Environ. Sci. Technol. 2000, 34, 966-972
Isotopic Studies of Sources of Uranium in Sediments of the Ashtabula River, Ohio, U.S.A. M I C H A E L E . K E T T E R E R , * ,† WILLIAM C. WETZEL,‡ RICKY R. LAYMAN,‡ GERALD MATISOFF,§ AND EVERETT C. BONNIWELL§ Department of Chemistry, Northern Arizona University, Box 5698, Flagstaff, Arizona 86011, Department of Chemistry, John Carroll University, University Heights, Ohio 44118, and Department of Geological Sciences, Case Western Reserve University, Cleveland, Ohio 44106
Uranium contamination of anthropogenic origin has been identified in unconsolidated sediments of a 1.5 km portion of the Ashtabula River near its confluence with Lake Erie. Uranium concentrations as high as 188 µg/g dry sediment are present. A small tributary of the Ashtabula River, Fields Brook, is the apparent point of origin of the uranium in the Ashtabula River sediments. 137Cs dating of a sediment core indicates that the U contamination occurred during the post-1964 time frame. The horizons of elevated U concentration also exhibit > 10× elevations in Zr, Nb, Hf, Ta, and W. 238U/235U isotopic ratios indicate that the uranium is largely but not exclusively of natural composition. Distinct horizons of slightly 235U-depleted (238U/ 235U > 137.88) and slightly 235U-enriched (238U/235U < 137.88) uranium are also present. 210Pb activities and 232Th/ 230Th isotopic measurements indicate that a significant portion of the uranium contains 238U daughters in approximate secular equilibrium. It is inferred that at least two distinct sources of anthropogenic U contamination exist: (A) discharges from the processing of enriched and depleted U metal by a DOE contractor facility and (B) U-bearing wastes from the production of TiO2 from ilmenite and associated minerals. These isotopic methodologies are potentially useful in settings where releases of nonnatural 238U/ 235U composition materials and/or “naturally occurring radioactive material” (NORM) have taken place.
Introduction The Ashtabula River drains an area of 350 km2 in northeast Ohio and northwest Pennsylvania and discharges into the central basin of Lake Erie at the city of Ashtabula (80°48′W, 41°54′N, Figure 1). The lower Ashtabula River and Harbor were designated as an Area of Concern (AOC) in 1985 by the International Joint Commission. There is concentrated industrial development in Ashtabula along the river and a tributary, Fields Brook. From the 1940s through late 1970s, unregulated discharges and mismanagement of hazardous * Corresponding author phone: (520)523-7055; fax: (520)523-8111; e-mail:
[email protected]. † Northern Arizona University. ‡ John Carroll University. § Case Western Reserve University. 966
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 6, 2000
wastes caused serious contamination of the sediments and biological communities in the river. In 1983 the 14 km2 Fields Brook watershed was designated by the U.S. Environmental Protection Agency (U.S. EPA) as a CERCLA (“Superfund”) National Priorities List site based upon elevated sediment concentrations of polychlorinated biphenyls, hexachlorobenzene, hexachlorocyclopentadiene, polycyclic aromatic hydrocarbons, and the elements Cd, Cr, Hg, and As (1). Sediments in the Ashtabula River AOC are classified by USEPA as “heavily polluted”, which currently precludes open-water disposal of dredged material; accordingly, the portion of the river channel located south of the 5th St. Bridge (Figure 1) has not been dredged since 1962. The accumulated sediment is imparing recreational and commercial uses of the river (1). Located in the Fields Brook watershed is the RMI Titanium Company. RMI extruded uranium metal into various rod and tube products from 1962 through 1988 under contracts with U.S. Department of Energy (DOE) and its predecessor agencies. The RMI facility extruded both uranium of 235Udepleted (238U/235U ∼ 500) and 235U-enriched (238U/235U ∼ 105 and 80) compositions (2). These isotopic compositions are markedly different from “natural” U having a 238U/235U of 137.88 (3). Present decommissioning studies at the RMI property have demonstrated soil and groundwater contamination with uranium, 99Tc, and