Measured Pb Concentrations Research Articles

Assessing uncertainties in modeling the risk of geogenic groundwater contamination.

Assessing groundwater contamination risk is a critical aspect of preventing and managing groundwater pollution. There was a research gap in the investigation of uncertainties in modeling groundwater contamination risks in aquifers. This study addresses this gap using Bayesian Model Averaging (BMA), with a novel focus on risk exposures from geogenic contaminants, such as lead (Pb). This was achieved through the following methodology: (1) assessing aquifer vulnerability using the SPECTR framework; (2) generating a risk index for geogenic contaminants through unsupervised methods; (3) enhancing geogenic risk through three individual models, including Gene Expression Programming (GEP), M5P, and Support Vector Machines (SVM); (4) combining results from individual models using BMA; and (5) examining inherent uncertainties, accounting for both between-model and within-model variances. The model's efficacy was evaluated using measured Pb concentrations within the aquifer. The findings indicated that the unsupervised risk index had an acceptable correlation, while the individual models were accurate and enhanced the predictability of the data. BMA assigned the higher posterior probabilities (weight) to the SVM model, which indicates a positive correlation between the performance criteria of individual models and the weight values. Also, BMA revealed that the modeling uncertainty is influenced by within-model variance, primarily by the kriging interpolation method.

Mineral and heavy metal variations and contaminations in raw honey of stingless bees, Heterotrigona itama, from selected geographical areas of origin in Malaysia

Introduction: Honey contains a complex matrix of different substances consisting of essential minerals, non-nutritive substances, and toxins, often due to environmental sources. The objectives of this study were i) to investigate the variation of mineral and heavy metal content in honey samples of Heterotrigona itama from different geographical origins, and ii) to evaluate the nutritional quality and safety of honey from different floral sources for human consumption. Methods: A total of 75 samples of raw H. itama honey were collected from 11 sites in Sabah, two sites in Sarawak, and two sites in Peninsular Malaysia. The mineral and heavy metal contents of honey were determined in triplicate using inductively coupled plasma mass spectrometry (ICP-MS). Results: There were significant differences in the composition of essential minerals and heavy metals in the honey samples according to geographical origins (p<0.001). All honey samples tested were below the permitted maximum proportion (ML) for cadmium (Cd) and lead (Pb) specified in the Malaysian Food Act 1983 for honey. However, all honey samples exceeded the ML for Pb set by Codex, with samples from bamboo sites having the highest levels for Pb. Conclusion: The composition of minerals and heavy metals in stingless bee honey was influenced by geographical origin. All measured Pb concentrations were above the ML value set by Codex, which raises concerns about possible toxicological risks to human health. Given the toxic nature of Pb in the environment, the measured concentrations emphasise the importance of monitoring Pb in honey from stingless bees.

Assessing lead sources in fishes of the northeast Pacific Ocean

Abstract Industrial lead (Pb) emissions have changed oceanic Pb concentrations and isotopic compositions significantly over the last century. Asian industrial emissions are currently the dominant Pb sources in the northwest and central Pacific Ocean. This study investigated major Pb sources in the northeast Pacific Ocean (inland, coastal, and open ocean), where no comprehensive data exist currently. We measured Pb concentrations and isotopic compositions of a variety of shellfish and fish collected in British Columbia (BC) and used them for Pb source apportionment applications in the marine environment. We identified a clear trend in Pb isotopic compositions, from higher 206Pb/207Pb in inland fish to lower 206Pb/207Pb in open ocean fish, with coastal fish possessing mid-range values. These results indicate that natural sources of Pb dominate freshwater ecosystems in the central BC coast, whereas anthropogenic Pb sources prevail in western North America and the northeast Pacific. Pacific herring that forage along BC coast exhibit Pb isotopic composition that deviates toward the Chinese Pb regression line. We estimate an Asian origin for about one third of their total Pb. This study shows that Pb isotopes in aquatic organisms are valuable tools for assessing Pb sources across coastal and offshore regions of the northeast Pacific, with great potential for identifying primary foraging areas of marine organisms.

