Anthropogenic Platinum and Palladium in the Sediments of Boston

Anthropogenic activity has increased recent sediment concentrations of Pt and Pd in Boston Harbor by approximately. 5 times background concentrations...
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Research Anthropogenic Platinum and Palladium in the Sediments of Boston Harbor CAROLINE B. TUIT* AND GREGORY E. RAVIZZA Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 MICHAEL H. BOTHNER U.S. Geological Survey, Woods Hole, Massachusetts 02543

Anthropogenic activity has increased recent sediment concentrations of Pt and Pd in Boston Harbor by approximately 5 times background concentrations. Surface sediments and downcore profiles were investigated to evaluate Pt and Pd accumulation and behavior in urban coastal sediments. There is no clear correlation between temporal changes in Pt and Pd consumption and sediment concentration. However, Pt/Pb and Pd/Pb ratios suggest that Pt and Pd flux into the Harbor may not be decreasing with cessation of sludge input as rapidly as other metals. This is supported by the large discrepancy between fluxes associated with sludge and effluent release and those calculated from surface sediment concentrations. This evidence supports catalytic converters as a major source of Pd and Pt to Boston Harbor but cannot preclude other sources. Pd does not exhibit signs of post-burial remobilization below the mixed layer in the sediment cores, although near-surface variability in Pd concentrations may indicate a labile Pd component. Pt displays an inverse correlation with Mn above the oxic/suboxic transition, similar to behavior seen in pristine sediments where Pt is thought to be chemically mobile. This study does not support the use of Pd and Pt as tracers of recent contaminated sedimentation. However, the possibility of a labile Pt and Pd in these sediments highlights the need for further study of the biological uptake of these metals.

Introduction Since their introduction in the early 1970s, catalytic converters have dramatically reduced emissions of carbon monoxide, hydrocarbons, and nitrogen oxides. However, based on Pt and Pd enrichment in road dust, soil, grass, riverine sediment, and sewage, catalytic converter use is believed to be responsible for the widespread dissemination of Pt and Pd to the environment (2-6). This study examines how anthropogenic release of Pt and Pd has increased sediment inventories of Pt and Pd in a coastal marine environment, if these enrichments can be linked to release from autocatalysts, and evidence for post-depositional mobility of Pt and Pd in contaminated sediments. The chemical behavior of anthropogenic Pt and Pd in the coastal marine environment is largely unknown, but there * Corresponding author e-mail: [email protected]; phone: (508)289-2460; fax: (508)457-2187. 10.1021/es990666x CCC: $19.00 Published on Web 02/02/2000

 2000 American Chemical Society

are two interesting possibilities. If chemically inert, Pt and Pd may serve as tracers of recent anthropogenic input, particularly for road runoff. Alternatively, if they are chemically labile, Pt and Pd could be available to the food web. Pt eroded from catalytic converters primarily consists of metallic Pt(0) sorbed to small particles of alumina matrix and is traditionally considered to be extremely inert (7). These particles could provide a passive sediment tracer similar to the use of Pb distributions (8). Studies suggest, however, that up to 10% of Pt associated with catalytic converter particles could be soluble in water (9) and that other industrial uses, such as in the medical, dental, chemical, electronic, and jewelry industries, may release significant quantities of dissolved Pt and Pd. Unlike Pb and Hg, whose environmental effects and toxicity have been widely studied even at low concentrations, such information on Pt and Pd is scarce. Toxicity studies on Pt and Pd are typically conducted at concentrations far exceeding those likely to occur in even the most contaminated coastal marine sediments. However, given the unmonitored and widespread dispersal of Pt and Pd to the environment and the potential for bioaccumulation, long-term toxicological and ecological effects are possible (2). Pt-containing anti-cancer drugs, such as cis-Pt(NH3)2(Cl)2, act by diffusing through the cell membrane, binding to cell DNA, and preventing cell replication. They produce serious side effects, and their Pd analogues are generally too toxic to use (10). To examine the sources and behavior of anthropogenic Pt and Pd in an urban coastal environment, the authors analyzed Pt and Pd concentrations in sediment from Boston Harbor. Boston Harbor has received significant wastes associated with regional industrial growth (11-14). Archived samples of surface sediment and sediment cores were available (13). These factors make Boston Harbor an excellent area for documenting anthropogenic Pt and Pd distributions in the marine system.