trichloroethylene; offsite soil samples have indicated only a small area of uranium contaminated soil. Radiochemical measurements of sediments from Fields Brook were conducted by RMI during 1985-1993. The highest activity found was 18.52 pCi/g (sum of activities of 234U, 235U, and 238U), with most samples exhibiting typical crustal activities of ∼1 pCi/g. Because these levels did not exceed the Nuclear Regulatory Commission’s free release guidelines of 30 and 35 pCi/g for enriched and depleted uranium, respectively, the Agency for Toxic Substances and Disease Registry (ATSDR) concluded that no apparent public health hazard exists in association with the RMI site (4). However, the releases reported to DOE by RMI indicate cumulative 1962-1988 air and water emissions of 886 and 3271 kg of uranium, respectively (5). The RMI facility therefore represents a significant potential source of past U releases to the Ashtabula River watershed via Fields Brook. The Millenium Chemical site represents an additional potential source of anthropogenic U in the Fields Brook basin. This site has been in continuous production since the late 1950s for the production of TiO2 using ilmenite (FeTiO3) as a raw material. Ilmenites are resistant minerals which are concentrated with other resistant minerals such as zircon (ZrSiO4) and monazite (Ce, La, Y, Th)PO4 following weathering of igneous rocks (6, 7). The Millenium plant has generally obtained ores from mine sites located in Australia and Canada; the naturally occurring radionuclides present in the ores become concentrated in residual process wastes (8). Prior to 1976, residues were discarded onsite; a 1998 EPA study found elevated levels of radium (226Ra + 228Ra) in onsite piles. Previous DOE aerial survey work (9) also identified elevated levels of 232Th- and 238U-series nuclides on the property of the Millenium plant. To date, no studies have addressed in detail the sources and characteristics of U contamination in the Ashtabula River. One regulatory reason for undertaking studies of this nature is to identify “potentially responsible parties”, who can be held liable under CERCLA for site assessment and cleanup costs. Information regarding this possible contamination is also essential for assessing the environmental and human health impacts of planned future dredging and disposal of 10.1021/es981314d CCC: $19.00
2000 American Chemical Society Published on Web 02/09/2000
FIGURE 1. Site map for the Ashtabula River Area of Concern (AOC), illustrating core sampling locations, the RMI Titanium extrusion facility, and the Fields Brook basin. Uranium concentration anomalies were detected at solid squares, and no anomaly was detected at hollow squares. the removed material. EPA has estimated that 760 000 m3 of contaminated sediments are to be removed from the Ashtabula River; the potential presence of elevated levels of 238 U and related nuclides must be taken into account in treatment/disposal practices based upon both regulatory and health risk assessment considerations. The existence of anthropogenic U contamination in the vicinity of nuclear plants and uranium mills has been recognized. Liator (10) attributed the 235U-enriched material in soils at the DOE Rocky Flats Plant near Golden, CO to accidential releases of U-laden oils, past burial of material in shallow trenches, and airborne releases. Batson et al. (11) demonstrated the episodic, storm-related off-site transport of sediment-associated U from contaminated flood plain sediments near the DOE Savannah River Site. The characteristics and possible sources of anthropogenic uranium contamination can be assessed by the following: (a) examining of U concentrations and their spatial relationships; (b) determining chemical/mineralogical species in soils and sediments via selective extractions or mineral separations (12); (c) determining the 238U/235U isotopic composition to establish if 235U-depleted or 235U-enriched material are possible sources; and (d) measuring concentrations/activities of concomitant elements and/or daughter decay products in the 238U and 235U series (13). Here we present a reconaissance-level survey of uranium in the Ashtabula River between Fields Brook and Lake Erie in which we employed procedures (a), (c), and (d). We also examined the nature of the U contamination via thorium isotopic measurements. U and Th isotopic measurements were utilized by Noakes et al. (14) to identify anthropogenic U contamination in localized areas of the Mississippi River. In addition to Noakes’ study, 232Th/230Th ratios in uncontaminated North American continental have also been reported by two other sets of