Estimates of Blood Lead Levels (BLLs) for Children in Coastal Madagascar: Accounting for Dietary Uptake of Lead (Pb)

Thousands of households in coastal Madagascar that employ pitcher-pump systems to provide water for domestic use may be at risk for harmful exposure to lead (Pb), which leaches from locally manufactured pump system components. The Integrated Exposure Uptake Biokinetic model (IEUBK) can predict blood lead levels (BLLs) in exposed children, thereby characterizing potential health risks. However, it is unclear if the existing methodology of the IEUBK accounts adequately for dietary Pb contributions from contaminated cooking water. Therefore, aims of this study are (1) to develop a method for modifying the IEUBK to account for contaminated cooking water, (2) to quantitatively estimate the importance of dietary Pb uptake (relative to other routes of Pb exposure) in coastal Madagascar, and (3) to estimate BLLs of children in that area, accounting for dietary uptake. Results show that if the Pb concentration in household drinking and cooking water is low (≤ 4 µg/L), Pb in cooking water is not a major route of exposure; predicted BLLs in children are low regardless of whether the dietary component is modified. However, the importance of dietary intake increases with water concentration: if the household aqueous Pb concentration increases from 4 to 24 µg/L, corresponding to the 90th percentile concentration measured in a field campaign, then the estimated dietary contribution to total Pb uptake can exceed 50%. Based on median measured Pb concentrations (11 µg/L), 7–14% of children in households using pitcher-pump systems in coastal Madagascar would present with BLLs > 5 µg/dL (i.e., levels implicated in developmental health issues); however, this number could exceed 90% in households or communities where the water concentration is particularly high. An important conclusion is that the IEUBK should be modified when applied to a developing-world context, where preparation of a starch food staple like rice may present considerable Pb exposure; omitting dietary uptake in cooking water potentially ignores the dominant route of Pb exposure.

Assessing the Lead Solubility Potential of Untreated Groundwater of the United States.

In the U.S., about 44 million people rely on self-supplied groundwater for drinking water. Because most self-supplied homeowners do not treat their water to control corrosion, drinking water can be susceptible to lead (Pb) contamination from metal plumbing. To assess the types and locations of susceptible groundwater, a geochemical reaction model that included pure Pb minerals and solid solutions of calcite (Ca xPb1- xCO3) and apatite [Ca xPb5-x(PO4)3(OH; Cl; F)] was developed to estimate the lead solubility potential (LSP) for over 8300 untreated groundwater samples collected from domestic and public-supply sites between 2000 and 2016 in the U.S. The LSP is the calculated amount of Pb metal that could dissolve at 25 °C before a Pb-bearing mineral precipitates. About 33% of untreated groundwater samples had LSP greater than 15 μg/L-the USEPA action level for dissolved plus particulate forms of Pb. Five percent of samples had high LSP (above 300 μg/L) and tended to occur in the eastern and southeastern U.S. Measured Pb concentrations above 15 μg/L were rarely detected (<1%) but always coincided with high LSP values. Future work will provide a better understanding of the relation between water chemistry, Pb-mineral formation, and dissolved Pb concentrations in tap water.

Uptake of trace elements by baryte during copper ore processing: A case study from Olympic Dam, South Australia

