Background • In 2010, the explosion and sinking of the Deepwater Horizon oil rig in the Gulf

of Mexico (GOM) resulted in the release of approximately 780 million liters of

crude oil. Seven million liters of the dispersant Corexit 9500 (C9500) were

applied both to the surface oil slick and at the wellhead [1].

• This first subsurface application of dispersants was controversial owing to the

uncertainty of the impact on the ecosystem.

• Polycyclic Aromatic Hydrocarbons (PAHs) are organic compounds with

multiple fused benzene rings, that are known to be toxic, carcinogenic,

mutagenic, and bioaccumulative [2, 3].

• JD-2000, listed on National Contingency Product Plan Schedule, was reported

to have satisfactory dispersant effectiveness and lower toxicity compared to

C9500 [4-6].

Biodegradation of Polycyclic Aromatic Hydrocarbons in Alaska North

Slope Crude Oil: Effect of Temperature and Dispersant Application

Mobing Zhuang1, Gulizhaer Abulikemu1, Pablo Campo-Moreno1, Makram Suidan 2*,

Albert D. Venosa (retired)3, and Robyn N. Conmy3

Experimental Setup

Results

Results (Continued)

Acknowledgements

References

Discussion and Conclusion

[1] The Federal Integracy Solutions Group; Oil Budget Calculator Science and Engineering team, in Oil Budget Calculator Deepwater Horizon.

2010.

[2] Harvey, J., L. Harwell, and J.K. Summers, Contaminant concentrations in whole-body fish and shellfish from US estuaries. Environ. Monit. Assess., 2008. 137(1-3): p. 403-12. [3] Keith, L.H. and W.A. Telliard, Priority pollutants I – a perspective view. Environ. Sci. Technol., 1979. 13(4): p. 416-423.

[4] Hemmer, M.J., M.G. Barron, and R.M. Greene, Comparative toxicity of eight oil dispersants, Louisiana Sweet Crude oil (LSC), and

chemically dispersed LSC to two aquatic test species. Environ. Toxicol. Chem., 2011. 30(10): p. 2244-2252.

[5] Judson, R.S., et al., Analysis of Eight Oil Spill Dispersants Using Rapid, In Vitro Tests for Endocrine and Other Biological Activity. Environ. Sci. Technol., 2010. 44: p. 5979–5985. [6] Venosa, A.D. and E.L. Holder, Determining the dispersibility of South Louisiana crude oil by eight oil dispersant products listed on the NCP Product Schedule. Mar. Pollut. Bull., 2013. 66(1-2): p. 73-7. [7] Haritash, A.K. and C.P. Kaushik, Biodegradation Aspects of Polycyclic Aromatic Hydrocarbons (PAHs): A review. J. Hazard. Mater., 2009. 169: p. 15. [8] Campo, P., A.D. Venosa, and M.T. Suidan, Biodegradability of Corexit 9500 and dispersed South Louisiana crude oil at 5 and 25 ℃. Environ. Sci. Technol., 2013. 47(4): p. 1960-7.

Contact: Mobing Zhuang, zhuangmg@mail.uc.edu

• Oil alone and dispersed oil treatments were studied. Triplicate killed controls

(KCs) for both treatments sterilized with 500 mg/L of sodium azide were also

included.

• The 5 °C culture (cryo) was isolated from water close to the plume location at

a depth of 1240 m near the Macondo wellhead. The 25 °C culture (meso) was

isolated from water within the top 5 m from the water surface in the vincinity of

the wellhead. Both cultures were collected from GOM on July 31, 2010,

enriched in the lab, and stored at -80 °C.

• Dispersed oil was prepared following the Baffled Flask Test method.

• The flasks were placed on orbital shakers operated at 200 rpm and kept at the

corresponding temperatures 5 or 25 °C. At a given sampling event, triplicate

flasks of each live treatment and KCs were sacrificed.

• Scarified samples were extracted, concentrated, and finally analyzed for PAHs

by GC/MS. The analyzed PAHs included 2-, 3- and 4- ring groups with both

the parent compounds and alkylated homologues [C0−4-naphthalenes(nap),

C0−3-dibenzothiophenes(dbt), C0−3-fluorenes(flu), C0−4-napthbenzothiophenes

(nbt), C0−4-phenanthrenes/anthracenes(phe), C0−2-pyrenes(pyr), and C0−4

chrysenes(cry)].

