Dec 1, 1984 - channel. Wakeham & Carpenter (1976) measured total aliphatic ..... House, London. pp. .... F. L., Stalling, D. L. & Johnson, J. L. 1972 Phthalate.
Estuarine, Coastal and Shelf Science (1985) 21,295-312
Geochemistry Narragansett
of Organic Contaminants Bay Sediments
Richard
and James
J. Pruell”
Graduate School of Oceanography, Rhode Island 02882, U.S.A.
G. Quinn
University of Rhode Island, Narragansett,
Received 23 July 1984 and in revised form
Keywords: contaminants; Narragansett Bay
in
petroleum;
1 December 1984
hydrocarbons;
sediments;
chronology;
Organic contaminants from several different chemical classes were analyzed in surface sediments along a transect from the head to the mouth of Narragansett Bay. The chemical classes included total hydrocarbons, polycyclic aromatic hydrocarbons, substituted benzotriazoles and phthalic acid esters. Sediment concentrations of all compounds were highest in the Providence River and decreased with distance downbay. The observed decreases were approximately exponential for all compounds; however, the distances at which the concentrations decreased to one-half of their initial concentrations (half-distances) were different. The depth distributions of these compounds in sediment cores from three locations were also investigated. A sediment core collected near the head of the bay (Conimicut Point) showed a well defined historical record of contaminant input to the bay. At a mid-bay location (North Jamestown), however, the record was smeared because of extensive bioturbation. A sediment core collected near the mouth of the bay (Rhode Island Sound) showed a subsurface increase for all of the measured compounds. The results of detailed analyses suggest that this horizon may have been influenced by dredge spoil material originally from the head of the bay.
Introduction Estuarine areas near industrial centers receive and retain large quantities of toxic organic contaminants. Due to the increased usage of petroleum products and advances in synthetic organic chemistry, a rapid increase in both the amount and complexity of these inputs has occurred during the past century. Processes controlling the retention and preservation of organic contaminants in an estuary are complex. Important factors include the chemical properties of the compounds (especially their water solubility), the quantity and physical properties of suspended sediments in the receiving water, biological and photoreactivity of the compounds, and sedimentary depositional patterns. The latter includes physically controlled “Present address: Science Applications International Corporation, U.S. Environmental Protection Agency, South Ferry Road, Narragansett, RI 02882, U.S.A. 29.5 0272-7714/85/090295
+
18 $03.00/O
0 1985 Academic Press Inc. (London) Limited
296
R. J. Pruell & 3. G. Quinn
sedimentation and resuspensionaswell as the effect of biological processesoccurring in the sediment. Environmentally stable contaminants with low water solubilities tend to accumulate in estuarine sediments. Because of this, the depth distributions of such compounds can provide information on their input histories (Goldberg et al., 1977, 1978; Hites et al., 1977; Wade & Quinn, 1978; Bopp et al., 1982). However, such depositional sequences are often hard to interpret due to the complex nature of sedimentary processes. In this report, we have used compounds from several different chemical classes [aliphatic and polycyclic aromatic hydrocarbons (PAHs), substituted benzotriazoles and phthalic acid esters] in order to obtain a better understanding of the depositional processes occurring in Narragansett Bay. Two of the compounds found in Bay sediments proved to be particularly useful in this respect. These compounds (C,,-benzotriazole and chloro-benzotriazole) were produced and released by a chemical plant located on the Pawtuxet River which empties into the Providence River at the northern end of Narragansett Bay (Jungclaus et al., 1978; Lopez-Avila & Hites, 1980). They have a unique source, a known history of inputs, and are strongly partitioned to particulate material. They are also environmentally persistent and are widely distributed throughout the bay. Several of the compounds analyzed in this study are important from public health and/or ecological perspectives. Someof the PAHs are of concern becausethey are widely distributed in the environment (Laflamme & Hites, 1978) and many have toxic and/or carcinogenic properties (Harvey et al., 1982). Some phthalic acid estershave been found to be widespread in the environment (Giam et al., 1978), particularly di-2-ethylhexyl phthalate (DEHP). This compound has also been shown to affect benthic communities in microcosm studies (Perez et al., 1983). The substituted benzotriazoles show very low acute toxicities (EPA, 1977); however, little is known about the chronic effects of these compounds.