Baryte is a common gangue mineral in many ore systems. Here, we report on a study of baryte chemistry in samples of ore and processing materials (flotation feed, flotation concentrate, flotation tailings, concentrate leach discharge, and tailings leach discharge) from the Olympic Dam Cu-U-Au-Ag deposit, South Australia. Elements that commonly substitute for Ba in the baryte lattice, including Sr and Ca, are measured in variable concentrations reflecting grain-scale zonation and heterogeneity at the scale of the deposit but appear unaffected during processing. Variation in the concentration of some other elements, notably Cu, reflect both the heterogeneous nature of flotation feed and the intimately intergrown character of the sulfide-sulfate assemblage. Measured Pb concentrations in baryte progressively increase during processing from flotation feed to flotation concentrate, and particularly in concentrate leach discharge. Such data suggest that, during sulfuric acid leaching, baryte contained within the concentrate is able to incorporate quantities of Pb that have been mobilized during break-down of Pb-bearing minerals (notably U-minerals containing radiogenic lead). This takes place via surface adsorption followed by rapid coupled dissolution-replacement driven incorporation throughout the grain. Results suggest that baryte may scavenge non-target elements during processing and contribute to an understanding of mobility, mineralogical location, and evolution in the deportment of radionuclides through the processing cycle.

Accumulation and potential sources of lead in marine organisms from coastal ecosystems of the Chilean Patagonia and Antarctic Peninsula area

Environmental concentrations of Pb have been increased due to anthropogenic activities, which have provoked the released of this element to the environment in large amounts. To understand how Pb behaves in remote southern marine ecosystems, we measured Pb concentrations and isotope ratios in biota from coastal marine ecosystems of the Chilean Patagonia and the Antarctic Peninsula area. Lead concentrations in the aquatic organisms ranged from 0.02 to 1.19 mg kg−1 d.w. In Patagonia, higher Pb levels were found in fish than in invertebrates (crab, shrimp, porifera, limpet and shellfish). In comparison with the baseline reference values from other parts of the world, fishes exhibited lower Pb levels. The results of Pb isotopic compositions indicated that the bioaccumulation of Pb in marine organisms come from different anthropogenic sources. These Pb levels might be useful for further studies that allow a deeper evaluation of sources for Pb contamination in these remote ecosystems.

Lead exposure, dietary magnesium and glucose homeostasis in Chinese adults

BackgroundThere is mounting evidence that pollutants, including toxic metals, contribute to the global epidemic of diabetes. Along with laboratory data suggesting that lead (Pb) exposure may disrupt insulin secretion and promote glucose intolerance, a handful of epidemiological studies have reported associations between Pb and poor glucose homeostasis. A growing literature also suggests that nutrients such as dietary magnesium (Mg)—an essential metal critical for insulin action—may delay the progression of impaired glucose regulation. Our aim was to evaluate whether this beneficial dietary metal may help to reduce the impaired glucose regulation associated with toxic metals such as Pb.MethodsWe used a subsample of more than 4000 adults aged 18–65y who provided fasting serum and toenail samples in the 2009 wave of the China Health and Nutrition Survey. We measured Pb concentrations in toenail samples using inductively coupled plasma mass spectroscopy (ICP‐MS), and measured fasting glucose using colorimetric assay methods. Dietary Mg intake was estimated from three days or 24‐h dietary recalls. We estimated the association between toenail Pb concentrations and fasting glucose levels using multivariable linear regression adjusting for age, gender, body mass index, waist circumference, physical activity, urbanicity, education level, toenail arsenic and selenium, and intakes of energy, meat and rice. Interactions with dietary Mg were examined using tertiles of intake.ResultsThe median (interquartile range) toenail Pb concentration was 1.15 (1.45) mg/kg, and the mean (SD) Mg intake was 296 (107) mg/dL. The mean fasting serum glucose level was 95.8 (24.7) mg/dL. After multivariable adjustment, among individuals in the lowest tertile of dietary Mg, there was a significant increase in fasting glucose associated with a 1‐unit increase in log‐transformed toenail Pb (β±SE 0.64±0.27 mg/dL, P&lt;0.05). However, among individuals in the highest intake tertile, toenail Pb was associated with a non‐significant reduction in fasting glucose (β±SE −0.34±0.28 mg/dL NS; interaction P&lt;0.05).ConclusionFindings suggest that exposure to Pb may promote impaired glucose homeostasis, and that dietary Mg may help to reduce the diabetogenic effects of Pb exposure. Further research is needed to determine whether essential metals such as Mg may help to mitigate the risk of diabetes associated with toxic metals such as Pb.Support or Funding InformationThis research uses data from the China Health and Nutrition Survey, funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)(R01‐HD30880). We also are grateful to the Carolina Population Center (R24 HD050924) for general support.

