Uptake, Distribution, and Elimination of Selenite in Earthworm Eisenia Fetida at Sublethal Concentrations Based on Toxicokinetic Model

Natural and anthropogenic causes have promoted the rapid increase of soil selenium (Se) level, and ecological risks of excess Se have attracted much attention. Exploring the dynamic of Se in organisms can help to better understand its toxicity. However, the full-process analysis of its uptake and elimination in soil biota has not been clearly revealed. In this study, toxicokinetic (TK) model was applied to investigate the dynamics of selenite in earthworm Eisenia fetida exposed to sublethal doses. The results showed earthworm Se bioaccumulation basically reached equilibrium on Days 14 and 28 in the uptake and elimination phases. The highest Se concentrations in the preclitellum (PC), postclitellum (PoC), and total earthworms were 95.71, 70.40, and 79.94 mg/kg (14 d, 20 mg Se/kg), respectively, which indicated a distinctive Se accumulation capacity among them. Se kinetic rates in PCs were faster than in the whole E. fetida in both uptake (Kus = 0.30-0.80 mg/kg/day) and elimination phases (Kee = 0.024-0.056 mg/kg/day), while shorter half-life times (LT1/2) were present in PCs (12.28-29.22 d) than in whole worms (17.85-47.15 d). The kinetic Se bioaccumulation factor (BAFk) in the PC and total earthworm were basically the same (12-19), and was higher than those at steady-state (BAFss) in both parts (3-10). Demonstrated that Se can be quickly enriched and cleared from earthworm PC. The excreted Se concentrations from earthworm PCs steadily increased (7.05-32.46 mg/kg) as the soil Se doses improved; nevertheless, it was relatively difficult for the PoC and total earthworms to eliminate Se. Revealing the kinetic accumulation and excretion characteristics of Se is helpful for understanding the metabolism or detoxification process of Se in earthworms and may also provide a theoretical basis for further study of the ecotoxicological effects of Se