Seasonal and annual loads of hydrophobic organic contaminants from the Susquehanna River basin to the Chesapeake Bay

Marine Pollution Bulletin 48 (2004) 840–851 www.elsevier.com/locate/marpolbul

Seasonal and annual loads of hydrophobic organic contaminants from the Susquehanna River basin to the Chesapeake Bay Fung-Chi Ko *, Joel E. Baker Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, P.O. Box 38, Solomons, MD 20688, USA

Abstract Water from the Susquehanna River was collected and analyzed for polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyl (PCB) congeners to estimate seasonal and annual riverine loads to the Chesapeake Bay. Temporal variations in the chemical loads resulted from the large changes in the water flow rates and in the particle-associated contaminant concentrations. Concentrations of PCBs and PAHs in river particles (ng/g) were twice as great as those in the northern Chesapeake Bay, indicating that the Susquehanna River is an important source of these contaminants to the bay. The river carries a majority of its hydrophobic organic contaminants (HOCs) in the particulate phase. During periods of high flow, large amounts of suspended particles in the river result in elevated HOC levels and increased loadings of these contaminants to the bay. From 1997 to 1998, 60% of the total annual HOC loading occurred in the early spring coincident with high river flows. The total PCB and PAH annual loadings from the Susquehanna River to the Chesapeake Bay were 76 and 3160 kg/year, respectively and 75% of the loaded organic contaminants were in the particulate phase. Principal component analysis of PAH and PCB congener patterns in the particles reveals that the river suspended particles were dominated by autochthonous production in the summer and by resuspended sediment and watershed erosion during the winter and early spring. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: HOCs; PCBs; PAHs; Chesapeake Bay; Susquehanna River

1. Introduction The Susquehanna River is the main tributary of the Chesapeake Bay, drains approximately 70,000 km2 or 42% of the bay’s watershed (Seitz, 1971), and contributes more than 50% of the freshwater flow to the Chesapeake Bay annually (Risser and Siwiec, 1996). More than 1 million tons of sediment enter from the Susquehanna River into the Chesapeake Bay annually (USGS, 2003). The large drainage area and water flows of the Susquehanna River result in significant loads of sediment and nutrients to the estuary which, therefore, affect the Chesapeake Bay water quality. Flow in the Susquehanna River is controlled by a series of dams

* Corresponding author. Tel.: +1-410-326-7427; fax: +1-410-3267341. E-mail address: [email protected] (F.-C. Ko).

0025-326X/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2003.10.014

between Harrisburg, Pennsylvania and its confluence with the Chesapeake Bay. In addition to their intended purpose of flood control, these dams trap river-bone particles and, therefore, have historically reduced the transport of sediments and their associated nutrients and contaminants into the Chesapeake Bay. The dams on the Susquehanna River may be reaching their sediment storage capacity, and therefore may not efficiently trap particles in the future. Hydrophobic organic contaminants (HOCs), including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), have high affinities for aquatic particles, especially those enriched in organic carbon (Karickhoff et al., 1979; Voice and Webber, 1983; Baker et al., 1985). Consequently, transport of HOCs in surface waters is tightly coupled to the movement of particles. Production of polychlorinated biphenyls (PCBs) in the United States was banned in 1972. Nevertheless, these contaminants are quite persistent and

F.-C. Ko, J.E. Baker / Marine Pollution Bulletin 48 (2004) 840–851

remain throughout the environment. Thus, PCBs are good indicators of general, non-specific contaminant sources to surface waters. Polycyclic aromatic hydrocarbons (PAHs) have both pyrogenic (combustion) and petrogenic (fossil fuel) sources. Unburned coal is a significant component of Susquehanna River sediments in areas where coal mining and processing have occurred; thus, the major constituent of coal may support petrogenic PAH levels in these sediments. Comparatively, many studies (Leister and Baker, 1994; Bamford et al., 1999, 2002; Larsen and Baker, 2002) suggest that atmospheric deposition of combustion products is an important source of pyrogenic PAHs to the northern Chesapeake Bay. The statistical analysis of HOC patterns and distributions in the Susquehanna River, therefore, makes an important contribution to our understanding of these contaminant sources to the Chesapeake Bay. Many studies regarding sediment transport and nutrient loads in the Susquehanna River have been conducted starting in early 1990’s (Ott et al., 1991; Langland and Hainly, 1997 and their references). However, the only previous study of HOC loads from the Susquehanna River was the Chesapeake Bay Fall Line Toxic Monitoring Program conducted in 1992 (FLTMP; Godfrey et al., 1995; Godfrey and Foster, 1996) and 1994 (Foster et al., 2000). The annual load of total PCB in 1992 was higher than that estimated for 1994. In contrast, the fluoranthene load from the Susquehanna River in 1994 was much greater than that in 1992. Temporally variable hydrology, particle dynamics, and chemical partitioning complicate the analysis of HOC loadings from the river into the estuary. The factors that control the distribution and transport of HOCs from the Susquehanna River into the Chesapeake Bay are still poorly understood. We sought to build upon the earlier studies of HOC loads by accurately measuring the phase distribution in comparing the seasonal and annual loads of PAHs and PCBs from the Susquehanna River and to relate these discharges to water flows and particle dynamics within the river. Our study strategy was to conduct intensive sampling campaigns every ninth day for a whole year to measure the suspended particle, particulate and dissolved PCBs, PAHs, organic carbon, and organic nitrogen concentrations in the Susquehanna River.

