ACCESS NUMBER: 15170

STUDY TITLE: Kinetics and Mechanisms of Slow PAH Desorption from Lower Cook Inlet and Beaufort

Sea Sediments

REPORT TITLE: Phenanthrene Adsorption and Desorption by Melanoidins and Marine Sediment Humic

Acids

CONTRACT NUMBER: 1435-01-98-CA 30909; TASK ORDER (TO): 15170

SPONSORING OCS REGION: Alaska

APPLICABLE PLANNING AREA: Lower Cook Inlet, Beaufort Sea

FISCAL YEAR OF PROJECT FUNDING: 1999

COMPLETION DATE OF REPORT: January 2004

COST: FY 1999: $58,668; CUMULATIVE PROJECT COST: $58,668

PROJECT MANAGER: Susan M. Henrichs

AFFILIATION: University of Alaska Fairbanks

ADDRESS: Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, AK 99775-7220

PRINCIPAL INVESTIGATOR*: Susan M. Henrichs

KEY WORDS: Lower Cook Inlet, Beaufort Sea, Kachemak Bay, Jakolof Bay, aromatic hydrocarbons,

phenanthrene, adsorption, desorption, sediments, humic substances

BACKGROUND:

Although aromatic hydrocarbons make up only about 10% of the complex mixture of compounds in

petroleum, they are of special concern because they are among the most toxic, mutagenic, and

carcinogenic constituents. Sediments are important reservoirs for PAH (polycyclic aromatic hydrocarbon)

contamination in the marine environment. A factor in their persistence could be the strong association

between sediment particles and aromatic hydrocarbons and a decrease in biodegradability associated

with this adsorption. Adsorption and biodegradation processes affecting the fate of aromatic hydrocarbons

in Lower Cook Inlet sediments have been studied previously: Braddock, J.F., and Z. Richter. 1998.

Microbial Degradation of Aromatic Hydrocarbons in Marine Sediments. Final Report. 005 Study MMS

97-0041, University of Alaska Coastal Marine Institute, University of Alaska Fairbanks and USD01, MMS,

Alaska OCS Region. 82 p.; Henrichs, S.M., M. Luoma and S. Smith. 1997. A Study of the Adsorption of

Aromatic Hydrocarbons by Marine Sediments. Final Report. 005 Study MMS 97-0002, University of

Alaska Coastal Marine Institute, University of Alaska Fairbanks and USD01, MMS, Alaska OCS Region.

47 p.; and Shaw, D.G., and J. Terschak. 1998. Interaction Between Marine Humic Matter and Polycyclic

Aromatic Hydrocarbons in Lower Cook Inlet and Port Valdez, Alaska. Final Report. 005 Study MMS 98-

0033, University of Alaska Coastal Marine Institute, University of Alaska Fairbanks and USD01, MMS,

Alaska OCS Region. 27 p. While these studies demonstrated strong adsorptive associations between

sediments or humic substances and aromatic hydrocarbons, and that adsorption inhibited their

biodegradation, the research addressed time scales of a week or less. Further research was needed to

investigate PAH adsorption and desorption over longer times, in order to predict their influence on

persistence of aromatic hydrocarbon contaminants in sediments.
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OBJECTIVES:

This study examined the role that humic acids and their structures play in the kinetics and mechanisms of

polycyclic aromatic hydrocarbon interactions with sediments. Natural humic acids, with a wide range of

properties, were isolated from Alaska coastal marine sediments. Melanoidins were synthesized and used

as humic acid analogs, because of the ability to control various aspects of their structural components

during synthesis and their initial lack of PAH. The research objectives were to test the following

hypotheses:

Aromatic hydrocarbon adsorption that was apparently irreversible in the experiments of Henrichs et al.

[1997] and Braddock and Richter [1998] is reversible with longer desorption times. The kinetics of

desorption largely control the persistence of petroleum-derived aromatic hydrocarbons in sediments.

Interactions of aromatic hydrocarbons with sediment organic matter are responsible for adsorption that

appears to be irreversible, at least under some conditions.

Diffusion into the 3-dimensional structure of organic matter slows desorption.

Binding to a variety of adsorption sites with different partition coefficients causes differences in the

apparent, experimental partition coefficient under conditions of adsorption and desorption.

3. Variations in organic matter properties influence the rate and extent of adsorption and desorption

processes. In particular, there is a direct correlation between the aromatic character of sediment humic

acid and the adsorption partition coefficient of phenanthrene.

Model organic substances similar to those occurring in sediments, but with well-controlled

composition and properties, will show a systematic relationship between adsorption and desorption

properties and organic structure.

The aspects of organic structure identified as important to adsorption properties using model

compounds will also show a systematic relationship to adsorption and desorption of aromatic

hydrocarbons by natural sediment organic matter.

