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

• Published in: Environmental science & technology 2005-11, Vol.39 (21), p.8227-8234
• Main Authors: Colombo, J. C, Cappelletti, N, Lasci, J, Migoya, M. C, Speranza, E, Skorupka, C. N
• Format: Article
• Language: English
• Subjects: Applied sciences; Argentina; Biological and physicochemical properties of pollutants. Interaction in the soil; Brackish; Chromatography, Gas; Contaminated sediments; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geologic Sediments - chemistry; Hydrocarbons; Hydrocarbons - analysis; Hydrocarbons - chemistry; Molecular weight; PCB; Pollution; Pollution, environment geology; Polychlorinated biphenyls; Principal components analysis; Sediments; Soil and sediments pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es051205g

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 μg·g-1; UCM 0.1−800 μg·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·m-2·day-1, RES and UCM) and total organic carbon fluxes (29 ± 26 g·m-2·day-1). The composition of RES and hopanes evaluated by principal component analysis indicated a consistent offshore gradient defined by the relative contribution of lower vs higher molecular weight components. Distant sites showed decreasing proportions of petrogenic n-C17 - 26 alkanes, isoprenoids, and C20 - 27 terpanes and relative enrichment of n-C27,29,31,33 terrestrial plant alkanes and C31 - 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-C23 - 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-C13 - 22 (1.0%) < isoprenoids (3.2%) < n-C23 - 35 (6.1%) < hopanes (47%) ∼ UCM (50%), compared to intermediate stability of organic carbon (12%) and quantitative preservation of polychlorinated biphenyls (PCBs) (91%).