researchers (15, 16). These early researchers reported 230Th/ 232Th activity ratios, which can be converted into an anticipated range of 140 000-200 000 for 232Th/230Th atomic ratios of “background” sediment. Sediments with 232Th/230Th atomic ratios greater than this crustal average may indicate 232Th mineralization/contamination and those with 232Th/ 230Th atomic ratios less than this value may indicate mineralization/contamination with daughter-containing 238U. For samples containing 230Th and 238U in secular equilibrium, 232Th/230Th yields information which is in accordance with the Th/U mass ratio, which is readily measured. However, 232Th/230Th is decoupled from Th/U mass ratios in contamination settings where chemically purified, daughter-devoid U is added. Thorium isotopic measurements can specifically distinguish daughter-containing U contamination (mining wastes, ores, mill tailings) from contamination arising from chemically purified, 230Th-devoid U (e.g. commercial U chemicals, alloys, miltary uses of depleted uranium, nuclear fuels). Similar information may be garnered through comparing U concentrations vs radiometric U daughter content (e.g. 214Bi, radium-equivalent U); however, the requisite γ spectrometric measurements require long counting times of hours-days for low activity samples. We demonstrate herein that 232Th/230Th isotope ratios, which can be rapidly measured by inductively coupled plasma mass spectrometry (ICPMS), are readily applied to differentiate daughter-containing vs chemically purified sources of environmental U contamination in Ashtabula River sediments.
Methods Sampling Procedures. Sediment cores were collected using 3 m lengths of 19 mm i.d. copper tubing. The tubing was inserted and removed manually from the sediment horizon, using rigid steel pipe extension rods as necessary. With VOL. 34, NO. 6, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
967
practice, and under calm wind/water conditions, this technique could be successfully used from an unanchored water raft at water column depths of up to 10 m. Water depths ranging from 1 m (core 10) to 8 m (cores 24 and 51) were encountered in the AOC. Following collection, the overlying water column was carefully decanted from the sediment core tube, which was then capped at both ends. Sampling sites were located on a topographic map to within 25 m, using manmade features (buildings, bridges, etc.) as reference points. Sediment cores were extruded intact from the 19 mm copper tubes using a fiberglass rod and a compressed paper plunger. The resulting extruded cores produced compressed lengths of 0.75-1.5 m. Relatively uniform compactions of 40-50% were observed. The intact cores were sectioned into 2 or 4 cm increments using a stainless steel spatula, and wet/dry masses of each layer were recorded. Drying to constant mass was accomplished at 60 °C in an air oven. Due to core compression and the resulting uncertainty in the relationship between position in the compressed sediment core and in situ depth in the river sediment profile, and to correct for variations in sediment porosity, all sample depths are referenced on a cumulative overlying dry mass/crosssectional area basis (17). The dried sediments were disaggregated using a porcelain mortar and pestle. The Ashtabula River sediments consisted of homogeneous silt-clay materials of 21 days) for ingrowth of 226Ra daughters. The self-absorption correction of Cutshall et al. (18) was used for measurements of the lowenergy 210Pb photon. All measured activities were additionally corrected for background, detector and geometry efficiencies, branching ratios, and decay. NIST Columbia River Sediment (SRM 4350B) was used as a quality control sample for 137Cs measurements.
