Toxicokinetics and toxicodynamics of nickel in Enchytraeus crypticus

Abstract

Metal toxicity is usually determined at a fixed time point, which may bias the assessment of risks associated with varied exposure time. Time-dependent accumulation and toxicity of nickel in the potworm Enchytraeus crypticus were investigated in solutions embedded in an inert quartz sand matrix. Internal Ni concentration and mortality were determined at 7 different time intervals and interpreted from the perspective of toxicokinetics and toxicodynamics. A 1-compartment model was used to describe the uptake and elimination kinetics of Ni. At each exposure concentration, Ni concentration in the organisms increased with increasing exposure time, reaching equilibrium after approximately 14 d. Median lethal concentration (LC50) decreased with time and reached an ultimate value of 0.182 mg/L. The LC50 values expressed as internal Ni concentrations (LC50inter) were almost constant (16.7 mg/kg body dry wt) at each exposure time. The LC50inter was independent of exposure time, suggesting that internal concentration was a better indicator of Ni toxicity than external concentration. The uptake rate constant was 11.9 L/kg/d, and elimination rate constants were 0.325/d (based on internal concentration) and 0.070/d (based on survival), indicating that not all internal Ni contributes to toxicity. The present study highlights the importance of taking time into account in future toxicity testing and risk assessment practices.

A generic biotic ligand model quantifying the development in time of Ni toxicity to Enchytraeus crypticus

“…Under the same cation composition of test solutions, LC50{Ni 2+ } decreased with exposure time, which was also found for the toxicity of Ni to E. crypticus and Folsomia candida (Broerse and Van Gestel, 2010;He and Van Gestel, 2013). In the present study, Ca 2+ , Mg 2+ and Na + exerted significant effects on Ni toxicity, however, with time the magnitude of their effect on Ni toxicity decreased.…”

“…Metals accumulate in organisms with time and cause toxic effects when the body metal concentration reaches a critical level (Jager et al, 2011). Consequently, toxicity of metals is time-dependent, with LC50 decreasing with exposure time and reaching equilibrium after certain exposure time (Verma et al, 2012;He and Van Gestel, 2013). When developing BLMs for predicting dynamic metal toxicity, the f 50 values for Cu, Co and Cd toxicity to Lemna paucicostata and As toxicity to Corbicula fluminea decreased with exposure time and approached equilibrium after 80 and 150 h, respectively (Hatano and Shoji, 2010;Chen and Liao, 2010).…”

“…The toxicity tests with adult E. crypticus were performed with three exposure times (7, 10 and 14 d) and three replicates for each treatment. The exposure times were selected based on the fact that equilibrium of Ni accumulation was reached in 10-14 d (He and Van Gestel, 2013). Ten adults were exposed in a 100 mL glass jar, containing 20.0 g pre-treated quartz sand and 5.4 mL test solution equilibrated for 1 d before starting exposures.…”

“…This system provides a means to manipulate the composition of the pore water, with minimum influence of the soil solid phase. Quartz sand was pretreated following He and Van Gestel (2013) and used as test matrix. All used chemicals were of reagent grade (Sigma-Aldrich; >99%).…”

Delineating the dynamic uptake and toxicity of Ni and Co mixtures in Enchytraeus crypticus using a WHAM-FTOX approach

“…The quartz sand was pretreated by combustion and acid washing; see He and Van Gestel (2013) for the pretreatment method and the particle size distribution of pretreated quartz sand. All used chemicals were of reagent grade (Sigma-Aldrich; >99%).…”