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Sustainability 2022, 14, x FOR PEER REVIEW 4 of 37

2.2 Sources of PFAS: 93

All stages of the manufacturing, distribution, use, and disposal of industrial and consumer products 94
result in the release of polyfluoroalkyl and perfluoroalkyl chemicals into the environment. While 95

indirect emission sources are defined as emissions from the transformation of their precursors, direct 96
emission sources of PFASs are characterised as emissions throughout their product cycle [21]. 97

Perfluorooctylsulfonyl fluoride (POSF)-based compounds, which serve as a key precursor for a number 98

of PFASs, were historically emitted in quantities ranging from 6800 to 45300 tonnes (direct and 99
indirect), as opposed to 3200 to 7300 tonnes (1951–2004) of PFCAs. More than 95% of these emissions 100

are released directly into the aquatic environment, while just 5% of them are thought to have entered 101
the atmosphere [22]. Perfluorobutane sulfonate and perfluorobutanoate are two short-chain PFASs that 102

are extensively used, as well as PFAS precursors that might eventually degrade to persistent 103
degradation products such as PFCAs and PFSAs [23]. Long-chain PFASs can be remobilized into the 104

water phase, for instance, from soil, sediment, and ice. The release of long-chain PFASs into the aquatic 105

environment will continue in the future due to the breakdown of PFAS precursors, or from past items 106
remaining in use or deposited [24]. 107

There are two sources namely point and non-point sources. Examples of PFAS point sources include 108

landfills, manufacturing facilities, and the application of PFAS-containing products in a concentrated 109
region, industrial and municipal sewage treatment plants [24]. While manufacturing facilities, sewage 110

treatment facilities, landfills, and homes are the primary sources of PFASs, wet and dry atmospheric 111
deposition represents a nonpoint source [25]. Even in very remote areas, PFASs that are volatile such 112

as fluorotelomer alcohols (FTOHs), perfluoroalkyl sulfonamides (FASAs), and perfluoroalkyl 113
sulfonamidoethanols (FASEs) have been found in outdoor air samples [26]. Additionally, PFSAs and 114

PFCAs in the aquatic environment can be produced as a result of the metabolic transformation of PFAS 115

precursors such as polyfluoroalkyl phosphoric acid esters (PAPs), fluorotelomer carboxylates (FTCAs), 116
fluorotelomer unsaturated carboxylates(FTUCAs), fluorotelomer sulfonates (FTSAs), and 117

perfluoroalkyl sulfonamido acetic acids (FASAAs). Runoff from streets or contaminated land as a 118
result of biosolid application or wet and dry air deposition is another significant nonpoint source [27]. 119

PFAS have a variety of uses, including as surfactants, friction-reducers, and water, oil, and 120
dirt repellents. As a result, they are employed in a vast array of consumer goods to confer low friction 121

and non-stick (waterproof, greaseproof, and stainproof) qualities. Examples of goods with or including 122

Glass, paper, carpets, clothing, and other items are coated with PFAS. Cookware, other textiles, plastic 123
products, food packaging, personal care items and electronics. Also employed are PFAS Dispersants 124

and emulsifiers, either directly or as technical aids, in there are numerous industrial uses, such metal 125