4. Previous phenanthrene adsorption of sediments affects subsequent adsorption.

DESCRIPTION:

Samples of Alaskan coastal sediments were taken from Port Valdez, Lower Cook Inlet, and the Beaufort

Sea:

Whole, acid-treated sediments were analyzed for total organic carbon (TOC) and nitrogen (TN) content

and their stable isotopic composition. The TOC and TN measurements for Port Valdez and Lower Cook

Inlet sediment organic matter were performed by the Marine Science Institute, University of California

Santa Barbara. TOC, TN, and stable isotopic ratio analyses of the Beaufort Sea sediments and all humic

acids were performed at the University of Alaska Fairbanks using a Finnigan MAT Delta Plus mass

spectrometer with a Conflo II interface and a Carlo Erba elemental analyzer. Sediment hydrocarbon

analyses were done as described by: Feder, H.M., and D.G. Shaw. 1996. Environmental Studies in Port

Valdez, Alaska. Final report to Alyeska Pipeline Service Company. Institute of Marine Science, University

of Alaska Fairbanks, 304 p.

Location Station Latitude (N) Longitude (W) Depth

Port Valdez PV25 610 05.5' 146° 23.3' 73

Port Valdez PV82 610 05.4' 146° 22.3' 79

Lower Cook Inlet HBH 59° 36.3' 151° 25.0' n/a

Lower Cook Inlet JB2 590 27.1' 151° 29.3' n/a

Lower Cook Inlet TB2 590 24.8' 151° 17.0' n/a

Beaufort Sea 5A 70° 29.7' 148° 46.0' 11.4

Beaufort Sea 6G 70° 31 .3' 149° 53.9' 2.1
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Humic acid was extracted from sediments or melanoidin preparations using 0.5 M NaOH (Anderson,

D.W., and J.J. Schoenau. 1983. Soil humus fractions, p. 391-395. In M.R. Lewis [ed.], Soil Sampling and

Methods of Analysis. Lewis Publishers, Ann Arbor). Melanoidins were prepared in the laboratory by

refluxing several ratios of glucose and bovine casein (1:1, 10:1, and 1:10) in buffered solutions for 24 to

48 hours (Yamamoto, S., and R. Ishiwatari. 1989. A study of the formation mechanisms of sedimentary

humic substances - II. Protein-based melanoidin mode. Organic Geochemistry 14:479-489). The humic

acids were characterized by elemental and isotopic analyses as described above.

Fourier transform infrared (FTIR) spectra were obtained using a Nicolet Magna 560 FT spectrometer with

an infrared source, KBr beam splitter, and a MCT/B detector. Cross-polarized magic-angle spinning 13C

nuclear magnetic resonance (CPMAS/13CNMR) spectroscopic data were obtained from the NMR

Laboratory at Florida State University in Tallahassee (Hatcher, P.G., R. Rowan and M.A. Mattingly. 1980.

1H and 13C NMR of marine humic acids. Org. Geochem. 2:77-85). The NMR spectrometer was a

Bruker/IBM WP200SY with Solid State Accessory package. A 7 mm standard Doty Scientific

multifrequency CPMAS probe was employed.

A montmorillonite standard (A.P.l. #26, 49 E 2600 from Clay Spur, Wyoming: Ward's Natural Science

Establishment, Inc.) was ground and sieved (53 pm mesh), and organic material was removed from the

clay by oxidizing it with 30% hydrogen peroxide. Humic acids were coated onto the inorganic substrate for

use in the adsorption experiments.

Radiolabeled phenanthrene was used to examine adsorption. All glassware and Teflon liners used in

this study were treated to remove any hydrocarbon contamination before use. Solutions were prepared by

dissolving [9-14C] phenanthrene (5-15 mCi mmor1, Sigma Chemical Co.) and nonlabeled phenanthrene

artificial seawater to yield concentrations of 50, 300, and 700 Lig L, with 0.500 g HgCl2 added as an

antibiologic agent. For adsorption experiments, 0.1 g of wet, hum ic-coated clay was weighed into vials

and 5 mL of a radiolabeled phenanthrene/seawater solution was added. After mixing the vials were

placed on a table shaker at 150-200 rpm for 1 h, 1 d, 3d, 7 d, or 14 d. Then the vials were centrifuged

and 1 .0 mL aliquots of the radiolabeled reaction solutions was removed and scintillation counted. Partition

coefficients, K0, were reported as the ratio of adsorbed phenanthrene to dissolved phenanthrene,

normalized to organic carbon. The remaining supernatant was discarded and replaced with a 300 pg L1

phenanthrene solution, without radiolabel, to begin the desorption phase of the experiment. Vials were

vortex mixed for 15 seconds and then placed on a table shaker. After desorption for 1 d, 3 d, 7 d, 14 d, 30

d, 60 d, or 90 d, the vials were centrifuged and 1 .0 mL aliquots of the supernatants were removed and

scintillation counted. Reported partition coefficients (K0) were normalized to the organic carbon content of

the clay-humic acid sorbent.