Methods Sediment
collection
Gravity sediment cores were collected from the RV Dulcinea and the RI/ Strider. Several were also collected by divers. All of the cores were collected between 27 March 1979and 9 September 1980 at the Narragansett Bay locations shown in Fig. 1. After collection, the cores were returned to the laboratory and frozen at - 10 “C. They were thawed slightly then extruded from the core liner. About 1 cm was scrapedfrom the outside of the cores to prevent contamination from the plastic core liner; then the coreswere sectioned into 5-cm sections for Providence River samples (Stations 1-5) and 2.5cm sections for samplesfrom the remainder of the bay. For the stations where only surface sampleswere to be analyzed, the appropriate surface sections of sediment cores were collected. All sections were stored frozen in solvent-rinsed glassjars until analyzed. Extraction
and separation
Samples to be analyzed were thawed and thoroughly mixed. An aliquot (lo-100 g wet weight) was placed in a round bottom flask along with internal standards and a 5:l (volume:weight) excess of methanol. This mixture was refluxed for 2 h, cooled, and filtered through a Whatman GF/C glassfiber filter. The filter was rinsed with petroleum
Geochemistry
of organic
contaminants
297
L
Figure 1. Map of Narragansett Bay, Rhode Island, U.S.A., showing the station locations: 1, Fox Point; 2, Fields Point; 3, Sabin Point; 4, Bullock Point; 5, Conimicut Point; 6, Ohio Ledge; 7, Pine Hill Point; 8, North Jamestown; 9, Rhode Island Sound.
ether and combined with the filtrate which was then added to distilled water (a volume equal to that of the methanol added to the sample) in a separatory funnel. The water:methanol mixture was extracted three times with petroleum ether and the extracts were combined and reduced to - 1 ml using rotary evaporation under reduced pressure at 20 “C. This methanol extraction procedure was checked against methanohmethylene chloride (1: 1) as a reflux mixture and found to produce similar results for the compounds analyzed in this study. The extracts were separated into three fractions by silica gel chromatography using a method modified from Pruell et al. (1984). According to this procedure, the sample was charged to a 0.5 x 10 cm column of fully activated silica gel (Grace Grade 922) and activated copper (to remove elemental sulfur) using nitrogen to produce a flow rate of 5 mlmin-‘. The first fraction (fi) was eluted with 15 ml of hexane and contains saturated hydrocarbons and olefinic hydrocarbons with one or two double bonds. The second fraction (fi) was then eluted with 15 ml of 80:20 hexane:dichloromethane. This fraction contains PAHs with 2-6 fused rings and two substituted benzotriazoles. Phthalic acid esters and other relatively polar compounds were eluted into the third fraction (f,) using 15 ml of 95 : 5, dichloromethane: ethyl acetate. The Rhode Island Sound samples contained low concentrations of substituted benzotriazoles relative to PAHs and other components in the sample; therefore, for these analyses, it was necessary to separate the benzotriazoles from interfering material. After
298
R. J. Pruell&
3.
G. Quinn
analysis of the f2 for PAHs, these fractions were evaporated to near dryness, then 0.5 ml of methanol was added. The sample was then charged to a 1.0 x 50 cm column of Sephadexa LH-20 (Pharmacia, Inc., Piscataway, New Jersey) in methanol. Nitrogen pressure was used to produce a solvent flow rate of - l-2 ml mini. The first 35 ml of methanol that eluted from the column was discarded and the next 15 ml was collected. This fraction contained the substituted benzotriazoles and 2 ring PAHs. Then 15 ml of distilled water was added to this fraction and it was extracted three times with petroleum ether to isolate the substituted benzotriazoles. Analysis Each fraction was concentrated on a rotary evaporator then analyzed on a Hewlett Packard 5710A gas chromatograph equipped with a 0.25 mm i.d. x 20-25 m glass capillary column (SE-30 or SE-52, J & W, Inc.). With helium as the carrier gas, - 1 ml min-‘), the column was heated from 40 to 260 “C at 4 “C min-’ for fi and f2 fractions. The column was heated from 100 to 260 “C at 4 ‘C/minute for fs fractions. Peaks were quantified against the internal standard using a Hewlett Packard 3385A Integrator. The unresolved complex mixture (UCM) was measured by planimetry and its area compared to that of the n-C,, internal standard. PAHs and the substituted benzotriazoles were quantified against anthracene which was added as the internal standard. PAHs with 2-6 fused rings were detected in the f2 fractions; however, only 2-4 ring PAHs were quantified because of problems that were encountered with the reproducibility of analysis for 5 and 6 ring PAHs. Di-2-ethylhexyl phthalate was the only phthalate measured and it was quantified using benzylbutyl phthalate as the internal standard. Dibutyl phthalate could be detected but it was not quantified because of interfering material in the samples. Several samples were initially analyzed without the addition of standards in order to assess the background levels of these compounds. In all cases the background levels were insignificant when compared with the amount of internal standard added. Authentic standards were obtained for all of the compounds analyzed. Peak identification by retention time was confirmed by gas chromatography-mass spectrometry. This instrumentation included a Shimadzu gas chromatograph (Model G&Km) equipped with a 30-m SE-52 glass capillary column connected to a Finnigan 