Results and Discussion Elemental Constituents in Ashtabula River Sediments. Uranium-contaminated sediments were found along a 1.5 968
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 6, 2000
TABLE 1. Summary of Parameters from Sediment Core 10, Representative of Local Backgrounda parameter 238U/235U
Zr Nb Hf Ta W Th U Th/U 232Th/230Thc
results (av ( SD)
crustal avb
138.7 ( 0.6 350 ( 100 ppm 17 ( 2 9(2 1.8 ( 0.5 4.5 ( 0.8 10 ( 1 3.0 ( 0.3 3.3 ( 0.4 180 000 ( 10 000
137.88 165 ppm 20 3 2 4.5 7.2 1.8 4.0 140 000-200 000d
a
Concentrations are averages from 18 individual 2 cm horizons; is the average of a composite of five 2 cm horizons. b Concentrations are from ref 24; the crustal 238U/235U is from ref 3. c Average of results from three different 2 cm horizons. d Results for North American continental sediments derived from refs 14-16. 238U/235U
km portion of the Ashtabula River extending from about 200 m upstream of the Fields Brook confluence to approximately the location of the 5th St. Bridge (Figure 1). Sediment core 10, obtained from the Ashtabula River approximately 0.5 km upstream of the Fields Brook confluence is considered to represent uncontaminated sediment. The concentrations of U and other elemental constituents in core 10 resembled average crustal abundance (Table 1), and the U isotopic composition is analytically undistinguishable from that of natural U. No systematic depthwise variations in the concentration of U and/or other constituents were detected. Elevated U concentrations (vs core 10) were not detected in eight coring locations in the Ashtabula River and harbor area north of the 5th Street Bridge (Figure 1). The U.S. Army Corps of Engineers has triennially dredged the river and harbor north of the 5th St. Bridge to maintain commercial access, so it seems likely that most U-contaminated sediments were previously removed from these areas. Similar vertical profiles of U concentration are observed in five cores (cores 17, 24, 45, 47, and 51) from the contaminated portion of the Ashtabula River (refer to Figures 2 and 3). Each core indicates that the most recently deposited material is of relatively low (< 10 ppm) U content. Nearbackground concentrations are typically present at depth (cores 17, 47, and 51). At least one distinctly elevated U horizon, representing concentrations > 30 ppm, is present in each of the five cores. Correlation of contaminated horizons between sites is complicated by probable nonuniform rates of deposition and differences in the degree of sediment disturbance. Figure 3 demonstrates that horizons with elevated U concentrations also contain elevated concentrations of several associated elements which are strongly correlated with U (r > 0.8, p < 0.0001). Uranium concentrations are most strongly correlated with Nb and Ta (r > 0.9, p < 0.0001). Additional ICPMS results also revealed significant positive correlations of U with Ti, V, Cr, Sn, Ba, and Pb. These findings suggest a similar source of U and several other elements, but a coincidental association cannot be ruled out. 137Cs and 210Pb Core Chronology. The depositional age of the U-rich horizon in core 47 was estimated using 137Cs chronology (19). During the years of atmospheric nuclear weapons testing, atmospheric deposition of 137Cs reached a maximum in the period about 1963. The 137Cs activity profile (Figure 4) exhibits a broad maximum ascribable to that time period. Comparison of the U and 137Cs profiles of core 47 indicates that the U maximum occurs at a shallower depth (i.e., post-dates) the 137Cs peak indicating that the most pronounced U accumulation has taken place since 1963. An independent attempt at dating via the 210Pb profile (20) was also made, as is shown in Figure 4. This method
FIGURE 2. 238U/235U and uranium concentration profiles for sediment cores 17, 24, 45, and 47 obtained from the Ashtabula River AOC. Uncertainties for 238U/235U are typically 0.5% relative (see text and Supporting Information). requires that excess (i.e., unsupported by 226Ra) 210Pb activity originating from atmospheric deposition of 222Rn daughters decrease exponentially downcore. However, the characteristic downcore decrease in 210Pb activity was not evident. Similar profiles for Ashtabula River sediments have recently been found by others (21). Although there are several possible explanations for the apparent absence of excess 210Pb in the surficial sediments, such as deep resuspension and nondeposition, the most likely explanation is that the entire 210Pb profile is dominated by supported 210Pb. There are several lines of evidence to support this explanation. The total 210Pb profile closely corresponds to the U concentration profile. This indicates that nearly all of the 210Pb is 238U supported and therefore also 226Ra supported. This is significant, because it suggests that the U contamination is daughter-bearing and contains 210Pb in approximate secular equilibrium. This finding has implications regarding sources of the U contamination. Also, cores collected upstream of Fields Brook as well as from other, similar tributaries display “normal” (i.e. decreasing downcore) 210Pb profiles (21). This suggests that the sedimentation environment in the Ashtabula River
is not unique and that there are other controls, such as source composition, that generate uniform 210Pb profiles found at the contaminated sites in the Ashtabula River. The nonnatural 238U/235U ratios strongly suggest that the RMI Titanium facility is a contributor to the sediment contamination. The sediment horizons contaminated with U of nonnatural isotopic composition appear to post-date initiation of uranium metal extrusion at RMI in 1962. Depthwise changes in 238U/235U could be explained by variation in the isotopic composition of U metal feedstock used for extrusion at RMI. Over its operational history, the RMI plant processed U metal consisting of 0.2-1.25% 235U. Additional studies of several selected horizons containing material revealed that small amounts of 236U were also present. This isotope is absent in natural uranium but is found in small amounts in “reprocessed” uranium recovered from spent reactor fuels. 236U abundances of up to 0.008% were found in core 2 samples from the Fields Brook outlet area; spectra demonstrating the presence of this isotope are given in the Supporting Information (Figure S-1).
235U-enriched
VOL. 34, NO. 6, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
969
FIGURE 3. Constituent concentration profiles for sediment core 51 from the Ashtabula River AOC. The top horizons of core 51 (0-20 g/cm2) consist of uncontaminated material which resembles local background (core 10) in terms of Th/U and constituent concentrations.
FIGURE 4. Activity profiles for
238U, 210Pb, 137Cs,
and 40K in the Ashtabula River, core 47.
Uranium contamination has entered the Ashtabula River via Fields Brook; one preliminary core (core 2) obtained from Fields Brook about 100 m upstream of the Ashtabula River confluence exhibited horizons containing up to 97 ppm uranium of 235U-enriched composition (238U/235U range 128134). More detailed sampling of the lower Fields Brook area was not attempted, as the sediments in this area are highly disturbed as a result of remediation activities. Sources of U Based Upon 232Th/230Th. The 232Th/230Th atom ratio can be used to distinguish between two possible site-specific scenarios for U contamination: (I) anthropogenic U is derived solely from discharges from RMI and (II) anthropogenic U is derived from RMI and one or more additional, anthropogenic, 230Th-bearing U source(s). Under scenario I, anthropogenic U would be devoid of long-lived daughters such as 230Th, 226Ra, and 210Pb, as these were absent in the chemically purified U metal used at RMI. Evidence for the absence of supported 226Ra in RMI’s discharges is provided 970
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 6, 2000
by an aeroradiometric survey of the RMI plant and environs performed by DOE in 1985 (9). Scenario I requires that the sediment 232Th/230Th is controlled by the core 10 (i.e., background) sediment Th and U concentrations of 10 ( 1 and 3.0 ( 0.3 ppm, respectively. A background 232Th/230Th atom ratio of 200 000 ( 30 000 in core 10 is calculated based on its U and Th concentrations and assuming approximate secular equilibrium between 230Th and 238U. Under scenario I, 232Th/230Th ratios in U-contaminated cores would be similar to core 10, as no 230Th is added from RMI’s discharges. Scenario II permits additional sources of U to contribute 230Th that could produce 232Th/230Th atom ratios of less than 200 000. Table 2 presents 232Th/230Th data for six selected Uelevated sediment horizons from the Ashtabula River. In all samples the 232Th/230Th atom ratio is significantly lower than the range expected based upon core 10. Some additional sources of 230Th (per scenario II) are indicated. The 232Th/
TABLE 2. 232Th/230Th in Uranium-Rich Sediment Horizons the Ashtabula River AOC core depth (g/cm2) U (ppm) Th (ppm) 17 17 18b 18 24 24
65.6 63.5 45.6 43.1 45.8 30.1
33 29 40 35 29 24
30 32 35 45 19 24
232Th/230Th
53 000 ( 2000 (n ) 5)a 72 000 ( 3000 (n ) 7) 52 000 ( 2000 (n ) 7) 79 000 ( 2000 (n ) 7) 44 000 ( 2000 (n ) 7) 59 000 ( 3000 (n ) 7)
a Uncertainties represent (2 SE of the mean; n refers to the number of mass spectrometric measurements. b Core 18 (samples 18-F and 18-H) was obtained from the Ashtabula River between cores 17 and 24.
