Contribution of ingestive/dietary uptake to bioaccumulation of organics in worms.

Abstract

Ingestive uptake is critical for understanding the accumulation and trophic transfer of chemicals and synthesized particles in general. This study explored the contribution of ingestion in the bioaccumulation of chemicals focusing on worms. Novel theory and equations were developed to derive fractional ingestive contribution, f_s, from a broad range of dietary uptake and accumulation studies, and to build a small dataset of f_s (n = 43) from relevant toxicokinetic and bioaccumulation measurements. Worm f_s could be fitted to log K_OW-based sigmoidal models with small errors (RSE < 0.15, RMSE<0.15). The basis and limitations of the applied f_s equations were elaborated. These included the assumption that aqueous-based and dietary-based elimination rate constants (k_T^w and k_T^S) may be statistically equivalent, as demonstrated using fish and worm data. Bioaccumulation and toxicokinetic parameters obtained at under-exposed conditions can also result in non-sensical, negative f_s. The developed f_s theory suggested a novel way to model bioaccumulation in the presence of aqueous and solid sources, and the potential to consolidate bioaccumulation data in their variant forms and definitions for assessment, modeling, and benchmarking purposes. While the presented f_s-log K_OW dependence remained to be explored in other species, the importance of ingestive uptake for high-log K_OW chemicals questioned the validity of characterizing and regulating bioaccumulation potential of hydrophobic organics - for which dietary uptake matters - using aqueous-only bioconcentration factor (BCF). This question, along with other less important ones, is yet to be explored in future works.