1015 mass spectrometer with a Systems Industries data system and Riber 400 D-8 software. Procedural blanks were very low for total hydrocarbons and no blank corrections were necessary. PAHs and substituted benzotriazoles could not be detected in the f2 fractions of procedural blanks. However, procedural blanks for the f3 fraction contained small amounts of DEHP. To correct for this an average blank concentration of 1.0 ng of DEHP was subtracted for each analysis. The results from the analyses of standard mixtures carried through the analytical procedure indicated that 20-30% of the substituted benzotriazoles may have been lost during column chromatography. Fifty to 60% of the 2-ring PAHs were recovered from standard samples and 90-100°/0 of the 3- and 4-ring PAHs and DEHP were recovered. Results were not corrected for recoveries or instrumental response factors and all of the concentrations are reported on a dry weight basis. The precision of the analysis procedures averaged 15”& for total hydrocarbons, 21 y0 for individual PAH compounds, 17% for the substituted benzotriazoles and 11 y0 for DEHP. Total organic carbon measurements were made using a method similar to that described by Boehm and Quinn (1978). The samples were treated to remove carbonates
Geochemistry of organic contaminants
299
12
Increoslng
time
and
temperature
-
Figure 2. Chromatograms of the (a) f,, (b) fi and (c) fs fractions of Sabin Point surface sediment. IS, Internal Standard, peak numbers refer to the following compounds: 1, naphthalene; 2, P-methyl naphthalene; 3, l-methyl naphthalene; 4, biphenyl; 5, fluorene; 6, dibenxothiophene; 7, phenanthrene; 8, fluoranthene; 9, pyrene; 10, benzo[a]anthracene; 11, chrysene+triphenylene; 12, C,,-benzotriazole; 13, chloro-benzotriazole; 14, di-2-ethylhexyl phthalate.
then combusted using a Carlo Erba model 1106 elemental analyzer. The reported values are the average of duplicate analyseswhich were generally within 5% of the mean.
Results and discussion Anthropogenic inputs have significantly influenced the concentrations and distributions of some organic compounds in Narragansett Bay surface sediments. For example, chromatograms of the fr fractions of surface sediment extracts from Narragansett Bay [Fig. 2(a)] are dominated by an unresolved complex mixture (UCM) of hydrocarbons as has been reported by other investigators (Farrington & Quinn, 1973; Van Vleet & Quinn, 1978). This UCM is believed to consist mainly of alicyclic hydrocarbons of petroleum origin (Eglinton et al., 1975; Farrington & Meyers, 1975). The UCM is most pronounced in sedimentsfrom the more contaminated stations from the head of the bay. With distance downbay and depth in sediment cores, the dominance of the UCM decreasesand other components, particularly the plant wax hydrocarbons (e.g. ~I-C~~, n-&J n-C,,), become increasingly apparent in the chromatograms. This trend has been previously described for Narragansett Bay sediment cores (Van Vleet & Quinn, 1977; Hurtt & Quinn, 1979; Wade & Quinn, 1979).
300
R. 3. Pruell Q 3. G. Quinn
25
4
n
II Compourd
Figure 3. Relative percent distribution Narragansett Bay. The error bars represent (n = 9). The numbers refer to the compounds
of PAHs in surface one standard deviation listed in Fig. 2.
sediments from from the mean
The fi fractions contain a UCM and many resolved peaks [Fig. 2(b)]. This fraction contains the PAHs, the substituted benzotriazoles and several compounds that were not identified in this study. The relative distributions of the 2-4 ring PAHs from all of the surface sediment samples are presented in Fig. 3. This distribution is dominated by unsubstituted PAHs. There were no consistent changes in the relative distributions of these PAHs with distance downbay; also no consistent changes in the distribution of PAHs with depth in the sediment cores were observed. Therefore, the PAH distributions presented in Fig. 3 are similar to those measured in all of the samplesin this study aswell asin those reported by Lake et al. (1979) for Narragansett Bay surface sediments. Such a distribution is believed to result from the input of combustion-derived PAHs (Youngblood & Blumer, 1975; Hites et al., 1977; Lake et al., 1979). Similar PAH distributions have been reported worldwide in Recent marine and lacustrine sediments (Laflamme & Hites, 1978; Wakeham et al., 1980; Tan & Heit, 1981). In Narragansett Bay sediments, the major sourcesof combustion-produced PAHs include urban runoff (Hoffman et al., 1984b),and atmospheric deposition (Lake et al., 1979). C,,-benzotriazole and chloro-benzotriazole are two substituted benzotriazole compounds that were also identified in the fi fractions. These compounds are produced by a chemical plant that is located on the Pawtuxet River which empties into the Providence River (Fig. 1). They are used asantioxidants in various plastics and coatings (EPA, 1977) and have previously been detected in river and bay sediments (Jungclaus et al., 1978, Lopez-Avila, 1979; Lopez-Avila & Hites, 1980). The f3 fractions of Narragansett Bay sediment extracts contain phthalic acid estersand numerous unidentified components [Fig. 2(c)]. Dibutyl phthalate and DEHP were detected in this fraction; however, the former compound was not quantified becauseof its low concentration relative to interfering peaks in these chromatograms. DEHP was detected in high concentrations in surface sediments throughout Narragansett Bay and this is consistent with other studies of phthalic acid esters in estuarine sediments (Murray et al., 1981; Peterson & Freeman, 1982).
