A Predictive Model for the Migration and Bioaccumulation of Residual Malachite Green in Aquaculture Sediments:...

Aquatic product safety is closely linked to human health, yet the effects of historical residual drugs in aquaculture pond sediment remain unclear. Malachite green (MG), a prohibited aquaculture drug, is rapidly converted to leucomalachite green (LMG) after illegal use and may persist in bottom sediment, raising the question of whether residue-positive sediment can cause positive detections in fish at harvest. In order to answer this question, we developed a time-dependent predictive model for the sediment-water-fish system based on a food web bioaccumulation model and a sediment-water equilibrium model. The model examines the relationship between historical MG residues in sediment and positive detections in aquatic products, and estimates LMG residue levels in fish at harvest. The reliability of this model was further validated through comparison with measured data. The results showed that when the sediment residue concentration was 227.48 μg/kg, the maximum LMG concentration in fish during the culture period reached 0.56 μg/kg, indicating a positive correlation with fish concentration. The closer the habitat water layer was to the sediment, the higher the risk of positive detection in fish; in the middle water layer, the LMG concentration in fish could reach 0.28 μg/kg, and, under ideal conditions, a two-fold relationship existed between the middle and lower water layers. Sediment organic carbon content determined the amount of LMG released into the water; when it was set to 0.0035, the initial LMG concentration in water was 0.07 μg/kg, showing a negative correlation with fish concentration. This study confirmed that a certain amount of residual malachite green in sediment could cause positive detection in mandarin fish during the culture period, which is consistent with the validation experiment. If the model predicted no positive detection at the pollutant concentration corresponding to the sediment of the positive detection pond, this would indicate that malachite green originated from other sources during the culture process; otherwise, the sediment may lead to the risk of positive detection in fish. One limitation of the model is that it may underestimate pollutant concentrations in fish during the early stages of aquaculture. In addition, its ability to predict the effects of combined pollutant exposure remains to be validated. The model developed here can be used to estimate residue levels of aquaculture drugs during the culture period and may provide regulatory authorities with a basis for distinguishing historical residues from illicit use, thereby improving the efficiency of aquatic product quality and safety supervision.