Phototoxicity Assessments of Field Sites in Barataria Bay, Louisiana, USA, and Heavily Weathered Macondo Crude Oil: 4 Years after the Deepwater Horizon Oil Spill.

The Deepwater Horizon oil spill resulted in the release of large amounts of crude oil into waters of the Gulf of Mexico (USA). A significant portion of the oil reached coastal waters and shorelines where aquatic organisms reside. Four years after the spill, oil remains in small quantities along the coast. Given the high volume of oil coupled with the high ultraviolet light intensities of the Gulf of Mexico, continued polycyclic aromatic hydrocarbon phototoxicity may be occurring in the Gulf region. The objective of the present study was to determine the potential for phototoxicity at 5 field sites (oiled, remediated, and unoiled) in Barataria Bay (LA, USA) to caged mysid shrimp and sheepshead minnows and to evaluate the phototoxic potential of field-collected oil water accommodated fractions (WAFs). Water chemistries were similar between field-collected oil WAFs and ambient waters, excluding the most oiled field site. Field bioassays indicated no phototoxic risk of heavily weathered crude oil under the highly turbid conditions present during the study. Laboratory WAFs of field-collected oil resulted in phototoxicity to mysid shrimp, suggesting a potential for phototoxicity of heavily weathered crude oil remaining in the Gulf of Mexico. Environ Toxicol Chem 2019;38:1811-1819. © 2019 SETAC.

Photo-enhanced toxicity of two weathered Macondo crude oils to early life stages of the eastern oyster (Crassostrea virginica).

Polycyclic aromatic hydrocarbons (PAHs) have been reported to absorb ultraviolet (UV) light, resulting in enhanced toxicity. Early developmental stages of bivalves may be particularly susceptible to photo-enhanced toxicity during oil spills. In the current study, toxicity tests were conducted with sperm and three larval ages of the eastern oyster (Crassostrea virginica) to evaluate the photo-enhanced toxicity of low-energy water-accommodated fractions (WAFs) of two weathered Macondo crude oils collected from the Deepwater Horizon incident. Larvae exposed to oil WAFs under UV-filtered light demonstrated consistently higher survival and normal development than larvae exposed to WAFs under UV light. The phototoxicity of weathered Macondo oil increased as a function of increasing UV light intensity and dose. Early developing oyster larvae were the most sensitive to photo-enhanced toxicity, whereas later shelled prodissoconch larvae were insensitive. Comparisons between two weathered crude oils demonstrated that toxicity was dependent on phototoxic PAH concentration and UV light intensity.

Differentiating the roles of photooxidation and biodegradation in the weathering of Light Louisiana Sweet crude oil in surface water from the Deepwater Horizon site.

We determined the contributions of photooxidation and biodegradation to the weathering of Light Louisiana Sweet crude oil by incubating surface water from the Deepwater Horizon site under natural sunlight and temperature conditions. N-alkane biodegradation rate constants were ca. ten-fold higher than the photooxidation rate constants. For the 2-3 ring and 4-5 ring polycyclic aromatic hydrocarbons (PAHs), photooxidation rate constants were 0.08-0.98day(-1) and 0.01-0.07day(-1), respectively. The dispersant Corexit enhanced degradation of n-alkanes but not of PAHs. Compared to biodegradation, photooxidation increased transformation of 4-5 ring PAHs by 70% and 3-4 ring alkylated PAHs by 36%. For the first time we observed that sunlight inhibited biodegradation of pristane and phytane, possibly due to inhibition of the bacteria that can degrade branched-alkanes. This study provides quantitative measures of oil degradation under relevant field conditions crucial for understanding and modeling the fate of spilled oil in the northern Gulf of Mexico.

Natural sunlight and residual fuel oils are an acutely lethal combination for fish embryos.

The majority of studies characterizing the mechanisms of oil toxicity in fish embryos and larvae have focused largely on unrefined crude oil. Few studies have addressed the toxicity of modern bunker fuels, which contain residual oils that are the highly processed and chemically distinct remains of the crude oil refinement process. Here we use zebrafish embryos to investigate potential toxicological differences between unrefined crude and residual fuel oils, and test the effects of sunlight as an additional stressor. Using mechanically dispersed oil preparations, the embryotoxicity of two bunker oils was compared to a standard crude oil from the Alaska North Slope. In the absence of sunlight, all three oils produced the stereotypical cardiac toxicity that has been linked to the fraction of tricyclic aromatic compounds in an oil mixture. However, the cardiotoxicity of bunker oils did not correlate strictly with the concentrations of tricyclic compounds. Moreover, when embryos were sequentially exposed to oil and natural sunlight, the bunker oils produced a rapid onset cell-lethal toxicity not observed with crude oil. To investigate the chemical basis of this differential toxicity, a GC/MS full scan analysis was used to identify a range of compounds that were enriched in the bunker oils. The much higher phototoxic potential of chemically distinct bunker oils observed here suggests that this mode of action should be considered in the assessment of bunker oil spill impacts, and indicates the need for a broader approach to understanding the aquatic toxicity of different oils.