SIGNIFICANT CONCLUSIONS:

The results were consistent with the hypothesis that aromatic hydrocarbon adsorption that was partly

irreversible in experiments lasting a few days would be reversible with longer desorption times.

Adsorbed phenanthrene was completely desorbed within one week under most experimental

conditions.

The results were consistent with the hypothesis that interactions of aromatic hydrocarbons with

sediment organic matter, specifically slow diffusion within the organic structure, are responsible for

adsorption that appears to be irreversible, at least under some conditions. A subhypothesis, that

binding to a variety of adsorption sites with different partition coefficients causes differences in the

apparent, experimental partition coefficient, was rejected, since phenanthrene concentration did not

affect adsorption.

The results were consistent with the hypothesis that variations in organic matter properties influence

the rate and extent of adsorption and desorption processes. Adsorption was negatively correlated with

the polarity of the humic acid. Desorption, on the other hand, was found to be inversely correlated with

the amount of humic acid coating the mineral substrate, but unrelated to its structural characteristics.

The subhypothesis that there is a direct correlation between the aromatic character of sediment humic

acid and the adsorption partition coefficient of phenanthrene was rejected. The subhypothesis that the
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synthetic humic substances would show clearer relationships between organic matter composition and

adsorption was rejected; trends for natural sedimentary humic acids and melanoidins were similar.

The hypothesis that previous phenanthrene adsorption by sediments affects subsequent adsorption

was rejected. The concentration of phenanthrene already adsorbed to sediment did not affect K0.

STUDY RESULTS:

Organic normalized partition coefficients (K0) were determined from the slopes of linear adsorption

isotherms. The initial concentration of phenanthrene in solution had no effect on the partition coefficient.

Adsorption isotherms were linear up to a concentration of 5500 pg phenanthrene g1 organic carbon,

indicating that binding sites within the organic matter are both uniform in strength and unlimited. A mixture

of strong and weak adsorption sites in the humic acid would lead to decreasing adsorption partition

coefficients with increasing concentration, which was not observed. The initial uptake of phenanthrene

was rapid, but the approach to steady state required approximately one week, consistent with slow

hydrocarbon diffusion into a 3-dimensional organic matrix. The K0 of sediments that already had

adsorbed phenanthrene did not differ from those phenanthrene-free sediments.

Phenanthrene adsorption was not related to the concentration (g organic carbon g1 clay) of humic acid

coating the mineral substrate. The percent nonpolar carbon of humic acid was weakly correlated to the

K0. However, K0 was more strongly, negatively correlated with the sum of amide and carboxylic carbons

and with N/C ratio, which in turn are related to the polarity of humic acids. Humic acids with properties

indicating a mixed terrestrial and marine origin adsorbed phenanthrene to a greater extent than did those

of a wholly marine origin. However, this was not because of greater aromaticity derived from lignin, but

rather to a relative lack of amide and carboxylic acid functional groups. In fact, there was no relationship

between humic acid aromaticity and K0. Another characteristic shared by humic acids exhibiting stronger

PAH adsorption and lower polarity was a subtidal sediment source, while the less adsorptive Lower Cook

Inlet samples were all from intertidal sediments. The intertidal sediments were probably richer in living

organisms and fresh detritus than the subtidal sediments, potentially another factor contributing to the

greater polarity of their humic acids. The number of samples studied was not sufficient to conclusively

identify geographic patterns in adsorptive properties of humic acids, but the data suggest that terrigenous

inputs and the extent of diagenetic alteration of organic matter should be investigated as predictors of

adsorptive properties.

The extent of desorption was less for greater adsorbed phenanthrene concentrations. The results were

further evidence against a mixture of strong and weak adsorption sites in the humic acid, which would

lead to greater desorption with increasing adsorbed phenanthrene concentration. Decreased desorption

with increasing adsorbed phenanthrene concentration was consistent with the interpretation that

adsorbed phenanthrene caused conformational changes to the humic acid structure. The initial rate of

desorption was directly proportional to the initial concentration of adsorbed phenanthrene. Desorption was

more rapid initially, with a subsequent slow approach to steady state requiring approximately one week,

reflecting slow diffusion processes within the organic matrix. Initial desorption decreased with the carbon

content of the humic acid coated clay, probably because thicker organic coatings led to loner diffusion

paths. Desorption was not related to the humic acid structural characteristics measured by 3C nuclear

magnetic resonance spectroscopy.

