Distributed Sequestration and Release of PAHs in Weathered Sediment:  The Role of Sediment Structure and Organic Carbon Properties

Abstract

Polycyclic aromatic hydrocarbon (PAH) contaminated sediments from Piles Creek (PC) and Newtown Creek (NC) in the NY/NJ Harbor estuary were separated into size fractions and further separated into low (<1.7 g cm(-3)) and high (>1.7 g cm(-3)) density fractions. The fractionated sediments were characterized for carbon content pore structure, surface area, and PAH concentration. Most PAHs (50-80%) in both sediments were associated with the low-density fraction, which represents only 3-15% of total sediment mass, at levels greater than expected based on equilibrium partitioning. PC low-density sediment had 10 times greater organic carbon-normalized equilibrium partitioning coefficients (Koc) than the other size fractions and whole sediment. Characterization of the sediment organic matter suggested that the preferential sequestration observed in PC sediment was not correlated with soot carbon but was likely due to the presence of detrital plant debris, an important food source for benthic animals. Fractional PAH desorption from whole PC sediment was significantly higher than from NC sediment after 3 months. For both sediments, a smaller percentage of the total PAHs was desorbed from the low-density fraction. However, because PAH concentrations were greatly elevated in these fractions, more PAH mass was desorbed than from the corresponding bulk and high-density fractions. These results demonstrate that PAHs are preferentially sequestered in a separable, low-density fraction at levels not predictable by equilibrium partitioning theory. Further, the low-density fraction apparently controls whole-sediment PAH release. Although plant debris appears to be an important sorbent for PAHs, this material may readily release PAHs into the aqueous phase.

Partitioning and sources of PAHs in wastewater receiving streams of Tianjin, China

“…This proved our hypothesis to some extent as Yongding New River acts as both water resources for agriculture irrigation and waterway for flood control in wet seasons except receiving wastewater from Tianjin. BC as well as kerogen carbon and diagenetically aged material are viewed as comprised of "glassy" organic matter responsible for strong HOC sorption, nonlinear adsorption behavior, and slow mass transfer rates (Rockne et al 2002;Ran et al 2007). Assuming the overall sedimentwater distribution coefficient K d can be apportioned into the terms representing organic carbon absorption and BC adsorption, Lohmann et al found that BC was responsible for over 90% of the total PAH sorption in Boston Harbor sediment and over 80% in New York Harbor sediment (Lohmann et al 2005).…”

“…Researchers observed that heterogeneity in naturally occurring carbonaceous materials (CMs) caused sorption processes of hydrophobic organic compounds (HOCs) in sediments to occur as a combination of absorption into amorphous organic matter and adsorption onto condensed forms of CMs such as black carbon (BC), coal, and kerogen, collectively termed "carbonaceous geosorbents" (CG) (Allen-King et al 2002;Cornelissen et al 2005). Many studies reported that adsorption of PAHs onto CG can greatly affect their bioavailability and toxicity as "sequestration" of PAHs in sediments often takes place (Gustafsson et al 1997;Luthy et al 1997;Nam et al 1998;Rockne et al 2002;Shor et al 2003;Abu and Steve 2005).…”

Use of Data on Contaminant/Sediment Interactions to Streamline Sediment Assessment and Management

“…The literature is rife with attempts to model contaminant behavior (e.g., flux, toxicity, or bioaccumulation) based on simple assumptions about specific sedi ment characteristics. In general, these attempts to find controlling parameters succeed for single sites, but do not extrapolate across disparate sites--contaminants behave differently in different environments (Chadwick et al, 2002;Rockne et al, 2002). Given this complexity, it is impossible to predict the absolute risk of a given mix of anthropogenic contaminants on an ecosystem or human health without extensive site-specific analyses.…”

Extraction of sediment‐associated polycyclic aromatic hydrocarbons with granular activated carbon

“…Refractory phases such as BC and weathered oil might significantly limit desorption of HOCs to AC [16,17]. However, a substantial fraction of HOCs is known to be associated with light-density organic carbon [18] composed of humic/fulvic substances, lignin, and plant debris or mineral particles [19]. This fraction of HOCs can be expected to desorb readily and bind to AC particles in a sediment slurry.…”