230
Th atom ratios (converted into activity ratios using specific activities), along with U and Th concentrations can be used to estimate the sediment 230Th/238U activity ratio. This estimation suggests in all cases that the 230Th/238U activity ratio is close to unity; a large portion of the anthropogenic 238 U is therefore associated with supported 230Th. Consistent with this result is the finding (Figure 4) that 210Pb is present at approximately 238U-supported levels in core 47. The majority of 238U is accompanied by a full complement of 230Th and other daughters and thus cannot be derived from a daughter-free source such as RMI. Additional Source(s) of Anthropogenic Uranium. Our findings indicate the presence of a uranium source which also contains 230Th and 210Pb. Most of the U added to sediments is of natural 238U/235U composition and exhibits approximate secular equilibrium throughout the 238U decay series. The development of secular equilibrium takes place in a closed system over a geologic time scale, and this suggests that the U is contained in unweathered rock/mineral material. The association of U with Zr, Nb, Hf, Ta, and W (Figure 3) suggests a mutual geochemical relationship among these elements. The present observations are most consistent with Millenium Inorganic Chemical’s TiO2 plant as being the additional anthropogenic U source. The specific U-containing host phases have not been identified, and this effort is the subject of ongoing studies; however, preliminary work indicates that the great majority (>90%) of the U from highly contaminated sediment horizons can be dissolved by leaching with nitric acid. Apportionment of Noncrustal Uranium. The U and Th isotopic data can potentially be used to apportion anthropogenic (noncrustal) U between RMI and ilmenite processing contributions for specific sediment horizons. One method involves using 235U abundances, along with U concentrations:
Abun235,mix ) [0.007 200(Ubkg + Uilmenite) + UrmiAbun235,rmi]/Utotal (1) Utotal ) Ubkg + Uilmenite + Urmi
(2)
In eqs 1 and 2, Abun235,mix and Abun235,rmi represent the 235U abundances of the sediment and RMI’s releases, respectively; 0.007 200 is the naturally occurring 235U abundance of background and ilmenite-associated U; Utotal, Ubkg, Uilmenite, and Urmi represent total and source-derived concentrations. Equations 1 and 2 may be solved for Uilmenite and Urmi if one assumes the following: (a) Ubkg is known (i.e., 3.0 ( 0.3 ppm, Table 1); (b) variations in 234U abundances are not significant (Abun234 ) 0.000 055); and (c) Abun235,rmi is known. An example of this calculation for a core 24 sediment horizon (depth ) 45.8 g/cm2; Utotal ) 29 ppm, Abun235,mix ) 0.007 575) yields Urmi of 2-5 ppm for various assumed Abun235,rmi of 0.009 43-0.0123 (refer to Introduction and ref 2). The precise definition of Abun235,rmi for each sediment horizon represents the difficulty with this approach, since RMI previously utilized
U metal feedstocks of varying isotopic compositions, and a detailed historical account is not available in the public domain. A second method of apportioning Uilmenite vs Urmi in a specific sediment horizon is based upon the measured 230Th/ 238U activity ratio, A 230/A238:
A230/A238 ) (A230,bkg + A230,ilm)/(A238,bkg + A238,ilm + A238,rmi) (3) This method assumes that RMI contributes 238U but no 230Th and that the Uilmenite contribution contains 230Th in secular equilibrium with 238U. The values of A230,bkg and A238,bkg are 0.044 and 0.037 Bq/g (from data of Table 1); A230/A238 and (A230,bkg + A230,ilm) are determined from 232Th/230Th, Thtotal, and Utotal. After eliminating A238,ilm as an independent term (i.e., A230,ilm ) A238,ilm assuming secular equilibrium from this source), eq 3 can be solved for A238,rmi. Using the same core 24 sediment horizon