Experimental Methods Sample Collection and Locations. The samples analyzed in this project were collected by Bothner et al. (13) as part of an ongoing project that monitors sediment quality in Boston Harbor as sewage and industrial waste discharges are reduced (Figure 1). Surface sediments were collected by grab sampling in the summer of 1978. Sediment cores were collected during the summers of 1987, 1993, and 1996 in Boston Harbor and during the summer of 1992 in Massachusetts Bay using the U.S. Geological Survey (USGS) hydraulically damped corer. This corer has a slow rate of penetration controlled by a water-filled piston that results in minimal disturbance of the sediment-water interface. The cores were maintained in a vertical orientation, extruded, and sectioned in 1-2-cm intervals. The sediment, sludge, and effluent particles were dried and ground, and aliquots were removed for platinum group element (PGE) analysis. Additional aliquots were completely dissolved in HF, HNO3, and HClO4 acids and analyzed for trace metals (Mn, Fe, and Pb) via atomic adsorption (13). Organic carbon concentrations and grain size analyses were determined by conventional methods (13). PGE Analysis. Sediment samples were preconcentrated via nickel-sulfur (NiS) fire assay and analyzed by isotopic dilution inductively coupled plasma mass spectrometry (IDICPMS) (15). PGEs are partitioned into the NiS, isotopically equilibrating spike and sample (16, 17). Dissolution of the NiS bead in 6.2 N HCl further preconcentrates the PGEs into VOL. 34, NO. 6, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. Map of Boston Harbor showing numbered sample locations for cores (squares) and grab samples (circles). Combined sewer outfalls (diamonds) and former sludge and effluent outfalls (stars) are also shown. an insoluble residue that is isolated by filtration onto a 0.45µm filter paper. The filter paper and residue are digested in HNO3, evaporated to about 30 µL, and diluted 10-fold with H2O. All sample preparation is done in a clean lab, using Seastar acids and Milli-Q water in order to maintain low blank values. Isotopic analyses were performed on either the Massachusetts Institute of Technology (MIT) Fisons Quadrapole ICP-MS or the Woods Hole Oceanographic Institute (WHOI) Finnegan Element ICP-MS. Pd and Pt concentrations are calculated from the measured 105Pd/106Pd and 198Pt/196Pt ratios corrected for instrumental mass fractionation. Isobaric interferences on Pd and Pt masses were corrected for by monitoring 111Cd and 200Hg, respectively. By measuring three isotopes of Pd, it is possible to identify isobaric interferences from ZnAr and CoAr molecular species (15). Samples so influenced, about 20% of the samples analyzed for this study, give erroneous results and are excluded from the data reported here. The procedural blank for most samples is less than 20% of the total analyte. Over 30 fusion reagent blanks were measured during the course of this study. The average fusion blank is 55.9 ( 22.1 pg/g for Pt and 22.9 ( 21.6 pg/g for Pd. The large uncertainty in Pd is due to problems with isobaric and molecular interferences that are especially evident in fusion blanks. The magnitude of the blank correction for each sample is determined by the fusion reagent to sample mass ratio. Due to the small sample size of the archived sediments, this ratio was approximately 10:1 for most samples; therefore, the sample blanks for Pt and Pd were about 0.55 and 0.23 ng/g, respectively. For low level samples and the 1996 sediment core, the flux:sample ratio was reduced to 2:1, and the associated blank corrections decreased by a factor of 5.

Results and Discussion Background Pt and Pd Concentrations. To determine background concentrations applicable to Boston Harbor sediments, we analyzed pre-anthropogenic sediment samples from the nearby Massachusetts Bay (18). Sediment samples from depths greater than or equal to 38 cm were analyzed. All of these samples have background concentrations of silver and lead, two elements that are sensitive tracers of anthropogenic input. 928

