Occurrence and toxicity of perfluoroalkyl acids along the estuarine and coastal regions under varied environmental factors

Species-specific profiles of per- and polyfluoroalkyl substances (PFAS) in small coastal sharks along the South Atlantic Bight of the United States

Per- and polyfluoroalkyl substances (PFAS) have gained widespread commercial use across the globe in various industrial and consumer products, such as textiles, firefighting foams, and surface coating materials. Studies have shown that PFAS exhibit a strong tendency to accumulate within aquatic food webs, primarily due to their high bioaccumulation potential and resistance to degradation. Despite such concerns, their impact on marine predators like sharks remains underexplored. This study aimed to investigate the presence of 34 PFAS in the plasma (n = 315) of four small coastal sharks inhabiting the South Atlantic Bight of the United States (U.S). Among the sharks studied, bonnetheads (Sphyrna tiburo) had the highest ∑PFAS concentration (3031 ± 1674 pg g - 1 plasma, n = 103), followed by the Atlantic sharpnose shark (Rhizoprionodon terraenovae, 2407 ± 969 pg g - 1, n = 101), blacknose shark (Carcharhinus acronotus, 1713 ± 662 pg g - 1, n = 83) and finetooth shark (Carcharhinus isodon, 1431 ± 891 pg g - 1, n = 28). Despite declines in the manufacturing of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), the long-chain (C8 - C13) perfluoroalkyl acids (PFAAs) were frequently detected, with PFOS, perfluorodecanoic acid (PFDA), and perfluorotridecanoic acid (PFTrDA) present as the most dominant PFAS. Furthermore, males exhibited significantly higher ∑PFAS concentrations than females in bonnetheads (p < 0.01), suggesting possible sex-specific PFAS accumulation or maternal offloading in some species. The results of this study underscore the urgency for more extensive biomonitoring of PFAS in aquatic/marine environments to obtain a comprehensive understanding of the impact and fate of these emerging pollutants on marine fauna.

Uptake and cellular responses of Microcystis aeruginosa to PFOS in various environmental conditions

Although PFOS has been banned as a persistent organic pollutant, it still exists in large quantities within the environment, thus impacting the health of aquatic ecosystems. Previous studies focused solely on high PFOS concentrations, disregarding the connection with environmental factors. To gain a more comprehensive understanding of the PFOS effects on aquatic ecosystems amidst changing environmental conditions, this study investigated the cellular responses of Microcystis aeruginosa to varying PFOS concentrations under heatwave and nutrient stress conditions. The results showed that PFOS concentrations exceeding 5.0 µg/L had obvious effects on multiple physiological responses of M. aeruginosa, resulting in the suppression of algal cell growth and the induction of oxidative damage. However, PFOS concentration at levels below 20.0 µg/L has been found to enhance the growth of algal cells and trigger significant oxidative damage under heatwave conditions. Heatwave conditions could enhance the uptake of PFOS in algal cells, potentially leading to heightened algal growth when PFOS concentration was equal to or less than 5.0 µg/L. Conversely, deficiency or limitation of nitrogen and phosphorus significantly decreased algal abundance and chlorophyll content, inducing severe oxidative stress that could be mitigated by exposure to PFOS. This study holds significance in managing the impact of PFOS on algal growth across diverse environmental conditions.

Source, transport, and fate of perfluoroalkyl acids (PFAAs) in turbid bay environments: Significant roles of suspended sediment and water column stratification

The coastal area was the major region receiving pollution from land-based sources into the sea. Perfluoroalkyl acids (PFAAs) in famous bays had aroused wide concern, but the importance of underdeveloped or small bays with notable levels of PFAAs were often neglected. Moreover, the roles of suspended sediment (SPS) and water column stratification on PFAA behaviors were unclear. In this study, PFAAs distribution in multiphase-multilayer in four underdeveloped bays (two urban bays and two island bays) were investigated. The urban bays not only had higher PFAA contamination but also posed a greater threat of short-chain PFAAs in water-SPS-sediment system than the island bays. The major source of PFAAs in water and SPS was domestic sewage in urban bays and was rainfall-runoff in island bays. Water column stratification with higher PFAA partition in water-SPS system in the surface layer than in the bottom layer was only found in the urban bays due to the higher human activity intensity. These provided new perspectives for managing emerging contaminants and establishing water quality criteria in the turbid coastal environment. The key role of SPS as a carrier offered possibilities to accurately differentiate the effects of dissolved and particulate PFAAs on bioavailability.

