Data on occurrence of perfluoroalkyl substances in influents and effluents collected from different wastewater treatment plants in Latvia

The data set provided in this paper contains occurrence data of 17 perfluoroalkyl substances (PFAS) (including 10 perfluorinated carboxylic acids and 7 perfluorinated sulfonic acids) in influent and effluent samples collected from 43 wastewater treatment plants (WWTPs) located in different cities in Latvia. Samples were collected in the period June-July 2021. In each WWTP one influent and one effluent sample were collected on the same day. Extraction and clean-up of the samples were performed using solid phase extraction (SPE) on a weak-anion SPE phase. Observed extracts were analysed using high performance liquid chromatography coupled with Orbitrap high resolution mass spectrometry (HPLC-Orbitrap-MS) on the content of selected PFAS representatives. The collected data are with fundamental scientific value and can be applied for local data analysis. The data set is useful for the estimation of overall background levels of PFAS and evaluation of local city WWTPs wastewater remediation efficiency towards the removal of PFAS contamination.


a b s t r a c t
The data set provided in this paper contains occurrence data of 17 perfluoroalkyl substances (PFAS) (including 10 perfluorinated carboxylic acids and 7 perfluorinated sulfonic acids) in influent and effluent samples collected from 43 wastewater treatment plants (WWTPs) located in different cities in Latvia. Samples were collected in the period June-July 2021. In each WWTP one influent and one effluent sample were collected on the same day. Extraction and clean-up of the samples were performed using solid phase extraction (SPE) on a weak-anion SPE phase. Observed extracts were analysed using high performance liquid chromatography coupled with Orbitrap high resolution mass spectrometry (HPLC-Orbitrap-MS) on the content of selected PFAS representatives. The collected data are with fundamental scientific value and can be applied for local data analysis. The data set is useful for the estimation of overall background levels of PFAS and evaluation of local city WWTPs wastewater remediation efficiency towards the removal of PFAS contamination.

Value of the Data
• Perfluorinated substances transport and spread in the environment through WWTPs are of increasing concern, with a lack of data available in Latvia. These data offer a comprehensive overview of the occurrence of 17 perfluorinated carboxylic and sulfonic acids in influents and effluents collected from different WWTPs in Latvia. • The data can be valuable for researchers studying contaminant transfer into the environment through the WWTPs. • These data may be used by local authorities, policy makers and researchers to improve the environmental quality standards. These data may be valuable in the optimisation of WWTP operation conditions. • These data may contribute to the existing worldwide need of monitoring data for PFAS to support future prioritisation of relevant compounds and the development of guidelines by national and international authorities.

Data Description
The presented data were obtained during a comprehensive monitoring study on the occurrence of 17 PFAS in influent and effluent samples collected from 43 WWTPs located in different regions of Latvia. Results are expressed as nanogram per liter concentrations (ng L −1 ). Data presented include (1) mapping of sampling locations in different regions of Latvia ( Fig. 1 ); (2) datasets with concentrations of selected PFAS in influent wastewater collected before any treatment and concentrations in effluent wastewater collected immediately before the discharge from WWTP ( Table 1 ); (3) constructed boxplots for datasets ( Fig. 2 ).

Experimental Design, Materials and Methods
Wastewater aliquots were collected into 1 L brown coloured glass bottles and transferred to the laboratory at + 4 °C. Samples were stored at + 4 °C and treated within seven days of receipt.    Selected PFAS were analysed according to the previously published method with minor modifications in order to extend the scope of the target analytes [1] . 250 mL sample aliquots were spiked with 13 C-isotopically labeled PFAS surrogates (5 ng of each component) served as internal standards and then 100 μL of formic acid was added to each sample. Samples were loaded at a flow rate of ∼ 5 mL min −1 on the weak anion-exchange SPE columns (Strata-X-AW 200 mg/3 mL (Phenomenex, Torrance, CA, USA)), which were previously pre-washed with 3 mL of 1% NH 4 OH in MTBE/MeOH (90:10, v/v), 3 mL of MeOH, and 3 mL of ultra-pure water. After the sample loading, the SPE cartridges were washed with 1 mL of 2% formic acid and 2 mL of MeOH, and after drying the cartridges for 30 min under vacuum, the analytes were eluted with 7 mL of 1% NH 4 OH in MTBE/MeOH (90/10, v/v) to a 10 mL glass vial. Eluted extracts were evaporated to dryness under a gentle stream of nitrogen at 30 °C, reconstituted with MeOH (100 μL) and subjected to the HPLC-Orbitrap-MS analysis. Prepared extracts were analysed within three days of sample preparation. Instrumental analysis was performed using HPLC-Orbitrap-MS operated in parallel reaction monitoring (PRM) mode, with detection of negative ions. Quantitation was carried out using isotope dilution and internal standardisation method with selected 13 C-labeled surrogates. The results from real samples were corrected by subtracting the PFAS concentrtions of the procedural blanks (see Supporting Information) analysed in each sample sequence. Method accuracy was controlled by the analysis of certified reference material (CRM) Standard Reference Material 2781 Domestic Sludge (NIST, Gaithersburg, MD, USA), which was analysed in each sample run in the frame of the current study. Boxplots were constructed for datasets as follows: the horizontal line within the box represents the distribution median. The ends of the box represent the 25th and 75th percentiles, while the interquartile range (IQR) is the difference between the 25th and 75th percentiles. The lines that extend from each end are whiskers, from the ends of the box to the outermost data point that falls within the distances computed as follows: 1st quartile −1.5 × (IQR) 3rd quartile + 1.5 × (IQR).

Ethics Statement
Not applicable .

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data Availability
Data on occurrence of perfluoroalkyl substances in influents and effluents collected from different wastewater treatment plants in Latvia (Original data) ( https://figshare.com/ ).