Geochemistry
of organic
301
contaminants
Distance 6.0
0 ~
IO
(km) 30 /
20
40 I -Tn,n,
“‘“““,C
50 carbon
024X
I
2
3
45
6
7
8
9
Stotlon
Figure 4. Semi-log plot of the surface sediment concentrations of (a) total organic carbon, total hydrocarbons, di-2-ethylhexyl phthalate, total PAHs, (b) C, a-benzotriazole and chlorobenzotriazole on a transect from the head to the mouth of Narragansett Bay. The equations shown for the substituted benzotriazoles are only for the line segments from Stations 4 to 9. The station numbers refer to the stations shown in Fig. 1.
Surface
sediments
Narragansett Bay is situated such that the head of the bay receives large inputs of organic contaminants from the densely populated and heavily industrialized area around the city of Providence, Rhode Island (Fig. 1). In contrast, the southern portion of the bay is less densely populated and has little industrial activity. Consistent with this trend, the sediments of the Providence River Portion of the bay contain high concentrations of organic contaminants and all of the parameters measured in this study showed concentration maxima in the Providence River (Fig. 4). In Fig. 4, total organic carbon, total hydrocarbons, total PAHs and DEHP concentrations are plotted for stations along a transect from the head to the mouth of Narragansett Bay. When plotted in this manner, the trends for these parameters can be approximated by a straight line with negative slopes which indicates that the concentrations decrease exponentially with distance downbay. Since the sediments for all stations except Brenton Reef were collected using a gravity corer, it is probable that surface flocculent material may have been lost during collection. Therefore, the actual sediment concentrations may be somewhat different from the results indicated; however, the differences should be small.
302
R. J. Pruell &J,
G. Quinn
TABLE 1. Half-distances” surface sediments
calculated
for the parameters
Parameter Organic carbon Total PAHs Total hydrocarbons Di-2-ethylhexyl phthalate Chloro-benzotriazoleb C,,-benzotriazole’
measured
Equation Y Y Y Y Y Y
= = = = = =
4.95-0024X 0%1+042X 3.77-0.047x 1.26-0.064X 0.82-0.077X 1.57-0.079x
in Narragansett
Bay
Half-distance (km) 12.5 7.18 6.40 4.70 3.91 3.81
“Half-distance = log 2/slope. “Chloro-benzotriazole is 2-(2’-hydroxy-3’,5’-di-t-butylphenyl)-5-chloro-2H-benzotriazole. ‘C,,-benzotriazole is 2-(2’-hydroxy-3’,5’-di-r-amylphenyl)-2H-benzotriazole.
The slopesof the lines are somewhat different for each of the parameters. In order to compare the rates at which the concentrations decrease,we have calculated the distances from the head of the bay at which these substancesreach one-half of their initial concentrations. We use the term half-distance to describe this measurement. The calculations are analogous to the calculations of biological half-lives which are often used to describe the elimination of chemicals from contaminated organisms (Farrington et al., 1982; Morales-Alamo & Haven, 1983). Similar approacheshave alsobeen used to study the loss of compounds from model ecosystems(Gearing & Gearing, 1982). The halfdistancesare listed in Table 1. Total organic carbon concentrations showed the longest half-distance (125 km) followed by total hydrocarbons and total PAHs which showed similar values (6.40 and 7.18 km, respectively). The concentration of DEHP decreased more rapidly (half-distance = 4-70 km). The substituted benzotriazoles occurred in highest concentrations in the sediments of the lower portion of the Providence River [Fig. 4(b)]. These results are consistent with the fact that these compounds enter the bay from the Pawtuxet River. The concentrations of these compounds in surface sediments below this point decrease exponentially with distance down the bay. The calculated half-distances of these compounds were similar (3.81 for C,,-benzotriazole and 3.91 for chloro-benzotriazole) and the shortest of all of the parameters measured. Many factors can influence the rate at which the sediment concentrations of various compounds decreasewith distance from a source. Some of these include: the physical properties of the compound such asits water solubility or n-octanol/water partition coefficient; the composition of the sediment such as grain size and organic carbon content; and characteristics of the depositional environment such as water depth, particle load and movements (currents, tides, turbulence). Also, other properties of the compound such as its environmental stability (photochemical and biological reactivity) will also affect the fate of a compound in an aqueoussystem. All of the compounds showed a steeper slope than that of total organic carbon. Therefore, the sediment organic carbon content is not the sole factor influencing contaminant distributions in the bay. Lopez-Avila i? Hites (1980) described a model to predict the sediment concentrations of compounds with distance away from an industrial source. This model was basedon the log of the n-octanol/water partition coefficient (log Ko,) of
303 -
Geochemistry of organic contaminants
TABLE
2. Approximate
log K,,
values
for some of the compounds
analyzed
in this
study Compound Naphthalene 2-methylnaphthalene I-methylnaphthalene Biphenyl Fluorene Dibenzothiophene Phenanthrene Fluoranthene Pyrene Benzo[a]anthracene Chrysene C,,-benzotriazole Chloro-benzotriazole Di-2-ethylhexyl “PAH data from (1982).
