Dissolved organic matter affects both bioconcentration kinetics and steady-state concentrations of polycyclic...

Dissolved organic matter (DOM) is ubiquitous in natural aquatic ecosystems. The association of hydrophobic organic compounds (HOCs), such as polycyclic aromatic hydrocarbons (PAHs), with DOM may have a large impact on HOC fractions in water and their bioconcentration in fish. However, the effects of DOM on HOC bioconcentration in fish are not well understood, especially whether DOM will affect the bioconcentration steady-state concentrations of HOCs in fish is still confusing. Thus, this study investigated the effects of three DOM including gallic acid (GA), tannic acid (TA), and humic acid (HA) with molecular weights ranging from 170 Da to about 10 kDa at different concentrations (1, 5, and 15 mgOC L^-1) on the bioconcentration of PAHs including phenanthrene, anthracene, fluoranthene, and pyrene in zebrafish (Danio rerio), with the PAH freely dissolved concentrations maintained constant by passive dosing systems. The results revealed that the presence of DOM generally increased the bioconcentration steady-state concentrations of the PAHs in zebrafish (C_b-ss), with the increase ranging from 28.1% to 204.0%, and the increase of C_b-ss promoted by TA with middle molecular weight (1700 Da) was the highest among the studied DOM. Moreover, the C_b-ss increased with the concentrations of GA with low molecular weight and TA with middle molecular weight in water, whereas decreased with increasing concentrations of HA with high molecular weight. The uptake rate constants of the PAHs in zebrafish with DOM were higher than that without DOM. Ingestion of DOM and direct accumulation of PAHs associated with DOM might be primary influencing mechanisms of DOM on the C_b-ss, and whether the facilitated diffusive mass transfer by DOM will affect the C_b-ss needs to be further studied. This study suggested that DOM-associated HOCs should be considered in future HOC risk assessment in addition to the freely dissolved HOCs.