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FIGURE 2. Pd (diamonds; dashed lines) and Pt (squares; solid lines) vs Al2O3 in Massachusetts Bay samples. For the range of Al2O3 concentrations (10.0-14.2%) in Boston Harbor, expected background Pt and Pd concentrations are between 0.2-0.8 and 0.4-0.9 ng/g, respectively. The Pt and Pd concentrations in deep Massachusetts Bay sediment both average 0.6 ( 0.3 ng/g, significantly lower than concentrations measured in Boston Harbor. Most of the Massachusetts Bay samples have lower organic carbon and higher clay concentrations than Boston Harbor sediment samples (13, 19). To correct for grain size and quartz dilution effects in the Massachusetts Bay samples, Pt and Pd are normalized to Al2O3, a major component of clay minerals and an indicator of terrigenous input to marine systems (Figure 2). Boston Harbor sediments have Al2O3 concentrations ranging from 10.0% to 14.2% (13), resulting in background Pt and Pd estimates of 0.2-0.8 and 0.4-0.9 ng/g, respectively. Sources of Anthropogenic Pt and Pd. The sources of Pt and Pd to Boston Harbor are not well documented. Local industrial sources may include the autocatalytic, chemical, jewelry, electrical, medical, and dental industries (20, 22, 23). There are few measurements of these metals in waste streams or sewage (20, 23). The extreme expense of Pt and Pd causes most industries to conserve and recycle these metals. Autocatalytic converters, which release Pt at a rate 0.5-0.8 µg/km driven (6), are likely to be the predominate source of these metals to the environment. The catalytic converter industry has been the major consumer of Pt (>60%) since the introduction of catalytic converters in 1973. Catalytic converter release of Pt has led to documented Pt enrichment of road dust (6), and the continued use of autocatalytic converters, due to air quality concerns, is likely to magnify this nonpoint source over time. Pd release rates from catalytic converters have not been independently measured but are likely to be proportional to Pt. Although Pd is a cheaper, more efficient catalyst than Pt, it is more susceptible to poisoning by Pb associated with gasoline(21). Therefore, until about 1993, when the complete phase out of leaded gasoline was accomplished, catalytic converters accounted for only about 10% of Pd usage (22). Catalytic converters produced in the 1980s had Pd/Pt ratios of approximately 0.6, giving release rates for Pd of about 0.3-0.5 µg/km. However, catalytic converters produced since 1993 have increasingly higher Pd/Pt ratios, and in the past decade the amount of Pd consumed by the autocatalyst industry has risen by an order of magnitude, accounting for 40% of the world Pd demand (22). The concentrations of Pt and Pd in sewage sludge and effluent particles from Boston were measured to estimate the magnitude of anthropogenic input. Boston sewage is a mixture of household and industrial waste as well as road runoff which is normally routed through the sewage treatment

TABLE 1. Estimated Pt and Pd Fluxes in Boston Harbor

station 8 cores 1987 1993 1996 sludge 1991 effluent 1998

Pt (ng/g)

Pt flux (kg/yr)

Pd (ng/g)

Pd flux (kg/yr)

5.0a 4.7a 4.2a 36 29.4

2.3b 2.2b 2.0b

10a 5.3a 9.2a 167 46.1

4.7b 2.5b 4.3b

0.24c

catalytic converters monolith

TABLE 2. Pt and Pd Concentrations in Surface Sediments

0.38c

(µg/km) 0.5-0.8

4.0-6.4d

a

Average mixed-layer sediment concentrations (Figure 4). b Sediment fluxes calculated from mixed-layer concentrations, the mass accumulation rate (0.96 g cm-2 yr-1; 13) and the depositional area of Boston Harbor 49.2 × 106 m2 (24). c The sewage flux is calculated from Pt and Pd concentrations in effluent assuming 15 × 106 kg/yr particulate effluent flux for 1998 (Morris Hall, MWRA, personal communication). Fluxes are corrected to account for the 45% of total suspended solids released that are lost from the Harbor (12). d Catalytic converter flux is calculated from a Greater Boston population of 1.2 million people with approximately 1 car for every 3 people. On average, a car is driven 20 000 km/yr, which results in about 8 billion km driven in Boston per year.

