Arsenic bioaccumulation and biotransformation in the marine copepod Tigriopus japonicus under chronic dietborne and waterborne exposure.

Arsenic (As) can be transferred along the food chain, while little is known about the toxic effects of dietborne As on marine copepods. In this study, we investigated the short-term and long-term effects of waterborne and dietborne As exposure on the bioaccumulation and biotransformation, as well as developmental toxicity of Tigriopus japonicus. Under acute As exposure, As bioaccumulation increased and reached a plateau with increasing exposure concentration. Moreover, As accumulation at dietborne exposure was 4.3 and 5.7 times greater than that at control group for AsIII and AsV, respectively. At chronic As exposure, As accumulation increased continuously with exposure time, with a 2.8-day extension of development time and a 45% reduction in 10-d fecundity under dietborne exposure compared to control, whereas 2.3-day extension of development time and a 20% reduction in 10-d fecundity were observed under waterborne exposure. Among As species, inorganic As had the highest concentrations, but the proportion of inorganic As decreased from 89% to 63% during 4 to 21 d of exposure, suggesting the conversion of inorganic As to organic As. The organic As was dominated by arsenobetaine (AsB, 13-25%), followed by monomethylarsenic (MMA, 8-25%). These results suggest that dietborne exposure has more pronounced toxic effects on T. japonicus, but the toxicity of As could be reduced through biotransformation under chronic exposure. Therefore, the arsenic species should be considered when assessing As toxicity.