Estimated lead (Pb) exposures for a population of urban community gardeners.

Urban community gardens provide affordable, locally grown, healthy foods and many other benefits. However, urban garden soils can contain lead (Pb) that may pose risks to human health. To help evaluate these risks, we measured Pb concentrations in soil, vegetables, and chicken eggs from New York City community gardens, and we asked gardeners about vegetable consumption and time spent in the garden. We then estimated Pb intakes deterministically and probabilistically for adult gardeners, children who spend time in the garden, and adult (non-gardener) household members. Most central tendency Pb intakes were below provisional total tolerable intake (PTTI) levels. High contact intakes generally exceeded PTTIs. Probabilistic estimates showed approximately 40% of children and 10% of gardeners exceeding PTTIs. Children's exposure came primarily from dust ingestion and exposure to higher Pb soil between beds. Gardeners' Pb intakes were comparable to children's (in µg/day) but were dominated by vegetable consumption. Adult household members ate less garden-grown produce than gardeners and had the lowest Pb intakes. Our results suggest that healthy gardening practices to reduce Pb exposure in urban community gardens should focus on encouraging cultivation of lower Pb vegetables (i.e., fruits) for adult gardeners and on covering higher Pb non-bed soils accessible to young children. However, the common practice of replacement of root-zone bed soil with clean soil (e.g., in raised beds) has many benefits and should also continue to be encouraged.

Lead (Pb) contamination of self-supply groundwater systems in coastal Madagascar and predictions of blood lead levels in exposed children.

Thousands of households in coastal Madagascar rely on locally manufactured pitcher-pump systems to provide water for drinking, cooking, and household use. These pumps typically include components made from lead (Pb). In this study, concentrations of Pb in water were monitored at 18 household pitcher pumps in the city of Tamatave over three sampling campaigns. Concentrations of Pb frequently exceeded the World Health Organization's provisional guideline for drinking water of 10 μg/L. Under first-draw conditions (i.e., after a pump had been inactive for 1 h), 67% of samples analyzed were in excess of 10 μg/L Pb, with a median concentration of 13 μg/L. However, flushing the pump systems before collecting water resulted in a statistically significant (p < 0.0001) decrease in Pb concentrations: 35% of samples collected after flushing exceeded 10 μg/L, with a median concentration of 9 μg/L. Based on measured Pb concentrations, a biokinetic model estimates that anywhere from 15% to 70% of children living in households with pitcher pumps may be at risk for elevated blood lead levels (>5 μg/dL). Measured Pb concentrations in water were not correlated at statistically significant levels with pump-system age, well depth, system manufacturer, or season of sample collection; only the contact time (i.e., flushed or first-draw condition) was observed to correlate significantly with Pb concentrations. In two of the 18 systems, Pb valve weights were replaced with iron, which decreased the observed Pb concentrations in the water by 57-89% in one pump and by 89-96% in the other. Both systems produced samples exclusively below 10 μg/L after substitution. Therefore, relatively straightforward operational changes on the part of the pump-system manufacturers and pump users might reduce Pb exposure, thereby helping to ensure the continued sustainability of pitcher pumps in Madagascar.

