Lead geochemistry of sediments in Galveston Bay, Texas

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The geochemical behavior of Pb in terrestrial and coastal water systems significantly influences Pb biogeochemical cycling and pollutant exchange at the land-sea continuum. An ideal case study of Pb environmental geochemistry is Galveston Bay, an anthropogenic estuary exposed to industrial runoff, wastewater and shipping vessel spills but also fed by natural rivers.

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Nội dung Text: Lead geochemistry of sediments in Galveston Bay, Texas

Environmental Advances 4 (2021) 100057 Contents lists available at ScienceDirect Environmental Advances journal homepage: www.elsevier.com/locate/envadv Lead geochemistry of sediments in Galveston Bay, Texas Amanda M. Lopez a,∗, Alan D. Brandon a, Frank C. Ramos b, Jessica N. Fitzsimmons c, Timothy M. Dellapenna d, Hannah M. Adams c a 3507 Cullen Boulevard, Room 312 Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77004 USA b 1255 N. Horseshoe Drive MSC3AB Department of Geological Sciences, New Mexico State University Las Cruces, NM 88003 USA c 3146 TAMU, O&M 403A Department of Oceanography, Texas A&M University, College Station, TX 77843 USA d 1001 Texas Clipper Rd Bldg 3029, Oﬃce 341 Department of Marine Sciences/Department of Oceanography, Texas A&M University at Galveston, Galveston, TX 77553 USA a r t i c l e i n f o a b s t r a c t Keywords: The geochemical behavior of Pb in terrestrial and coastal water systems signiﬁcantly inﬂuences Pb biogeochemi- Marine biogeochemistry cal cycling and pollutant exchange at the land-sea continuum. An ideal case study of Pb environmental geochem- Lead isotope ﬁngerprinting istry is Galveston Bay, an anthropogenic estuary exposed to industrial runoﬀ, wastewater and shipping vessel spills but also fed by natural rivers. Here, sediments from Galveston Bay were measured for Pb isotope ratios and abundances to constrain Pb sources and ﬂuxes and understand Pb pollution history in the bay. Lead isotopes have been established as source tracers of environmental pollution and allow Pb sources to be reliably ﬁngerprinted and identiﬁed. Sediments were leached to distinguish authigenic sediment coatings from lithogenic residual sedi- ments, in addition to bulk sediment digestions. Total Pb concentrations ranged from 1.76 μg/g–29.19 μg/g in bulk digests, which are below federal toxicity thresholds and aligns well with prior measurements of Pb in Galveston Bay sediments in the 20th century. Lead concentrations are spatially constrained by ﬂocculation in eastern bay ar- eas where the Trinity River enters the bay and positively temporally correlated to freshwater discharge. Sediment 206 Pb/204 Pb, 207 Pb/204 Pb, and 208 Pb/204 Pb ratios range between 18.338–19.777±0.002, 15.557–15.755±0.002 and 37.913–43.340±0.005, respectively, and were used in an advanced Bayesian isotope mixing model to iden- tify Pb sources in the Galveston Bay sediment fractions analyzed. Anthropogenic sources supply approximately 83.8%, 16.6% and 25.5% of Pb to the leachates, residues and bulk sediments, respectively. This study showcases the importance of estuaries in moderating terrestrial and marine Pb distribution and provides insight for future contaminant studies in Galveston Bay and other estuarine systems around the world. MAIN FINDINGS Pb isotope ratio and abundance measurements of Galveston Bay sediments demonstrate signiﬁcant anthropogenic Pb inputs to the estuary despite low Pb levels. Introduction water column, and the biota (Turner and Millward, 2002). Previous studies demonstrate that aqueous Pb is largely scavenged by particles The biogeochemical cycle of lead (Pb) has been greatly inﬂuenced by and removed to sediments (Elbaz-Poulichet et al., 1984; Ip et al., 2007; humans such that up to 95% of Pb in the biosphere is estimated to be an- Marsan et al., 2014). In this way, Pb and other particle-reactive heavy thropogenic (Smith and Flegal, 1995). Once emitted, Pb can persist and metals are “naturally ﬁltered” out of water systems before reaching the accumulate in the natural environment (Wright and Welbourn, 2002). ocean. Lead in sediments accrue; thus, sediment cores become records Eﬀects of Pb exposure include a variety of detrimental health issues, of Pb loadings at a given location over time. most notably neurotoxicity (Tchounwou et al., 2012). Lead geochem- Datasets constraining Pb ﬂuxes, abundances, sources and mobility istry of rivers and coastal environments plays a signiﬁcant role in the between sources and sinks are necessary to improve the understanding biogeochemical cycling of Pb and pollutant delivery at the land-sea in- of Pb biogeochemical cycles and their application to pollution manage- terface. In aqueous environments, processes such as desorption, dissolu- ment in coastal environments worldwide (Lester and Gonzalez, 2011; tion, resuspension, precipitation, ﬂocculation, deposition, and biotrans- Morse et al., 1993; Rauch and Pacyna, 2009). While knowledge of Pb formation allow Pb to be exchanged between bottom sediments, the concentrations is important for understanding toxicity, concentration data alone are often insuﬃcient to distinguish pollutant sources. Lead ∗ Corresponding auhtor. E-mail addresses: amlopez@uh.edu (A.M. Lopez), abrandon@uh.edu (A.D. Brandon), framos@nmsu.edu (F.C. Ramos), jessﬁtz@tamu.edu (J.N. Fitzsimmons), dellapet@tamug.edu (T.M. Dellapenna), hadams@uscd.edu (H.M. Adams). https://doi.org/10.1016/j.envadv.2021.100057 Received 31 March 2021; Received in revised form 13 April 2021; Accepted 14 April 2021 2666-7657/© 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
A.M. Lopez, A.D. Brandon, F.C. Ramos et al. Environmental Advances 4 (2021) 100057 isotopic compositions of environmental samples reﬂect the isotope sig- fractions of surface and core sediments, with an emphasis on readily natures of their respective Pb sources. Thus, each Pb source possesses exchangeable surface-adsorbed Pb, which as most labile would be most a unique isotopic composition or “ﬁngerprint” by which it can be iden- harmful to the coastal ecosystem. tiﬁed. Accordingly, Pb isotopes have been used to identify Pb sources and trace Pb pollution pathways in water systems (Garcon et al., 2012; Materials and methods Komarek et al., 2008; Marcantonio et al., 2000). Here, Pb concentrations and isotope signatures are used to constrain the sources and cycling of Galveston Bay surface sediment samples were acquired on 11 ship- Pb in Galveston Bay, an idealized study site of Pb environmental geo- board expeditions on the R/Vs Lithos and Trident from June 2017 to chemistry due to its strong anthropogenic inﬂuence within the natural June 2019 (Fig.1, black). A Van Veen grab sampler was used to col- “ﬁltration system” of an estuary. lect the upper 18.2 MΩ cm were used by human activity, making it an ideal location to study how an estuar- during sample processing and analysis. ine system “naturally ﬁlters” anthropogenic Pb from the environment Sediment samples were leached using 0.02 M hydroxylamine hy- (Harmon et al., 2003). The Galveston Bay watershed drains largely ur- drochloride (HH, Fisher Scientiﬁc) in 25% CH3 COOH (Optima, Fisher banized areas surrounding Houston and Dallas-Fort Worth (Morse et al., Scientiﬁc) to extract surface exchangeable and Fe-Mn bound fractions 1993). The Houston Ship Channel (HSC), an extension of the Port of from the residual fraction (Basak et al., 2011; Berger et al., 2008; Houston, is situated within the estuary and contains ∼30-50% of all Gutjahr et al., 2007; Wilson et al., 2013). Each sample leachate was petrochemical facilities in the US (Santschi et al., 2001). Pb may enter volumetrically split in half making an aliquot for concentration analysis the bay via atmospheric deposition, industrial runoﬀ, improper disposal and an aliquot for Pb isotope ratio measurements. Residues remaining of contaminants at industrial facilities, shipping vessel oil, and chemi- after the leach were digested in three steps using a 2:1 mixture of con- cal leaks. Between 1966–1979, the HSC was deemed one of the most centrated HF (Optima, Fisher Scientiﬁc) and concentrated HNO3 (trace polluted waterways in the country. Since then concerted eﬀorts have metal grade twice distilled, Fisher Scientiﬁc), concentrated HCl (trace been underway to clean up the HSC and greater Galveston Bay (Lester metal grade once distilled, Fisher Scientiﬁc), and 2N HCl. During each and Gonzalez, 2011; US Environmental Protection Agency, 1980). De- step, the residues were digested on a 120–160 °C hot plate for a min- spite these changes, pollutant discharges into the bay continue, since imum of one hour and then taken to dryness. After each residue was enormous quantities of chemicals and oil are transported across the bay dissolved in 2N HCl, half of each solution was pipetted into a new, and processed by industry along the Galveston Bay coastline annually acid-cleaned Savillex vial, creating two residue subsamples. The two (Saleh and Wilson, 1999; Santschi et al., 2001). residue subsamples were then dried and separately processed for Pb Here, a quarterly time-series of Pb concentrations and isotope ratios isotope and heavy metal concentration analyses. Bulk sediment sample in Galveston Bay sediments during 2017–2019 is presented, with the digestions were also performed, in which 10 mg of dried, homogenized goal of identifying Pb sources and constraining source mixing within sediment was digested following the same digestion procedure as the this anthropogenic estuary. This time-series resolves the controls on the residues. Procedural blanks and standard reference materials were pre- spatial variability of Pb concentrations across Galveston Bay sediments pared alongside all samples. from bay waters, the rim of the bay, and source waters entering the Leachate, residue and bulk concentration aliquots were dissolved in bay, and it also resolves the controls on the seasonality of sedimentary 3 mL 0.45N HNO3 spiked to 1 nanogram per gram indium (In), then vol- Pb loadings. Importantly, this study’s use of Pb isotope measurements to umetrically diluted by a factor of 100 with the same In-spiked HNO3 so- assign Pb sources brings state-of-the-art geochemical modeling into en- lution, and then analyzed for Pb abundances on a ThermoFisher Element vironmental use. Finally, this study assesses Pb across several sediment XR high resolution inductively coupled mass spectrometer (ICPMS) at 2
A.M. Lopez, A.D. Brandon, F.C. Ramos et al. Environmental Advances 4 (2021) 100057 Fig. 1. Study area map showing surface and core sediment locations. Black labels designate surface sediment samples collected during TAMU Galveston Bay cruises. Red labels indicate surface sediment samples that were hand collected from the Galveston Bay shoreline. The dark blue label shows the E3 sediment core location. Five of the main freshwater inﬂows to Galveston Bay (Trinity River, San Jacinto River, Buﬀalo Bayou, Dickinson Bayou and Oyster Bayou) are labeled for reference. Diﬀerent areas with Galveston Bay including Trinity Bay, West Bay and East Bay are noted for reference. the R. Ken Williams Radiogenic Isotope Laboratory at Texas A&M Uni- by the highest Pb concentrations in this study (26.3 μg/g, 21.0 μg/g, versity. Lead was assessed in low resolution and quantiﬁed using 9-point and 29.2 μg/g respectively; Fig. 2). standard curves bracketing the natural concentration range. Anion ex- The Pb mass balances of leachate ± residue = bulk digest (± 5 μg/g) change chromatography using AG1 × 8 200–400 mesh and HBr columns are consistent for 93% of samples; the eight exceptions are Station 5 were used to purify Pb for isotopic measurements (Chen et al., 2016; June 2018, Station 13 September 2018, Station 402, Station GB2, and Marcantonio et al., 2000; Sun et al., 2011). Samples were dissolved in E3 core subsamples E3-5, E3-6, E3-9, E3-19. Leachable Pb, comprising 0.45N HNO3, spiked with the National Institute of Standards thallium surface-exchangeable and Fe-Mn oxide-bound phases, ranges between isotope standard reference material NBS 997 and then measured for 8.6–98.7% (mean±SD of 29.5±0.12%) of total Pb in the sediments. The Pb isotope ratios using a Neptune Plus high-resolution multi-collector only exception is the September 2018 Station 13 data point for which the ICPMS at the Johnson Mass Spectrometry Laboratory at New Mexico Pb concentration is higher in the leachate fraction (2.8 μg/g) than in the State University. Blank Pb concentrations were less than 1% of the sed- bulk digest (1.9 μg/g), likely reﬂecting leachate sample contamination. iment sample Pb concentrations. Additional data quality information is Additional discussion of Pb mass balance is provided in the SM. provided in the SM. Leachate Pb isotope ratios in surface sediments (shoreline, bay and endmember) are 206 Pb/204 Pb = 18.417–19.523±0.004, 207 Pb/ 204 Pb = 15.567–15.778±0.003, and 208 Pb/204 Pb = 38.432–38.952± Results 0.008. Surface sediment residues 206 Pb/204 Pb, 207 Pb/204 Pb, and 208 Pb/204 Pb ratios range between 18.380–19.731±0.002, 15.601– Galveston Bay sediment Pb isotope ratios and concentrations deter- 15.721±0.002, and 37.919–40.704±0.005, respectively. Bulk sur- mined in this study are tabulated in SM Table S1. Lead concentrations face sediments have 206 Pb/204 Pb between 18.338–19.777±0.001, range from 1.8–29.2 micrograms per gram (μg/g) in bulk sediment di- 207 Pb/204 Pb between 15.598–15.755±0.001, and 208 Pb/204 Pb between gests for bay, shoreline, and endmember stations, with concentrations of 37.913–43.340±0.003. The E3 core sediment leachates have Pb iso- 1.9–16.8 μg/g, 1.8 – 15.8 μg/g and 2.3 – 29.2 μg/g, respectively (Fig. 2). tope compositions of 206 Pb/204 Pb between 18.956–19.211±0.004, In the E3 core, Pb concentrations are between 1.9–14.0 μg/g in the 207 Pb/204 Pb between 15.557–15.656±0.003, and 208 Pb/204 Pb between leachates, 5.0–22.5 μg/g in the residues, and 8.9–18.0 μg/g in the bulk 38.652–38.976± 0.007. The E3 core residue Pb isotope ratios are sediments (Fig. 3). Aside from stations 202, 203 and 402, Pb concentra- 206 Pb/204 Pb = 19.018–19.309±0.002, 207 Pb/204 Pb = 15.653–15.684± tions at the bay, shoreline, and endmember stations are within 15 μg/g 0.002, and 208 Pb/204 Pb = 38.804–39.415±0.004. The E3 core bulk sedi- of each other. Endmember Stations 202, 203, and 402 are characterized 3
A.M. Lopez, A.D. Brandon, F.C. Ramos et al. Environmental Advances 4 (2021) 100057 Fig. 2. Spatial and temporal variation of Galveston Bay bulk sediment Pb concentrations. The x-axis shows temporal variation in bulk sediment Pb concentrations. Bay stations were sampled multiple times, all other stations were sampled once. Colors distinguish the geographically diﬀerent bay, shoreline, endmember and E3 core samples. Among bay samples, circles indicate stations located to the east of the HSC and triangles denote stations located to the west of the HSC. The NOAA Pb T20 limit is shown for reference. ments 206 Pb/204 Pb, 207 Pb/204 Pb, and 208 Pb/204 Pb ratios range between Bay, and so the northeast corner of Galveston Bay carries the low- 19.001–19.313±0.002, 15.649–15.681±0.001, and 38.807–39.468± est salinity (Guthrie et al., 2012). Critically, high riverine concentra- 0.003, respectively. Weak linear correlations (R2
A.M. Lopez, A.D. Brandon, F.C. Ramos et al. Environmental Advances 4 (2021) 100057 Fig. 3. E3 core sediment Pb concentra- tions and 206 Pb/204 Pb ratios through time. dry conditions prevailed in the November 2017, June 2018, and Septem- Pb isotope composition spatial variations ber 2018 sampling events and wet conditions were dominant in the remaining sampling campaigns (SM Table S2). Hurricane Harvey de- Sediment leachates in lower Galveston Bay (Stations 1-5, 10-11, posited record-breaking rainfall totals over Texas from August 26-30, 14) have more radiogenic Pb isotope ratios than do those from up- 2017, which resulted in massive freshwater ﬂuxes through Galveston per Galveston Bay (Stations 7-9, 12-13) (Fig. 4). Lower bay sta- Bay that prohibited the typical ﬂocculation of dissolved metals (Steichen tion sediment leachates range from 208 Pb/204 Pb = 38.616±0.006 – et al., 2020; Wen et al., 1999). Consequently, the September 2017 bulk 38.952±0.009, while upper bay sediment leachates are less radiogenic sediment metal concentrations resemble samples collected during dry with values between 208 Pb/204 Pb = 38.569±0.005 – 38.778±0.006. conditions and are included in the dry condition category rather than Residue Pb isotope compositions are generally less radiogenic wet. than the leachates with the lower bay station residues between In the Trinity Bay E3 core, sediment Pb concentrations in the 208 Pb/204 Pb = 38.268±0.004 – 40.459±0.006 and upper bay sta- leachates, residues, and bulk sediments increase from the late 1800s tion residues between 208 Pb/204 Pb = 38.601±0.003 – 39.400±0.003 to the late 1990s and early 2000s (Fig. 3, excepting anomalous E3- (Fig. 4). Shoreline stations GB9-GB11 leachates showed the most dis- 19 subsample). All Pb concentrations then stabilize during the 2000s tinctly radiogenic Pb isotope ratios of all sample leachates, with through to present day to reach modern values (except the E3-5 and 206 Pb/204 Pb = 19.523 and 208 Pb/204 Pb = 38.710 at GB10, 208 Pb enrich- E3-6, roughly 1998–2002, residue Pb concentrations that do not reﬂect ment at GB9 (208 Pb/204 Pb of 40.704) and a very high 208 Pb/204 Pb of mass balance and are thus likely contaminated; thus, they are excluded 43.340 at GB11. from further discussion). Overall, the total sediment Pb concentrations Low concentration leachates from Trinity River endmember stations over the past 150 years agree with modern Galveston Bay concentra- 501, 502, and 503 do not diﬀer in Pb isotope compositions from the tions (Fig. 2) and collectively demonstrate an increase in Pb deposition other station leachates, indicating that the source of surface-adsorbed from industrialization to the 1990s. Notably, there has been a leveling Pb is the same in both the Trinity River and Galveston Bay sediments. oﬀ in Pb deposition since the 1990s, perhaps in alignment with the re- However, the residues and digests in Trinity River samples cluster at moval of leaded gasoline from US markets (Bollhofer and Rosman, 2001; less radiogenic values, with average 208 Pb/204 Pb values of 38.321 and Harmon et al., 2003; Morse et al., 1993; TCEQ, 2020; Wen et al. 2008). 38.045 compared to the average 208 Pb/204 Pb values of 38.909 and 5
A.M. Lopez, A.D. Brandon, F.C. Ramos et al. Environmental Advances 4 (2021) 100057 Fig. 4. Spatiotemporal variation in Galveston Bay surface sediment 208 Pb/204 Pb ratios in (a) sediment leachates and (b) sediment residues. Variations in bulk sediment 208 Pb/204 Pb ratios are shown in SM Fig. S2. Leachate Pb isotope ratios are more radiogenic (warmer colors) in lower Galveston Bay and less radiogenic (cooler colors) in upper Galveston Bay. The opposite spatial trend is seen in the residues. No clear temporal trend is seen in the Pb isotope compositions rather episodic Pb ﬂuxes evidenced by discrete shifts in Pb isotope ratios occur in September 2017 (leachates Stations 1 and 5), March 2018 (leachates Stations 13-14), September 2018 (residues Stations 3 and 14), and November 2018 (leachates Station 9). 6
A.M. Lopez, A.D. Brandon, F.C. Ramos et al. Environmental Advances 4 (2021) 100057 38.893 at other stations. Together with the low concentrations and low Pb toxicity % leachable Pb referenced above, these data indicate that the Trinity River supplies low quantities of “natural riverine Pb” to Galveston Bay NOAA Screening Quick Reference Tables provide T20 and T50 that are characterized by less radiogenic 208 Pb/204 Pb ratios in residues toxicity thresholds for Pb concentrations in marine sediment (low time-integrated U/Pb and low Th/Pb) compared to other bay (Buchman, 2008). The T20 and T50 values are the concentrations stations. of a given element that result in 20% and 50% of marine benthic life experiencing toxic mortality, respectively. The T20 Pb concentration is 30 μg/g and the T50 Pb concentration is 94 μg/g. None of the Pb isotope composition temporal variations study samples exceeded the NOAA thresholds (Fig. 2). By this metric Galveston Bay sediments are not toxic for Pb and do not deliver toxic In September 2017, Stations 1 and 5 leachates were more radio- levels of Pb into the Gulf of Mexico. This is particularly poignant for genic (206 Pb/204 Pb = 19.062 at Station 1 and 206Pb/204Pb = 19.138 the leachates, as these fractions represent the Pb that is most readily at Station 5) than the other time points (206 Pb/204 Pb < 19.050 at accessible to biota in Galveston Bay. Station 1, 206 Pb/204 Pb < 19.082 at Station 5). As noted above, Hur- ricane Harvey resulted in massive freshwater ﬂuxes through Galve- Galveston bay versus other estuaries ston Bay in late August 2017 (Steichen et al., 2020). A thick sed- iment layer was deposited across the bay following severe Har- The Galveston Bay surface sediment Pb concentrations are within the vey ﬂooding, which may have redistributed sediments at Stations lower end of the 5-767 μg/g range of reported sedimentary Pb concen- 1 and 5 more than under normal bay conditions resulting in the trations in rivers and other coastal areas in North America (e.g., Chesa- unique leachate Pb isotope ratios observed (Dellapenna et al., 2021 in peake Bay, Narragansett Bay, St. Lawrence Estuary), China (e.g., Pearl review). River Estuary, Yangtze River Estuary), Europe (e.g., Gironde Estuary), There are additional temporal variations in Pb isotope ratios that do and Australia (e.g., Botany Bay), where nearby industrial and urban de- not correspond with exceptional Pb concentrations, pointing to changes velopment exists (SM Table S3, Alyazichi et al., 2016; Bricker, 1996; in Pb source to the bay over time. These variations are located nearest to Chen et al., 2017; Elbaz-Poulichet et al., 1984; Gobeil et al., 1995; the freshwater sources that might be most susceptible to these varying Ip et al., 2007; Marcantonio et al., 2002; Millot et al., 2004; Zhang et al., Pb sources. For example, near the HSC the Station 13 and 14 leachate 2008). The highest Galveston Bay sediment Pb concentration (∼29 μg/g) Pb isotope ratios decrease from 206 Pb/204 Pb = 18.894 and 19.037 in is similar to or even lower than some of the lowest Pb concentrations ob- November 2017 to 206 Pb/204 Pb = 18.813 and 18.858 in March 2018, served in other estuaries, which is particularly impressive given the large which are the least radiogenic of all bay station data in the time-series. petrochemical footprint in the Galveston Bay watershed. This may result March 2018 was a wet period in the time-series (SM Table S2), which from low natural Pb input from the Trinity River and regulatory eﬀorts may have changed the sediment Pb supply to the HSC and/or the region to clean up Galveston Bay (Lester and Gonzalez, 2011; Warnken and of ﬂocculation driving these Pb distributions. Additionally, the bulk di- Santschi, 2009). Galveston Bay bulk sediments have Pb isotope ratios gest 208 Pb/204 Pb ratio at Station 13 in June 2018 is 39.280 and at Sta- most closely matching the Pb isotope compositions of coastal sediments tion 13 in March 2019 is 39.214 and at Station 14 in November 2018 in Bayou Trepagnier, the Mississippi River, and Chesapeake Bay, indi- is 39.350; all of these time points are enriched in 208 Pb compared to cating that Pb sources (Mississippi Valley Type (MVT) Pb ores, gaso- the other bulk sediments, which typically have 208 Pb/204 Pb < 39.066, line, coal) in these regions may be similar to those in the Galveston Bay again pointing to unique pulses of Pb through the HSC. On the Trinity (Marcantonio et al., 2000, 2002; Millot et al., 2004). River side, a similar pulse at Station 9 is observed as 206 Pb/204 Pb de- creases from 18.954 in November 2018 to 18.866 in March 2019, both Pb sources wet months, though November 2018 had particularly strong river dis- charge. Continental weathering of bedrocks contributes natural Pb to sed- Finally, the Texas City area appeared to push pulses of more ra- iments, while mining and reﬁning of Pb-bearing ores, which are sub- diogenic Pb toward nearby Stations 3 and 14 over time. For exam- sequently used for industrial Pb applications, supplies anthropogenic ple, the Station 3 and 14 residues in September 2018 are consider- Pb to the environment. Comparison of Galveston Bay sediment Pb iso- ably more radiogenic (206 Pb/204 Pb > 19.459, 208 Pb/204 Pb > 40.165) tope data from this study with literature identiﬁed Pb source isotope than the other bay station residues (206 Pb/204 Pb < 19.296, 208 Pb/204 Pb ratios reveals the presence of both natural and anthropogenic Pb in < 39.326) during this particularly dry sampling event, perhaps re- Galveston Bay (Fig. 5, SM and SM Table S4-S5). Atlantic marine sed- lated to inputs from nearby Texas City. Similarly, the bulk digest Pb iments and granitoids from the North American Cordillera, the White isotope compositions at Station 3 in September and November 2017 Creek batholith in the Southern Canadian Cordillera, and the southeast- are more radiogenic (average±standard deviation (SD) 208 Pb/204 Pb ern portion of the North American Craton in Texas and Mexico col- of 39.184±0.460) than other Station 3 measurements over time lectively serve as a proxy for the presence of naturally weathered de- (average±SD 208 Pb/204 Pb of 38.875±0.146) and point toward a Pb ﬂux trital Pb in Galveston Bay (Brandon and Lambert, 1993; Brandon and from the Texas City area that may have been exacerbated by Hurricane Smith, 1994; James and Henry, 1993; Kesler et al., 1994; Sun, 1980). Harvey. There are no Pb ore deposits in the Galveston Bay watershed, therefore The E3 core sediment leachates, residues, and bulk digests become Pb ore contributions to Galveston Bay sediments are considered anthro- less radiogenic from the mid-1940s to the present (Fig. 3). Temporal pogenic (Ulery et al., 1993; Ferring, 1990; Jones et al., 1972). Historic Pb concentration trends in E3 core sediments are mirrored in liter- US Pb smelting and reﬁning facilities, MVT ores and their use in US and ature studies of Galveston Bay cores and regulatory agency datasets, Central American gasoline, and North American coal are potential an- which leads to the following conclusions: 1) gasoline consumption and thropogenic Pb sources in Galveston Bay (Bollhofer and Rosman, 2001; industrial activity resulted in increased anthropogenic Pb emissions Chow and Earl, 1972; Rabinowitz, 2005; Stillwell et al., 2011; “Texas into Galveston Bay between the early and late 20th century, and 2) State Energy Proﬁle Overview”, U.S. Energy Information Administra- Pb concentrations in Galveston Bay have stabilized from the late 20th tion). Further details on diﬀerences in literature Pb isotope ratio datasets century into the 21st century, likely in response to reduced anthro- and Pb endmember source categorization as anthropogenic versus nat- pogenic emissions and regulatory eﬀorts (Al Mukaimi et al., 2018a; ural are given in the SM. Bollhofer and Rosman, 2001; Lester and Gonzalez, 2011; Santschi et al., MixSIAR is a software package that creates and implements Bayesian 2001; TCEQ, 2020). mixing models of Pb isotopes to estimate the proportions of source con- 7
A.M. Lopez, A.D. Brandon, F.C. Ramos et al. Environmental Advances 4 (2021) 100057 Fig. 5. Galveston Bay sediment and literature Pb source 206 Pb/204 Pb, 207 Pb/204 Pb and 208 Pb/204 Pb ratios in three-dimensional scatter plots, (a) leachates (b) residues (c) bulk sediments. Case numbers and corresponding sample IDs for outliers in the Pb isotope modeling are labeled. Literature Pb source isotope compositions are from Rabinowitz, 2005; Bollhofer and Rosman, 2001; Brandon and Smith, 1994; Kesler et al., 1994; Brandon and Lambert, 1993; James and Henry, 1993; Sun, 1980; Chow and Earl, 1972. tributions to a sample mixture (Stock et al., 2018). Data convergence is and 2.06451) and US Pb ores from the Eastern Tennessee mining dis- assessed using the Gelman-Rubin and Geweke diagnostics (Cowles and trict (average 207 Pb/206 Pb and 208 Pb/206 Pb of 0.80621 and 2.00840) in Carlin, 1996; Longman et al., 2018). All models presented here are con- 208 Pb/206 Pb versus 207 Pb/206 Pb space (Asmerom and Jacobsen, 1993; sidered converged. Model uncertainty is summarized at the 95% cred- Sangster et al., 2000; Zartman and Haines, 1988). The E3-7L point may ible interval. Further details regarding the MixSIAR model used in this reﬂect a discrete period in which gasoline made with Pb from the East- study are in the SM. The Pb sources shown in Fig. 5 were used in ern Tennessee mining district was used in the Houston-Galveston area, MixSIAR models to assess Pb sources to Galveston Bay. The Pb sources making it a discrete regional Pb source. The GB10L data point has and their estimated proportions in Galveston Bay sediment leachates, a distinctly radiogenic Pb isotope composition (206 Pb/204 Pb = 19.523, residues, and bulk sediments are tabulated in SM Table S5. 207 Pb/204 Pb = 15.699, 208 Pb/204 Pb = 38.710) that cannot be clearly at- The Pb sources and their estimated proportions in Galveston Bay sed- tributed to previously identiﬁed Pb sources in the literature, signify- iment leachates are crustal rocks 16.2%, Central Appalachian MVT ores ing that Pb in this sample may result from contamination or a hitherto 20.4%, ores processed at historic US smelters and reﬁneries 22.0%, US uncharacterized Pb source(s). For residues, GB9R, 3R 09-18 and 14R and Central American aerosols 20.9%, and North American coals 20.6%. 09-18 have distinctly high 208 Pb/204 Pb values of 40.704, 39.326, and In contrast, Galveston Bay sediment residues are crustal rocks 83.4% 40.459, respectively, that are outside of the range of other Galveston and ores historically smelted and reﬁned in the US 16.6%. Together, the Bay sediments and cannot be attributed to any literature Pb sources. leachates and residues compose bulk sediments with Pb source contri- Consequently, these three points are excluded the MixSIAR modeling. butions of crustal rocks 74.5% and ores historically smelted and reﬁned The Missouri MVT Pb ores source has notably high 208 Pb/204 Pb ratios in the US 25.5%. ranging from 39.283 to 41.694 that are closer in range to these sta- Outliers in the MixSIAR model must be noted. The E3-7L point has a tion data (39.326 – 40.704), and so it is possible that Missouri MVT 207 Pb/204 Pb of 15.557 that forms the lower bound of 207 Pb/204 Pb values Pb ores contribute at least in part to GB9R, 3R 09-18 and 14R 09-18 observed in the study area sediments, which typically have 207 Pb/204 Pb in addition to other unknown Pb inputs (Sverjensky, 1981). Finally, all > 15.617. The point E3-7L (207 Pb/206 Pb = 0.80982±0.00002 and Galveston Bay sediment bulk digests have 208 Pb/204 Pb ratios < 39.480 208 Pb/206 Pb = 2.01807 ±0.00008) falls on a mixing line between aver- except GB5D and GB11D, which have 208 Pb/204 Pb ratios of 40.352 and age continental crust (average 207 Pb/206 Pb and 208 Pb/206 Pb of 0.82351 43.340 respectively. These values indicate the presence of a heretofore 8
A.M. Lopez, A.D. Brandon, F.C. Ramos et al. Environmental Advances 4 (2021) 100057 unknown source of thorogenic Pb stemming from the northeastern rim Declaration of Competing Interest of East Bay. No source with a similar Pb isotopic composition to GB11D has been identiﬁed in the literature, making it diﬃcult to contextualize The authors declare that they have no known competing ﬁnancial this data point. For this reason, GB11D is not included in the MixSIAR interests or personal relationships that could have appeared to inﬂuence model. the work reported in this paper. Upper versus lower Galveston Bay Pb isotope ratio trends in sed- iment leachates and residues were used to model the regional distri- CRediT authorship contribution statement bution of Pb in the bay (SM Table S5). The Galveston Bay sediment leachate regional distribution MixSIAR model indicates that upper bay Amanda M. Lopez: Conceptualization, Methodology, Software, For- stations receive more Pb from North American coals and Central Ap- mal analysis, Investigation, Writing - original draft, Writing - review palachia MVT Pb ore sources (28.4% and 28.9%) than US and Central & editing, Visualization, Project administration, Funding acquisition. American aerosols, soils from US Pb smelters and reﬁneries, and crustal Alan D. Brandon: Conceptualization, Methodology, Writing - review rocks (20.3%, 20.1%, and 2.4%). Conversely, lower bay station leachate & editing, Supervision, Funding acquisition. Frank C. Ramos: Formal Pb is dominated by US and Central American aerosols and historic US analysis, Writing - review & editing. Jessica N. Fitzsimmons: Concep- Pb smelters and reﬁnery sources (44.6% and 47.9%). The Galveston Bay tualization, Methodology, Writing - review & editing, Project adminis- sediment residue MixSIAR model output indicates that stations in upper tration, Funding acquisition. Timothy M. Dellapenna: Formal analysis, and lower bay stations generally receive Pb from the same sources de- Writing - review & editing. Hannah M. Adams: Formal analysis, Writ- spite slightly variant Pb isotope compositions in the residue fractions. ing - review & editing. The lack of consistent Pb isotopic mass balance and the presence of anthropogenic Pb in the residual sediment fraction gives way to Funding sources two possibilities 1) that the sequential leaching method used did not fully leach surface adsorbed Pb from sediment sample grain surfaces This work was supported by the Texas A&M University T3 Triad and/or 2) heterogeneity in sediment sample powders. In scenario 1, and the Texas Commission on Environmental Quality (Federal ID #CE- the operationally-deﬁned residual fraction here likely does not repre- 00655007). sent the true natural Pb isotopic signal. Previous work has shown that HH-CH3 COOH may not thoroughly access surface adsorbed heavy met- Acknowledgments als (Chester and Hughes, 1967; Graney et al., 1995; Sholkovitz, 1989), though stronger leaches have also recorded natural Pb in the leachate Special thanks to Perry Akrie, Audrey Schmitt, and Janelle Steﬀen fraction. It is also plausible that leaching artifacts are being observed. for their assistance with sample processing, as well as Nathan Lanning, This idea has been explored in several previous studies, which have Laramie Jensen, Kimber De Salvo, Brett Farran, and all members of found that re-adsorption of leached metals onto sediment grains of- Texas A&M Oceanography’s Galveston Bay sampling team for assistance ten occurs during sequential leaching procedures, including when us- with sample collection. ing the HH-CH3 COOH leach method (Nirel and Morel, 1990; Piper and Wandless, 1992; Sholkovitz, 1989). In scenario 2, a true comparison Supplementary materials between leachate, residue and bulk digestion cannot be made as there are diﬀerences between the starting sample powder processed. Addi- Supplementary material associated with this article can be found, in tional information regarding Pb isotopic mass balance is provided in the online version, at doi:10.1016/j.envadv.2021.100057. the SM. References Conclusions Al Mukaimi, M.E., Kaiser, K., Williams, J.R., Dellapenna, T.M., Louchouarn, P., Santschi, P.H, 2018a. Centennial record of anthropogenic impacts in Galveston Bay: evidence from trace metals (Hg, Pb, Ni, Zn) and lignin oxidation products. Environ. The Galveston Bay watershed encapsulates a high density of US Pollut. 237, 887–899. petrochemical facilities. This work shows that, despite this, modern Al Mukaimi, M.E., Dellapenna, T.M., Williams, J.R, 2018b. 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