Organic matter dependent toxicokinetic of lindane in soil: Insights from enchytraeid bioaccumulation studies

The bioavailability and toxicity of a given chemical can vary considerably depending on specific soil properties, especially the organic matter (OM) content. These properties determine the partition of organic chemicals between soil particles and porewater, and hence, its bioaccumulation potential in soft bodied soil invertebrates. LUFA 2.2 soil (3 % OM) better represents European arable soils than the standard OECD soil (10 % OM), commonly used in regulatory studies. This discrepancy, may lead to an underestimation of bioaccumulation and toxicity in natural environments in regulation assessments. The current study, therefore, investigates how soil organic matter (OM) content affects the bioaccumulation of lindane in Enchytraeus crypticus. A two-week toxicokinetic experiment was conducted using LUFA 2.2 soil (2.85 % OM) and an amended LUFA 2.2 soil (10 % OM). Results showed that kinetic bioaccumulation factors (BAF_k) were twice as high in LUFA 2.2 soil compared to amended LUFA 2.2 soil, mainly due to differences in uptake rate constants. Elimination rate constants remained similar between soil types, suggesting that OM content primarily affects uptake processes. The study also compared findings with literature data on enchytraeids and earthworms, revealing higher uptake rate constants and BAF_k in enchytraeids. The inverse correlation between OM content and BAF_k was consistent across studies, highlighting the importance of soil composition in influencing bioaccumulation. These findings highlight how soil properties influence the bioavailability and potential toxicity of persistent, lipophilic chemicals like lindane, emphasizing the need for risk assessment practices to use soils with representative OM levels for more accurate environmental toxicity predictions.