Fate of petroleum hydrocarbons in bioturbated pristine sediments from Caleta Valdés (Patagonia Argentina): An ex situ bioassay

Abstract

Petroleum can pollute pristine shorelines as a consequence of accidental spills or chronic leaks. In this study, the fate of petroleum hydrocarbons in soft pristine sediment of Caleta Valdés (Argentina) subject to ex situ simulated oil pollution was assessed. Sedimentary columns were exposed to medium and high concentrations of Escalante Crude Oil (ECO) and incubated in the laboratory during 30 days. Levels of aliphatic hydrocarbons at different depths of the sedimentary column were determined by gas chromatography. Oil penetration was limited to the first three centimetres in both treatments, and under this depth, hydrocarbons were clearly biogenic (terrestrial plants) as in the whole sedimentary column of the control assay. Bioturbation by macrobenthic infauna was strongly impacted by oil pollution which resulted in reduced sediment oxygenation and low burial of petroleum hydrocarbons. This may partly explain the limited hydrocarbon biodegradation observed, as indicated by the relatively high values of the ratios nC17/pristane, nC18/phytane, and total resolved aliphatic hydrocarbons/unresolved complex mixture. Correspondingly, at the end of the experiment the most probable number of hydrocarbon-degrading bacteria reached ~ 10 MPN g dry weight. These values were lower than those found in chronically polluted coastal sediments, reflecting a low activity level of the oil-degrading community. The results highlight the low attenuation capacities of Caleta Valdés pristine sediments to recover its original characteristics in a short time period if an oil spill occurs. In this work, we present a novel and integrative tool to evaluate the fate of petroleum hydrocarbons and their potential damage on pristine sediments.

Seasonal composition and activity of the intertidal macrobenthic community of Caleta Valdés (Patagonia, Argentina) applying in situ and ex situ experimental protocols

“…These results are particularly useful as a reliable alternative for ecotoxicological studies in protected environments where in situ addition of pollutants to the sedimentary matrix won't be feasible (see Ferrando et al, 2015Ferrando et al, , 2019Sturla Lompré et al, 2018;Romanut, 2019;among others).…”

“…In order to assess biological reworking activity, in each sediment core, 4 g of luminophores (inert fluorescent particles, Duport et al, 2007) of two sizes and colors (pink: 65-125 μm; green: 125-355 μm) were homogeneously spread at the sediment surface at initial time (T=0 day). Luminophores sizes were selected according to the two major size distribution modes of sedimentary particles in the studied site (Sturla Lompré et al, 2018). After 13 days of in situ incubation, the cores were withdrawn and carried out to the laboratory.…”

Estructura y actividad de los ensamblajes de poliquetos en sedimentos contaminados con petróleo (Patagonia, Argentina)

“…The first four layers were 0.5 cm thick while the remaining ones (up to 16 cm) were 1 cm thick (Figure 2b). To assess the percentages of water content and organic matter in them, each sample was homogenized (25% of each layer; 7 layers; with 4 replicates per treatment), in agreement with previous work on Patagonian coastal sediment characterization (Sturla Lompré et al 2018;Ferrando and Sturla Lompré 2020;Ferrando et al 2022). A subsample of 2 g (wet weight) was dried in an oven at 105 °C until constant weight (dry weight).…”

“…Inputs of nutrients, organic matter and pollutants from anthropogenic activities can significantly alter environmental conditions, although natural variability can be a major source of stress for various organisms (Venturini et al 2004). In particular, oil deposition at the sediment-water interface can have a negative effect on the biogeochemistry of benthic systems (Rivero et al 2005;Sturla Lompré et al 2018). In the present study, a decrease in the density of polychaetes assemblages was observed with the addition of crude oil.…”

“…For example, on the Chubut coast, there was a low amount of crude oil spill in 1991 (Commendatore and Esteves 2007), while there was a spill of 100 m³ in Caleta Córdova in 2007 (Pucci et al 2011). In particular, the loading of crude oil at buoys and ports in the south of the country and its subsequent transport by sea in tankers to refineries in the center and north of the country pose a constant threat of pollution to the Patagonian marine ecosystem (Sturla Lompré et al 2018).…”