referred to in the previous method (depth ) 45.8 g/cm2; Utotal ) 29 ppm, Thtotal ) 19 ppm, 232Th/ 230Th ) 44 000), an A 238,rmi corresponding to Urmi ∼ 3 ppm is obtained. These two apportionment methods demonstrate that quantitative discrimination between two anthropogenic U sources is possible, provided that the underlying assumptions can be reasonably satisfied. Moreover, the examples given above amplify our contentions that the vast majority of the anthropogenic U is from the non-RMI source. Implications for Abatement and Sediment Treatment/ Disposal. Cleanup efforts of EPA and collaborators in the Ashtabula River AOC will require dredging of contaminated sediments from the Ashtabula River followed by treatment/ disposal (22). Chlorinated organic compounds and the elements Cd, Cr, Hg, and As are the chief contaminants which have been considered. The results of this study indicate that additional considerations exist regarding above-background sediment concentrations of radionuclides in portions of the Ashtabula River. The chief radiologic hazard is derived from 238U and daughters such as 226Ra. Natural U concentrations in dry sediment exceed the Nuclear Regulatory Commission’s Free Release Guidelines (23) of 30 pCi/g (44 ppm). Moreover, risk management and treatment considerations applicable solely to uranium contamination are inadequate as the daughters 230Th and 210Pb have been identified at supported levels. Therefore, other hazardous 238U-series nuclides such as 226Ra and 210Po are also present at above-background levels in Ashtabula River sediments. A 1.5 km portion of the Ashtabula River AOC has been impacted by post-1964 releases from two distinct sources of anthropogenic U: RMI Titanium is the source of U metal of nonnatural 238U/235U composition, and Millenium Chemicals is the likely source of accessory minerals containing U of natural isotopic composition as well as 238U-series daughters. Recent sedimentation in the Ashtabula River displays nearbackground concentrations of U and associated elements, indicating that contaminated materials are now overlain by less contaminated material. The existence of unusual horizons of anthropogenic uranium, associated daughters, and concomitant trace elements represents a unique opportunity to evaluate the fate and transport of other known contaminants in this watershed. The resuspension and dispersion of contaminated sediments during planned remediation activities may potentially be monitored using the radionuclide markers which have been described in this study. The elemental and isotopic signatures of Ashtabula River sediments may also afford a mechanism of tracing recent sediment deposition into Lake Erie’s eastern basin from this specific point source location. The ICPMS technique can rapidly provide U and Th isotopic measurements of suitable precision for similar VOL. 34, NO. 6, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
971
investigations at other sites. These settings include locations where past uses of enriched or depleted U have occurred. Thorium isotopes, along with 230Th/238U activity measurements, are expected to be of use in many settings where releases of “naturally occurring radioactive material” (NORM) have taken place.
Acknowledgments The ICPMS instrument at JCU is a donation of Van Waters & Rogers Corp., which the authors gratefully acknowledge. Laboratory and field work were supported by the authors’ institutions. W.C.W. acknowledges Summer 1997 salary support from BP America, Inc. The use of P. McGannon’s watercraft in harbor sampling is appreciated. The authors acknowledge C. J. Khourey and P. L. McCall for helpful discussions and suggestions. The authors also thank R. P. Van Camp and E. R. Christensen for sharing their recent unpublished 210Pb results in the Ashtabula River.
