Relative phytoplankton growth responses to physically and chemically dispersed South Louisiana sweet crude oil.

We conducted controlled laboratory exposure experiments to assess the toxic effects of water-accommodated fractions (WAFs) of South Louisiana sweet crude oil on five phytoplankton species isolated from the Gulf of Mexico. Experiments were conducted with individual and combinations of the five phytoplankton species to determine growth inhibitions to eight total petroleum hydrocarbon (TPH) equivalent concentrations ranging from 461 to 7,205 ppb. The composition and concentration of crude oil were altered by physical and chemical processes and used to help evaluate crude oil toxicity. The impact of crude oil exposure on phytoplankton growth varied with the concentration of crude oil, species of microalgae, and their community composition. At a concentration of TPH < 1,200 ppb, dinoflagellate species showed significantly better tolerance, while diatom species showed a higher tolerance to crude oil at higher concentrations of TPH. For both groups, the larger species were more tolerant to crude oil than smaller ones. The toxicity potential of crude oil seems to be strongly influenced by the concentration of polycyclic aromatic hydrocarbons (PAHs). The addition of the dispersant, Corexit® EC9500A, increased the amount of crude oil up to 50-fold in the water column, while the physical enhancement (vigorous mixing of water column) did not significantly increase the amount of TPH concentration in the water column. The species response to crude oil was also examined in the five-species community. Each phytoplankton species showed considerably less tolerance to crude oil in the five-species community compared to their individual responses. This study provides baseline information about individual phytoplankton responses to crude oil and dispersed crude oil for subsequent research efforts seeking to understand the impacts of oil on the phytoplankton in the bigger picture.

In-situ burning of oil in coastal marshes. 2. Oil spill cleanup efficiency as a function of oil type, marsh type, and water depth.

In-situ burning of spilled oil, which receives considerable attention in marine conditions, could be an effective way to cleanup wetland oil spills. An experimental in-situ burn was conducted to study the effects of oil type, marsh type, and water depth on oil chemistry and oil removal efficiency from the water surface and sediment. In-situ burning decreased the totaltargeted alkanes and total targeted polycyclic aromatic hydrocarbons (PAHs) in the burn residues as compared to the pre-burn diesel and crude oils. Removal was even more effective for short-chain alkanes and low ring-number PAHs. Removal efficiencies for alkanes and PAHs were >98% in terms of mass balance although concentrations of some long-chain alkanes and high ring-number PAHs increased in the burn residue as compared to the pre-burn oils. Thus, in-situ burning potentially prevents floating oil from drifting into and contaminating adjacent habitats and penetrating the sediment. In addition, in-situ burning significantly removed diesel oil that had penetrated the sediment for all water depths. Furthermore, in-situ burning at a water depth 2 cm below the soil surface significantly removed crude oil that had penetrated the sediment. As a result, in-situ burning may reduce the long-term impacts of oil on benthic organisms.