1% Ko, 3.30” 3.90 3.95 4.14 4.27 4.64 5.29 5.12 6.10 6.01 5.90b 5.80b 5.11’
phthalate Mackay
et al. (1980);
‘Lopez-Avila
& Hites
(1980);
‘Geyer
et al.
the compound. Their analysis indicated that the rate of concentration decreasewith distance in sedimentswas inversely related to the K,, of the compounds that they studied (these included C,,-and chloro-benzotriazole). Therefore, compounds with the highest K,, values could be detected furthest from the source. Approximate log K,, values for some of the compounds analyzed in this study are listed in Table 2. Although the PAHs show a wide range of I(,, values (3.30-6.10), the constant PAH ratios throughout the bay (Fig. 3) shows that their distribution is not strongly correlated with their K,, values. Also, the slopesof the lines describing concentration decreaseswith distance down the bay for DEHP, C,,-benzotriazole and chloro-benzotriazole (Fig. 4) do not show the trends expected if their distributions in the bay were solely controlled by their partitioning behavior. That is, although DEHP has a lower log K,, value than the substituted benzotriazoles (Table 2), its slope-isnot steeper than those of the substituted benzotriazoles. One explanation of this phenomenon is that a fraction of the contaminants on the sediment particles may not freely partition between the dissolved and particulate phases. This is consistent with several studies which have shown that a significant fraction of chlorinated hydrocarbons (Pierce et aE., 1974; DiToro & Horzempa, 1982; Horzempa & DiToro, 1983) and phthalates (Freeman & Cheung, 1981; Sullivan et al., 1982), spiked onto sediments can be resistant to desorption. Little is known about the mechanismsby which organic compounds are retained on sediment particles. However, some studies indicate that a large portion of the material retained by particles may be trapped in the gel-like matrix of humic substances(Khan & Schnitzer, 1972; Freeman & Cheung, 1981). Incorporation of compounds in this matrix may ‘ protect ’ these compounds by retarding or preventing exchange with the aqueous phase. High concentrations of photoreactive compounds such as some PAHs (Korfmacher et al., 1980) and readily biodegraded compounds such as phthalates (Johnson & Lulves, 1975) in sediments support the idea of a protective mechanism for organic compounds by the particulate material.
304
R. J. Pruell &J.
G. Quinn
Concentrotlon (/lq q-i
x C,,-benrotwzole 0 Lhloro-berrotriarole a Dim?-ethylhexyl phthalate l Total nydrocarbans (mg g$i m Total PAHs
Figure 5. ethylhexyl Conimicut section (e.g.
Depth distributions of C,,-benzotriazole, chloro-benzotriazole, di-2phthalate, total hydrocarbons and total PAHs in a sediment core from Point (Station 5). The data are plotted at the midpoint of the appropriate O-5 cm plotted at 2.5 cm).
A secondlook at the half-distance data (Table 1) indicates that it can be explained by considering the major inputs of the different classesof compounds to the bay. Total organic carbon has a large input from sewageboth asorganic carbon and indirectly as a result of nutrient inputs. However, in situ production throughout the bay and runoff along the bay probably reduces the gradient in bay sediments and therefore the calculated half-distance was large (12.5 km). Total hydrocarbons and total PAHs showed similar and relatively long half-distances (6.40 and 7.18 km, respectively). These compounds have major sourcesin the upper bay from urban runoff (Hoffman et al., 1983, 19846) and sewage(Van Vleet & Quinn, 1977, 1978; Hoffman et al., 1984a). However, these compounds also enter the bay via urban runoff all along the bay as well as from direct atmospheric deposition (Hoffman et al., 19846).
The major inputs of DEHP are believed to be industrial effluents and sewagetreatment plants (Peakall, 1975; Pruell, unpublished data). In Narragansett Bay, the majority of these inputs are in the Providence River. The concentration of this compound decreasesrapidly with distance downbay (half-distance = 4.70 km). The Pawtuxet River is the unique source of the substituted benzotriazoles to Narragansett Bay. These compounds show the shortest half-distances for concentrations in the bay sediments. In summary, although many factors influence the distribution of these organic compounds in sediments, the uniqueness of the inputs to the northern portion of the bay appears to primarily determine the rate at which the concentrations decreasewith distance from the head to the mouth of Narragansett Bay. Conimicut
Point sediment core
Sediment cores were collected from three locations in the bay and analyzed for total hydrocarbons, PAHs, DEHP, C,,-benzotriazole and chloro-benzotriazole. The cores were collected from Conimicut Point, North Jamestown and Rhode Island Sound. The depth profiles of the five parameters measured in the Conimicut Point core (Station 5) are shown in Fig. 5. This core was 53 cm in length, and it was divided into ten 5-cm sections and one 3-cm section.