2. Experimental methods 2.1. Sample collection Surface water samples were collected from the downstream side of Conowingo Dam (MD, USA; 00 00 39°390 31 N, 76°100 28 W), which is located in the tid-

841

SusquehannaRiver Conowingo Dam (sampling site) Baltimore Washington DC

Chesapeake Bay

Fig. 1. Water sampling site at Conowingo Dam (Susquehanna River).

ally-influenced portion of the Susquehanna River 16 miles upstream from the Chesapeake Bay (Fig. 1), every ninth day from March 1997 to March 1998. The water was pumped by a submersible stainless steel groundwater pump (FULTZ, model SP-201-A) through Teflon tubing and stored in three 18 l sealed stainless steel tanks (the total volume of each sample was 54 l). A separate 1 l sample was taken for ancillary measurements including total suspended particles, particulate carbon, and nitrogen. Samples were returned to the laboratory for processing within 12 h of collection. The water was forced from the tanks with compressed nitrogen and passed through a glass fiber filter (Schleicher and Scheull #25, 0.7 lm) then through a glass column packed with Amberlite XAD-2 macro-reticular resin (Sigma), which effectively isolates dissolved nonpolar hydrophobic substances from solution. Prior to sampling, the glass fiber filters were cleaned by ashing at 450 °C for 24 h. The Amberlite XAD-2 resin was exhaustively cleaned and conditioned by sequential 24 h extraction with methanol, acetone, hexane, and dichloromethane, followed by rinses in hexane, acetone, methanol, and deionized water to develop a wettable surface. The resin was stored as aqueous slurry until use to prevent drying. The empty tanks were rinsed with acetone to collect any analytes which may have adsorbed during processing, and the rinse and XAD resin were stored at 4 °C until extraction. The glass fiber filters were wrapped in foil and stored at )20 °C until analysis. Sediment samples were collected along the Susquehanna River upstream of the Conowingo Dam by sediment core in September 2000. Surficial sediments (top <3 cm)

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were analyzed for PCBs, PAHs, and carbon to compare to those in the suspended particles. Total suspended particle (TSP) concentrations were measured by filtering about 100 ml of water through duplicate tared filters (Nucleopore; 0.45 lm). These filters were dried to a constant weight at 60 °C and reweighed. Additional subsamples (10 ml) were filtered through combusted glass fiber filters (Whatman GF/F) to measure concentrations of carbon. The filter samples were folded in half inward, wrapped in aluminum foil, and frozen for later analysis. The sample, standard, and blank filters were combusted at 875 °C to analyze total organic carbon using an Elemental Analyzer (Model CE-440, Exeter Analytical, Inc).

2.2. Analytical techniques for HOCs Each sample was analyzed for 36 polycyclic aromatic hydrocarbons and 70 + polychlorinated biphenyl congeners. The extraction, preparation, and analysis procedures of water, filter and sediment samples are identical to those of Ko and Baker (1995). Sediment samples were dried by grinding with cleaned anhydrous Na2 SO4 and the filter and resin samples were extracted without drying. Samples were extracted for 24 h with 1:1 (v/v) hexane:acetone in a Soxhlet apparatus. The acetone was removed by liquid–liquid partitioning into water. Before the PAH analysis, the filter sample extract was fractionated using a column packed with 8 g of 6.0% deactivated aluminum to remove polar interferences. After PAH quantification, the remaining extract was further fractionated by elution through a column packed with 13 g of 1.25% (wt/wt) deactivated Florisil with 80 ml of hexane. Each fraction was further concentrated to about 1 mL by rotary evaporation and under a purified nitrogen stream. Instrumental analysis PAHs were identified and quantified using a capillary gas chromatograph (Hewlett Packard 5890) and a mass spectrometer (5970A) operated in selected ion monitoring mode (Ko and Baker, 1995). Each PAH was identified by its retention time relative to the retention time of mixed standards (Supelco Separation Technologies, Bellefonte, PA). The mass of each PAH in the extract was determined by isotopic dilution with a series of perdeuterated PAH internal standards. PCB congeners were analyzed using a Hewlett Packard 5890 gas chromatograph equipped with a 63 Ni electron capture detector and a 5% phenylmethyl silicon capillary column (J&W Scientific). PCB congener identification and quantification procedures were modified from the method of Mullin (1985) and described in Ko and Baker (1995). Each congener was identified based on its retention time relative to a standard solution comprised of a 25:18:18 mixture of Aroclors 1232, 1248