system. Treated sewage was released to Boston Harbor as sludge (discontinued in 1991) and effluent (discontinued in 2000). Unquantified by this study, untreated road runoff is still released from storm drains unconnected to the sewage treatment system as well as through combined sewer overflows (CSOs) along with untreated sewage during periods of exceptionally heavy rains. Pt and Pd concentrations in Boston sewage sludge collected in 1991 are respectively 60 and 275 times background concentrations in Massachusetts Bay (Table 1). Sewage effluent particles collected in 1998 had Pt and Pd concentrations of 29.4 and 46.1 ng/g, respectively. Multiplying the concentrations by the annual discharge of effluent particles and sludge yields a lower limit estimate of the total PGE flux. Concentrations in Boston’s sludge are similar to those measured in sludge from New York and from over 24 German towns and cities (23). This implies that PGE enrichment in sewage is ubiquitous throughout the industrialized world. It is interesting to note that concentrations of Pd are greater than Pt in the sludge sample analyzed, even though it was all collected prior to 1993. This suggests that there is an additional source of particulate Pd in sludge and effluent and/or that Pd is more particle reactive than Pt. Helmers et al. (6) found that Pd concentrations in sludge from Stuttgart was correlated with use by the German dental industry. Another possible source is electroplating waste associated with the jewelry and electrical industries. The industrial source of anthropogenic Pt and Pd is important because it determines the chemical form in which these elements are released to the environment and their potential reactivity and toxicity. The chemical and electrical industries may release large quantities of dissolved Pt and Pd, which could behave very differently from the small metallic particles released from autocatalysts. Surface Sediment Concentrations. The archived sediment available provided an opportunity to evaluate Pt and Pd concentrations in surface sediments of Boston Harbor in 1978, 1993, and 1996 (Table 2). Surface sediments collected at some locations in 1978 show 17- and 50-fold enrichment of Pt and Pd concentrations, respectively, relative to background. This is much higher than expected so soon after the introduction of catalytic converters and suggests that there may have been important industrial sources for the metals at this time. Samples from other areas of the Harbor collected in 1978 are at or near background concentrations. Samples

sample

year

1978 G16 1978 G12 1978 G13 1978 G18 1978 G14 1978 G2 AST 1-93 SC10-3 AST 1-93 SC3-2 AST 1-93 SC4-1 AST 1-93 SC8-2 AST 9601 10C-1 AST 9601 3C-2 AST 9601 4C-4 AST 9601 8C-6

1978 1978 1978 1978 1978 1978 1993 1993 1993 1993 1996 1996 1996 1996

a

Pt stationa (ng/g) 16 12 13 18 14 2 10 3 4 8 10 3 4 8

Pd Pb (ng/g) Pt/Pd (µg/g)

1.88 7.58 0.89 12.5 36.3 0.77 0.45 4.86 39.9 4.33 15.4 5.34 3.58 0.58 5.16 4.30 4.40 4.82 4.13 3.72 2.39 3.11 4.42 6.05

0.32 0.34 1.70 0.16 0.28 6.10 1.20 0.91

113 60 165 42 225 156 110 73 53 94 83

1.56 58 77

0.73

Station locations are shown in Figure 1.

