Interaction mechanism of nonpolar organic contaminants in natural organic matter: Dominating role of adsorption (micropore-filling)

ENVR 10

Yong Ran, yran@gig.ac.cn1, Ke Sun1, Baoshan Xing, bx@pssci.umass.edu2, and Li Zhou, zhouli@public.tpt.tj.cn3. (1) State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 511 Kehuajie, Tianhe District, Guangzhou, 510640, China, (2) Department of Plant, Soil and Insect Sciences, University of Massachusetts, Stockbridge Hall, Amherst, MA 01003, (3) School of Chemical Engineering, Tianjin University, Tianjing, 300072, China
Although microporosity and surface area of natural organic matters (NOM) are crucial for mechanistic evaluation of the sorption process for nonpolar organic contaminants (NOCs), they have been underestimated by the N2 adsorption technique. Here we investigated the CO2-derived microporosity (Vo) and specific surface area (SSA) and related them to sorption behaviors of NOCs in a range of NOM including Pahokee peat fractions, kerogen isolates, coals with varied maturation and soils/sediments. The correlation between micropore volumes Vo or surface area SSA and organic carbons contents (OC %) is very significant for the investigated 11 NOM samples (R2=0.72 and 0.77, respectively) and is also consistent with that reported in the previous investigations on the 10 peat, humic acid and soil/sediment samples, demonstrating that microporosity primarily originated from the NOM matrices. The average Vo and CO2-SSA per gram OC are respectively 75.1 μL/g-OC and 192 m2/g-OC from the correlation analysis on the 21 samples. The rigid aliphatic carbon in the Pahokee peat significantly contributes to the microporosity of NOM. A linear correlation has been discovered between the micropore volume and the sorption capacity for each of four NOCs (phenanthrene, naphthalene, 1,3,5-trichlorobenzene and 1,2-dichlorobenzene). The micropore volume is high enough for accommodating the sorption of NOCs. The small molecular solutes, DCB and Naph, and the gas adsorbate have equal accessibility to the same microporous domain of NOM. We, for the first time, provide direct evidence that adsorption (micropore-filling) rather than linear partitioning dominates the mechanism for NOC sorption by NOM. Our new observation on the interaction mechanism of NOCs with NOM offers new clues for explaining the often observed nonideal sorption behaviors of NOCs such as nonlinear sorption, slow sorption/desorption, desorption hysteresis, reduced bioavailability and long persistence.
 

Fate of Persistent Organic Pollutants in Urban Systems
8:30 AM-11:30 AM, Sunday, August 19, 2007 Boston Park Plaza -- Beacon Hill Rm, Oral

Division of Environmental Chemistry

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007