Metal levels in Trachurus trachurus and Cyprinus carpio in Turkey

Concentrations of five toxic metals were determined in two fish species from Turkish cities during 2010–2011. The obtained lead concentrations for all of the studied Trachurus trachurus (mean 777 μg kg−1) and Cyprinus carpio (mean 439 μg kg−1) samples were found to be higher than the maximum level (ML) of 300 μg kg−1, while Cd concentrations in the same samples were lower than the ML. Mean chromium (501 μg kg−1), Ni (272 μg kg−1) and Cu (785 μg kg−1) concentrations in T. trachurus were significantly higher than in C. carpio (336 μg Cr kg−1, 229 μg Ni kg−1 and 394 μg Cu kg−1), similar to those of Pb and Cd. Measured Pb concentrations in T. trachurus tissues are significantly higher than the ML, while those of Cd in both T. trachurus and C. carpio species were lower than the ML values.

Lead isotopes as a tracer of Pb origin in the sediments from Beijiang River, South China

Concentrations and enrichment of heavy metals were determined in sediments collected from Beijiang River, South China. The Pb isotopic compositions in these sediment samples were also employed to effectively identify metal pollution sources. According to the measured Pb concentrations, the total Pb concentrations in sediments varied from 62.1 to 1,152.5 μg/g, with an average concentration of 249.6 μg/g. The assessment by Geoaccumulation Index indicates that Pb is at the 'strongly contaminated' level, indicating that the Pb pollution was mainly due to anthropogenic inputs. The observed isotopic ratios varied from 1.174 to 1.204 for ²⁰⁶Pb/²⁰⁷Pb, 2.452 to 2.478 for ²⁰⁸Pb/²⁰⁷Pb, 18.404 to 18.937 for ²⁰⁶Pb/²⁰⁴Pb, 15.631 to 15.790 for ²⁰⁷Pb/²⁰⁴Pb, 38.455 to 39.121 for ²⁰⁸Pb/²⁰⁴Pb. The majority of these ratios are lower than those reported for natural geological sources, especially for sediments collected from a smelter. Significant correlation between Pb concentration and isotopic ratios suggested possible binary mixing of Pb. Combined with Pb concentration and enrichment levels, our results show that Pb pollution in the sediments of Beijiang River was mainly derived from anthropogenic sources. The mining activities and metal smelting processing was the main source of Pb pollution in this region.

Seasonal variability in the input of lead, barium and indium to Law Dome, Antarctica

Lead (Pb) isotopic compositions and concentrations, and barium (Ba) and indium (In) concentrations have been determined at monthly resolution in five Law Dome (coastal Eastern Antarctica) ice core sections dated from ∼1757 AD to ∼1898 AD. ‘Natural’ background Pb concentrations in ∼1757 AD average ∼0.2 pg g −1 and can be attributed to mineral dust and volcanic emissions, with 206Pb/ 207Pb ratios reaching up to 1.266 ± 0.002. From ∼1887 AD to ∼1898 AD, Pb concentrations reached ∼5 pg g −1 and 206Pb/ 207Pb ratios decreased to 1.058 ± 0.001 as a result of additional inputs of Pb from anthropogenic sources. Seasonal variability in the late 1880s has been investigated by decoupling volcanic Pb from the total measured Pb concentrations, revealing spring and autumn maxima, and consistent winter minima, in anthropogenic Pb and mineral dust (Ba) concentrations. We link this variability to the annual cycle in the position and strength of the Antarctic Circumpolar Trough and, the Southern Ocean westerly winds to the north of the trough region. During the autumn and spring seasons, these systems increase in strength, transporting more impurity laden air from the Southern Hemisphere continental regions to Eastern Antarctica and Law Dome. As this Pb is isotopically identical to that emitted from south-eastern Australia (Broken Hill, Port Pirie) this implies a relatively direct air trajectory pathway from southern Australia to Law Dome (Eastern Antarctica).

