Dissolved organic matter (DOM) and suspended particles are important components of natural waters, which are key environmental factors for the bioavailability of hydrophobic organic compounds (HOCs) in rivers and lakes. However, the bioavailability of DOM- and particle-associated HOCs is not clear. In this research, pyrene was selected as a model HOC and its freely dissolved concentration (Cfree) was maintained by passive dosing systems. The immobilization and pyrene content in the tissues excluding gut of Daphnia magna were examined to quantify the bioavailability of DOM- and particle-associated pyrene. The results indicated that both DOM and particles promoted the bioavailability of pyrene when the Cfree of pyrene was kept constant. The bioavailability of pyrene associated with DOM of various molecular weights was ordered as middle molecular weight (5-10K Da) DOM > lower molecular weight (<1K Da, 1-3K Da, and 3-5K Da) DOM > higher molecular weight (>10K Da) DOM. The immobilization caused by pyrene associated with different grain size suspended particles was ordered as 50-100 μm> 0-50 μm> 100-150 μm. The influencing mechanisms of DOM molecular weight and particle size were related with the partition of pyrene between DOM/particles and water, the uptake routes of DOM and particles by Daphnia magna, and the desorption or release of pyrene from DOM and particles in the gut of Daphnia magna. The findings obtained in this research suggest that the bioavailability of HOCs associated with DOM of different molecular weights and particles of different grain sizes should be taken into account for the eco-environmental risk assessment of HOCs in water systems. A water quality evaluation model was proposed to comprehensively consider the bioavailability of free-dissolved, DOM- and particle-associated HOCs.
Corresponding author: xiaxh@bnu.edu.cn