnostic evidence, confidence level 2 was assigned to compounds with spectral matches >80% to the NIST26 library. Confidence level 3 encompasses further tentative candidates that could not be identified unequivocally. Structures were only confirmed, corresponding to confidence level 1, when reference standards were available. This additionally enabled compound quantification based on experimentally determined response factors (RFs).