title: Oil spill in the Rio de la Plata estuary, Argentina: 2-hydrocarbon disappearance rates in sediments and soils.
abstract: The 6-month assessment of the oil spill impact in the Rio de la Plata described in the preceding paper [Colombo, J.C., Barreda, A., Bilos, C., Cappelletti, N., Demichelis, S., Lombardi, P., Migoya, M.C., Skorupka, C., Suarez, G., 2004. Oil spill in the Rio de la Plata estuary, Argentina: 1 - biogeochemical assessment of waters, sediments, soils and biota. Environmental Pollution] was followed by a 13- and 42-month campaigns to evaluate the progress of hydrocarbon decay. Average sediment hydrocarbon concentrations in each sampling include high variability (85-260%) due to contrasting site conditions, but reflect a significant overall decrease after 3 years of the spill: 17 +/- 27, 18 +/- 39 to 0.54 +/- 1.4 microg g(-1) for aliphatics; 0.44 +/- 0.49, 0.99 +/- 1.6 to 0.04 +/- 0.03 microg g(-1) for aromatics at 6, 13 and 42 months, respectively. Average soil hydrocarbon levels are 100-1000 times higher and less variable (61-169%) than sediment values, but display a clear attenuation: 3678 +/- 2369, 1880 +/- 1141 to 6.0 +/- 10 microg g(-1) for aliphatics and 38 +/- 26, 49 +/- 32 to 0.06 +/- 0.04 microg g(-1) for aromatics. Hydrocarbon concentrations modeled to first-order rate equations yield average rate constants of total loss (biotic+abiotic) twice as higher in soils (k = 0.18-0.19 month(-1)) relative to sediments (0.08-0.10 month(-1)). Individual aliphatic rate constants decrease with increasing molecular weight from 0.21 +/- 0.07 month(-1) for isoprenoids and <n-C22 to 0.10 +/- 0.08 month(-1) for >n-C27, similar to hopanes (0.10 +/- 0.05 month(-1)). Aromatics disappearance rates were more homogeneous with higher values for methylated relative to unsubstituted species (0.17 +/- 0.05 vs. 0.12 +/- 0.05 months(-1)). Continued hydrocarbon inputs, either from biogenic (algal n-C15,17; vascular plant n-C27,29) or combustion related sources (fluoranthene and pyrene), appear to contribute to reduced disappearance rate. According to the different loss rates, hydrocarbons showed clear compositional changes from 6-13 to 42 months. Aliphatics disappearance rates and compositional changes support an essentially microbiologically-mediated recovery of coastal sediments to pre-spill conditions in a 3-4 year period. The lower rates and more subtle compositional changes deduced for aromatic components, suggest a stronger incidence of physical removal processes.
authors.affiliation: Laboratorio de Química Ambiental y Biogeoquímica, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Av. Calchaqui km 23500 (1888) Florencio Varela, Buenos Aires, Argentina. laqab@arnet.com.ar
authors.forename: J C
authors.initials: JC
authors.lastname: Colombo
authors.forename: A
authors.initials: A
authors.lastname: Barreda
authors.forename: C
authors.initials: C
authors.lastname: Bilos
authors.forename: N
authors.initials: N
authors.lastname: Cappelletti
authors.forename: M C
authors.initials: MC
authors.lastname: Migoya
authors.forename: C
authors.initials: C
authors.lastname: Skorupka
mesh_terms: D001118:Argentina; D001673:Biodegradation, Environmental; D004190:Disasters; D017753:Ecosystem; D004781:Environmental Exposure / Q000009:adverse effects; D004784:Environmental Monitoring / Q000379:methods; D019015:Geologic Sediments; D006838:Hydrocarbons / Q000032:analysis*; D010578:Petroleum / Q000633:toxicity*; D045483:Rivers; D012989:Soil Pollutants / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D006838:Hydrocarbons; D010578:Petroleum; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical