The reported persistence of the dioctyl sodium sulfosuccinate (DOSS) surfactant in Corexit 9500 in the oil plumes formed during the Deepwater Horizon oil spill has contributed to concerns regarding the biodegradability and bioavailability of dispersed oil and dispersants used as an oil spill countermeasure in the Gulf of Mexico. We studied the biodegradation of DOSS and dispersed South Louisiana crude oil (SLC) in laboratory microcosms. Two oil-degrading cultures from the Gulf of Mexico were isolated, one from the surface (meso) and one from close to the area of the Macondo well (cryo). Each was enriched on SLC, the former at 25 °C, the latter at 5 °C. Results indicated that the meso culture rapidly and completely degraded DOSS, alkanes, and aromatics. The cryo culture metabolized the same compounds but with a lag of 28 d and a remaining residual of iso-alkanes, n-C(30-35), and the 4-ring PAHs.

To better understand the impacts of Corexit 9500 on the structure and activity levels of hydrocarbon-degrading microbial communities, we analyzed next-generation 16S rRNA gene sequencing libraries of hydrocarbon enrichments grown at 5 and 25°C using both DNA and RNA extracts as the sequencing templates. Oil biodegradation patterns in both 5 and 25°C enrichments were consistent with those reported in the literature (i.e., aliphatics were degraded faster than aromatics). Slight increases in biodegradation were observed in the presence of Corexit at both temperatures. Differences in community structure were observed between treatment conditions in the DNA-based libraries. The 25°C consortia were dominated by ,, ,, and species, while the 5°C consortia were dominated by several species of the genera, , and Most of these genera have been linked to hydrocarbon degradation and have been observed after oil spills. and, known aromatic degraders, were also found in these enrichments. The addition of Corexit did not have an effect on the active bacterial community structure of the 5°C consortia, while at 25°C, a decrease in the relative abundance of was observed. At 25°C,, , and were present at higher relative abundances in the RNA than DNA libraries, suggesting that they were active in degradation. Similarly, was greatly stimulated by the addition of oil at 5°C. While dispersants such as Corexit 9500 can be used to treat oil spills, there is still debate on the effectiveness on enhancing oil biodegradation and its potential toxic effect on oil-degrading microbial communities. The results of this study provide some insights on the microbial dynamics of hydrocarbon-degrading bacterial populations in the presence of Corexit 9500. Operational taxonomic unit (OTU) analyses indicated that several OTUs were inhibited by the addition of Corexit. Conversely, a number of OTUs were stimulated by the addition of the dispersant, many of which were identified as known hydrocarbon-degrading bacteria. The results highlight the value of using RNA-based methods to further understand the impact of dispersant on the overall activity of different hydrocarbon-degrading bacterial groups.

In 2001 and 2003, geospatial surveys of lingering oil were conducted in Prince William Sound (PWS) resulting in a prediction of significant acreage being contaminated with substantial subsurface oil from the 1989 Exxon Valdez oil spill (EVOS). In 2007, other researchers developed a mass weathering index (MWI) based on the degree of weathering of PAHs normalized to conserved biomarkers: if the degree of weathering of oil is 70% or more, further attempts at bioremediation would be unjustified. The objective of our study was to measure the biodegradability of the 19-year lingering oil in laboratory microcosms. Samples of beach substrate were collected from representative sites in PWS contaminated with oil residues of varying weathering states according to the MWI model. Enough sacrificial microcosms were set up to accommodate two treatments for each site (natural attenuation and biostimulation). Results indicated that lingering oil is biodegradable. Nutrient addition stimulated biodegradation compared to natural attenuation in all treatments regardless of the degree of weathering. The most weathered oil according to the MWI was the most biodegradable. Substantial biodegradation occurred in the natural attenuation microcosms due to the high sediment Total Kjeldahl Nitrogen (TKN), which served as a nitrogen source for biodegradation. Most of the observed biodegradation was due to the presence of dissolved oxygen. Nitrogen was a limiting factor but oxygen was the predominant one.

The distribution of Cu, Pb, Ni and Zn between particulate, colloidal and truly dissolved size fractions in wastewater from a trickling filter treatment plant was investigated. Samples of influent, primary effluent, humus effluent, final effluent and sludge holding tank returns were collected and separated into particulate (i.e. > 0.45 μm), colloidal (i.e. 1 kDa to 0.45 μm), and truly dissolved (i.e. < 1 kDa) fractions using membrane filters. In the influent, substantial proportions of Cu (60%), Pb (67%), and Zn (32%) were present in the particulate fraction which was removed in conjunction with suspended particles at the works in subsequent treatment stages. In final effluent, sizeable proportions of Cu (52%), Pb (32%), Ni (44%) and Zn (68%) were found within the colloidal size fraction. Calculated ratios of soluble metal to organic carbon suggest the metal to be adsorbed to or complexed with non-humic macromolecules typically found within the colloidal size range. These findings suggest that technologies capable of removing particles within the colloidal fraction have good potential to enhance metals removal from wastewater.