and 1262 (Ultra Scientific) including 45 individual congeners and 25 chromatographically unresolved peaks of congener groups. 2.3. Analytical quality assurance PCB congeners which had not been produced in industrial synthesis (3,5-dichlorobiphenyl, 2,3,5,6-tetrachlorobiphenyl, and 2,3,4,40 ,5,6-hexachlorobiphenyl) and perdeuterated PAHs (d8 -napthalene, d10 -fluorene, d10 -fluoranthene and d12 -perylene) were added to each sample and matrix blank prior to extraction as surrogates to assess the overall procedural recovery. Recoveries of the three PCB congeners averaged 83 ± 19%, 76 ± 15%, and 79 ± 17% in dissolved samples and 81 ± 13%, 84 ± 13%, and 82 ± 12% in filters. PAH surrogate recoveries were comparable, and ranged from 62 ± 5% for fluorene in filters to 80 ± 33% for perylene in dissolved samples. Data were not corrected for surrogate recoveries. Matrix blanks consisting of clean filters or resin were analyzed using the same procedures used for the samples. The mass of PCB congeners and individual PAHs analyzed in the blanks were insignificant relative to those in the samples. A signal to noise ratio of five was used to calculate an instrumental detection limit because the peaks generated by the blank matrix are what truly limit detection for PCB congeners and PAHs. In this study, the method detection limits (MDLs) of the analytes were estimated as equal to three times the average mass of each PCB congener or individual PAH in all the blanks. As 54 l water samples and 72 mg to 1 g particle samples in filters were analyzed in this study, the detection limits of total PCB for water and suspended particle samples were 0.12 ng/l and 5–56 ng/g, respectively. The detection limits of total PAH for water and particle samples were 3.8 ng/l and 34–760 ng/g, respectively. Less than 10% of PCB congeners and individual PAHs in each sample had concentrations lower than the detection limits. All data reported exceeded the detection limits. 2.4. Contaminant loading estimation Daily contaminant loadings for each PAH and PCB from the Susquehanna River were calculated by multiplying the chemical concentrations measured every ninth day by the measured daily river flow Li ¼ Q
Ci
n where Li is the calculated load for contaminant i (g/day), Q the daily average river discharge rate (m3 /s), Ci the concentration of contaminant i (ng/l) and n the conversion factor (0.0864 l s g/m3 day ng). The water flow rate ðQÞ is cited from the daily records at the Conowingo Hydrological Power Plant (USGS,

F.-C. Ko, J.E. Baker / Marine Pollution Bulletin 48 (2004) 840–851

843

water flow rate was 200 ± 70 m3 /s during low flow (April–October; Fig. 2A). The TSP increased to 22 mg/l when the water flow rate reached 4000 m3 /s during high flow (Fig. 2A). High water discharges (2500 ± 1500 m3 /s) in winter and early spring resulted from snow melt and storm water runoff. In this study, the suspended particle concentrations (TSP) covaried with the river flow rate (Q, m3 /s).

2003). The HOC concentrations during the four days preceding and four days following the sampling day were assumed to be equal to the measured concentrations on the sampling day. The annual loads of HOCs were calculated as the sum of the daily loads.

3. Results and discussion

TSP ¼ ð2:3  0:3ÞQ=1000 þ ð7:5  3:1Þ;

3.1. Particle concentration and composition as a function of river flow

The correlation between TSP and flow increases (r2 ¼ 0:91) when only the data with flow rates greater than 2000 m3 /s are used (Fig. 2A), implying that TSP is dominated by resuspended and freshly eroded particles during high flow. In contrast, when the river flow rates are low, the importance of autochthonous production by phytoplankton as a particle source relative to erosion and resuspension increases. The carbon content of the particles supports this observation. The fraction of organic carbon (foc) in the river particles varied from 0.06

In the Susquehanna River, watershed erosion, river sediment resuspension, and autochthonous algal production supply suspended particles in the water, and subsequently to the Chesapeake Bay. The concentration of total suspended particles (TSP) in the Susquehanna River averaged 10 ± 4 mg/l ðn ¼ 41Þ during this study from March 1997 to March 1998. Most TSP concentrations were below 10 mg/l when the average daily

25

10 9

(A) 20

8 7

15

6 5 4

10

TSP

TSP (mg/L)

Flow Rate ( x 1000 m 3 /sec)

r2 ¼ 0:53

3 2

5

Flow Rate

1

0 12

(B)

11

C:N Ratio

10 9 8 7 6 5

Mar

Feb

Jan

Dec

Nov

Oct

Sept

Aug

Jul

Jun

May

Apr

Mar

4

Fig. 2. Total suspended particle concentrations and daily water discharge rates (A) and the ratio of particulate carbon to nitrogen (B) measured in the Susquehanna River at Conowingo Dam from March 1997 to March 1998. The low C/N ratios in the shaded area indicated the significant autochthonous production during this period.

F.-C. Ko, J.E. Baker / Marine Pollution Bulletin 48 (2004) 840–851

Total Suspended Particles (mg/L)

844 25

(A) 20

1 r2 = 0.9

15

10

5

Flow rate > 2000 m3 /sec

(B)

Fraction of Carbon

0.25 0.20 0.15 0.10 0.05

0

1

2

3

4

5

6

7

8

3

Flow Rate ( x 1000 m /sec)

Fig. 3. Total suspended particle concentrations (A) and the fraction of carbon in the particles (B) related to the river water flow rates.

to 0.25 during low flow periods, but was less variable during high flows (Fig. 3). When flow rates exceeded 2000 m3 /s, the foc of suspended particles was constantly low (0.093 ± 0.022, n ¼ 9), which was identical to the average foc of surface sediments in this stretch of the Susquehanna River (0.09 ± 0.02). During the low flow season, the contribution of primary production to the proportion of the suspended particles caused the foc to reach 0.25 in the Susquehanna River. The significance of the autochthonous production in the river was also supported by the consistently low carbon/nitrogen (C/N) ratio values (5–7) during low flow rates; the C/N ratios ranged from 7 up to 12 during the high flow season (Fig. 2B) indicating comparably low biotic production. TSP in the northern Chesapeake Bay was reported as 20–50 mg/l (Nelson et al., 1998), which coincided with the seasonal variation in the Susquehanna River’s flow rates and TSP. The highest TSP concentration in the northern Chesapeake Bay (50 mg/l) was found when the river flow was high in early spring. This suggests that the Susquehanna River is a dominant source of solids entering the Chesapeake Bay. 3.2. Concentration and distribution of HOCs Concentrations of total PCB (t-PCB, calculated as the sum of all detected congeners) including both the particulate and dissolved phases in the Susquehanna

