Time-dependent toxicokinetics of [14C]lindane in the terrestrial isopod Porcellionides pruinosus

Preliminary acute soil toxicity tests are a starting point for risk assessment. These tests are performed at one exposure time and are used to estimate the lethal concentration for 50% of the population (LC50). However, it is known that LC50 varies over time, following an exponential decay model. Here, we present the variation of LC50 over time in the isopod Porcellionides pruinosus exposed to [14C]lindane when considering the concentrations measured in bulk soil and in extracted water. Using a wide range of concentrations, the percent mortality was recorded over various time intervals. Higher concentrations strongly influenced isopod survival. The LC50 infinity value for P. pruinosus was 3.57 micrograms/g for bulk soil concentration, suggesting a great sensitivity of this species to lindane. Simultaneously, the values estimated for the lethal body concentration (LBC) were 2.36 micrograms/g animal for bulk soil concentrations and 2.79 micrograms/g animal when extracted water concentrations are considered. An alternative to the LC50 determination is the estimation of LBC, which is proposed as a better way to describe the acute toxicity of chemicals. Kinetic-based toxicity models were fitted to the data and revealed uptake rate constants of 1.1 g soil/g animal/week and 84.3 ml extracted water/g animal/week for bulk soil and extracted water concentrations, respectively. Elimination rate constants of 1.7 per week were found for both pathways of exposure.