Effects of Dispersants and Biosurfactants on Crude-Oil Biodegradation and Bacterial Community Succession.

This study evaluated the effects of three commercial dispersants (Finasol OSR 52, Slickgone NS, Superdispersant 25) and three biosurfactants (rhamnolipid, trehalolipid, sophorolipid) in crude-oil seawater microcosms. We analysed the crucial early bacterial response (1 and 3 days). In contrast, most analyses miss this key period and instead focus on later time points after oil and dispersant addition. By focusing on the early stage, we show that dispersants and biosurfactants, which reduce the interfacial surface tension of oil and water, significantly increase the abundance of hydrocarbon-degrading bacteria, and the rate of hydrocarbon biodegradation, within 24 h. A succession of obligate hydrocarbonoclastic bacteria (OHCB), driven by metabolite niche partitioning, is demonstrated. Importantly, this succession has revealed how the OHCB Oleispira, hitherto considered to be a psychrophile, can dominate in the early stages of oil-spill response (1 and 3 days), outcompeting all other OHCB, at the relatively high temperature of 16 °C. Additionally, we demonstrate how some dispersants or biosurfactants can select for specific bacterial genera, especially the biosurfactant rhamnolipid, which appears to provide an advantageous compatibility with Pseudomonas, a genus in which some species synthesize rhamnolipid in the presence of hydrocarbons.

A standardised approach to the environmental risk assessment of potentially polluting wrecks.

The potential risk to the marine environment of oil release from potentially polluting wrecks (PPW) is increasingly being acknowledged, and in some instances remediation actions have been required. However, where a PPW has been identified, there remains a great deal of uncertainty around the environmental risk it may pose. Estimating the likelihood of a wreck to release oil and the threat to marine receptors remains a challenge. In addition, removing oil from wrecks is not always cost effective, so a proactive approach is recommended to identify PPW that pose the greatest risk to sensitive marine ecosystems and local economies and communities. This paper presents a desk-based assessment approach which addresses PPW, and the risk they pose to environmental and socio-economic marine receptors, using modelled scenarios and a framework and scoring system. This approach can be used to inform proactive management options for PPW and can be applied worldwide.

Extraction of bioavailable contaminants from marine sediments: an approach to reducing toxicity using adsorbent parcels.

This paper demonstrates an approach to reducing acute toxicity in marine sediments using adsorbent parcels. Acute toxicity tests were carried using the marine amphipod Corophium volutator. Marine sediments were spiked with two know contaminants tributyltin and naphthalene and then treated with adsorbent parcels containing either amberlite XAD4 or activated carbon. Results showed that both types of adsorbent parcels were effective in reducing acute toxicity, not only within spiked sediments containing naphthalene and/or tributyltin, but also in an environmental field samples form an expected contaminated site. Adsorbent parcels such as these could provide a practical approach to remediate areas of contaminated sediment within marine environments. Furthermore adsorbents can be used as an identification tool for problematic contaminants using a toxicity identification evaluation approach.