Geochemistry of organic contaminants
305
Total hydrocarbon concentrations were very high in the upper few sections of this core and then decreasedwith depth until about 45 cm where the values levelled out. The maximum concentration observed was - 1900ug g-’ (5-10 cm section). The 50-53 cm section had the lowest concentration (50 ugg-‘). The maximum hydrocarbon concentrations measured in this core are higher than those measured by Van Vleet & Quinn (1977) from a nearby location. They reported a Surface sediment concentration of 570 pg g-l and found that the concentrations reached a background level of 20 ug g- ’ at a depth of 20-30 cm. The reason for the differences may be that the core they analyzed was probably collected in or near the dredged channel in the Providence River. The core that was analyzed for the present study was taken in a depositional area away from the channel. Wakeham & Carpenter (1976) measured total aliphatic hydrocarbons concentrations of -17oougg - i in surface sediments of a core from Lake Washington and hydrocarbon concentrations reached background levels of - 30 ug g-i at 40-42 cm in the core. This depth was assignedan approximate date of 1850 by ‘i”Pb and i3’Cs analyses. Similar results were reported by Meyers & Takeuchi (1981) in a core from Lake Huron. These authors indicated a trend of increasing petroleum hydrocarbon input since the mid-1800s. Barrick et al. (1980) measured total aliphatic hydrocarbons in a 210Pbdated core from Puget Sound. Their results indicated that petroleum hydrocarbon input had increased significantly since - 1875. The relative distributions of PAHs did not change with depth in the three sediment cores analyzed in the present study. Therefore, only the mean distribution (Fig. 3) and total PAH concentrations are reported. In the Conimicut Point core (Fig. 5) total PAH concentrations were highest in surface sections and generally decreased with depth to - 50 cm. Several other reports have also described the depth distribution of unsubstituted PAHs in sediments (Hites et al., 1977, 1980; Prahl & Carpenter, 1979; Gschwend & Hites, 1981). Most of these studies concluded that sediment PAH concentrations have increased since about The late 1800s due to increasing usage of fossil fuels. Di-2-ethylhexyl phthalate showed a relatively constant concentration in the top 15 cm of the Conimicut Point core (Fig. 5). Between 15 and 25 cm depth, a sharp gradient was noted and the concentrations reached apparent background levels at about 25 cm. The DEHP surface sediment concentration at this location was 3.7 ug g- ’ and the surface sediment concentrations throughout the Providence River ranged from 3.7 to 117 ug g- ‘. These concentrations are considerably higher than concentrations that have been reported by most investigators (Mayer et al., 1972; Giam et al., 1978; Murray et al., 1981a,b; Peterson & Freeman, 1982) but similar to those reported by Schwartz et al. (1979). Peterson & Freeman (1982) measured DEHP in two sediment cores from ChesapeakeBay. One of these showed no consistent concentration trends with depth; however, the core collected further up the estuary showed decreasing concentrations with depth. They reported that the DEHI? concentrations reached background concentrations at a depth dated at - 1946-1952. Peakall (1975) reported that DEHP usage began in - 1949 and has since increased dramatically. In the Conimicut Point core, the DEHP reached background levels at a depth of - 25 cm. The sediment profile of C,,-benzotriazole shows the highest concentrations in the surface followed by a rapid decreasewith depth. The chloro-benzotriazole compound showed a subsurface concentration maximum in the 10-15 cm horizon then decreasedin
306
R. 3. Pruell & 3. G. Quinn
TABLE 3. Calculated sediment accumulation rates (S) for the Conimicut These values were corrected for sediment compaction and were calculated maximum depth of each of the chemical markers
Chemical
Approximate dates fnst released
marker
1970 1963 1949 1880 1880
C,,-benzotriazole Chloro-benzotriazole DEHP Total PAHs Total hydrocarbons
Point core. based on the
S(cmyearr’) 2.02 1.41 1.04 0.76 0.76