River ranged from 0.9 to 3.5 ng/l (mean P ¼ 1.7 ± 0.6 ng/l). The concentrations of total PAHs ( 36 PAHs, equal to the sum of 36 individual PAHs) ranged from 17 to 150 ng/l with a mean of 67 ± 28 ng/l (Fig. 4). These contaminant levels were generally higher than those in the northern and mid-Chesapeake Bay (Ko and Baker, 1995; Nelson et al., 1998; Ko et al., 2003), suggesting that the Susquehanna River may be an important source of PCBs and PAHs to the Chesapeake Bay. The dissolved phase concentrations of PAHs and PCBs in the Susquehanna River were relatively constant with time (Fig. 4). From PMarch 1997 to March 1998, the dissolved t-PCB and 36 PAH concentrations were 0.51 ± 0.17 and 22 ± 11 ng/l, respectively. However, the corresponding concentrations associated with suspended particles ranged from P0.5 to 2.5 ng/l for t-PCB and from 12 to 130 ng/l for 36 PAHs. Therefore, the temporal variation in the total HOC levels in the river resulted from changes in the particle-associated HOC concentrations. Also, particulate HOCs made up a large fraction of the total inventory, P an average of 69 ± 8 % of t-PCB and 65 ± 15 % of 36 PAHs, demonstrating that particles play a significant role in organic contaminant transport in the Susquehanna River. Dissolved PAHs were dominated by a few low molecular weight compounds including phenanthrene, 2-methylnaphthalene, fluoranthene, and pyrene which P made up one half of the P 36 PAHs in the dissolved phase. Two thirds of the 36 PAHs in the particulate phase were contributed by 10 PAHs, including phenanthrene, fluoranthene, pyrene, benz[a]anthracene, chrysene + triphenylene, benzo[b]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, and benzo[ghi]perylene (Table 1). These compounds are predominately derived from combustion (Neff, 1979) suggesting that the sources of PAHs to the Susquehanna River were pyrogenic rather than unburned hydrocarbons. Two water samples in August and October contained unusual distributions of PAHs (marked by * in Fig. 4), containing higher portions of PAHs in the dissolved phase relative to the particulate phase. Three PAHs (2-methylnapthalene, acenapthene, and phenanthrene) were exceptionally enriched in the dissolved phase in these samples for unknown reasons. Because they were relatively constantPduring the study period, concentrations of t-PCB and 36 PAH in the dissolved phase did not systematically vary with water flow rates (Fig. 5). In contrast, particulate HOC concentrations (ng/l) increased linearly with flow rates in proportion to the TSP concentrations. This suggests that high river flows increase the amount of the suspended particles that are enriched in PAHs and PCBs into the Susquehanna River water column. Overall, P about 50–60% of the variance in the t-PCB and 36 PAH concentrations in the Susquehanna River are explained by variations in river flow rate:

t -PCB Concentrations (ng/L)

F.-C. Ko, J.E. Baker / Marine Pollution Bulletin 48 (2004) 840–851

845

4

3

2

1

Dissolved Phase Particulate Phase

150

100

*

* 50

Mar

Feb

Jan

Dec

Nov

Oct

Sept

Aug

Jul

Jun

May

Apr

0 Mar

Total 36 PAH Concentrations (ng/L)

0 200

Fig. 4. Seasonal distribution of total HOC concentrations and the chemical speciation in dissolved and particulate phases in the Susquehanna River from 1997 to 1998: (*) samples with higher proportion PAH in the dissolved phase.

½t-PCB ¼ ð0:28  0:05ÞQ=1000 þ ð0:88  0:32Þ; r2 ¼ 0:48 "

X

# PAH ¼ ð19  2:5ÞQ=1000 þ ð23  17Þ;

culate HOC in the Susquehanna River results from sediment resuspension and other upstream and terrestrial particle sources. 3.3. Factors related to particulate HOC concentrations

r2 ¼ 0:61

36

where the PCB and PAH concentrations are in ng/l and Q is the water flow rate less than 5000 m3 /s (Fig. 5). One extremely high flow rate of 7000 m3 /s in January 1998 (marked by * in Fig. 5) resuspended high amounts of the sediment, which contained lower HOC concentrations than the suspended particles, causing the dilution of the contaminant concentrations in the water column. Based on our current study, t-PCB and P 36 PAH concentrations in the Susquehanna River surface sediment (36 ± 10 ng/g and 3 ± 1 lg/g, respectively) are lower than their particulate phase concentrations in the water column which varied from 50 to 400 and 2 to 16 lg/g, respectively (Fig. 6). The parti-

The particulate HOC concentrations were only slightly correlated with the carbon content in the suspended particles (r2 < 0:3) because the observed foc range was relatively narrow. Fig. 6 shows the seasonal variation of the particulate HOC (ng/g) in suspended particles compared to their average concentrations in surface sediments behind the Conowingo Dam represented by the P horizontal solid lines in the figure. The t-PCB and 36 PAH concentrations in suspended particles were higher than those in the sediment, indicating that the suspended particles in the Susquehanna River were the mixture of the sediment resuspension and the other types/sources of particles enriched in organic contaminants. The other possibility is that the resuspended particles were only contributed by the fine size

846

Table 1 Average concentrations of PAH and PCB in the Susquehanna River and their annual loads to the Chesapeake Bay in 1997–1998 Compounds

Abbreviation

Particulate (ng/l)

Total PAHs Monochlorobiphenyl Dichlorobiphenyl Trichlorobiphenyl Tetrachlorobiphenyl Pentachlorobiphenyl