The results of this study warn against applying results regarding adsorption of pollutants by sediments

from one study to another. Predictions need to be made on a case-by-case basis, because of the clear

dependence of adsorption/desorption processes on sediment organic matter properties.

STUDY PRODUCTS:

Henrichs, S.M. 2000. Kinetics and mechanisms of slow PAH desorption from Lower Cook Inlet and

Beaufort Sea sediments. University of Alaska Coastal Marine Institute Annual Research Review, March

2000, Fairbanks, Alaska.
*pIs affiliation may be different than that listed for Project Manager.

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Henrichs, S.M. 2000. Kinetics and mechanisms of slow PAH desorption from Lower Cook Inlet and

Beaufort Sea sediments, p. 76. In University of Alaska Coastal Marine Institute Annual Report No. 6.

OCS Study MMS 2000-046, University of Alaska Fairbanks and USD01, MMS, Alaska OCS Region.

Henrichs, S.M., and J.A. Terschak. 2000. Kinetics and mechanisms of slow PAH desorption from Lower

Cook Inlet and Beaufort Sea sediments, p. 42-50. In University of Alaska Coastal Marine Institute

Annual Report No. 7. OCS Study MMS 2000-070, University of Alaska Fairbanks and USD01, MMS,

Alaska OCS Region.

Henrichs, S.M., and J.A. Terschak 2001. Kinetics and mechanisms of slow PAH desorption from Lower

Cook Inlet and Beaufort Sea sediments. University of Alaska Coastal Marine Institute Annual

Research Review, February 2001, Fairbanks, Alaska.

Henrichs, S.M., and J.A. Terschak 2001. Kinetics and mechanisms of slow PAH desorption from Lower

Cook Inlet and Beaufort Sea sediments. Alaska OCS Region of the Minerals Management Service, 8th

Information Transfer Meeting, 3-5 April 2001. Anchorage.

Henrichs, S.M., and J.A. Terschak. 2002. Kinetics and mechanisms of slow PAH desorption from Lower

Cook Inlet and Beaufort Sea sediments, p. 28-38. In University of Alaska Coastal Marine Institute

Annual Report No. 8. OCS Study MMS 2002-001, University of Alaska Fairbanks and USD01, MMS,

Alaska OCS Region.

Henrichs, S.M., and J.A. Terschak 2002. Kinetics and mechanisms of slow PAH desorption from Lower

Cook Inlet and Beaufort Sea sediments. University of Alaska Coastal Marine Institute Annual

Research Review, February 2002, Fairbanks, Alaska.

Henrichs, S.M., J.A. Terschak and D.G. Shaw. 2003. Kinetics and mechanisms of slow PAH desorption

from Lower Cook Inlet and Beaufort Sea sediments, p. 8. In University of Alaska Coastal Marine

Institute Annual Report No. 9. OCS Study MMS 2003-003, University of Alaska Fairbanks and USD01,

MMS, Alaska OCS Region.

Terschak, J.A. 2002. Phenanthrene Adsorption and Desorption by Melanoidins and Marine Sediment

Humic Acids. Ph.D. Dissertation, University of Alaska Fairbanks, 179 p.

Terschak, J.A., and S.M. Henrichs. In preparation. Phenanthrene adsorption to mineral-bound humic

acid: Kinetics and influence of previous phenanthrene adsorption.

Terschak, J. A., and S.M. Henrichs. In preparation. Desorption kinetics of phenanthrene from mineralbound humic acids: Consequences of conformational changes.

Terschak, J.A., S.M. Henrichs and D.G. Shaw. 2004. Phenanthrene Adsorption and Desorption by

Melanoidins and Marine Sediment Humic Acids. Final Report. OCS Study MMS 2004-001, University

of Alaska Coastal Marine Institute, University of Alaska Fairbanks and USD01, MMS, Alaska OCS

Region. 65 p.

Terschak, J.A., S.M. Henrichs, and D.G. Shaw. In preparation. Effects of humic acid properties on

phenanthrene adsorption.
Applicable planning area: Cook Inlet area of the Gulf of Alaska subregion.

CHUKCHI SEA

GULF OF ALASKA SUBREGION

BEAUFORT SEA

Applicable planning area: Beaufort Sea area of the Arctic Subregion.

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ARCTIC SUBREGION it Ha
71°N

70 °N

Sample sites within the Beaufort Sea region.

59° 36' N

59° 30' N

59°24' N

61° 08' N

61°06'N

61° 04' N

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Bishop Beach

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Sample sites within the Lower Cook Inlet region.

150°N 148°N

Homer ud Flat Harbor

I I 146°40'W 146°30'W 146°20'W

Sample sites within the Port Valdez region.

Beaufort Sea

.. 2F I CanLen Bay

146°N 144°N

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Barter I

5A

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151°45'W 1510 30' W 151° 15'W