Treatment system for solid matrix contaminated with fluoranthene. II--Recirculating photodegradation technique.

A laboratory-scale solar reactor and photodegradation technique were developed to enhance the degradation process of fluoranthene. Fluoranthene was used in this study to represent toxic polycyclic aromatic hydrocarbons (PAHs) that are persistent in the environment. The extracted fluoranthene from soil in organic solvent (EFOS) and hydrogen peroxide (H2O2) were pumped from a 100 ml vessel into a solar glass cell coated with titanium dioxide (TiO2) at 80 microl min(-1). This work compares the efficiency of the developed photocatalytic degradation technique with the conventional batch process. The degradation efficiency of the developed technique was assessed at different initial concentrations of fluoranthene and percentages of H2O2 in the extract using different flow rates. Preliminary results indicated that the developed technique degraded 99% of fluoranthene from EFOS in the presence of H2O2 and 83% without H2O2. There was no significant difference between fluoranthene degradation rates by the developed technique and the batch method. The developed technique however, treated double the volume of solution that was treated by the batch reactor method which was time consuming and required continuous attention.

Potential for photoenhanced toxicity of spilled oil in Prince William Sound and Gulf of Alaska waters.

Photoenhanced toxicity is the increase in the toxicity of a chemical in the presence of ultraviolet light (UV) compared to a standard laboratory test conducted with fluorescent lighting (minimal UV). Oil products, weathered oil, and specific polycyclic aromatic compounds present in oil are 2 to greater than 1000 times more toxic in the presence of UV. The photoenhanced toxicity of oil to fish and aquatic invertebrates appears to occur through a process of photosensitization, rather than photomodification of the aqueous phase oil. In photosensitization, the bioaccumulated chemical transfers light energy to other molecules causing toxicity through tissue damage rather than a narcosis mechanism. The available evidence indicates that phototoxic components of oil are specific 3-5 ring polycyclic aromatic hydrocarbons (PAHs) and heterocycles. Determinants of photoenhanced toxicity include the extent of oil bioaccumulation in aquatic organisms and the spectra and intensity of UV exposure. No studies have specifically investigated the photoenhanced toxicity of spilled oil in Alaska waters. Although there are substantial uncertainties, the results of this evaluation indicate there is potential for photoenhanced toxicity of spilled oil in Prince William Sound and the Gulf of Alaska. The potential hazard of photoenhanced toxicity may be greatest for embryo and larval stages of aquatic organisms that are relatively translucent to UV and inhabit the photic zone of the water column and intertidal areas. Photoenhanced toxicity should be considered in oil spill response because the spatial and temporal extent of injury to aquatic organisms may be underestimated if based on standard laboratory bioassays and existing toxicity databases. Additionally, the choice of counter measures and oil removal operations may influence the degree of photoenhanced toxicity.

Petroleum asphaltenes: generated problematic and possible biodegradation mechanisms.

Petroleum asphaltenes are hydrocarbons that present an extremely complex molecular structure. They are conformed by different proportions of nitrogen, sulfur and oxygen. These compounds cause diverse problems like the blockage of crude oil extraction and transport pipes, the reduction of their economic use and the pollution of ecosystems. Biodegradation of asphaltenes is an important process that can eliminate these compounds and reduce the problems they cause. However, it is a process that occurs naturally in very reduced proportions. The purpose of this revision is to show the chemical structure of these compounds, the problems they cause and to represent their possible biodegradation mechanisms, based on the processes known for other hydrocarbons of complex structure. Elimination of the micelar structure, through the application of non-polar solvents, and fragmentation of the asphaltenes through photooxidation are the initial processes necessary to be able to degrade these compounds. The produced structures, such as the heteropolyaromatic and aromatic, lineal and ramified hydrocarbons, could be degraded in this order through biochemical reactions, such as omega oxidations, beta oxidations and aromatic oxidations respectively. These processes are distributed in an important variety of microorganisms. The elimination period's length can vary from one week, for the simplest structures, to 990 days for those with several condensed aromatic rings.