Table 1. Summary of Experimental Layout

Test Temperature Treatment Sampling

Events

Sample

Replicate

Experimental

Units

ANS-JD-2000 5 °C

ANS dispersed by JD-2000 11 3 33

ANS alone 11 3 33

Killed ANS control 1 3 3

Killed ANS+JD-2000 control 11 3 33

Sampling Events: days 0, 2, 4, 8, 12, 16, 24, 32, 40, 48, 56

ANS-JD-2000 25 °C

ANS dispersed by JD-2000 9 3 27

ANS alone 9 3 27

Killed ANS control 1 3 3

Killed ANS+JD-2000control 9 3 27

Sampling Events: days 0, 2, 4, 8, 12, 16, 24, 32, 40

1. University of Cincinnati, 2901 Woodside Drive, Cincinnati, OH 45221, USA

2. Faculty of Engineering and Architecture, American University of Beirut, Beirut, Lebanon

3. U.S. Environmental Protection Agency, NRMRL, 26 W. MLK Drive Cincinnati, OH, 45268, USA

The research was a product of the U.S. Environmental Protection Agency’s National Risk Management Research Laboratory (NRMRL)

and was partially funded by EPA, NRMRL, Cincinnati, OH, under Pegasus Technical Services, Inc. Contract EP-C-11-006.

• At 25 °C, the presence of dispersant increased the biodegradation rate of

individual PAH. For instance, the rates of C2-phe, C2-flu, and C2-dbt were

enhanced by two fold. At 5 °C, the first-order rates of individual PAHs exhibited

negligible differences in the presence and absence of JD-2000 with the

exception of nap, which degraded faster in the absence of dispersant.

• The biodegradation rates for individual PAHs at 5 °C were lower than the

rates at 25 °C. Except for nap in ANS alone treatment, the rate was higher in

the 5 °C samples ( -0.44 d-1 vs. -0.34 d-1).

• The extent of removal of total PAHs was higher in the presence of JD-

2000 than in its absence at both temperatures (5 °C: 82% vs. 77%, 25 °C:

85% vs. 80% ).

• It was also observed that the % removal of C4-nap, C2-4-phe, C2-3-flu, and

C3-dbt was higher in the presence of JD-2000, regardless of temperature,

as depicted in the figure above.

• To summarize, JD-2000 had certain improvement on the biodegradation

of PAHs in ANS at 25 °C, while the impact was less significant at 5 °C.

• PAHs comprising two or three fused rings have a certain solubility in water

(e.g., nap = 30 mg/L), and their uptake occurs mostly within the aqueous

phase [7]. Surfactants could increase the transfer rate of these more

soluble compounds from the oil to aqueous phase by forming small oil

droplets, which increase the interfacial area.

• Similar enhancement effect was observed with C9500 on the biodegradation

rates of PAHs in South Louisianan crude oil [8].

• Chemical dispersion increased the extent of removal of some less

soluble PAH compounds, which could be critical in terms of the aromatics

toxicity issue.

Figure 3: Removal percentage of individual PAH at 5 °C and 25 °C.

in the absence (A) and presence (B) of JD-2000

* naphthobenzothiophene, pyrene, and chrysene homologues are not plotted because they persisted

during the experiment.

Figure 2: First order biodegradation rate coefficients of individual PAH

at 5 °C and 25 °C in the absence (A) and presence (B) of JD-2000.

Objective • We conducted biodegradation batch experiment of chemical dispersion

prepared with Alaska North Slope (ANS) crude oil and JD-2000 at 5 and

25 °C. The objective of this research is to investigate the effect of temperature

and JD-2000 on the biodegradation of PAHs.

(A) ANS alone

time, days

0 20 40 60

mg

to

ta

l P

AH

s/m

g h

op

an

e

0

20

40

60

80

100

120

5 °C : 77%

25 °C : 80%

(B) ANS + JD-2000

time, days

0 20 40 600

20

40

60

80

100

120

5 °C : 82%

25 °C : 85%

Figure. 1: Biodegradation of hopane-normalized total PAHs at 5 °C and 25 °C

in the absence (A) and presence (B) of JD-2000

Removal: Removal: