20 Using Sediment Cores to Assess Inputs of ...

Sediment Cores 20 Using to Assess Inputs of Organochlorines and Polycyclic Aromatic Hydrocarbons in Coastal Georgia Estuaries Clark Alexander, Allen D. Uhler, and Richard F. Lee Contents 20.1 Introduction...........................................................................................................................465 20.2 Materials and Methods.......................................................................................................... 467 20.2.1 Preliminary Sampling and Sediment Analysis......................................................... 467 20.2.2 Coring Procedures..................................................................................................... 467 20.2.3 Analysis of Sediments, PCBs, and PAHs.................................................................. 467 20.2.3.1 Physical Characterization of Sediment....................................................... 467 20.2.3.2 Analysis of Polycyclic Aromatic Hydrocarbons and Polychlorinated Biphenyls.....................................................................................................468 20.3 Results and Discussion..........................................................................................................469 20.3.1 Advantages of Using Abandoned Boat Slips for Historical Core Studies.................469 20.3.2 PAHs in Savannah River Estuary..............................................................................469 20.3.3 PCBs in Savannah River Estuary.............................................................................. 470 20.3.4 Pesticides in Savannah River Estuary....................................................................... 471 20.3.5 PCBs in Brunswick Harbor....................................................................................... 471 20.3.6 PCBs in Sapelo Island Core....................................................................................... 472 20.4 Summary and Conclusions.................................................................................................... 473 Acknowledgments........................................................................................................................... 474 References....................................................................................................................................... 474

20.1  Introduction The sediment record, as revealed in sediment cores, has been widely used to reconstruct the history of contaminant input in estuaries [1–9]. The basic assumption in using the sediment record to reveal contaminant input trends is that contaminant inputs of synthetic organochlorine compounds and polycyclic aromatic hydrocarbons (PAHs) readily adsorb to sedimenting particles and equilibrate relatively rapidly with the sediment. In addition, sedimentary processes must not act to disturb the 465

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building of this record. If these requirements are satisfied, then the sediment column represents a continuous, complete historical sequence of contaminant accumulation. Deposition and accumulation are two terms used by sedimentologists and the distinction between these two terms has been discussed by McKee et al. [10]. Deposition is the temporary emplacement of particles in the seabed. Accumulation is the net sum of many episodes of deposition and removal over long time scales. Differences between rates of deposition and accumulation affect the ability of an environment to record sedimentary events. Using radiochemical chronologies, such as those derived from the decay of Pb-210, it is possible to date sediment cores. Pb-210, formed by the decay of radon in the atmosphere (residence time of Pb-210 in the atmosphere ∼10 days) is deposited by wet and dry deposition on land and sea. The Pb-210 decays at a known rate, allowing the determination of sediment accumulation rates by measuring Pb-210 activity with depth in the cores. Pb-210 (half-life of 22.3 years) characterizes accumulation rates over approximately a 100 year time period (approximately five decay half-lives) in undisturbed cores. Cs-137 (half-life 30 years) is an anthropogenic impulse tracer commonly used to complement temporal studies using Pb-210. Cs-137, which is delivered by atmospheric fallout, was first introduced into the environment in significant quantities in 1954 and peaked in 1963 in conjunction with the peak in atmospheric weapons testing and provides an independent estimate of sediment accumulation rates. A third isotope, Be-7 (half-life of 53 days), is a naturally produced radionucleotide formed by cosmic ray bombardment of atmospheric nitrogen and oxygen, which is rapidly removed from the atmosphere and incorporated onto particles of land, which are then subsequently removed by flooding to aqueous environments. Be-7 has its greatest flux to sediments during the rainy season, so it can be used to identify sediments that are brought into estuaries and continental margins on a seasonal basis (e.g., within five half-lives, or 8 months). Dating procedures using these isotopes have been used to successfully date cores, and to identify seasonal flood layers from a variety of coastal environments [1,3–6,11,12]. Sediment accumulation rates can be determined using the constant sedimentation model [13]. The present study reports the results of analysis of polychlorinated biphenyls (PCBs) and PAHs in dated sediment cores taken from three estuarine sites in coastal Georgia, i.e., the Savannah River Estuary, the Brunswick Estuary, and the Duplin River Estuary, which is located behind Sapelo Island. PAHs are often at high concentrations in sediments near urban areas due to oil spills, creosote releases from treated piling, aqueous emissions from historic manufactured gas plant wastes, and urban runoff, and particulate emissions from fossil fuel burning [14]. PCBs are ubiquitous, persistent, and toxic pollutants, which were widely produced in the 1930s and 1970s in the United States [15,16]. Changes in the contaminant concentrations of these compounds over time were correlated with various activities at the coring sites. Additionally, this contribution was intended to generally illustrate the historic coring approach for assessing contaminant inputs to coastal systems. Two cores were taken from the Savannah River Estuary (Savannah, Georgia, the United States). This estuary is typical of estuaries of the South Atlantic Bight, which are formed within the mouths of the Piedmont rivers. Within the Savannah River Estuary is the port of Savannah, which is the fourth busiest port in the United States and handles containerized shipping of all kinds, i.e., kaolin, coal, ferrous minerals, fuel oil, and other raw and processed chemicals. Industries that have developed around this port include paper, fertilizer, and chemical manufacturing. Hundreds of thousands of metric tons of sediment are transported down the Savannah River and are trapped in the Savannah estuary. As a result of farming and deforestation, soil eroded from the upland watershed area moves toward the estuary via the Savannah River. Thus, chemicals used in the upland areas can enter the sediments of the Savannah Estuary many years after their initial use. The second sample site was in the Brunswick Estuary, near the Port of Brunswick. The core was taken in Brunswick Harbor at a site, now abandoned, where Liberty ships were built and launched during World War II. The Brunswick Port, while not as busy as the Savannah Port (total weight shipped in 2002 from Brunswick Port was 3 million tons while Savannah Port shipped 10

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million tons), is an active port handling wood products, agricultural products, automobiles, and heavy machinery. The third sampling site was in the pristine salt marshes along the Duplin River, in the Sapelo Island National Estuarine Research Reserve, located behind and directly adjacent to Sapelo Island, Georgia. The Altamaha River, a relatively undisturbed river in Georgia, drains an area of 38,000 km2 and empties into the Atlantic Ocean, although some of it flows into Doboy Sound and into the Duplin estuary, both to the north of the river. Sapelo Island was a private preserve from 1934 to 1964 and then, in 1976, a portion of the island was designated a National Estuarine Research Reserve by National Oceanographic and Atmospheric Administration (NOAA). For the past 75 years, there have only been a small number (∼200) of permanent residents on the island, allowing preservation of a near-pristine environment.

20.2  Materials and Methods 20.2.1  Preliminary Sampling and Sediment Analysis Surface sediment samples were collected from potential coring sites, with selection based on sediment type and radionucleotide activities. Sediments with obvious biological or physical mixing, high sand content, and/or a non-accumulating, over-consolidated character were rejected since such sediments cannot be used for historical coring studies. The properties of the sediments selected for coring had rapidly accumulating sediment (i.e., high porosity and oxidized coloration), bedded sediment structure, a strong radiochemical signal, and/or Be-7 in the surficial sediment.

AQ1

20.2.2  Coring Procedures Box cores were taken via a single-spade box corer. Three subcores were taken from each box with PVC or stainless steel pipe for the following: (1) Organochlorine and/or PAH analysis, (2) radiochemical dating and textural analysis, and (3) additional core for analytical studies if extra material was needed because of high core porosity, which means that the amount of sediment in each interval might be limited. The subcores were placed on extruders that allowed core subsampling intervals of 1 cm. After cutting away the sediment edges (which may have been contaminated by sediment drawn along the barrel sides), the cores were sequentially sectioned at 1 cm intervals in the upper 10 cm and at 2 cm intervals to the bottom of the cores. The subsamples for the analytical evaluation were placed in precleaned glass jars and frozen. The subsamples for radiochemical dating were placed in plastic bags and sealed. A slab for x-radiographic examination sediment structure was collected in a custom-designed Plexiglass tray. X-radiographs were produced using a portable veterinary x-ray unit with Kodak AA x-ray film.

20.2.3  Analysis of Sediments, PCBs, and PAHs 20.2.3.1  Physical Characterization of Sediment 20.2.3.1.1  X-Radiographs and Sedimentary Structure X-radiographs allow determination of the extent of sediment mixing and to identify breaks in the stratigraphic record. If sediments are well laminated, then profiles of radionuclides or contaminants contained within the sediment column have not been disturbed and thus provide a means of studying contaminant input histories. In estuarine environments, most cores will display some amount of biological mixing (e.g., crab or clam burrows) in addition to bedded or laminated structure. The degree and intensity of mixing can be assessed visually in x-radiographs. Truncation of layering suggests erosion and removal of some part of the preserved record. In our studies, we tried to use sediments that were well laminated, to the greatest extent possible. X-radiographs were used to

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identify bioturbation and erosional disturbance in cores as well as to determine any disturbance associated with the coring operations. 20.2.3.1.2  Grain Size Each core was analyzed at 5 cm intervals for inorganic grain size. The subsamples were wet sieved with the retained sand fraction (>63 μm) and analyzed at 0.25 phi intervals using nested sieves. The sediment that passed through the 63 μm sieve was captured and analyzed for size distribution within the silt and clay fraction with a Sedigraph 5100, which provided a complete distribution down to 0.25 μm particle sizes. 20.2.3.1.3  Geochronology Sediment accumulation rates were determined by Pb-210 geochronologies. Additional age constraints were derived from the distributions and activities of Cs-137 and Be-7 within the cores. Activities of radiotracers within each sample were determined concurrently using two lowbackground, planar intrinsic germanium detectors, computer-based multichannel analyzers, and Maestero-II analysis software. Accumulation rates were calculated by producing profiles of excess Pb-210 activity (i.e., not supported by production of Pb-210 in the sediment column) with core depth. Total Pb-210 activity was directly determined by gamma spectroscopic measurement of its 46.5 keV gamma peak in dried, homogenized sediment [17]. Supported levels of Pb-210 from the decay of Ra-226 were determined for each depth interval by concurrently measuring the gamma activity of Pb-214 and Bi-214, the short-lived granddaughters of Ra-226. Excess Pb-210 is simply the difference between total and supported Pb-210. Activities of Cs-137 and Be-7 were directly determined by gamma spectroscopic measurement of their 662 and 477 keV gamma peaks, respectively, in dry, homogenized sediment [18,19]. Sediment accumulation rates were calculated using the constant flux (also known as the constant rate of supply) geochemical model [18,20–23]. This model is applicable in areas where the flux of excess Pb-210 (unsupported by the decay of Ra-226) and dry-mass sediment rate at the seabed have remained constant. This assumption has been shown to be reasonable in areas where the supply of Pb-210 is dominated by atmospheric sources, such as estuarine environments. Dry mass accumulation rates (in g/cm2/year) were calculated for cores and ages were assigned to depth intervals within each core. 20.2.3.2  Analysis of Polycyclic Aromatic Hydrocarbons and Polychlorinated Biphenyls Sediments from cores H and F in the Savannah River Estuary were analyzed for 22 selected PAHs using the procedures described by MacLeod et al. [24]. Sediment sections were extracted with dichloromethane and organic extracts were fractionated on columns of silica gel after using activated copper to remove elemental sulfur. The first fraction, which contains PCBs and some chlorinated pesticides, was eluted with hexane. The second fraction, which contains the PAHs and most of the chlorinated pesticides, was eluted with dichloromethane in hexane (1:1 v/v). The internal standard added to each sample was 4,4′-dibromooctafluorobiphenyl. Total PAHs refers to the total concentration of the 22 selected PAHs. For analysis of PAHs, a series of internal standards (d8-naphthalene, d10-acenaphthene, d10-phenanthrene, d12-chrysene, and d12-perylene) were added to each sample and blank before workup to allow determination of recovery. PCBs were analyzed by high-resolution fused silica capillary gas chromatography with electron capture detection (Varian 3400CS gas chromatograph). PCB congeners were identified and quantified by comparisons to reference congeners. PCBs were run on two different columns (DB-5 and Db-17) to confirm the identification of the various compounds. Where identification was in question, full scan gas liquid chromatography/mass spectrophotometry was used and compared with the mass spectra of the authentic standards. Standard solutions of 28 PCB congeners from the National Institute of Standards and Technology (NIST, Gaithersburg, MD) were used to calibrate the GC-EDC. High-purity solvents, reagents, and process gases were used throughout the analysis.

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Procedural blanks analyzed in conjunction with the sample indicated insignificant levels of all target analytes.

20.3  Results and Discussion 20.3.1  Advantages of Using Abandoned Boat Slips for Historical Core Studies Two of the sites (Savannah River Estuary and Brunswick, GA harbor) selected for coring were abandoned boat slips. These types of sites have many advantages when conducting historical coring studies in and near ports and other urban centers on the water. Initially, the slip is deeper than the equilibrium depth and thus after abandonment, the slip rapidly accretes to fill accommodation space, often at rates of many centimeters per year. The sedimentation rates slow as they approach equilibrium depth. Thus, there is the possibility of a high-resolution sediment record that can span decades or more in cores taken from abandoned boat slips.

20.3.2  PAHs in Savannah River Estuary Two cores were taken in the Savannah River Estuary. Core H (Figure 20.1) was taken from an abandoned boat slip across the river from the city and port of Savannah. Core F (Figure 20.2) was taken from a back-levee Spartina marsh several kilometers away from the city of Savannah. The major feature of core H was a large increase in PAH concentrations from a depth of 175 cm

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Total PAH concentration core H (ng/g dw) 1000 2000 3000 4000 5000 6000 7000

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Figure 20.1  Total PAH concentrations in sections of core H from Savannah River Harbor. (Data from Alexander, C.R. et al., Limnologica, 29, 267, 1999.)

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Total PAH concentration core F (ng/g dw) 100 200 300 400 500 600 700 800 900 1000 1989 1987 1984

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Figure 20.2  Total PAH concentrations in sections of core F from Savannah River Estuary. (Data from Alexander, C.R. et al., Limnologica, 29, 267, 1999.)

(age-1948) to 135 cm (age-1958) followed by a decrease in concentrations from 135 cm to the surface. We suggest that the increased PAH concentration from 1948 to 1958 was due to increases in the population, port activity, and industry in the Savannah area, while the decrease after 1958 was likely due to the effects of a number of regulations dealing with emissions and effluents from industry located along the Savannah River. Core F had lower PAH concentrations than core H for the same dates, which is likely due to its locations at some kilometers from the port of Savannah and its associated industry.

20.3.3  PCBs in Savannah River Estuary PCBs were extensively used as heat transfer fluids in transformers and capacitors throughout the United States in the 1930s and 1970s. Because of their persistence and toxicity, their production was banned in the United States in 1976. Highest concentrations of PCBs in cores F (Figure 20.3) and H (Figure 20.4) were 32 and 207 ng/g, respectively, which were found at depths dated at 1967. Total PCBs is the sum of the concentration of 20 PCB congeners. Concentrations of PCBs in core H were very low in core sections dated from 1920 to 1937, with a gradual increase from 1944 to the 32 ng/g peak in 1967 followed by lower concentrations (16–22 ng/g) after 1967. PCB concentrations in core F show a profile similar to the one observed in core H (i.e., increasing concentrations from 1944 to 1967 and lower but significant PCB concentrations after 1967). The detection of significant concentrations of PCBs in cores after 1976, when PCB production was banned, is likely due primarily to soil exposed earlier (before 1976) in the watershed area of the Savannah River and transport of these

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Total PCB concentration core F (ng/g dw) 10

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80 90 100 110 120

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Figure 20.3  Total PCB concentrations in sections of core F from Savannah River Estuary. (Data from Alexander, C.R. et al., Limnologica, 29, 267, 1999.)

sediment down the Savannah River to sites F and H. Dated cores at various sites in North America generally have high PCB concentrations in sections dated in the 1960s [4].

20.3.4  Pesticides in Savannah River Estuary An earlier study on cores F and H in the Savannah River Estuary showed that in core F, the major pesticides found were isomers of DDT (4,4′-DDE, 4,4′-DDD) and dieldrin, which peaked in the 1984 layer [2]. Since the manufacture of DDT was based in the United States in 1972, it seems likely that the source of the DDTs and dieldrin in 1984 in soil earlier exposed in the watershed to DDT with later transport down the river to site F. The profile of 2,4′-DDE and dieldrin in core H correlates with their peak usage in the United States with a gradual increase from 1954 to a peak in 1967 and then a decrease from 1967 to recent times. It is likely that much of the DDT found in core H was used at that site since site H has large populations of breeding mosquitoes that were controlled by DDT until its application was stopped in the late 1960s. The dieldrin was used in the 1960s to control white-fringed beetles in this area.

20.3.5  PCBs in Brunswick Harbor A core to a depth of 50 cm was taken from an abandoned boat slip in Brunswick Harbor, GA. There were two different accumulation rates determined from Pb-210 geochronology of this core. The

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Total PCB concentration core H (ng/g dw) 10 15 20 5 25 30 1989

1973

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Depth (cm)

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1948

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Figure 20.4  Total PCB concentrations in sections of core H from Savannah River Harbor. (Data from Alexander, C.R. et al., Limnologica, 29, 267, 1999.)

accumulation rate for the upper 23 cm (1963–2004) of the core was 0.2 cm/year while the accumulation rate of the lower section of the core (1954–1963) was 1.8 cm/year. PCBs in a sectioned Brunswick core were not detected before 1948 but were followed by peaks in 1955 (110 ng/g), 1958 (120 ng/g), and 1961 (130 ng/g) (Figure 20.5—ng PCBs/g sediment normalized to percent sediment carbon). PCB concentrations decreased after 1961 with concentrations of 37 and 40 ng/g sediment in 1974 and 2004, respectively.

20.3.6  PCBs in Sapelo Island Core An intact core was collected on March 13, 1997, from a back-levee marsh in the upper Duplin River, an estuarine river adjacent to and behind Sapelo Island, Georgia. Sapelo Island is a National Estuarine Research Reserve and has only a small number of permanent residents. The core was sectioned at 1 cm intervals and these sections were used for the dating and analysis of PCBs. The x-radiograph of the core showed conspicuous Spartina root mass and rhizomes down to 20 cm. The 33 cm core represents approximately 100 years of accumulation with total PCB concentrations near or below detection limits throughout the column (non-detectable to 2.1 ng/g sediment; minimum detection limits—2 ng/g) (Table 20.1). PCB congeners identified in the core included congeners 52, 44, and 101/90, although all concentrations were near detection limits (