Salinity mediates the toxic effect of nano-TiO 2 on the juvenile olive flounder Paralichthys olivaceus.

Increased production of engineered nanoparticles has raised extensive concern about the potential toxic effects on marine organisms living in estuarine and coastal environments. Meanwhile, salinity is one of the key environmental factors that may influence the physiological activities in flatfish species inhabiting in those waters due to fluctuations caused by freshwater input or rainfall. In this study, we investigated the oxidative stress and histopathological alteration of the juvenile Paralichthys olivaceus exposed to nano-TiO ₂ (1 and 10 mg L ^-1 ) under salinities of 10 and 30 psu for 4 days. In the gills, Na ⁺ -K ⁺ -ATPase activity significantly deceased after 4 days 10 psu exposure without nano-TiO ₂ compared with 1 day of acclimating the salinity from the normal salinity (30 psu) to 10 psu. Under this coastal salinity, low concentration (1 mg L ^-1 ) of nano-TiO ₂ exerted significant impacts. In the liver, the activities of superoxide dismutase, catalase, the levels of lipid peroxide and malondialdehyde increased with nano-TiO ₂ exposed under 30 psu. Such increase indicated an oxidative stress response. The result of the integrated biomarker responses showed that P. olivaceus can be adversely affected by high salinity and high concentration of nano-TiO ₂ for a short-term (4 days) exposure. The histological analysis revealed the accompanying severe damages for the gill filaments. Principal component analysis further showed that the oxidative stress was associated with the nano-TiO ₂ effect at normal salinity. These findings indicated that nano-TiO ₂ and normal salinity exert synergistic effects on juvenile P. olivaceus, and low salinity plays a protective role in its physiological state upon short-term exposure to nano-TiO ₂ . The mechanism of salinity mediating the toxic effects of NPs on estuarine fish should be further considered.
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