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Decliningsbut PersistentsAtmospheric Contamination in Central California from the Resuspension of Historic Leaded Gasoline Emissions As Recorded in the Lace Lichen (Ramalina menziesii Taylor) from 1892 to 2006 A . R U S S E L L F L E G A L , * ,† ´ LINE GALLON,† SHARON HIBDON,† CE ´ O F. LAPORTE‡ ZEKA E. KUSPA,† AND LE WIGS Laboratory, Institute of Marine Sciences, University of California, Santa Cruz, Santa Cruz, California 95064, and Department of Earth and Planetary Sciences, University of California, Santa Cruz, Santa Cruz, California 95064
Received January 26, 2010. Revised manuscript received May 10, 2010. Accepted May 25, 2010.
Analyses of lead concentration and isotopic composition of recent and archived samples of the lace lichen (Ramalina menziesii) chronicle more than a century of atmospheric lead contamination in central California. The contamination extends back to our oldest sample from 1892, when lead levels in lichen from the northern reach of the San Francisco Bay estuary were 9-12 µg/g and their isotopic composition corresponded to those of high lead emissions from the Selby smelter (e.g., 206Pb/207Pb ) 1.165) that were killing horses in adjacent fields at that time. By the mid-1950s lead isotopic compositions of lichens shifted to the more radiogenic leaded gasoline emissions (e.g., 206Pb/207Pb ) 1.18-1.22). Lead concentrations in the lichen peaked at 880 µg/g in 1976, corresponding with the maximum of leaded gasoline emissions in California in the 1970s. After that, lead concentrations in lichen declined to current levels, ranging from 0.2 to 4.7 µg/g. However, isotopic compositions of contemporary samples still correspond to those of previous leaded gasoline emissions in California. This correspondence is consistent with other observations that attest to the persistence of environmental lead contamination from historic industrial emissions in central California.
have been used to identify the sources and dispersion of atmospheric lead contamination, based on their stable lead isotopic composition (5-7). This paper presents new information demonstrating that historic and contemporary collections of epiphytic lichens may be employed to compare temporal variations in both atmospheric lead concentrations and isotopic compositions. These comparisons are qualified by the limitations of using lichens as biomonitors (9, 10), and they are further qualified by the documented problems of lead contamination of environmental samples during sampling, storage, processing, and analysis (11). Despite these qualifications, we believe the following data provide evidence for (i) the temporal increase and subsequent decline of atmospheric lead contamination in the San Francisco Bay Area over the past century and (ii) the persistence of lead contamination within that area from those historic industrial emissions. Moreover, lead isotopic compositions of the lichen are consistent with those of contemporary waters and sediments in the Bay and its drainage basin, corroborating reports of the legacy of lead contamination in the state from historic leaded gasoline emissions (12-14).
Materials and Methods This study was catalyzed by the discovery of an unpublished report written by an undergraduate, Thomas McClure, at Stanford University over 30 years ago (15). He measured lead concentrations of lace lichen (Ramalina menziesii Taylor) collected from and adjacent to the university’s Jasper Ridge Biological Preserve (JRBP). He did this as the use of leaded gasoline in the U.S. was peaking at ∼5 × 1010 L/yr (12), with the intent of establishing a baseline to quantify atmospheric decreases in lead contamination that were projected with the phase-out of leaded gasoline in the U.S. that was completed in 1992. Because he used relatively rigorous trace metal clean techniques and the lead concentrations in his samples were relatively high (80-880 µg/g, see his Table 1), we determined that his data could be compared with new samples collected and processed in a similar manner to document the decline in atmospheric lead concentrations that he had anticipated. Sample Materials. Like most lichens, the lace lichen (R. menziesii) is a symbiosis between a green alga and a fungus (Figure 1). The lichen occurs uniquely in a pendulous mode