with high Pt and Pd also exhibit elevated Pb concentrations, implying that all of these contaminants may have a similar source or a similar affinity for fine-grained, organic-rich sediments. The patchy distribution of Pt and Pd in the 1978 surface samples implies a local source for these metals or focused deposition in areas where fine grained sediments accumulate (24). The extreme enrichments in Pd and Pt could be due to the higher release rates [0.6-1.9 µg of Pt/km (9)] of the early Pt/Pd pelletized catalytic converter versus today’s more stable monolith converters [0.5-0.8 µg of Pt/km (6)], but with relatively few cars equipped with catalytic converters at this time, the source is just as likely to be other industrial uses of these metals. By 1993, surface sample concentrations had become more homogeneous and were elevated at 4-5 times background. The 1996 surface samples show similar concentrations and distributions to the 1993 suite. The decrease in concentrations between 1978 and 1993 samples could be a function of efforts to clean up the Harbor that included the discontinuation of sludge release in 1991 and enforced reductions in metals discharged by industry (13). Several metals, including Pb, Cr, and Hg, show significant decreases in surface sediment concentrations due to cleanup activity (13). Those metals, however, continue to decrease through 1996 while Pt and Pd concentrations remain stable. Pt and Pd concentrations of Boston Harbor sediments are clearly elevated relative to preanthropogenic sediment from Massachusetts Bay. It should be noted, however, that Pt and Pd concentrations of Harbor sediments are similar to uncontaminated pelagic sediments (25-27). The Boston Harbor measurements demonstrate that anthropogenic activity can lead to elevated Pt and Pd in the urban coastal sediments. Given the widespread use of catalytic converters, it is likely that these enrichments will be found in many urban coastal marine environments. Down-Core Profiles. Variability in down-core Pt and Pd profiles reflects the combined influence of changes in metal accumulation through time and post-depositional redistribution. Potentially important post-depositional redistribution processes include both the mixing of particles caused by organisims and currents and the chemical redistribution related to diagenetic processes. Examining Pt and Pd concentration variations in isolation does not allow us to assess the relative importance of these different potential causes of down-core variability. We have used down-core Pb concentration data to provide a framework to infer whether down-core variation in Pt and Pd concentration are influenced more strongly by changing metal accumulation rate or by post-depositional redistribution within the sediment column. VOL. 34, NO. 6, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. (1) Pd, (2) Pb, and (3) Pt blank-corrected sediment concentrations in cores from station 8. The verticle axis has been converted to time taking into account the date of collection collected [1996 (circles), 1993 (diamonds), 1987 (squares), or 1978 (triangles)] and assuming a constant sedimentation rate of 1.8 cm/yr and a 15-cm mixed-layer depth. Bothner et al. (13) have analyzed Pb in cores collected from station 8 in the summers of 1978, 1987, 1993, and 1996. They determined a sedimentation rate (1.8 cm yr-1) and a mixed-layer depth (15 cm) for station 8 using 210Pb and 137Cs profiles in a 1978 core. Assuming that the sedimentation rate and mixed-layer depth have remained constant since 1978, it is possible to recalculate all of the Pb profiles versus time (Figure 3.2). When corrected for their collection time, the Pb profiles fall on top of one another. The good fit of the Pb profiles provides empirical evidence that there has been no significant chemical or physical remobilization of Pb at this site between core collections. It suggests that Pb is chemically immobile in these sediments and that Pb profiles may give a good indication of the changing inputs of anthropogenic metals to Boston Harbor as modified by bioturbation and other physical redistribution processes at station 8. In comparison to the Pb profiles, when the Pt concentrations at station 8 are plotted versus time, they show little correlation with each other (Figure 3, panel 3). This implies that Pt was remobilized in the interval between core collection while Pb was not. All of these profiles show a subsurface peak, exceeding replicate variability, at about 3 cm depth (Figure 4, panels 1-4). Variability of Pt concentrations within the mixed layer implies that Pt is remobilized within these sediments on short time scales. The Pt peaks occur at the base of the amphipod mat that grows over much of the Harbor (28). Below the amphipod mat, Pt and Mn profiles are positively correlated, but within the mat, they are anticorrelated (Figure 5). A similar relationship has been reported at the suboxic/anoxic transition zone in burn-down layers in turbidites (1). This type of diagenetic redistribution occurs on abyssal plains when bottom water oxygen and nitrate diffuse into the turbidite sediments oxidizing organic matter. The oxidation front progressively deepens, redistributing trace elements as it burns downward. Colodner et al. (1) suggests that Pt in the turbidite, associated with organic matter, is remobilized due to organic matter oxidation and diffuses into the anoxic portion where it is scavenged again. Subsurface Pt maxima close to the oxic/suboxic transition (Figure 5) suggests that a similar mechanism may be operating in Boston Harbor sediments, indicating that Pt may be chemically labile in these sediments. This implies that either Pt particles released from catalytic converters are more soluble than previously assumed and/or the existence of additional sources of mobile Pt. Alternatively, the Pt peaks at the base of the amphipod mat could be the result of particle size-dependent bioturbation in which smaller particles are 930

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preferentially selected by organisms (29). The amphipods may act to concentrate small catalytic converter particles directly below the mat. It is impossible to distinguish between these two mechanisms at this time. Palladium also exhibits near-surface peaks in the 1993 and 1996 cores (Figure 4, panels 5-8). But, once fixed in the anoxic portion of the core, Pd does not appear to be remobilized. Pd down-core profiles, with the exception of the deep samples from the 1987 core, realign when corrected for collection time (Figure 3, panel 1). This implies that the Pd profile is subject to a lesser degree of remobilization in the sediments than Pt and may better reflect input history. Pd concentrations begin to rise from background in the early 1970s, which correlates with the introduction of catalytic converters in 1973. A maximum of about the same magnitude (8-13 ng/g) is present at about 10 cm in 1987, 20 cm in 1993, and appears to be buried with time although sample resolution within the 1996 core does not allow it to be traced further toward the present. This peak corresponds to the late 1970s and could be related to the high surface sediment Pd concentrations seen in 1978. This could be the result of Pd use by industry such as the electrical industry or the higher release rates for the earlier pellet converters as discussed above. Lower concentrations of Pd in the early 1990s could be due to the end of sludge discharge in December 1991. The upper 20 cm of the 1996 core has extremely variable Pd concentrations ranging from 6 to 16 ng/g (Figure 4, panel 5). The variability in the upper 20 cm do not allow us to draw any direct correlation to Pd usage or to estimated changes in input rates, but the higher concentrations do suggest that Pd is not decreasing in step with Pb and other metals. These findings neither confirm nor refute a catalytic converter source for Pd. Potential Trends in Pt and Pd Fluxes. Another indication that Pt and Pd input into the Boston Harbor is not decreasing relative to Pb and other metals can be seen by the Pt/Pb and Pd/Pb ratios versus depth in the 1996 core (Figure 6). All Pt/Pb and Pd/Pb ratios for sediment younger than 1990 are greater than or equal to 0.04. This further supports the observation that Pt and Pd inputs are not decreasing like other industrial metals. Pb was discharged to Boston Harbor primarily (>60%) in sewage effluent and sludge (11). The cessation of sludge release has dropped Pb loadings by 27% (11) and, combined with lower atmospheric fluxes, has resulted in a decrease in Pb sediment concentrations seen in both surface sediments and core profiles (13). We suspect

