Reality Check on the Deepwater Horizon Oil Spill Impacts

As the litigation for the Deepwater Horizon (DWH) oil spill lurches through the legal system, the case has become a magnet for those seeking to take advantage of the deep-pockets oil industry defendant. In addition to those looking to prosper directly from the spill, the environmentalists and their mainstream media allies have exploited the situation to make their case against the use of oil in general -- and more specifically, against offshore drilling and oil production.

If you restrict your reading on the topic to what appears in the mainstream media, you may be convinced that the science shows the DWH oil spill had catastrophic impacts across much of the Gulf of Mexico. But a critical review of the peer-reviewed science on the topic reveals that many of the concerns have been wildly overblown.

We know that negligible quantities of methane were released to the atmosphere from the DWH blowout. During 7 days in June 2010, the methane flux was measured at less than 0.01% of the methane released from the reservoir. Evaporating hydrocarbons from the spill generally had a short photochemical lifetime (on the order of less than a few days), indicating no medium through long-term air-pollution impacts.

Between 28 April 2010 and 19 July 2010, 410 controlled burns of surface oil were conducted at and near the DWH site. Approximately 220,000 to 310,000 barrels were burned. Plume samples at 27 sites from these burns were sampled for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). A screening level assessment of risks from PCDD/F emissions was undertaken considering the scenarios of (1) inhalation exposure to workers, (2) inhalation exposure to residents on the mainland, and (3) fish ingestion exposures to residents. Upper bound respective lifetime incremental cancer risks for these three scenarios were all well below the regulatory acceptance risk range that would trigger the consideration of mitigation actions.

Approximately 20,000 airborne breathing zone BTEX (benzene, toluene, ethylbenzene, and xylene) concentration measurements were obtained between 27 April 2010 and 18 October 2010 for offshore cleanup workers. Among all samples, 99% of measurements were 32-, 510-, 360-, and 77-fold below the respective permissible exposure limits. Because the BTEX concentrations on ships involved in the cleanup effort were similar to those on ships outside the oil slick region, the BTEX exposures of cleanup crews appeared to be from engine exhausts rather than from oil slick evaporations.

The National Institute for Occupational Safety and Health (NIOSH) conducted personal breathing zone and area air sampling investigations aboard the Development Driller II (preparing one of the relief wells at the DWH site) and the Enterprise (recovering oil at the DWH site) on 21 June 2010 and 23 June 2010, respectively. Airborne concentrations of all contaminants (e.g., BTEX, carbon monoxide, glycol ethers, hydrogen sulfide, polyaromatic hydrocarbons [PAHs], etc.) on both vessels were <10% of the lowest applicable occupational exposure limits. The investigation did not reveal exposure levels for any contaminants that would require routine wearing of respiratory protection at the site.

Oyster feeding and growth was not significantly affected by DWH oil exposure along the Mississippi-Alabama coast, and there was no evidence of "an oyster-based conduit to higher trophic levels" for oil-derived carbon and nitrogen. Similarly, no PAHs were detected in oysters from oiled sites in Louisiana east of the Mississippi River. Any differences in oyster condition, infection, and/or reproductive state between oiled and control sites were ascribed to salinity differences rather than exposure to DWH contamination. Oil incorporation by barnacles and marsh mussels from Louisiana estuaries near the DWH spill was estimated at <0.3%.

The Gulf of Mexico supports a major fishing industry. Soon after the disaster began, on 2 May 2010 the National Oceanic and Atmospheric Administration (NOAA) closed commercial and recreational fisheries in federal waters. Subsequently, Louisiana, Mississippi, Alabama, and Florida closed their fisheries in state waters. As of 21 June 2010, fisheries closures extended to about 37% of the entire Gulf of Mexico from Louisiana to Florida. By 19 April 2011, all Gulf of Mexico federal waters had been reopened for fishing. Levels of concern (LOCs) were calculated for major contaminants with regard to children and adult men and women eating 1-2 seafood meals per week. Based on these calculated LOCs, PAH concentrations measured by the Food and Drug Administration (FDA) and NOAA in potentially impacted seafood were "well below" (approximately an order of magnitude safety margin) levels of concern for human health.

In a study of seafood samples collected from the closed fishing grounds along the Mississippi Gulf Coast starting approximately one month after the DWH blowout and continuing through August 2011, no significant difference was found between PAH levels in oysters collected following the DWH spill compared to those collected during the decade prior to the spill as part of the NOAA Mussel Watch program. Similar PAH levels were observed between seafood from the Gulf of Mexico after the DWH spill with seafood purchased in local grocery stores. PAH concentrations in all samples collected during the year after the DWH spill were substantially below the applicable NOAA/FDA LOCs. Another study used sensory and instrumental approaches to determine PAH and DOSS (dioctyl sodium sulfosuccinate; the active ingredient in the oil dispersant used around the site) levels in more than 8,000 seafood samples from the Gulf of Mexico following the DWH spill. Concentrations were always greater than two orders of magnitude lower than the respective LOCs.

Finfish samples collected throughout the Gulf of Mexico during July 2011 contained iso- and n-alkanes in the same background range as samples purchased in Washington, DC region supermarkets and more than an order of magnitude below the LOC for the more toxic compound naphthalene. Pristane:phytane ratios in the fish also suggested an absence of significant DWH oil contamination. Levels of PAHs, various metals, and DOSS were determined in seven species of reef fish from the Gulf of Mexico between March 2011 and April 2012. All samples contained all analytes below any LOCs.

A review of greenhouse and field studies conducted in coastal Louisiana concluded that marsh vegetation impacted by the DWH spill would recover naturally without substantial remediation efforts, and that oiling of marsh vegetation roots would not lead to permanent damage. Within salt marshes, exposure to DWH oil negatively impacted the intertidal crab and terrestrial anthropod communities (e.g., insects and spiders), but within a year the populations had effectively recovered. Field work and modeling of a coastal salt marsh in Mississippi also indicated that photosynthesis rates of salt marsh grass at heavily oiled sites recovered to the status of non-oiled control locations within about 5 months.

In response to the spill's impacts, 182 oil-rehabilitated brown pelicans were translocated from southeastern Louisiana to a non-impacted region in the southwestern area of the state. No mortality was observed and the translocated birds appeared to integrate normally with local pelican flocks. Northern gannets breeding in eastern Canada that overwintered in the Gulf of Mexico during 2010-2011 were examined for the potential impact of oil exposure on the circulating status of the reproductive hormones prolactin and corticosterone. No quantifiable PAHs were present in the gannets' red blood cells. Prolactin and corticosterone levels and body mass measurements also failed to show oil spill exposure related effects.

DWH surface oil did not affect the majority of Atlantic bluefin tuna spawning habitat during spring 2010. Similarly, the potential effects of the DWH spill on four pelagic fishes (blackfin tuna, blue marlin, dolphinfish, and sailfish) that inhabit the outer shelf and slope waters of northern Gulf of Mexico was examined. No direct causal link could be established between the DWH spill and the larval abundance for these species. Similarly, a five-year study of potential DWH impacts on the early stage survival of 20 fish species living in seagrass nurseries found no statistically significant responses of any species to the spill.

There was damage from the DWH oil spill, but not nearly to the degree suggested in the mainstream media. Ideally, future penalties assigned by the legal and regulatory systems will reflect actual -- rather than perceived -- damage, and that policies governing offshore drilling and oil production will not be unduly affected by erroneous exaggerations of the spill's impacts.