Introduction The use of lichens as biomonitors of atmospheric pollution is both long and extensive (1). In 1866 Nylander reported on the applicability of epiphytic lichens as bioindicators of air quality (2), and in 1973 Ferry et al. reported that lichens were the most studied bioindicators of air quality (3). This included their value as biomonitors of elemental contamination that was initiated half a century ago (4). And more recently, lichens * Corresponding author e-mail:
[email protected]; phone: 831459-2093; fax: 831-459-2088. † WIGS Laboratory, Institute of Marine Sciences. ‡ Department of Earth and Planetary Sciences. 10.1021/es100246e
2010 American Chemical Society
Published on Web 06/07/2010
FIGURE 1. Lace lichen (Ramalina menziesii Taylor) on a Valley Oak at the Jasper Ridge Biological Preserve in central California (Photo by L.F. Laporte). VOL. 44, NO. 14, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. Lichen (Ramalina menziesii) collection sites. Sites 1-5 are within or immediately adjacent to Jasper Ridge Biological Preserve (JRBP) where McClure collected lichen in 1976. We recollected from these sites in 2006 and an additional location (site 6) within the Preserve. Also shown are the sites of other archived samples of lichen from herbariums at JRBP, UC Berkeley, and San Jose State University that were analyzed for this report. of growth, hanging net-like from tree limbs and absorbing moisture and nutrientssas well as air-borne pollutantssfrom the surrounding atmosphere. Because it cannot metabolically shed those pollutants and it is among the lichens most sensitive to pollution (16), it is an especially appropriate biomonitor. In addition, it is one of the fastest growing lichens (17), making it a better monitor of temporal changes than other lichens with notoriously slow growth rates. Consequently, we restricted our collections to relatively small (e20 cm) samples of that lichen so their lead concentrations and isotopic compositions would represent contemporary exposures, rather than values averaged over decades of exposure. Study Area. JRBP is located near Stanford University and the southern reach of the San Francisco Bay estuarine system (Figure 2). Public access to the preserve has been restricted since 1976. Before then, it was used for recreation with relatively heavy auto traffic both within the preserve and in surrounding areas. There still is a modest amount of traffic within the Preserve (e.g., electric carts for researchers and docents), and traffic in the surrounding outside area has increased substantially over the past three decades. However, none of those vehicles have used leaded gasoline for over a decade. 5614
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In 2006, we collected lichen (R. menziesii) from five sites where McClure had previously collected that species in 1976 (Figure 2). These included one location near (150 m) a major roadway (Interstate 280), where he had found the highest concentration of lead in lichen (880 µg/g), and a site near another road (Sand Hill Road), where he also found high levels of lead in lichen (622 µg/g). The other three sites were within the Preserve where he found relatively lower lead concentrations in lichen (80-120 µg/g). We collected another sample from an additional location (Site 6) well into the preserve, away from heavily traveled roads surrounding the Preserve. Our lichen samples (e20 cm length) were collected with established trace metal clean techniques (11). They were hand-collected, by personnel wearing plastic gloves, and immediately enclosed in plastic bags that were then sealed within larger plastic bags. The samples were stored in a HEPA (Class 100) filtered air, trace metal clean room at the University of California, Santa Cruz (UCSC), until they were processed for analysis. The processing was conducted in a HEPA (Class 100) filtered air hood, within a trace metal clean room, using established protocols (11). The samples were processed without any pretreatment, as in McClure’s original study. They were digested with two sequential additions (10 mL) of concentrated, trace metal grade, HNO3 (Fisher Scientific) in acid-cleaned Teflon containers. The dried digests were brought up to volume with 1 M HNO3 diluted with high purity (18 MΩ cm) water (Milli-Q, Millipore Corporation), and then analyzed for both their lead concentration and stable lead isotopic composition with a Finnegan Element magnetic sector, high-resolution, inductively coupled plasma mass spectrometry (HR ICP-MS) using established procedures (18). Concurrent processing and analysis of National Institute of Standards and Technology (NIST) standard reference material SRM 1547 (peach leaves) yielded recoveries of 99.1 ( 4.7% (mean ( RSD, n ) 12). To verify the accuracy of the isotopic composition analyses, aliquots of the samples were concentrated on an ion-exchange resin (AG 1 × 8) and reanalyzed with a Finnegan Neptune magnetic sector multicollector inductively coupled plasma mass spectrometer (MC ICP-MS), combined with an APEX HF sample introduction system (Elemental Scientific), using established procedures (19). The sensitivity of the measurements was 5.5 V for 208Pb at 100 ng/g lead. Measured isotopic ratios were corrected for mass bias using thallium additions according to an exponential function (205Tl/203Tl ) 2.388). Counts of 204Pb were corrected online for isobaric interferences from 204Hg by monitoring 202Hg and assuming natural abundances of mercury isotopes (204Hg /202Hg ) 0.2298). Analyses were calibrated with concurrent measurements of 20 ppb NIST SRM 918 (common lead). Procedural blanks (including column extraction blanks) were processed and measured concurrently. Isotopic composition data (e.g., 206 Pb/207Pb) from the two independent analyses (HR ICP-MS and MC ICP-MS) were within 0.3% of each other. Based on the preliminary results showing marked temporal decreases in lead concentrations of the samples McClure collected and analyzed in 1976 and those we collected and analyzed three decades later, we then sought to determine if that temporal gradient in lead concentrations in lichen from the San Francisco Bay area could be extended over a greater period. This was done with archived samples of lichens from collections at the JRBP, the University Herbarium at UC Berkeley, and the Biology Department at San Jose State University. Collection dates and locations of those samples are listed in Table 1, along with their lead concentrations and isotopic compositions that were determined with the same procedures with comparable sensitivity, accuracy, and precision.
TABLE 1. Lead Concentrations and Isotopic Compositions of Lichens (Ramalina menziesii) Collected from the Jasper Ridge Biological Preserve (JRBP) in 1976 and 2006, As Well As Those from Archived Samples from JRBP Herbarium, the UC Berkeley Herbarium, and the Biology Department at San Jose University (Samples from the San Francisco Bay Area Are Marked with an Asterisk) year
location
Pb (µg/g)
1892* 1894 1894* 1906 1907 1912* 1927 1930 1945 1947* 1950 1954 1955 1955 1955 1957* 1959 1976* 1976* 1976* 1976* 1976* 1976* 1978 1982 1983* 1982* 1983* 1983* 1983* 1987 1988 1988 1992 1995* 1999 2000* 2006 March* 2006 March* 2006 March* 2006 March* 2006 March* 2006 March* 2006 September* 2006 September* 2006 September* 2006 September* 2006 September* 2006 September* 2006 September*
Sausalito, CA Santa Monica, CA Olema Marin Co, CA San Juan Is, Canada Paso Robles, CA Saratoga, CA Alton Humboldt Co, CA Sooke Harbor, Vancouver IS Del Norte, CA San Mateo, CA Clallam Olympic, WA Carmel, CA Santa Margarita, CA Pinnacles, CA - a Pinnacles, CA - b Searsville Lake, Palo Alto, CA Carmel, CA JRBP (site 1) near McClure F JRBP (site 3) McClure G JRBP (site 4) McClure K JRBP (site 5) McClure L JRBP (site 2) McClure M JRBP (site 2) McClure N Windsor, CA Point Lobos CA Sand Hill Rd, JRBP CA JRBP (site unknown) JRBP (site unknown) JRBP (site unknown) JRBP (site unknown) Hastings NHR, Monterey, CA San Clemente, CA - a San Clemente, CA - b Kern Co, CA JRBP (site unknown) Pfeiffer S.P., CA Pilarcitos Lake, CA JRBP (site 1) near McClure F JRBP (site 2) McClure N JRBP (site 3) McClure G JRBP (site 4) McClure K JRBP (site 5) McClure L JRBP (site 6) no McClure site JRBP (site 1) McClure F JRBP (site 2) McClure N JRBP (site 3 duplicate 1) McClure G JRBP (site 3 duplicate 2) McClure G JRBP (site 4) McClure K JRBP (site 5) McClure L JRBP (site 6) no McClure site
11.9 4.0 9.1 13.7 22.9 4.0 1.0 5.7 49.9 9.4 4.1 11.7 13.7 8.2 13 34.2 28.4 880.0 622.0 80.0 100.0 120.0 80.0 50.9 10.0 12.9 3.2 9.8 4.6 13.3 1.0 1.3 1.0 1.3 1.9 0.8 0.4 2.1 0.9 3.1 0.7 0.7 0.2 4.2 1.8 4.1 4.7 2.0 1.1 1.0
Geographical coordinates of sampling sites within JRBP and more detailed isotopic composition data are available upon request.
Results and Discussion Temporal Gradients in Lead Concentrations. As previously indicated, there was a marked decrease in lead concentrations of lichen collected in 2006 compared to those collected in 1976 (Table 1). This decrease over three decades is consistent with the decrease of atmospheric lead concentrations measured by the San Francisco Air Board (12). Both declines attest to the efficacy of the elimination of leaded gasoline and other efforts to reduce atmospheric lead emissions in California and the rest of the U.S. during that period.
206
Pb/207Pb
208
Pb/207Pb
1.165 1.155 1.175 1.154 1.157 1.139 1.171 1.168 1.187 1.182 1.173 1.190 1.185 1.190 1.189 1.185 1.172
2.431 2.431 2.441 2.431 2.433 2.416 2.444 2.439 2.438 2.450 2.443 2.461 2.453 2.459 2.459 2.449 2.448
1.221 1.215 1.221 1.212 1.220 1.224 1.218 1.198 1.199 1.199 1.204 1.202 1.188 1.184 1.162 1.180 1.183 1.175 1.175 1.176 1.150 1.184 1.187 1.185 1.179 1.169 1.170
2.458 2.457 2.452 2.457 2.454 2.462 2.448 2.450 2.461 2.462 2.461 2.453 2.463 2.444 2.426 2.441 2.442 2.432 2.437 2.441 2.417 2.443 2.442 2.442 2.432 2.428 2.433
That gradient is illustrated in Figure 3 where the two data sets (1976 and 2006) are combined with measurements of the archived samples that predate the 2006 collections. This suite of data documents the temporal increase of lead concentrations in lichen in the San Francisco Bay Area from 1892 up to the maximum levels measured by McClure in 1976 at the peak in atmospheric emissions of leaded gasoline in California (12) and then follows the decline seen in subsequent years associated with the phase-out of leaded gasoline in the U.S. Although lead concentrations of the earliest samples from the 1800s predate the introduction of leaded gasoline in the U.S., they are not considered to reflect natural levels of lead in lichen in the San Francisco Bay Area. This is because industrial lead emissions in the area extending back into the VOL. 44, NO. 14, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 3. Lead concentrations in lichen along Western North America from 1892 to 2006, and estimated lead emissions from leaded gasoline (20). 1800s have been documented in San Francisco Bay sediments (21), as well as those of Lake Tahoe to the east (22). Historic industrial lead emissions, predating the use of leaded gasoline, include those from fossil fuel combustion at the start of the California Gold Rush in the mid-1800s (21) and those from the Selby smelter, located in the northern reach of San Francisco Bay (Figure 2), which originated in the late 1800s (23). Atmospheric lead emissions from the smelter, which was in operation from 1885 to 1971, were so large (∼45 kg of lead/day) (24) that they were lethal to horses in adjacent pastures during the early 1900s (23) and continued to contribute (along with leaded gasoline emissions) to acute lead toxicity in horses within the area through the mid-1900s (24). The surprisingly high lead concentrations (11.9 and 9.1 µg/g) measured in lichen from both Sausalito in 1892 and Marin in 1894, which are also located in the northern reach of the Estuary, are presumably due to industrial lead emissions from that smelter. The relatively lower, but still high, lead concentration (4 µg/g) in lichen subsequently collected from Saratoga in 1912 is presumably due to its greater distance from the smelter, as well as the implementation of better emission controls at the smelter in the early 1900s (23). We do not have sufficient information for attribution of the sources of lead in lichen samples collected from other California sites outside of the Bay Area (Santa Monica, San Juan, Paso Robles, and Humboldt) and in Canada (Vancouver) between 1894 and 1930, but have included these data should they be useful for others. Lead concentrations in all lichen samples collected from the 1940s to the present are primarily attributed to atmospheric emissions from the combustion of leaded gasoline. This includes values ranging from a low of 0.4 µg/g in Pilarcitos (2000) to a high of 50.9 µg/g in Windsor (1978). It also includes all the lead in samples collected by McClure in 1976 from JRBP, which ranged from 80 to 880 µg/g. The lowest of the former values (80 µg/g) was for lichen (R. menziesii) collected from a relatively remote location within JRBP, and the highest (880 µg/g) was for lichen collected 150 m from Interstate 280 that borders JRBP to the north. The lichens that we subsequently collected from JRBP in 2006 had lead concentrations ranging from 0.2 to 4.7 µg/g. We attribute the higher concentrations in lichen collected in the dry period (September), compared to wet period (March), to the greater amount of dust accumulated on their surfaces during that time, and we attribute most of the lead in these lichen collected during both of those seasons to previous emissions from the combustion of leaded gasoline, based on the following analyses of their isotopic compositions. Temporal Gradients in Lead Isotopic Composition. The proposed industrial origins of lead in all of the lichen samples, dating from 1892 to 2006, are corroborated by their isotopic compositions (208Pb/207Pb versus 206Pb/207Pb), as listed in Table 1 and illustrated in Figures 4 and 5. Also plotted in 5616
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FIGURE 4. Temporal variation in lead isotopic compositions (206Pb/207Pb and 208Pb/207Pb) in lichen (Ramalina menziesii) collected from western North America. This includes lichen collected from the Jasper Ridge Biological Reserve and adjacent locations in the San Francisco Bay Area between 1892 and 2006. Also included are isotopic compositions of archived samples of R. menziesii collected from other locations in California, Washington, and British Columbia that were obtained from the JRBP Herbarium, University of California at Berkeley, and the Biology Department at San Jose State University. Archive samples from the San Francisco Bay area are marked with an asterisk.
FIGURE 5. Isotopic ratios (206Pb/207Pb: 208Pb/207Pb) of lichen and principal sources of industrial lead along Western North America from 1892-2006. Lichen data are from this study. Other data are from Bollho¨fer and Rosman, 2001 (28), Dunlap et al., 2008 (14), Mukai et al, 2001 (30), Rabinowitz and Wetherill, 1972 (24), Ritson et al., 1999 (21), Steding et al., 2000 (12), and references therein. Samples from the San Francisco Bay area are marked with an asterisk (archives) or represented by diamonds (JRBP). Figure 5 are the lead isotopic compositions attributed to historic (∼1900) industrial lead emissions from the Selby smelter (21) and those of subsequent (1960-1990) leaded gasoline emissions in California. The latter have most recently been compiled in a report on persistent lead contamination
in California’s largest river, the Sacramento, which drains California’s Central Valley and discharges into San Francisco Bay (14). The isotopic composition of the oldest lichen sample collected along the northern reach of the Bay in 1892 (206Pb/207Pb ) 1.165) is similar to that of highly lead contaminated grass (9645 µg/g) collected near the Selby smelter eight decades later (24) (Figure 5). Both approach the value (206Pb/207Pb ) 1.168) observed in a sediment core from Richardson Bay ca. 1950, following a dramatic shift from a natural value (21). Similarly, the isotopic composition (206Pb/207Pb ) 1.175) of the second oldest lichen sample, collected in Marin in 1894, is bracketed by that old value for Richardson Bay and comparably old values (206Pb/207Pb ) 1.172-1.175) for San Pablo Bay (25). Therefore, essentially all of the lead in lichen collected along the northern reach of the Bay in the late 1800s appears to have been derived from the smelter’s atmospheric emissions, based on (i) their locations down-wind from the smelter, (ii) their high lead concentrations, and (iii) their isotopic compositions. Isotopic compositions of the lichen samples collected from San Mateo in 1947 (206Pb/207Pb ) 1.182) and Searsville in 1957 (206Pb/207Pb ) 1.185) in the southern Bay Area differed from those of the earlier samples collected in the northern Bay Area, but were comparable to each other (Figure 4; Table 1). More notably, both were bracketed by the isotopic composition of leaded gasoline in the U.S. in 1947 (206Pb/207Pb ) 1.204; 208Pb/207Pb ) 2.467) (26); in California in the early 1960s (206Pb/207Pb ) 1.145 ( 0.018; 208Pb/207Pb ) 2.422 ( 0.015) (26); and in the San Francisco Bay area in 1970 (206Pb/207Pb ) 1.206 ( 0.010) (24). Moreover, the isotopic composition of the two lichen samples was indistinguishable from those of