Sources, Vertical Fluxes, and Accumulation of Aliphatic Hydrocarbons in Coastal Sediments of the Río de la Plata Estuary, Argentina

Abstract

Settling particles and underlying sediments collected at 1, 2.5 and 4 km off the metropolitan Buenos Aires coast were analyzed to evaluate the sources and accumulation of resolved (RES), unresolved (UCM), and biomarker aliphatic hydrocarbons. Sedimentary aliphatic concentrations (RES 0.11-14 microg x g(-1); UCM 0.1-800 microg x g(-1)) included variability associated with north-south gradients and an exponential offshore reduction. Highest concentrations were registered close to Buenos Aires port and sewer, compared to cleaner northern stations and southward sites affected by a seaward residue transport. Sediment traps deployed in the sewer area revealed large hydrocarbon (38 and 319 mg x m(-2) x day(-1), RES and UCM) and total organic carbon fluxes (29 +/- 26 g x m(-2) x day(-1). The composition of RES and hopanes evaluated by principal component analysis indicated a consistent offshore gradient defined bythe relative contribution of lower vs higher molecular weight components. Distant sites showed decreasing proportions of petrogenic n-C(17-26) alkanes, isoprenoids, and C(20-27) terpanes and relative enrichment of n-C(27,29,31,33) terrestrial plant alkanes and C(31-33) homohopanes. Sediment hydrocarbon profiles showed an average 2-fold reduction down to 20 cm depth with preferential removal of lower molecular weight components and enrichment of n-C(23-35) alkanes and hopanes. Sediment inventories and trap depositional fluxes indicate the accumulation of 5800-9700 tons of aliphatic hydrocarbons in the top 0-5 cm sediments with a strong interfacial alteration and selective preservation of refractory components: n-C(13-22) (1.0%) < isoprenoids (3.2%) < n-C(23-35) (6.1%) < hopanes (47%) approximately UCM (50%), compared to intermediate stability of organic carbon (12%) and quantitative preservation of polychlorinated biphenyls (PCBs) (91%).

Characteristics of petroleum hydrocarbons in surficial sediments from the Songhuajiang River (China): spatial and temporal trends

“…A significant correlation between organic carbon and PH has been confirmed (Colombo et al 2005). In the study, the total organic carbon content was 0.08% to 3.71% in the sediments, and the silt-clay content was 3.24% to 56.31% (Table 1).…”

Use of aliphatic hydrocarbons to infer terrestrial organic matter in coastal marine sediments off China

“…On the other hand, long-range atmospheric transport can introduce terrestrial organic materials to areas distant from the points of discharge. One approach to understanding the sources and transport mechanisms of organic materials accumulated in continental shelf sediments is to utilize molecular organic geochemical methods, among which aliphatic hydrocarbons (n-alkanes) have been widely utilized (Colombo et al, 2005;Doskey, 2001;Tolosa et al, 1996). There are allochthonous and autochthonous sources for n-alkanes preserved in sediments (Doskey, 2001).…”

Depositional History of Polycyclic Aromatic Hydrocarbons: Reconstruction of Petroleum Pollution Record in Peninsular Malaysia

“…Homohopanes are the name of hopane series in which the number of carbon arises by thirty (n=30). The relatively more abundant homohopanes (C 31 -C 35 ) are showed in less oil contaminated sites with significant loss of C 30 (Colombo et al, 2005). In environmental samples from the biomass burning, hopane appears together with moretanes with abundance of C 27 and C 31 (Standley and Semoneit, 1987) that overlaps in common peaks (Omar et al, 2006).…”

“…We believe that the stereochemistry of twin peaks provides resistibility against temperature increase rather than single peaks. Thus, it is criticized that high temperature especially in combustion process of petroleum in internal engines may cause destruction on compound structure appear as demolished or depleted peaks in chromatograms (Peters et al 1992;Colombo et al, 2005). Hence, application of some compound and isomer pair ratios of hopane are failed to assist source identification of PAHs (Peters et al, 1992).…”