2MeN 1MeN Aceny Biph Acen Fluo Phen Anth 1MeF 45MeP 2MeP 2MeA 1MeA 1MeP 9MeA Flua Pyre 36MeP 910MeA BaFI BbFI BaAn Chry + TriPhe Napt BbFa BkFa BePy BaPy Pery MeBaA 3MeCh In123Py BgihP Anthan BahacA Coro

1.25 0.49 0.26 0.52 0.22 0.68 3.42 0.68 0.80 0.31 0.82 0.24 0.62 1.21 0.01 4.22 4.35 0.16 0.02 0.92 0.50 2.05 2.14 0.20 3.05 1.93 1.83 2.67 1.44 0.08 0.00 3.52 2.39 0.42 0.28 0.40

2.8 1.1 0.6 1.2 0.5 1.5 7.7 1.5 1.8 0.7 1.9 0.5 1.4 2.7 0.0 9.5 9.8 0.4 0.0 2.1 1.1 4.6 4.8 0.5 6.9 4.4 4.1 6.0 3.3 0.2 0.0 7.9 5.4 1.0 0.6 0.9

44 0.034 0.054 0.104 0.256 0.159

(ng/l) 2.98 1.54 0.36 0.59 1.54 1.36 2.76 0.40 0.59 0.49 0.60 0.13 0.80 0.44 0.06 2.88 2.69 0.14 0.01 0.26 0.20 0.13 0.34 0.02 0.11 0.07 0.08 0.03 0.09 0.00 0.00 0.02 0.02 0.02 0.00 0.00

% of t-PAH or t-PCB

Total (ng/l) (particulate + dissolved)

13.6 7.0 1.7 2.7 7.1 6.2 12.7 1.9 2.7 2.3 2.8 0.6 3.7 2.0 0.3 13.3 12.4 0.7 0.1 1.2 0.9 0.6 1.6 0.1 0.5 0.3 0.4 0.2 0.4 0.0 0.0 0.1 0.1 0.1 0.01 0.01

4.24 ± 2.66 2.04 ± 1.27 0.63 ± 0.37 1.12 ± 0.71 1.79 ± 2.31 2.04 ± 1.55 6.22 ± 2.87 1.09 ± 0.60 1.41 ± 0.69 0.80 ± 0.39 1.44 ± 0.68 0.37 ± 0.22 1.44 ± 0.58 1.65 ± 2.58 0.07 ± 0.08 7.15 ± 3.19 7.12 ± 3.01 0.31 ± 0.11 0.03 ± 0.08 1.20 ± 0.51 0.71 ± 0.35 2.21 ± 1.40 2.56 ± 2.21 0.24 ± 0.34 3.22 ± 1.72 2.05 ± 1.21 1.96 ± 1.26 2.76 ± 1.78 1.54 ± 0.74 0.08 ± 0.06 0.01 ± 0.03 3.56 ± 2.36 2.45 ± 1.57 0.45 ± 0.30 0.29 ± 0.22 0.41 ± 0.64

59 24 14 22 11 30 178 34 35 17 44 11 34 63 1 239 241 8 1 48 26 114 124 16 152 98 102 150 63 4 1 199 134 24 16 34

118 62 14 28 52 51 104 11 23 13 26 4 28 16 1 94 96 5 1 8 6 5 12 1 4 3 3 1 1 0 0 1 1 1 0 0

177 85 28 50 64 81 282 46 58 30 71 15 62 78 2 333 333 14 2 56 32 119 136

67 ± 28

2370

794

3164

2 3 6 10 7

1 1 3 7 4

2 4 9 17 11

22 3 5 9 21 13

0.026 0.031 0.072 0.167 0.099

5 6 14 32 19

0.06 ± 0.08 0.09 ± 0.06 0.18 ± 0.12 0.42 ± 0.14 0.26 ± 0.08

Annual loads (kg) Particulate

Dissolved

Total

156 105 151 63 4 1 200 135 25 16 34

F.-C. Ko, J.E. Baker / Marine Pollution Bulletin 48 (2004) 840–851

2-Methylnapthalene 1-Methylnapthalene Acenapthylene Biphenyl Acenapthene Fluorene Phenanthrene Anthracene 1-Mefluorene 4,5-Methylenephenanthrene 2-Methylphenanthrene 2-Methylanthracene 1-Methylanthracene 1-Methylphenanthrene 9-Methylanthracene Fluoranthene Pyrene 3,6-Dimethylphenanthrene 9,10,dimethylanthracene Benzo[a]fluorene Benzo[b]fluorene Benz[a]anthracene Chrysene + Triphenylene Napthacene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[e]pyrene Benzo[a]pyrene Perylene Dimethylbenz[a]anthracene 3-Methylcholanthrene Indeno[1,2,3-c,d]pyrene Benzo[g,h,i]perylene Anthanthrene Dibenz[a,h + ac]anthracene Coronene

Dissolved % of t-PAH or t-PCB

F.-C. Ko, J.E. Baker / Marine Pollution Bulletin 48 (2004) 840–851

847

A

76

2.5 Total PCB (ng/L)

20

3 1 0 0

14 9 6 5

3 8 0.4 2 r =

2 1.5 *

1

57

11 8 5 5

0.5 150

Particulate Dissolved

Total PAH (ng/L)

1.73 ± 0.55

r

2

.61 =0

100

*

50

0

14 6 2 1

0.33 ± 0.15 0.20 ± 0.08 0.13 ± 0.05 0.09 ± 0.06

B

0

1

2

3

4

5

6

7

8

3

0.52

Fig. 5. Relation of water flow rates to HOC concentrations in dissolved P and particulate phases: (A) t-PCB; (B) 36 PAH and (*) extremely high water flow rate may resuspend high amount of surface sediment decreasing the particulate HOC which, therefore, was excluded in the linear regression analysis.

0.259 0.170 0.113 0.089

1.21

Hexachlorobiphenyl Heptachlorobiphenyl Octachlorobiphenyl Nonachlorobiphenyl

t-PCB

21 14 9 7

0.075 0.032 0.012 0.005

Flow Rates ( x 1000 m /sec)

sediments enriched in HOC. Based on principal component analysis (PCA) of the compound distribution patterns of particulate PAH and PCB in this study, the river water particles can be classified into groups depending on the different collection periods (Fig. 7). Samples collected from April to October were a group of particles dominated by the autochthonous primary production, which was also evidenced by the relatively low C/N ratio in Fig. 2B. Samples collected during the high flow rate from October to March contained particles from resuspended sediments and other sources such as watershed erosion and washout. Most of the variance can be explained by first and second principal component (i.e. 27% and 21% for the PCB congener pattern, 53% and 20% for PAH pattern). P Total PCB in all the samples and the 36 PAH in most of the samples occur more than 50% in the particulate phase. Their distribution between the particulate and dissolved phases varied during the low flow rate; however, the proportion of particulate P HOC reached above 75% and 80% for t-PCB and 36 PAH respectively when the flow rates were greater than 2000 m3 /s, indicating that the amount of suspended particles

t-PCB Concentrations (ng/g)

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F.-C. Ko, J.E. Baker / Marine Pollution Bulletin 48 (2004) 840–851

significantly control the contaminant loads in the Susquehanna River.

600 500

3.4. Comparison of particulate HOC in the Susquehanna River and in the northern Chesapeake Bay

400 300

Total PAH concentrations in the Susquehanna River particles (this study) and the northern Chesapeake Bay (Nelson, 1996) cannot be directly compared since the number of PAHs analyzed was different (i.e. 36 PAHs were selected in this study but 17 PAHs in the northern Bay study). The concentrations of most PAHs on the Susquehanna River particles were higher than those on the northern Chesapeake Bay particles (Table 2). Total PCB concentrations on the Susquehanna River particles were twice as high as those in the northern Chesapeake Bay (Table 2), demonstrating a declining gradient in particulate contaminants from the Susquehanna River to the Chesapeake Bay. This also suggests that the enriched organic contaminants in the river particles may settle quickly or are diluted by the other sources of particles such as the resuspended bay sediments once the particles reach the northern Chesapeake Bay.

200

20

15

10

Mar

Feb

Jan

Dec

Nov

Oct

Sept

Aug

Jul

Jun

Apr

May

5

Mar

Total 36 PAH Concentrations (ug/g)

100

Fig. 6. Particulate HOC concentrations in the Susquehanna River. Solid lines represent the average concentrations of t-PCB and P 36 PAH in the Conowingo surface sediments (36 ng/g and 3 lg/g, respectively). 15

PCB Congener Pattern

8/27/97

PC2 (21 %)

10 5 Apr 97 - Oct 97

0 -5

Mar 97 - Apr 97

Oct 97 - Mar 98

-10 -15 -10

0

10

PC1 (27 %)

PAH Compound Pattern

PC2 (20 %)

5 Apr 97- Sept 97 and Jan 98 - Mar 98 Mar 97 - Apr 97

0

Sept 97 - Jan 98

-5 0

10

20

PC1 (53 %) Fig. 7. Principal components analysis of the compound distribution patterns of particulate PAH and PCB congeners in the Susquehanna River from March 1997 to March 1998.

3.5. HOC loads from the Susquehanna River to the Chesapeake Bay The total PAH and PCB concentrations (particulate and dissolved) measured in water were multiplied by the daily flow rate to yield annual loads of HOCs from the Susquehanna River to the Chesapeake Bay. From March 1997 to March 1998, the total PCB load was 76 kg including 20 kg in the dissolved phasePand 56 kg in the particulate phase. The annual load of 36 PAHs was 3160 kg/year, which included only about 800 kg/year in the dissolved phase. The loadings of HOCs from the Susquehanna River to the Chesapeake Bay were highest during the early spring (Fig. 8) coincident with high river flows and elevated suspended solids. Sixty percent of the total annual loads of HOCs were measured during the high flow rate season when the water flow rate was greater than 2000 m3 /s, which occurred during only 18% of the days. More than one half of the annual PAH and PCB input from the Susquehanna River enters the Chesapeake Bay during the early spring (February and March) period. Table 3 compares these HOC loads from the Susquehanna River to the Chesapeake Bay to previous estimates. The total PCB loads estimated in this study was lower than the 176 kg/year reported in 1994–1995 (Foster et al., 2000) and the 198 kg/year reported in 1992–1993 (Godfrey et al., 1995). River flow rates in both 1992 and 1994 were higher than those during this study, again indicating the dependence of HOC loads on river discharge. Due to inter-annual variations in river

F.-C. Ko, J.E. Baker / Marine Pollution Bulletin 48 (2004) 840–851

849

Table 2 Comparison of the particulate HOC concentrations (ng/g) in the Susquenhanna River and the northern Chesapeake Bay Susquehanna River n ¼ 41

