Fish can acclimate to chronic arsenic (As) exposure, but the mechanisms of acclimation remain unclear to date. Therefore, this study conducted 28-d chronic inorganic As [As(III) and As(V)] exposures in freshwater medaka (Oryzias mekongensis), examined the As bioaccumulation and biotransformation during exposure, and the As acute toxicity and toxicokinetics after exposure. After chronic As(V) exposure, the 96-h lethal concentration (96-h LC50) of As(V) increased 1.3-fold (from 223 to 286 μmol/L), indicating that the fish became more tolerant to As(V). The As bioaccumulation in As(V)-exposed fish increased gradually during the initial 21-d exposure period and then decreased at 28 d, indicating that acclimation occurred to regulate the total As levels. Toxicokinetics measurement suggested that As(V) uptake (uptake rate constant, ku) was significantly decreased and As(III) elimination (efflux rate constant, ke1) was significantly increased, both of which could reduce As bioaccumulation. Furthermore, the organic As species became more predominant (50.1-69.3%) in exposed fish, while the inorganic As species were predominant (53.6-56.4%) in the control fish, suggesting that the capability of As biotransformation increased to acclimate inorganic As during chronic exposure. In summary, this study elucidated the acclimation strategies (reduced bioaccumulation and increased biotransformation) of O. mekongensis to counter the ambient As contamination.
Keywords: Acclimation; Arsenic; Bioaccumulation; Biotransformation; Freshwater fish.
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