Sorption of perfluorooctane sulfonate (PFOS) on kaolinite coated with humic acid and its oxidative stress to Daphnia magna

Abstract

PFOS was reported as potentially persistent, bioaccumulative, and toxic (PBT) and as a priority hazardous substance. The PFOS can be released into various environmental media and be transported to biotic and abiotic components. Determining sorption of PFOS helps to provide information for managing PFOS in the environment. Confirmation of toxic effects using oxidative stress analysis is one of the methods to determine the toxic effects of hazardous chemicals. In this study, sorption, bioaccumulation, and oxidative stress analysis of PFOS was determined in the presence of kaolinite (KN), kaolinite coated with humic acid (HA-KN), and Daphnia magna. The nominal concentration of the PFOS was 10 µg L-1. The concentration of PFOS was determined using Triple Stage Quadrupole Mass Spectrometer (LC-MS/MS). Oxidative stress analysis was performed through GSH and CAT assay in Daphnia magna. The results showed the ability to get PFOS was strong in the order of HA-KN b, HA-KN a, KN, and Daphnia. The Log Kd (L kg-1) values of the KN group was 3.65 ± 0.10, that of HA-KN a group was 4.26 ± 0.08, and that of HA-KN b group was 4.33 ± 0.04. This suggests that the foc values of sorbent may affects the sorption of PFOS. In particular, the ability to get PFOS increased as the foc values of the sorbent increases. The results of bioaccumulation experiment represented the body burden (µg g-1) of the control group was 26.71 ± 5.82, that of the KN group was 24.85 ± 4.65, that of HA-KN a group was 23.42 ± 0.91, and that of HA-KN b group was 17.72 ± 1.44. This suggested that the amount of PFOS accumulated in daphnia decreased when daphnia was with the sorbent coated with higher foc values. On the other hand, there was no significant difference in Log BAFss values between control group and treatment group, suggesting that the inorganic particles and organic particles did not significantly affect the BAF value at PFOS 10 µg L-1. The GSH content of Daphnia was decreased in the group affected by both PFOS and HA-KN compared to the group affected only by PFOS. This may suggest that HA-KN may affect the GSH content of Daphnia, The GSH content at various concentrations of PFOS represents no significant difference from 10 to 5000 µg L-1 of PFOS. This suggests that in order to identify the change of GSH content by PFOS in daphnia, it is necessary to expose a concentration more than PFOS5000 µg L-1 or use another toxicity test. The CAT activity of daphnia with kaolinite decreased than control group, and as the foc values increased, the CAT activity increased. This may suggest that CAT activity of daphnia can be affected by particles in aquatic ecosystem at PFOS 10 µg L-1. The relatively higher CAT activity was represented in daphnia at 5000 µg L-1 of PFOS. This suggests that in order to identify the change of CAT activity by PFOS in daphnia, it is necessary to expose 5000 µg L-1 of PFOS or more than that.