Toxicity of perfluooctane sulfonate (PFOS) and perfluorobutane sulfonate (PFBS) to Scenedesmus obliquus: Photosynthetic characteristics, oxidative damage and transcriptome analysis

With the wide application as an alternative for perfluorooctane sulfonate (PFOS), perfluorobutane sulfonate (PFBS) has been frequently detected in the aquatic environment. However, the aquatic toxicity of PFBS is still poorly understood. The present work studied the aquatic toxicity of PFBS using freshwater algae Scenedesmus obliquus (S. obliquus) as indicator, and the toxicity of PFOS was also examined for comparison. The results showed that PFBS exhibited much lower toxicity to S. obliquus than PFOS. The EC₅₀ value was higher than 1800 mg L^-1 after 7 days of exposure to PFBS. By contrast, a much lower EC₅₀ value of 136.69 mg L^-1 was obtained for PFOS. Photosynthetic efficiency analyzed by chlorophyll fluorescence also verified that PFOS induced a higher toxic effect on the algae than PFBS. The malondialdehyde, catalase and superoxide dismutase results indicate that PFOS exposure led to the accumulation of ROS, which caused oxidative damage to the algae, thereby resulting in the inhibition in the growth and photosynthesis of the algae. Furthermore, transcriptome analysis indicates that the significant down-regulation of key genes related to photosynthesis induced by PFOS was the fundamental mechanism for the inhibition in photosynthetic efficiency and biomass growth of S. obliquus.

Perfluorinated compounds disrupted osmoregulation in Oryzias melastigma during acclimation to hypoosmotic environment

Perfluorinated compounds (PFCs) are a type of ubiquitous contaminants spreading in the estuarine and coastal areas. Anadromous fish should deal with hypoosmotic challenge with PFCs stress during their migration from seawater to estuaries. However, few studies have been carried out to investigate the adverse impact of PFCs on fish osmoregulation and the underlying mechanism. In this study, Oryzias melastigma, an euryhaline fish model, were exposed to four representative PFC congeners including perfluorobutane sulfonate (PFBS), perfluorooctane sulfonates (PFOS), perfluorooctanoic acid (PFOA), and perfluorododecanoic acid (PFDoA) separately under both seawater and freshwater conditions. Histopathological changes in gills, ion homeostasis, Na⁺/K⁺-ATPase (NKA) activity, as well as the expression of related genes was detected upon exposure. Results showed that PFCs induced morphological changes in gills, disturbed the levels of major ions (Na⁺, Ca²⁺, Mg²⁺), and inhibited the NKA activity. Transcriptome analysis in fish gills during the acclimation to freshwater revealed that PFCs influenced the osmoregulation mainly by interfering with the endocrine system, signal transduction, as well as cellular community and motility. Validation with qRT-PCR confirmed that the mRNA expressions of osmoregulatory genes encoding hormones and receptors, as well as ion transmembrane transporters were disturbed by PFCs. Longer chain homolog (PFOS) showed a greater impact on osmoregulation than the shorter chain homolog (PFBS). Within the same carbon chain, sulfonic congener (PFOS) induced more serious injury to gills than carboxylic congener (PFOA). The interaction between PFCs and salinity varied in different adverse outcome. These results help to further understand the mechanism of how PFCs influence osmoregulation and elicit the need to assess the ecological risk of PFCs and other pollutants on anadromous migration.