Supporting Information Available Experimental details, table of radionuclides measured in environmental samples and laboratory standards, and figures of Th-U ICP mass spectra illustrating identification of 236U and Th isotopes and a multiple box-and-whisker plot depicting 238U/235U (11 pages). This material is available free of charge via the Internet at http://pubs.acs.org.
Literature Cited (1) U.S. EPA. 40 CFR Part 300, Appendix B, 1997. (2) RMI Environmental Services. Environmental Report for Decommissioning Activities at the RMI Titanium Company Extrusion Plant; Document Number RDP-ESH-009; RMI Environmental Services: Ashtabula, OH, 1995. (3) Cowan, G. A.; Adler, H. H. Geochim. Cosmochim. Acta 1976, 40, 1487-1490. (4) Brooks, M. D.; Arredondo, L. Petitioned Public Health Assessment, Fields Brook NPL Site, Specifically Concerning Radiological Contaminants at RMI Titanium Company, Ashtabula, Ashtabula Co., OH; Agency for Toxic Substances and Disease Registry: Atlanta, GA, 1991.
972
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 6, 2000
(5) U.S. DOE. Historical Radionuclide Releases from Current DOE Oak Ridge Operations Office Facilities; Publication OR-890; U.S. DOE Oak Ridge Operations Office: 1988. (6) Force, E. R. Geology of Titanium-Mineral Deposits; Geological Society of America Special Paper 259; GSA: Boulder, CO, 1991. (7) Handbook of Geochemistry; Wedepohl, K. H., Ed.; SpringerVerlag: Berlin, 1969; Vol. II, Part 5, Chapter 92: Uranium. (8) U.S. EPA, Region V, Office of Public Affairs. Project Update: Fields Brook Superfund Site, November 1998. (9) Hoover, R. A. An Aerial Radiological Survey of the RMI Facility and Surrounding Area, Ashtabula, OH; EGG-10282-1107; EG&G Energy Measurements: 1986. (10) Liator, M. I. J. Environ. Qual. 1995, 24, 314-323. (11) Batson, V. L.; Bertsch, P. M.; Herbert, B. E. J. Environ. Qual. 1996, 25, 1129-1137. (12) Rose, A. W.; Keith, M. L. J. Geochem. Explor. 1976, 6, 119-137. (13) Uranium-Series Disequilibrium: Applications to Earth, Marine, and Environmental Sciences, 2nd ed.; Ivanovich, M., Harmon, R. S., Eds.; Clarendon Press: Oxford, U.K., 1992. (14) Noakes, J. E.; Supernaw, I. R.; Akers, L. K. J. Geophys. Res. 1967, 72, 2679-2682. (15) Moore, W. S. Earth Planet. Sci. Lett. 1967, 2, 231-234. (16) Scott, M. R. Earth Planet. Sci. Lett. 1968, 4, 245-252. (17) McCall, P. L.; Robbins, J. A.; Matisoff, G. Chem. Geol. 1984, 44, 33-65. (18) Cutshall, N. H.; Larsen, I. L.; Olsen, C. R. Nucl. Instr. Meth. 1983, 206, 309-312. (19) Ritchie, J. C.; McHenry, J. R. J. Environ. Qual. 1990, 19, 215233. (20) Robbins, J. A.; Edgington, D. N. Geochim. Cosmochim. Acta 1975, 39, 285-304. (21) Van Camp, R. P.; Christensen, E. R. private communication. (22) US Nuclear Regulatory Commission. Status of Efforts to Finalize Regulations for Radiological Criteria for License Termination: Uranium Recovery Facilities, Report SECY-98-084, NRC, 1998. (23) Ashtabula River Partnership. Environmental Impact Statement/ Comprehensive Management Plan; September 10, 1999. (24) Mason, B. Principles of Geochemistry, 3rd ed.; John Wiley & Sons: New York, 1966.
Received for review December 16, 1998. Revised manuscript received December 20, 1999. Accepted December 23, 1999. ES981314D