aerosols collected in San Francisco (206Pb/207Pb ) 1.185) and those of the snowpack in the High Sierras east of San Francisco (206Pb/207Pb ) 1.183) a decade later by Hirao and Patterson (27). Similarly, the subsequent shift in isotopic composition of lichen collected from the Preserve between 1982 and 1995 (206Pb/207Pb ) 1.202-1.224) corresponds with the shift in the isotopic composition of leaded gasoline during that period (14) (Figure 5). Consequently, the lead in all of those lichen is primarily attributed to contemporary emissions of leaded gasoline during that sampling period. Isotopic compositions of lichen that we collected from the Preserve in 2006 (206Pb/207Pb ) 1.150-1.187) were intermediate to those of lichen collected from the Bay Area during the preceding century (1892-1978), and with one exception (site 1, 206Pb/207Pb ) 1.150 in September 2006), were close to or within the range of values measured in aerosols collected in 1998 and 1990 in Berkeley and Davis (28). They were also intermediate to the range in isotopic composition of leaded gasoline in California during the 1964-1979 period. Although lead concentrations in these most recent samples are considerably lower than those during the previous century (0.2-4.7 µg/g), the isotopic ratios are notably different from pre- industrial values measured in sediments of the San Francisco Bay (206Pb/207Pb ) 1.222 ( 0.001; 208Pb/207Pb)2.485 ( 0.001) (21), indicating that the lead is anthropogenic. Temporal variations in lead isotopic compositions in cities along the west coast of North America have been tentatively attributed to the replacement of anthropogenic lead emissions within the U.S. with those from Asia (28), following the dramatic increase of Asian anthropogenic lead emissions during the 1970s-2000s caused by increased fossil fuel combustion and the protracted use of leaded gasoline in that region (29). However, isotopic values for these recent lichens do not correspond to the domain formed by aerosols collected in major Japanese and Chinese cities during the 1990s (28, 30) (Figure 5). Therefore, we propose that the lead concentrations measured in the most
recent (2006) set of lichen samples are primarily derived from the resuspension of historic emissions of leaded gasoline, as illustrated in Figure 5. This interpretation is consistent with the analyses of a suite of complementary studies in California and elsewhere. For example, lead concentrations in surface sediments of San Francisco Bay (21) are primarily attributed to legacy contamination from leaded gasoline emissions, as is the lead in surface waters and suspended sediments now being discharged into the Bay (12, 14). While this conclusion is primarily based on lead isotopic composition analyses, others have arrived at comparable conclusions based on lead concentration gradients and mass balance calculations. The former includes the study of origin of lead in surface sediments in Lake Tahoe (22), and the latter includes the study of the origins of lead in resuspended soils in the South Coast Air Basin, which extends over Los Angeles and its suburbs (31). In that study, it was calculated that 54,000 kg (more than 12 tons) of lead that was being resuspended in the Basin every year was primarily derived from previous emissions of leaded gasoline. All of these studies substantiate our claims that (i) essentially all of the atmospheric lead now being deposited in lichen within the San Francisco Bay Area is from historic emissions of leaded gasoline that were terminated in the state nearly two decades ago and (ii) still continue from that legacy contamination.
Acknowledgments We thank Brent Mishler and Kim Kersh for providing access to specimens of R. menziesii in the University Herbrarium at UC Berkeley, and the Biology Department at San Jose State University for providing one sample of R. menziesii. We also thank Alicia Kriewall for assistance in sample collecting; Nona Chiariello for references in the literature; Diane Renshaw for English Elm identification; and Trevor He´bert for the GSP data and locality map. This research was funded by grants from the University of California Toxic Substances Research & Teaching Program and the National Science Foundation (OCE-0751681).
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