Toxicokinetics of typical halogenated organic pollutants (HOPs) in frogs (Rana tigrina cantor) via skin exposure and effects of hibernation

Abstract

Dermal uptake and hibernation represent critical but understudied factors affecting the bioaccumulation of halogenated organic pollutants (HOPs) in frogs. In this investigation, female frogs were initially exposed to HOPs through skin exposure, then divided into hibernation and non-hibernation groups to examine depuration dynamics. The bioaccumulation fraction calculated by representative tissues (muscle, skin, liver, and egg) ranged from 4.1 % to 52 %, which increased linearly with log K_OW (r = 0.51, p < 0.05) for most compounds. However, the elimination rate (k_d, excluding BDE209) exhibited a significant negative correlation with log K_OW (r = -0.45, p < 0.05). Bioaccumulation reflects the net balance of absorption and elimination during exposure, the observed positive correlation in bioaccumulation fraction likely stems from the negative correlation of elimination. The tissue distribution patterns exhibited both temporal variations and compound-specific characteristics. The maternal transfer ratios (EMRs, egg to maternal tissue ratios) demonstrated distinct tissue-specific relationships with log K_OW. Significant positive linear correlations were observed for EMR_skin (r = 0.70-0.99, p < 0.01) and EMR_muscle (r = 0.70-0.99, p < 0.01), while liver tissues showed significant negative correlations (EMR_liver: r = -0.42 to -0.83, p < 0.01). Hibernation reduced the elimination rate of liver. The k_d values for non-hibernation frogs ranged from 0.027 to 0.080, which was 0.84 (PCB20) to 3.0 (BDE209) times that of hibernation ones. After accounting for physiological amplification due to weight loss, the hibernation magnification factors (HMFs) for liver tissues ranged from 1.00 (PCB95) to 2.81 (PCB77). In contrast, most compounds exhibited HMFs <1 in eggs, indicating that hibernation suppressed contaminant transfer from maternal tissues to eggs.