Northern Chesapeake Baya n ¼ 4

2-MeNapthalene 1-MeNapthalene Acenapthylene Biphenyl Acenapthene Fluorene Phenanthrene Anthracene 1-Mefluorene 4,5-Methylenephenanthrene 2-Methylphenanthrene 2-Methylanthracene 1-Methylanthracene 1-Methylphenanthrene 9-Methylanthracene Fluoranthene Pyrene 3,6-Dimethylphenanthrene 9,10,dimethylanthracene Benzo[a]fluorene Benzo[b]fluorene Benz[a]anthracene Chrysene + Triphenylene Napthacene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[e]pyrene Benzo[a]pyrene Perylene Dimethylbenz[a]anthracene 3-Methylcholanthrene Indeno[1,2,3-c,d]pyrene Benzo[g,h,i]perylene Anthanthrene Dibenz[a,h + ac]anthracene Coronene Total PAHs (lg/g)

172 ± 98 67 ± 36 32 ± 15 74 ± 86 28 ± 18 83 ± 58 439 ± 230 84 ± 41 105 ± 71 42 ± 27 109 ± 68 32 ± 23 80 ± 45 111 ± 189 2±3 521 ± 297 550 ± 303 21 ± 11 16 ± 13 121 ± 64 63 ± 34 260 ± 166 245 ± 226 25 ± 42 394 ± 184 243 ± 104 230 ± 136 339 ± 197 189 ± 94 12 ± 11 7±2 473 ± 338 308 ± 187 61 ± 49 36 ± 23 49 ± 81 6±3

Monochlorobiphenyl Dichlorobiphenyl Trichlorobiphenyl Tetrachlorobiphenyl Pentachlorobiphenyl Hexachlorobiphenyl Heptachlorobiphenyl Octachlorobiphenyl Nonachlorobiphenyl

3.3 ± 4.0 6.4 ± 4.4 12.5 ± 8.7 36.0 ± 22.0 23.0 ± 15.3 34.3 ± 17.9 22.1 ± 10.5 15.1 ± 7.4 12.8 ± 10.5

0.9 ± 0.3 2.6 ± 0.8 6.6 ± 1.5 18.5 ± 4.4 8.6 ± 1.8 14.6 ± 3.2 10.6 ± 2.5 8.1 ± 2.9 9.5 ± 4.7

t-PCB (ng/g)

165 ± 81

80 ± 21

a

53 ± 26 17 ± 3 64 ± 41 306 ± 111 82 ± 38

80 ± 11

40 ± 6 414 ± 90 406 ± 78

145 ± 48 324 ± 106

106 ± 35 162 ± 51 206 ± 55

196 ± 61 184 ± 64 39 ± 13 3±1

Nelson (1996).

flow, it is not proper to compare PCB loads among years to determine if the loads are declining with time. After normalizing the contaminant loads to the annual water loads, we found that the flow-normalized t-PCB loads (kg/m3 year) decreased from 37 kg/m3 year in 1992 to 24 kg/m3 year in 1998. Since the limited data of PAHs in the earlier study were available, Table 3 only compares the fluoranthene, benz[a]anthracene, and benzo[a]pyrene as PAH annual loads. The PAH loading levels were low in 1992, high in 1994 and intermediate in this study. No

systematic trend was found in the PAH loadings. This may be explained by the great variety of contaminant source and input into the water column of the Susquehanna River.

4. Conclusion PAHs and PCBs occur predominantly in the particulate phase due to the high levels of suspended solids in

850

F.-C. Ko, J.E. Baker / Marine Pollution Bulletin 48 (2004) 840–851

mainly caused by changes in particle-associated HOC concentrations. HOC loading to the Chesapeake Bay is determined by the HOC concentrations in the suspended particles as well as the flow rate of the Susquehanna River. The suspended particles were dominated by autochthonous production during low flow conditions in the summer and were the mixture of the resuspended sediments and eroded solids during high flows in the winter and the early spring. Even though the HOC concentrations in the river sediment were relatively low, the great amounts of sediment resuspension resulted in large organic contaminant loadings to the bay. If the Susquehanna River dams reach sediment–retention saturation, particle-associated contaminant loadings to the Chesapeake Bay will potentially increase. Further studies are required to (1) understand the relative importance of release of contaminants from Susquehanna River sediments and (2) monitor Ônew’ inputs from watershed erosion resulting in increasing loads to the Chesapeake Bay.

Total PCB Loads (g/day)

1000 800 600 400 200 0 Total 36 PAH Loads (kg/day)

60 50 40 30

dissolved particulate

20 10

Mar

Feb

Jan

Dec

Nov

Oct

Sept

Aug

Jul

Jun

May

Apr

Mar

Acknowledgements 0

Fig. 8. Seasonal variation of hydrophobic organic contaminant loads in particulate and dissolved phases from the Susquehanna River to the Chesapeake Bay from 1997 to 1998.

the Susquehanna River. Dissolved phase PAH and PCB concentrations were relatively constant with time, thus the variations in total HOC levels in the river were

We express our appreciation to Laura McConnell and Clifford Rice (USDA, Beltsville, MD) for providing the vehicle and laboratory used for water collection and filtration. We acknowledge Bo Liu for her assistance with the field sampling during this study. This work is part of the AEOLOS project sponsored by the US Environmental Protection Agency (EPA CR 822046-01-0). This is the University of Maryland Center for Environmental Science Contribution No. 3694.

