Comparative Toxicity of Perfluoroalkyl Carboxylic acids (PFCAs) Exposure using Aquatic Organisms

Per- and poly-fluoroalkyl substances (PFAS) are persistent organic pollutants that consist of a diverse class of more than 5,000 anthropogenic chemicals and are used in a variety of industrial and consumer products due to their physicochemical properties. PFASs are widely distributed in environmental compartments like surface water, groundwater, rainwater, soils, and sediments. They are persistent and resistant to degradation. PFAS are partially hydrophilic and may enter the aquatic environment via surface runoff, discharge of wastewater, or product degradation. Perfluoroalkyl acids (PFAAs) are a group under the PFAS family of chemicals that are the most tested and detected in the environment. PFAAs are divided into two subgroups: Perfluoroalkyl carboxylic acids (PFCAs) and Perfluoroalkane sulfonic acids (PFSAs). PFAAs can be classified as long or short chains. Concerns about the health and environmental impacts of long chains have led to their phase-out and replacement with short chains. Short-chain PFAAs are now widely detected in the environment and PFBA, PFBS, PFPeA, PFHxA, and PFHpA are the most widely detected short-chain PFAAs, of these PFBA, PFPeA, PFHxA, PFHpA are PFCAs. Studies have focused mostly on PFOA (long-chain PFCA) and PFOS (long-chain PFSA) with little information known about the toxicity of short-chain PFAS. Water facilitates PFAS’s transfer between environmental compartments, contributing to their distribution. Aquatic organisms (microalgae, crustaceans, fishes) are often exposed to different pollutants in water bodies and are used as models for the evaluation of toxicity to aquatic ecosystems. Microalgae and zebrafish are commonly used models due to their sensitivity, quick response to environmental changes, and short generation times. Prymnesium parvum commonly called golden alga is a haptophyte unicellular microalga that occurs in marine or estuaries waters. Chlorella sorokiniana is a unicellular green microalga that can be found in freshwater environments and is also one of the most regularly studied microalgal species. Zebrafish are an ideal aquatic model for assessing aquatic toxicity because they are highly prolific with a short generation time and can be easily observed during embryonic development with all the major organs emerging within 36 hours post fertilization. This study investigated the toxic effect of two PFCAs, one long-chain (PFOA) and one short-chain (PFBA) on two microalgal species and zebrafish, assessing cytotoxicity in microalgae and developmental toxicity in zebrafish. The endpoints measured in P. parvum and C. sorokiniana were growth, morphology, chlorophyll content, and oxidative stress. In P. parvum, the 3-day and 9-day IC50 values of PFOA were 64.30 and 49.41 respectively, while PFBA was 25.81 and 20.16 respectively. PFOA and PFBA both affected cell growth but PFBA had more inhibitory effects on growth indices. PFOA had no effect on cell size, chlorophyll content, and ROS formation while PFBA caused an increase in cell size, chlorophyll content, and ROS formation. PFBA was more toxic to P. parvum than PFOA inducing oxidative stress and an increase in chlorophyll production. In Chlorella sorokiniana, the IC50 values of PFOA and PFBA for day 3 were 277.1 and 101.4 mg/L respectively, PFBA was more toxic to chlorella than PFOA. The two chemicals significantly affected growth at higher concentrations but had no effect on cell size, and chlorophyll content at any of the concentrations tested. Both PFCAs caused an increase in ROS formation and oxidative stress with PFBA having a greater effect. There was no consistent dose-dependent effect observed for both PFCAs, but a threshold toxicity point was observed. The zebrafish study assessed the effects of PFOA and PFBA on mortality, morphological changes, behavioral alterations, reactive oxygen species production, and alterations in gene expression as endpoints for developmental toxicity. Glucose transporter genes were used as they are implicated in various processes involved in embryonic zebrafish development. Neither of the two PFCAs significantly affects mortality and morphological parameters. Both PFCAs significantly influenced behavior by inducing hypoactivity (PFOA) and hyperactivity (PFBA). PFOA and PFBA induced oxidative stress by increasing ROS formation but did not significantly alter gene expression of glucose transporter genes. PFOA and PFBA induced toxicity at different magnitudes in microalgae and similar magnitudes in zebrafish.