The present study aimed to examine whether the use of dispersant would be suitable for favoring the hydrocarbon degradation in coastal marine sediments without impacting negatively micro- and macrobenthic organisms. Mudflat sediments, maintained during 286 days in mesocosms designed to simulate natural conditions, were contaminated or not with Ural blend crude oil (REBCO) and treated or not with third-generation dispersant (Finasol OSR52). While the dispersant did not lead to an increase of hydrocarbon biodegradation, its use enables an attenuation of more than 55 % of the sediment concentration of total petroleum hydrocarbons (TPH). Canonical correspondence analysis (CCA) correlating T-RFLP patterns with the hydrocarbon content and bacterial abundance indicated weak differences between the different treatments except for the mesocosm treated with oil and dispersant for which a higher bacterial biomass was observed. The use of the dispersant did not significantly decrease the macrobenthic species richness or macroorganisms' densities in uncontaminated or contaminated conditions. However, even if the structure of the macrobenthic communities was not affected, when used in combination with oil, biological sediment reworking coefficient was negatively impacted. Although the use of the dispersant may be worth considering in order to accelerate the attenuation of hydrocarbon-contaminated mudflat sediments, long-term effects on functional aspects of the benthic system such as bioturbation and bacterial activity should be carefully studied before.

2017-410 Mangroves are among the most sensitive marine ecosystems to oil pollution due both to the sensitivity of mangroves species and to the high persistence of hydrocarbons in these environments. Despite their ecological and socio-economic value, the potential effects of an oil spill on French Guiana mangroves remain so far unknown. Yet, there is an increasing transboundary risk of oil spill due to Brazilian offshore oil exploitation (in mid-April 2013, there were 122 offshore drilling rigs in Brazil, including 29 under construction – Brazilian Amapá region located in the French Guiana border area is thought to become an important world oil production area in the coming years). The aim of the PRISME project was to assess the natural degradation of oil in mangrove sediment as well as its impact on benthic communities (micro, meio and macrobenthos): a one-month in situ experiment was conducted in the young French Guianese mangrove (around 3 years old) at the mouth of the Sinnamary estuary. The experimental units consisted in eight plastic cores (Ø : 10 cm ; height: 30 cm) manually introduced within sediments. A thin layer of oiled sediment (2 cm, 20 000 ppm) was applied on four cores while the remaining four cores were considered as control (no oil addition). Three cores were additionally sampled at the beginning of the experiment as initial control sediments. After one month in situ, the eight cores were collected and sliced on site into different sedimentary layers aliquots for later analyses (hydrocarbons, bacterial, meio, macrofauna fauna diversity, bioturbation, biogeochemical parameters). Samples were sent to the different laboratories involved in this multidisciplinary project. Results and knowledge gained from this experimental work were used to develop an approach for assessing coastal vulnerability for oil spills preparedness in mangroves.

No abstract

(ID 2017-410) Bioremediation is considered as a soft green technique which can be deployed on an oil contaminated shoreline to treat the remaining oil after the initial clean-up operations have taken place. This technique relies on the ability of bacteria to use the hydrocarbon molecules as a carbon source for growth. Nevertheless, specific environmental conditions are needed for ensuring effective biodegradation of oil, such as sufficient concentrations of nutrients and dissolved oxygen. To address these issues, the industry has developed commercial products, called bioremediation agents, which can be nutrient solutions (i.e. nitrogen, phosphorus and potassium) (biostimulation) or hydrocarbonoclastic bacterial solutions (bioaugmentation). In France, Cedre is in charge, at a national level, of the validation of response products currently used to treat oil spill (e.g. sorbents, dispersants, cleaning agents): standardised protocols are routinely used to assess their efficiencies and select the most efficient products. So far, no such procedure exists for bioremediation agents. In 2014, Cedre developed a new protocol to test the efficiency of bioremediation agents at a pilot scale: a small portion of shoreline is simulated in small tanks filled with contaminated sand and placed on an oscillating table. The periodic movements of this table recreate a continuous and identical wave action in each tank. In order to simulate the dilution that occurs in the natural environment due to the tidal cycle, the test is conducted in a semi-open circuit, with natural seawater automatically renewed twice a day. For three months, oiled sediment was sampled and oil extracted to assess its biodegradation rate according to the experimental conditions: oil alone, oil with biostimulation agent, oil with bioaugmentation agent.