concentration below this depth. Both of these compounds could not be detected below 20 cm in the core. These profiles are very similar to those found by Lopez-Avila & Hites (1980) in a sediment core collected in the Pawtuxet River near the chemical plant and are consistent with the production history of the substituted benzotriazoles. The chloro-benzotriazole was produced from 1963 to 1972 and the C,,-benzotriazole has been produced since 1970 and was still being produced at the time of our samplings (Lopez-Avila & Hites, 1980). Lopez-Avila (1979) also reported the concentrations of these compounds in three sectionsof a core collected near the location of our Conimicut Point station. That study reported relatively high concentrations (3 and 4 ug g- ‘) of C,,-benzotriazole in the two sections (O-7 and 7-14 cm); however, this compound was not detected in the 14-21 horizon. Chloro-benzotriazole concentrations were reported to be 3,4 and 1 ug g-r for the O-7,7-14 and 14-21 cm sections, respectively. The five chemical markers that were measured in the Conimicut Point core all show the expected trends with depth and all have well defined profiles. This is indicative of a location with a high sediment accumulation rate and a small bioturbation zone. The analysisof nutrient pore water profiles obtained on a Providence River core by Elderfield er al. (198lb) produced similar conclusions. A simple expression was used to estimate the sediment accumulation rate in this core using the depth profiles and input histories of the parameters measured (Boehm & Quinn, 1978; Wade & Quinn, 1979): d= ts+m,
where d = maximum depth of a marker, t = length of time a marker has entered the environment in significant concentrations, s = sediment accumulation rate, and m = mixing depth or depth of the bioturbation zone. A mixing depth of 2 cm was used for the calculations. This is based on other work done on Providence River sediment cores (Elderfield et al., 1981aJ). About 2 cm is probably a maximum value for this location; however, smaller values would have little effect on the sediment accumulation rate calculations. To correct for sediment compaction, the porosity of each section was calculated (from o/0water measurements)using an equa- Jn from Pilson et aE.(1984). Assuming that the water content of the surface layer is representative of sediment historically deposited at this location, the predicted initial depth of each section was calculated and an adjusted depth of each chemical marker was used to calculate sediment accumulation rates. These values are listed in Table 3. These measurementsindicate that the sediment accumulation rates decreasewith the
307
Geochemistry of organic contaminants
Concentration 0
25
50
75
(ng g-1)
I00
125
x C,,- benzotmrole 0 Chloro-benrotr~arole nD!-2-ethylhexyl l Total hydrocarbons oTotal PAHs
I50
175
200
phthalate (pig g-‘I
Figure 6. Depth distributions of C,,- benzotriazole, chloro-benzotriazole, ethylhexyl phthalate, total hydrocarbons and total PAHs in a sediment North Jamestown (Station 8).
di-Zcore from
depth or age of the markers used for the calculations. Therefore, the sediment accumulation rate appears to have increased over the past century from about 0.8 (1880 chemical marker) to 2.0 cm year- ’ (1970 chemical marker) at this location. Elder-field et al. (1981b) calculated sediment accumulation rates for a Providence River core based on the results of pore water nutrient profiles. The values that they calculated ranged from 0.6 to 1.8 cm year-‘. North Jamestown
sediment core
All of the parameters measured in the sediment core from North Jamestown (Station 8) have their highest concentrations near the surface (Fig. 6) and the concentrations decreasewith depth. Unlike in the Conimicut Point core, there are no abrupt concentration changesor subsurface maxima in this core and all of the parameters show similar decreasing trends with depth. The substituted benzotriazoles could be detected to about 12.5 cm depth in the core and the other three components reach apparent background levels in the 15-175 or 17.5-20.0cm sections. These results provide evidence that bioturbation has smearedthe historical record of inputs at this location. The data indicate that the bioturbation zone may extend to at least 10 cm at this location. We did not calculate sediment accumulation rates becauseof the influence of bioturbation. McCaffrey et al. (1980) and Elderfield et al. (1981b) found that nutrient pore water profiles in sediment cores from this location of the bay showed the influence of bioturbation to a depth of -20 cm. Also, Santschi (1980) calculated (using radionuclide data from Goldberg et aE., 1977) that the bioturbation zone extends to - 14 cm in this area of Narragansett Bay. Santschi et al. (1983, 1984) measured radionuclides in several cores from this area of the bay and reported rapid bioturbation zones ranging from 2 to 12.5 cm in depth. They calculated a sediment accumulation rate of 0.01 cm year-l at this location. Wade & Quinn (1979) analyzed a sediment core from North Jamestown for several organic contaminants. Their results indicated that the sediment accumulation rate was higher at this location ( - 0.1 cm year - ‘) and bioturbation had not greatly inlluenced the historical profiles in the core. The reason for this discrepancy is not clear; however, patchiness of biological activity in sedimentsmay explain the differences observed in the two studies.