FIGURE 4. Core profiles of Pt and Pd from station 8 in 1996, 1993, and 1987 and from station 3 in 1993 plotted versus depth. The horizontal line at 15 cm represents the 210Pb mixed-layer depth. Boxes indicate sample replicates. The station 8 1987 surface samples were unavailable. All of the Pt and some of the Pd profiles show peaks above sample variability at 3 cm, within the mixed layer indicated by the dashed line, suggesting that Pt is post-depositionally remobilized in the Harbor.

FIGURE 5. Pt (squares) and Mn (circles) plotted versus depth for (1) the 1996 core at station 8 and (2) core 11334 analyzed by Colodner et al. (1). Dashed lines indicate the oxic/suboxic transition in both cores. Mn concentrations decrease approaching the transition due to reductive dissolution. Pt is anti-correlated with Mn above the transition with peak concentrations at the base. This behavior implies that Pt is chemically mobile in both these environments (1). the additional source of Pt and Pd is untreated road runoff from CSOs and storm drains. Estimates of Pt and Pd fluxes into Boston Harbor sediments were calculated from mixed-layer sediment concentrations, from effluent particle concentrations com-

FIGURE 6. (1) Pt/Pb and (2) Pd/Pb ratios versus year for station 8 1996 core. Most samples above 20 cm (∼1990) have Pt/Pb and Pd/Pb ratios greater than 0.04, implying that Pt and Pd are not following the recent decreasing trend seen in Pb and other metals (13). bined with sewage particle discharge rates, and from catalytic converter release rates (Table 1). Sediment burial fluxes for Pt exceed sludge and effluent estimates by an order of magnitude; however, Pt release estimated from autocatalysts is more than sufficient to balance the apparent discrepancy. Although these estimates are subject to considerable uncertainty, arising from potential temporal variability in the Pt and Pd concentrations of effluent particles and possible storage of catalytic converter particles in the terrestrial environment, the calculated fluxes imply that release from VOL. 34, NO. 6, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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autocatalysts can comprise a significant fraction of the total Pt flux to the Harbor. We suspect that the same is true for Pd, although Pd release rates from autocatalysts have not been quantified to date. It is likely that Pt and Pd from autocatalysts is supplied directly to the Harbor by road runoff passing through storm drains and CSOs. Despite the cessation of sludge release in 1991, the surface sediment Pt and Pd concentrations have not decreased during the past decade. This is consistent with inference of an additional non-sewagerelated Pt and Pd flux. This study clearly demonstrates that anthropogenic activity has increased environmental concentrations of Pt and Pd in Boston Harbor by at least 5-fold relative to pristine sediment concentrations, indicating that anthropogenic enrichments can significantly influence coastal marine inventories of PGEs. The inverse correlation of Pt and Mn in the 1996 core suggests that Pt is associated with organic matter in these sediments and is remobilized due to organic matter oxidation. This implies that the chemical form of Pt in Boston Harbor sediments is similar to pristine sediments (1) and indicates either that Pt associated with catalytic converters is much more soluble than expected or that there is an additional source of dissolved Pt to the Harbor. There is no clear evidence of post-burial Pd remobilization in the Harbor, but sample variability makes any correlation of sediment profiles and input estimates difficult. This study does not support the use of Pd and Pt as tracers of recent sedimentation and transport; however, the possibility of a labile component in these sediments supports the need for further study of the biogeochemical behavior of these metals.