Toxicogenomics of water chemistry influence on chronic lead exposure to the fathead minnow ( Pimephales promelas)

Establishment of water quality criteria (WQC), intended to protect aquatic life, continues to rely principally on water hardness (i.e. Ca 2+) for lead (Pb) despite growing evidence that other chemical parameters also strongly influence toxicity. To more clearly define the water chemistry parameters mediating Pb toxicity, we evaluated the effects of hardness as CaSO 4 and dissolved organic carbon (DOC) as humic acid during chronic (150 days) exposures to the fathead minnow. Measured Pb concentrations ranged from 157 ± 5 nM (33 ± 1 μg/L) Pb in base water to 177 ± 7 (37 ± 1 μg/L) and 187 ± 7 nM (39 ± 1 μg/L) Pb in CaSO 4- or HA-supplemented water, respectively. Fish were collected at 2, 4, 10, 30, 63, 90 and 150 days of exposure. Traditional toxicological endpoints were examined alongside gene transcription analyses to help clarify the underlying mechanisms of Pb toxicity and to identify candidate molecular markers that might ultimately serve as robust indicators of exposure and effect. Addition of CaSO 4 did not prevent whole body Pb accumulation whereas DOC afforded strong protection (about half the amount accumulated by fish in base water) suggesting that current, hardness-based WQC are likely inaccurate for predicting chronic Pb effects in aquatic systems. Custom-made microarrays were co-hybridized with base water samples ± Pb up to the 30 days time point. Quantitative PCR was employed to verify gene transcription responses and to extend analysis to the CaSO 4 and HA treatments and the 150 days time point. Identification of four genes by microarray analysis revealed clear Pb-induced responses over time: glucose-6-phosphate dehydrogenase, glutathione- S-transferase, ferritin and β-globin. Results obtained by qPCR were in strong agreement with microarray data by regression analysis ( r 2 = 0.82, slope = 1.28). The associated pathways implicated herein for these genes provide further evidence supporting roles for anemia and neurological disorders in chronic Pb toxicity. Effects of water chemistry on Pb accumulation and gene transcription responses were in close parallel, though alterations in ionoregulatory and morphological endpoints were not observed. Whereas DOC was protective against Pb accumulation and mRNA expression changes, Ca 2+ was not. Additionally, several hypothesis-driven genes (ECaC, DMT-1, and ALA-D) were examined by qPCR but revealed either no change or small Pb-induced responses lacking any clear influence attributable to water chemistry. These findings should help pave the way toward development of a new chronic Pb BLM and a Pb-responsive gene transcript profile for fathead minnows, both of which would greatly aid future environmental monitoring and regulatory strategies for Pb.

Prediction of Pb speciation in concentrated and dilute nutrient solutions

Despite the presence of numerous studies in the literature examining the phytotoxicity of Pb, there is a lack of precise quantitative data on limiting concentrations of Pb for plant growth. Using the PhreeqcI chemical equilibrium model, simulations were conducted to examine the speciation of Pb in concentrated and dilute nutrient solutions. Due to the higher P concentration of Hoagland's solution (1000 μM), precipitation of chloropyromorphite (Pb 5(PO 4) 3Cl) was predicted to occur at lower pH values, and at lower Pb concentrations, than for a dilute nutrient solution (2 μM P). Although nutrient solutions prepared in the glasshouse were supersaturated (and Pb concentrations were substantially higher than predicted by modeling), they confirmed the importance of the P concentration in influencing the precipitation of Pb. Given the low solubility of Pb-phosphates, nutrient solutions with low P concentrations should be utilized, and plant growth should be related to measured Pb concentrations rather than to the quantity of Pb initially added.