Table 3 Historical comparison of the annual loads of water, particles, and HOCs from the Susquehanna River to the Chesapeake Bay

1992–1993a 1994–1995b 1997–1998

Water (m3 /year)

Particles (kg/year)

(kg/year)

%

(kg/year)

5.42E+010 5.10E+010 3.19E+010

1.30E+009 1.94E+009 5.21E+008

198 176 76

50 41 74

140 1130 333

PCB

Fluoranthene

Benz[a]anthracene

Benz[a]pyrene

%

(kg/year)

%

(kg/year)

%

81 88 72

98 380 119

75 97 96

120 440 151

100 98 99

Total HOC loads normalized by the water loads 1992–1993a 1994–1995b 1997–1998

(kg/m3 ) 37 35 24

Particulate HOC loads normalized by the particle loads (lg/kgTSP) 76 1992–1993a 1994–1995b 38 1997–1998 107 % denotes the percentage of HOC loaded in the particulate phase. a Godfrey et al. (1995). b Foster et al. (2000).

(kg/m3 ) 26 222 104

(kg/m3 ) 18 75 37

(kg/m3 ) 22 86 47

(lg/kgTSP) 87 515 459

(lg/kgTSP) 56 191 219

(lg/kgTSP) 92 222 288

F.-C. Ko, J.E. Baker / Marine Pollution Bulletin 48 (2004) 840–851

References Baker, J.E., Eisenreich, S.J., Johnson, T.C., Halfman, B.M., 1985. Chlorinated hydrocarbon cycling in the benthic nepheloid layer of Lake Superior. Environ. Sci. Technol. 19, 854–861. Bamford, H.A., Offenberg, J.H., Randolph, K.L., Ko, F.C., Baker, J.E., 1999. Diffusive exchange of polycyclic aromatic hydrocarbons across the air–water interface of the Patapsco River, an urbanized subestuary of the Chesapeake Bay. Environ. Sci. Technol. 33, 2138–2144. Bamford, H.A., Ko, F.C., Baker, J.E., 2002. Seasonal and annual air– water exchange of polychlorinated biphenyls across Baltimore Harbor and the northern Chesapeake Bay. Environ. Sci. Technol. 36, 4245–4252. Foster, G.D., Lippa, K.A., Miller, C.V., 2000. Seasonal concentrations of organic contaminants at the fall line of the Susquehanna River basin and estimated fluxes to northern Chesapeake Bay, USA. Environ. Toxicol. Chem. 19, 992–1001. Godfrey, J.T., Foster, G.D., Lippa, K.A., 1995. Estimated annual loads of selected organic contaminants to Chesapeake Bay via a major tributary. Environ. Sci. Technol. 29, 2059–2064. Godfrey, J.T., Foster, G.D., 1996. Kalman filter method for estimating organic contaminant concentrations in major Chesapeake Bay tributaries. Environ. Sci. Technol. 30, 2312–2317. Karickhoff, S.W., Brown, D.S., Scott, T.A., 1979. Sorption of hydrophobic pollutants on natural sediments. Water Res. 13, 241–248. Ko, F.C., Baker, J.E., 1995. Partitioning of hydrophobic organic contaminants to resuspended sediments and plankton in the mesohaline Chesapeake Bay. Mar. Chem. 49, 171–188. Ko, F.C., Sanford, L.P., Baker, J.E., 2003. Internal recycling of particle reactive organic chemicals in the Chesapeake Bay water column. Mar. Chem. 81, 163–176. Langland, M.J., Hainly, R.A., 1997. Changes in bottom surfaceelevations in three reservoirs on the lower Susquehanna River, Pennsylvania and Maryland, following the January 1996 flood–– implications for nutrient and sediment loads to Chesapeake Bay:

851

US Geological Survey Water-Resources Investigations Report 974138, 34p. Larsen, R.K., Baker, J.E., 2002. Source apportionment of polycyclic aromatic hydrocarbons in the urban atmosphere: a comparison of three methods. Environ. Sci. Technol. 37, 1873–1881. Leister, D.L., Baker, J.E., 1994. Atmospheric deposition of organic contaminants to the Chesapeake Bay. Atmos. Environ. 2, 1499– 1520. Mullin, M.D., 1985. PCB Workshop, US EPA Large Lakes Research Station, Grosse, MI, June 1985. Neff, J.M., 1979. Polycyclic aromatic hydrocarbons in the marine environment. Applied Science Publishers, Essex, England. Nelson, E.D., McConnell, L.L., Baker, J.E., 1998. Diffusive exchange of gaseous polycyclic aromatic hydrocarbons and polychlorinated biphenyls across the air–water interface of the Chesapeake Bay. Environ. Sci. Technol. 32, 912–919. Nelson, E.D., 1996. Water column inventories, partitioning and air– water gas exchange of hydrophobic organic contaminants in the Chesapeake Bay. MS Thesis, University of Maryland, College Park. Ott, A.N., Takita, C.S., Edwards, R.E., Bollinger, S.W., 1991. Loads and yields of nutrients and suspended sediment transported in the Susquehanna River Basin, 1985–89: Susquehanna River Basin Commission Report, Publication no. 136, 253p. Risser, D.W., Siwiec, S.F., 1996. Water-quality assessment of the lower Susquehanna River basin. Pennsylvania and Maryland: Environmental Setting: US Geological Survey Water-Resources Investigations Report 94-4245, 7. Seitz, R.C., 1971. Drainage area statistics for the Chesapeake Bay freshwater drainage basin. Chesapeake Bay Institute Special Report no. 19. 21p. US Geological Survey, 2003. Water resources data. USGS 01578310 Susquehanna River at Conowingo, Maryland. Available from . Voice, T.C., Webber Jr., W.J., 1983. Sorption of hydrophobic compounds by sediment, soils and suspended solids. I. Theory and background. Water Res. 17, 1433–1441.