Acknowledgments We would like to thank Peter Gill, Barry Grant, and Lary Ball for field and technical assistance. This work was supported by a Joint Funding Agreement between the Massachusetts Regional Water Resources Authority (MWRA) and the U.S. Geological Survey (USGS) and by a Mellon Independent Study Award from the Woods Hole Oceanographic Institution. The views expressed herein are those of the authors and do not necessarily reflect the views of the USGS or the MWRA.

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(8) Callender, E.; Van Meter, P. C. Environ. Sci. Technol. 1997, 31, 424A. (9) Hill, R. F.; Mayer, W. J. TEEE Trans. Nucl. Sci. 1977, NS-24, 2549-2554. (10) Lippard, S. J.; Berg, J. M. Principles of Bioinorganic Chemistry; University Science Books: Mill Valley, CA, 1994. (11) Alber, M.; Chan, A. B. Massachusetts Water Resources Authority Environmental Quality Department Technical Report 94-1; 1994. (12) Stolzenbach, K. D.; Adams, E. E.; Bothner, M. H.; Buchholtz-ten Brink, M. R.; Farrington, J. W. Contaminated Sediments in Boston Harbor; MIT Sea Grant Program, Marine Center for Coastal Processes: Cambridge, MA, 1998; p 182. (13) Bothner, M. H.; Buchholtz ten Brink, M.; Manheim, F. T. Mar. Environ. Res. 1998, 45, 127. (14) Menzie, C. A.; Cura, J. J., Jr.; Freshman; J. S.; Potocki, B. Massachusetts Water Resources Authority Environmental Quality Department Technical Report 91-4; 1991. (15) Ravizza, G.; Pyle, D. Chem. Geol. 1997, 141, 251. (16) Robert, R. V. D.; van Wyk, E.; Palmer, R. Concentration of the noble metals by a fire-assay technique using nickle sulphide as the collector; National Institute for Metallurgy: 1971. (17) Hoffman, K. G.; Naldrett, A. J.; Van Loon, J. C.; Hancock, R. G. V.; Mason, A. Anal. Chim. Acta 1978, 102, 157-166. (18) Ravizza, G.; Bothner, M. H. Geochim. Cosmochim. Acta 1996, 60, 2753. (19) Bothner, M. H.; Buchholtz ten Brink, M.; Parmenter, C. M.; d’Angelo, W. M.; Doughten, M. W. The Distribution of silver and other metals in sediments from Massachusetts and Cape Cod Bays; U.S. Geological Survey Open File Report 93-725; USGS: Reston, VA, 1993. (20) Helmers, E.; Schwarzer, M.; Schuster, M. Environ. Sci. Pollut. Res. 1998, 5, 44. (21) Fogg, C. T.; Cornellisson, J. L. Availability of Platinum and Platinum-Group Metals; Information Circular 9338; U.S. Bureau of Mines: Washington, DC, 1992. (22) Cowley, A. Platinum 1998; Johnson Matthey: London, England, 1998. (23) Lottermoser, B. G. Int. J. Environ. Stud. 1994, 46, 167. (24) Knebel, H. J.; Rendigs, R. R.; Bothner, M. H. J. Sediment. Petrol. 1991, 11, 791. (25) Goldberg, E. D.; Koide, M.; Yang, J. S.; Bertine, K. K. In Metal Speciation, Theory, Analysis and Application; Kramer, J. R., Allen, H. E., Eds.; Lewis: Chelsea, MI, 1988; pp 210-217. (26) Koide, M.; Goldberg, E. D.; Niemeyer, S.; Gerlch, D.; Hodge, V.; Bertine, K. K.; Padova, A. Geochim. Cosmochim. Acta 1991, 55, 1641. (27) Crocket, J. H. In Platinum Group Elements; Mineralogy, Geology and Recovery; Cabri, L. J., Ed.; Special Volume 23; Canadian Institute of Mining and Metallurgy: Montreal, Canada, 1981; pp 47-64. (28) MWRA. The State of Boston Harbor 1995; MWRA Technical Report 96-6; MWRA: Boston, MA, 1996. (29) Wheatcroft, R. W. Limnol. Oceanogr. 1992, 90-104.

Received for review June 15, 1999. Revised manuscript received December 14, 1999. Accepted December 15, 1999. ES990666X