Phytoaccumulation of Lead by Sunflower (Helianthus annuus), Tobacco (Nicotiana tabacum), and Vetiver (Vetiveria zizanioides)

The ability of three plant species: Helianthus annuus, Nicotiana tabacum, and Vetiveria zizanioides for phytoaccumulation of Pb was studied. Plants were grown in hydroponic solution containing Pb(NO3)2 at concentration of 0.25 and 2.5 mM Pb in the presence or absence of chelating agents (EDTA or DTPA). Lead (Pb) transport and localization within the tissues of the plant species was determined using scanning electron microscope equipped with energy dispersive X-ray spectrometers (SEM-EDS). The addition of chelators increased Pb uptake as compared to plants grown in solution containing Pb alone. Lead taken up by the plant species were concentrated in both leaf and stem at the region of vascular bundles with greater amounts in the leaf portion. Lead granules were also found in the H. annuus root tissue from the epidermis layer to the central axis. After four weeks of growth a 23-fold increase in shoot Pb content for H. annuus and N. tabacum and 17-fold increase in shoot Pb for V. zizanioides resulted from plants grown in the 2.5 mM Pb-EDTA treatment. The higher Pb treatment (2.5 mM Pb containing EDTA) resulted in higher concentrations of Pb in plant tissue at the fourth week of exposure as compared to Pb treatment containing DTPA. Overall, Pb accumulation potential of H. annuus was greater than that of N. tabacum and V. zizanioides as indicated by the bioconcentration factor (171, 70, and 88, respectively). The highest measured Pb concentrations were found in H. annuus roots, stems, and leaves (2668, 843, and 3611 μg/g DW, respectively) grown in the 2.5 mM Pb-EDTA treatment. The addition of chelators caused some reduction in plant growth and biomass. Results showed that the three plant species tested have potential for use in phytoaccumulation of Pb since the Pb was concentrated in leaf and stem as compared to control plants. H. annuus however best meet the prerequisites for a hyperaccumulator plant and would have the potential for use in the restoration of abandoned mines and factories sites contaminated with elevated Pb levels in the soil.

Lead in Three Peat Bog Profiles, Jura Mountains, Switzerland: Enrichment Factors, Isotopic Composition, and Chronology of Atmospheric Deposition

One metre cores were taken from three peat bogs in the Jura Mountains of Switzerland: Etang de la Gruere (EGr), La Tourbiere des Genevez (TGe), and Praz Rodet (PRd). Dried peat samples were analyzed for lead (Pb) using the EMMA XRF and scandium (Sc) using INAA. Enrichment factors (EF) were calculated by normalizing to the background Pb/Sc ratio at EGr. Age dates were obtained using 210Pb (CRS Model) and confirmed using pollen chronostratigraphic markers in replicate cores. The isotopic composition of Pb in selected peat samples from EGr and TGe was determined using TIMS. Two pronounced peaks in Pb EF occur in the uppermost sections of all three bogs: the upper one corresponds to the late 1960's to late 1970's and the lower one to approximately 1900 to 1920. At EGr, sample 2f5 (11 cm, 86 µg/g Pb, EF = 91, and dated at A.D. 1967 ± 2) has an isotopic composition similar to that of leaded gasoline used in Berne in the 1970's. For comparison, the older peak at EGr (sample 2fl 1 at 29 cm, 84 µg/g Pb, EF = 79 and dated at A.D. 1905 ± 6) is significantly different. In contrast to these two samples, the isotopic composition of sample 2fl 5 (41 cm, 30 µg/g Pb, EF = 13 and pre-dating ca. A.D. 1800) approaches the present day "average terrestrial lead" and is likely to be predominately lithogenic. Therefore, the isotopic data show that the Pb introduced to the bog from leaded gasoline has not penetrated to this depth in the profile. A simple mass balance using the measured Pb concentrations and the isotopic compositions shows that vertical migration of gasoline Pb cannot explain the deeper, older peak in Pb EF. A more likely explanation is that the older peak reflects the rates of atmospheric Pb deposition during the first two decades of the 20th century. Taken together, the Pb concentrations, age dates, and isotopic data suggest that these peat profiles have preserved the record of changing rates of atmospheric Pb deposition. In addition, the results indicate that the isotopic composition of Pb deposited on the surface of the bogs gradually shifted away from lithogenic ratios as long ago as the middle of the 19th century, a change which clearly pre-dates the introduction of leaded gasoline.