Introduction
Per-and polyfluoroalkyl substances (PFAS) are a group of persistent organic pollutants that remain in the environment for an extended period and have been known to accumulate to harmful levels. PFAS have unique properties, most notably, thermal and chemical stability. These properties explain the longevity of persistent pollutants in the environment, and their limited degradation. Colloquially, PFAS have come to be known as “forever chemicals” for this very reason. For several decades, PFAS have been widely used in industrial processes and consumer products, for example surfactants, non-stick pans, fire retardant coating and waterproof clothing.[1]
PFAS contamination and fluorine mass balance in sediments of the Upper Ganges River and Ganges Canal
The Ganges River is one of the most significant rivers in the world, supporting the livelihood of approx. 7% of the worlds’ population and serves as a rich site for biodiversity.[2] Famously, the Ganges river serves as a source of drinking water and a place for religious activities, as well as a myriad of industrial processing centres. Consequently, this makes any contamination a direct human health concern.
Several PFAS are regulated under the Stockholm Convention on Persistent Organic Pollutants.[3] The UN treaty was established in May 2001, with major signatories including Canada, China, Germany, Japan, France and more. To date, 186 parties have ratified or acceded to the treaty; including India.
The presence of PFAS in India has been well documented. However, the majority of initial research on PFAS in India focused on the occurrence and distribution of PFAS in industrial regions of the country. Subsequently, more recent interest has expanded analysis to include water sources as well.[4] As a result, studies have shown the presence of short and long-chain PFAS (e.g. C4 and C8 perfluoroalkylsulfonic acids, and C6, C8, C9 perfluorocarboxilic acids, PFBS, PFOS, PFHxA, PFOA, PFNA) in surface water, sediment and biota from the Ganges.[5],[6],[7]
Sediments act as a long-term sink for contaminants such as PFAS; and due to the varied turbidity, contaminants can be remobilised and redistributed easily. In this study, researchers analysed Ganges River sediments for 40 targeted species, including ultrashort chain (USC, such as trifluoroacetic acid, TFA) –, legacy (perfluorosulfonic and perfluorocarboxylic acids) – and precursor – PFAS (e.g. fluorotelomer sulfates, perfluorosulfonamides, or perfluorosulfonamido acids and sulfonamido ethanols) using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). LC-MS/MS methods offer the highest selectivity and sensitivity, however require analytical and isotopically labelled standards.
Sample Preparation
Sediment samples from the Ganges River were collected at 14 locations spanning Rishikesh to Haridwar, and from the Upper Ganges Canal, as seen in adjacent image. This was done in an attempt to capture major anthropogenic and hydrological disturbances, thereby also allowing quantification of downstream transport of emerging contaminants. Subsequently, samples were transported to the laboratory at the University of Graz for processing and analysis.
An exhaustive list of Mass Spec standards used included the following products from Cambridge Isotope Laboratories Inc.:
- Perfluoro(2-ethoxyethane)sulfonic acid (PFEESA)
- Perfluoro-3,6-Dioxa-4-Methyl-7-Octenesulfonic Acid (Nafion Bp1)
- 8:2 perfluoroalkyl phosphate diester (diPAP)
- Perfluoro-2-ethoxypropanoic acid (PEPA)
- 3-Perfluoroheptyl propanoic acid (7:3 FTCA)
- 2H,2H-Perfluorodecanoic acid (8:2 FTA)
- Perfluoro-3-methoxypropanoic acid (PFMPA)
- Perfluoro-4-methoxybutanoic acid (PFMBA)
- 3:3 fluorotelomer carboxylic acid (3:3 FTCA)
- Perfluoro-3,6-dioxaheptanoic acid (PFDHA)
- PFAS RM-41 Native Spiking Mixture (ES-5665), which contained, in addition to the PFAS found in PFAC30PAR, C16 and C18 PFCA, C3 and C12 PFSA, C12 FTS, N-Methylperfluorooctanesulfonamidoethanol, N-Ethylperfluorooctanesulfonamidoethanol, PFMPA, PFMBA, PFDHA and PFEESA.
- Trifluoroacetic acid (TFA)
- Individual C3 PFSA
- 13C labelled TFA
- 13C labelled PFPrA
Conclusion
The results of this study has provided essential insights into the occurrence of PFAS in the Ganges River sediment. The abundance of short and ultra-short chained PFAS would likely suggest substantial and continued contamination from municipal and industrial waste. In addition, it has been heavily suggested that a potential underestimation of PFAS contamination is a result of solely relying on targeted analysis. Extractable Organic Fluorine (EOF) analysis revealed that less than 1% of the organofluorine content was identified. It stands to reason that the presence of new and unknown PFAS compounds is highly likely in this instance. Alarmingly, these results highlight the urgent need for a comprehensive regulatory framework with regards to PFAS emissions in all Indian aquatic ecosystems, not only the Ganges.
