The role of carbonaceous materials in pavement dust, soils, and lake sediments on the fate of organic pollutants in small urban watersheds

Sorption to carbonaceous materials (CMs) is an important process controlling the transport and fate of particle-associated contaminants (PACs) in the environment. PACs sorbed to CM particles in the terrestrial environment, including pavement dust and soils, may enter receiving water bodies with storm water runoff and become a primary source of contaminants in lake sediments. The overall objective of this study is to characterize the role of CMs in pavement dust, soils and lake sediments on the fate of PACs in small urban watersheds, with a focus on polycyclic aromatic hydrocarbons (PAHs). The specific objectives are (1) to determine the origin, distribution and properties of CM particles in an urban watershed and the types of CM particles that concentrate, transport, and retain PAHs in urban watersheds; (2) to explore the effects of asphalt and coal tar on the quantification of black carbon (BC) in environmental samples from an urban watershed with chemical and thermal oxidation methods; and (3) to investigate the correlations between CM properties and their corresponding sorption affinity to PAHs.;Field samples were collected from the Lake Como watershed in Fort Worth, Texas, USA, including parking lot and street dust, soils, and stream and lake sediments. Characteristics of CM particles determined by organic petrography were compared to PAH concentrations. A significant correlation between PAH concentrations and organic carbon (OC) in soot, coal tar, and asphalt indicates that these three CM particle types are the major sources and carriers of PAHs in the watershed. Estimates of the distribution of PAHs in CM particles indicate that coal-tar pitch, used in pavement sealants, is a dominant source of PAHs in the watershed.;Black carbon (BC) has been considered as the most important CM that affects the fate and bioavailability of PAHs due to its strong sorptivity. To investigate the potential influence of asphalt and coal tar on BC quantification, total BC in field samples and reference asphalt and coal-tar materials was quantified using chemical treatment through acid dichromate (Cr2O7) oxidation and chemo-thermal oxidation at 375°C (CTO-375). Comparison of results by the two oxidation methods and organic petrography indicates that both coal tar and asphalt contribute to BC quantified by Cr2O 7 oxidation, and that coal tar contributes to BC quantified by CTO-375. Caution is therefore advised when interpreting BC measurements in urban environmental dust, soil, and sediment samples with these methods.;Field samples were fractionated into light (LFr), heavy (HFr), and condensed CMs (CCMs) fractions with sequential physical and chemical treatment. These fractions and bulk samples were characterized with elemental analysis, Fourier transform infrared spectroscopy, specific surface area measurement, and solid state 13C nuclear magnetic resonance spectroscopy. Sorption isotherms of phenanthrene to these fractions and bulk samples fitted with Freundlich models are nearly linear (N = 0.90--1.00), suggesting a partitioning-dominated mechanism which likely is attributed to the sorption contribution from asphalt and coal tar. No statistically significant correlation was observed between CM properties and sorption parameters. The phenanthrene sorption to bulk samples is dominated by CCMs in HFr fractions.