Article pubs.acs.org/est
Trace Element Distributions in the Water Column near the Deepwater Horizon Well Blowout DongJoo Joung* and Alan M. Shiller Department of Marine Science, The University of Southern Mississippi, 1020 Balch Blvd. Stennis Space Center, Mississippi 39529, United States S Supporting Information *
ABSTRACT: To understand the impact of the Deepwater Horizon well blowout on dissolved trace element concentrations, samples were collected from areas around the oil rig explosion site during four cruises in early and late May 2010, October 2010, and October 2011. In surface waters, Ba, Fe, Cu, Ni, Mn, and Co were relatively well correlated with salinity during all cruises, suggesting mixing with river water was the main influence on metal distributions in these waters. However, in deep oil/gas plumes (1000−1400 m depth), modestly elevated concentrations of Co and Ba were observed in late May, compared with postblowout conditions. Analysis of the oil itself along with leaching experiments confirm the oil as the source of the Co, whereas increased Ba was likely due to drilling mud used in the top kill attempt. Deep plume dissolved Mn largely reflected natural benthic input, though some samples showed slight elevation probably associated with the top kill. Dissolved Fe concentrations were low and also appeared largely topographically controlled and reflective of benthic input. Estimates suggest that microbial Fe demand may have affected the Fe distribution but probably not to the extent of Fe becoming a growth-limiting factor. Experiments showed that the dispersant can have some limited impact on dissolved-particulate metal partitioning.
1. INTRODUCTION As a result of the April 2010 Deepwater Horizon oil rig explosion and blowout, an estimated 4.4 ± 0.8 million barrels (∼ 5.0 ± 1.0 × 108 L) of crude oil were released into the Gulf of Mexico.1 Such a large oil release has the potential to seriously impact marine and coastal environments of the northern Gulf.2−4 In addition to the crude oil, up to 1.25 × 1010 moles of methane were released to the deep water,5 and nearly all the methane released was consumed by methanotrophic bacteria.5,6 The consumption of these hydrocarbons caused an estimated respiration of 2−4 × 1010 moles of oxygen at the same time.6,7 About 6.8 × 106 L of dispersant was used: 3.8 × 106 L for the surface and 3.0 × 106 L for the deep plume.8 The dispersant used and the polycyclic aromatic hydrocarbons (PAHs) from the crude oil may have had a toxicological impact.9,10 Other work has shown that some trace metals can be highly enriched in crude oil and the metal composition may vary with source.11,12 However, there are few studies on trace element distributions in marine aquatic environments affected by spills. For example, Santos-Echeandia et al.13 and Prego and CobeloGarcia14 observed significantly elevated dissolved Cu, Ni, and Zn in the water column above the Prestige fuel oil tanker wreckage off the coast of Spain. Fowler et al.2 found elevated concentrations of V, Ni, and Cr in Saudi Arabian sediments following the oil spill and fires from the 1991 Gulf War. Massoud et al.4 and Al-Abdali et al.15 likewise reported that © 2013 American Chemical Society
contamination of V and Ni in Arabian Gulf sediments was related to the wartime oil spill. Despite these contamination reports, Portella et al.16 found that the complexation of metals with ligands in crude oil is very stable at pH 8. On the basis of an oil spill simulation in seawater, they concluded that metal ions stayed in the oil due to this strong ligand complexation. Cantu et al.17 reported that the partitioning rate of Ni and V complexed with deoxophyllorythroetioporphyrin (DPEP) from crude oil into the aqueous phase is very slow, and so, the contamination of drinking water by metals released from crude oil is small. This paper reports the results of selected dissolved metal concentrations in the water column near the Deepwater Horizon (also called the Macondo well or MC252) site after the blowout. Samples were collected during cruises to the area, two during the blowout and two after the well was capped, with the basic objective of understanding how and to what extent metal distributions were affected after the oil rig explosion. Received: Revised: Accepted: Published: 2161
August 3, 2012 February 4, 2013 February 5, 2013 February 5, 2013 dx.doi.org/10.1021/es303167p | Environ. Sci. Technol. 2013, 47, 2161−2168
Environmental Science & Technology
Article
Table 1. Metal Concentration in the Crude Oil from the Macondo Well and Dispersants Used in This Spill (in ppm) crude oil dispersant Macondo well crude oil South Louisiana sweet crude oil previous studies (oil)
V
Cr
Mn
0.8 0.003 0.2 0.1