308
R. J. Pruell & J. G. Quinn
Concentration (nqq+, 0
50 I
I
100 1
zoo 1
I50 I
250 ,
x C,,- benrotmzole 0 Cnlora- benzotrioroie
A Oi-2-ethylhexyl phtholote Total hydrocarbons @q g”l n Total PAHs
l
Figure PAHs, Island
7. Depth distributions of di-2-ethylhexyl C,,-benzotriazole and chlorobenzotriazole Sound (Station 9).
phthalate, total hydrocarbons, in a sediment core from
total Rhode
Concentration (ngg-1) Conlmlcut 0 1
5000 I
Point
North
10000 . IRat,o*
Jamestown
Brenton I.0
0 p’ig
5.5
2.0 1
Id
Reef 30 1
4.0 I
50
i
I Rat10 3.4
:,
3.6
3.0
0.2
-f 01
-
I
x C,o-benzotriazole OChloro-benrotriazole
Figure 8. C,,- and chloro-benzotriazole Narragansett Bay sediment cores.
Rhode Island
depth
*
c,,-beniotr~oloie Chloro-benzotrlorole
distributions
and ratios
in the three
Sound sediment core
The results obtained for a core collected in Rhode Island Sound (Station 9) are shown in Fig. 7. The concentrations of all parameters decreasedfrom the surface to a depth of - 7.5 cm; however, below this depth subsurface concentration increasesoccurred for all of the compounds which are from three distinct chemical classes(hydrocarbons, phthalic acid estersand substituted benzotriazoles). The reason for this subsurface layer is not known; however, the chemical distributions in these sections may provide information on the source and history of this material. Of particular interest are the substituted benzotriazoles. These compounds have a known source and history of inputs, and their concentrations and ratios can provide much useful information. Figure 8 showsa compilation of the substituted benzotriazole profiles in the three sediment cores from the bay. The ratios of these compounds are also included for each of the core sections analyzed.
Geochemistry of organic contaminants
309
In the surface samplesof all three cores, the C,,- benzotriazole/chloro-benzotriazole ratios are all greater than 3: 1. However, in the Conimicut Point core, the ratio decreases with depth reflecting the input histories of these compounds. At a depth of - 10 cm these compounds are found in an approximate 1:l ratio. Since the chloro-benzotriazole was produced between 1963 and 1972 and the C,,-benzotriazole from 1970 to the present, this probably represents material deposited between 1970 and 1972. The substituted benzotriazole ratios in the subsurface layer of the Rhode Island Sound core ( - 10-15 cm) are also close to l:l. This suggeststhe influence of material deposited between 1970 and 1972. Seavey & Pratt (1979) reported that 10 000 000 cubic yards of dredged material was removed from the Providence Harbor and Channel between 1967 and 1971. This dredged material was dumped at Brenton Reef about 6 km south of Newport and about 6 km south-east of the location of our Rhode Island Sound station. They also reported that there is some evidence of erosion of material from the dump site. Therefore, the material detected in this core may be a small amount of sediment that was originally deposited in the Providence River then dredged and dumped in Rhode Island Sound. It is difficult to explain, however, why this material is found so deep in the Rhode Island Sound sediment core. The sediment accumulation rate in this area is considerably lessthan the 1 cm year- ’ required to bury this layer to its present depth. Boehm and Quinn (1978) reported a sediment accumulation rate of -0.1-0.3 cm year- ’ in Rhode Island Sound. However, sediments near the Rhode Island Sound sampling location can be resuspended by storm generated currents (Collins, 1976). Therefore, one possible explanation is that storm generated currents may cause sediment to accumulate periodically at high rates in localized areasin this region. Conclusions
(1) Total hydrocarbon, total PAH and DEHP concentrations in Narragansett Bay surface sediments show exponential concentration decreasesalong a transect from the head to the mouth of the bay. The half-distances of these compounds appear to be strongly influenced by the locations of their major inputs to the bay and lessstrongly by their physical properties. (2) Two synthetic organic compounds (substituted benzotriazoles) are useful as unique geochemical markers in Narragansett Bay sediments. They show a concentration maximum in surface sediment from lower portions of the Providence River then decreasein concentration with distance downbay. (3) The PAH distributions are dominated by combustion derived parent compounds and are constant both in surface sedimentsand with depth in sediment cores. (4) The historical record of contaminant inputs to Narragansett Bay is recorded in the sediments of a core collected in the Providence River (Conimicut Point). However, this record is smeared by bioturbation in a sediment core from the mid-bay region (North Jamestown). (5) A sediment core from the mouth of the bay (Rhode Island Sound) showed a subsurface increase for all parameters. The sediment chemistry of this area may have been influenced by dredge spoil material removed from the Providence River and deposited near the mouth of the bay.
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Acknowledgements We would like to thank Dr Adolf0 Requejo (URI) for the organic carbon data that he provided, Curt Norwood and Dr James Lake of the EPA Environmental Research Laboratory, Narragansett for the GC-MS analyses and Dr Eva Hoffman (URI) for her thorough review of the manuscript. This work was funded by the United States Environmental Protection Agency through a grant (No. R803902030) to the Marine Ecosystems Research Laboratory (MERL) at the Graduate School of Oceanography, University of Rhode Island. This report has not been subjected to the EPA’s review process and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred.
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