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Lead-sheathed telecom cables and historic leaded gasoline emissions substantially raise environmental lead levels in Portland, Oregon

Environmental Studies and Forestry

Lead-sheathed telecom cables and historic leaded gasoline emissions substantially raise environmental lead levels in Portland, Oregon

A. E. Shiel, S. Jovan, et al.

Discover how urban moss in Portland, Oregon reveals the hidden legacy of lead contamination linked to old infrastructures and past practices. This research by Alyssa E. Shiel, Sarah Jovan, and Christina J. Murphy uncovers the lasting effects of leaded gasoline and relic telecommunication cables on our environment. Further insights are needed to understand human exposure risks.

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Playback language: English
Introduction
Lead (Pb) is a highly toxic metal causing various health problems, particularly affecting children's neurodevelopment. Identifying and mitigating lead pollution sources is crucial. Leaded gasoline, used extensively until 1996 in the US and 2021 globally, is a major historical source of lead pollution. Recent reports have highlighted lead-sheathed telecommunication cables, installed from the late 1800s to the 1960s, as a potential ongoing source of lead contamination in urban areas. These cables, often found near schools and homes, are a largely unrecognized source of environmental lead. This study uses high-resolution spatial sampling of lead in urban moss, a biomonitor reflecting atmospheric lead levels, to investigate the contribution of leaded gasoline and lead-sheathed cables to Portland's lead pollution landscape. Lead isotope fingerprinting further helps to differentiate lead sources. The study aims to characterize legacy lead sources in Portland and quantify the impact of lead-sheathed telecommunication cables.
Literature Review
Biomonitors like epiphytic mosses and lichens effectively assess metal emissions and changes in metal levels over time. Their lack of roots means they absorb metals from air, precipitation, and dust, reflecting atmospheric levels. Previous studies have used mosses and lichens to monitor pollution sources but often lacked high spatial resolution, limiting their ability to pinpoint localized sources. High-resolution sampling has proven effective in identifying previously unknown pollution sources. Existing literature demonstrates strong correlations between lead levels in moss and atmospheric deposition, and the use of lead isotopic fingerprinting to trace lead emissions to their sources. While studies have shown the persistence of leaded gasoline's impact, the contribution of lead-sheathed cables remains largely unquantified.
Methodology
Moss samples (*Orthotrichum lyellii*) were collected across Portland in 2013 (347 samples) and 2023 (38 samples), with additional archival samples (6) and rural samples (11) for comparison. The 2013 sampling used a random grid approach, while the 2023 sampling focused on areas with identified lead-sheathed telecommunication cables. Moss samples were prepared by removing foreign material, drying, grinding, and digesting with acids. Lead concentrations were analyzed using ICP-MS, with indium or rhenium as internal standards. Lead isotope ratios (²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁴Pb) were measured for a subset of samples (70 in 2013, 45 in 2023) using ICP-MS and a sample-standard bracketing protocol. The NIST SRM 1949 lead standard was used for quality control. The presence of lead-sheathed telecommunication cables was verified using Google Street View imagery and in-person confirmation. Statistical analysis, including ANOVA and Tukey's post-hoc test, were performed on log-transformed lead concentration data to account for data skewness. Geometric means were used for lead concentrations, reflecting the log-normal distribution.
Key Findings
The 2013 Portland moss samples showed a mean lead concentration of 5.42 ppm, 1.17 times higher than the rural background (0.463 ppm). The highest concentration in 2013 was 129 ppm (279x background). Resampling in 2023 revealed sustained high concentrations, reaching up to 271 ppm (586x background). Lead concentrations varied significantly by neighborhood age, with older neighborhoods showing much higher levels. However, even within the same neighborhood, significant variation in lead levels was observed, often over short distances. Moss samples near lead-sheathed cables had significantly higher lead concentrations (geometric mean of 16.7 ppm in 2013 and 15.3 ppm in 2023) compared to those without cables (7.88 ppm and 2.74 ppm, respectively). The highest lead concentrations (up to 129 ppm in 2013 and 271 ppm in 2023) were found within 1 meter of cables. Lead isotope ratios revealed a complex lead landscape. While the isotopic signatures of moss samples from Portland (excluding those near cables) were consistent with historical leaded gasoline emissions, samples near lead-sheathed cables showed a wider range of ratios, outside the range of leaded gasoline, indicating additional lead sources. The isotopic signature of lead cables varied across neighborhoods, reflecting differences in the lead ore sources used in their production. Other localized sources, such as a gun range, also contributed to elevated lead levels in specific areas.
Discussion
The findings demonstrate that both historical leaded gasoline emissions and relic lead-sheathed telecommunication cables significantly contribute to Portland's current lead pollution. The persistent presence of leaded gasoline's legacy is clear, but the high concentrations near cables emphasize their substantial impact. The high-resolution sampling effectively revealed localized pollution sources that would have been missed by lower-resolution studies. The variation in lead isotope ratios near cables highlights the heterogeneity of lead sources and the need for more detailed investigation of cable composition and leaching rates. The persistence of elevated lead levels even after cable removal highlights the long-term environmental impact and the need for effective remediation strategies.
Conclusion
This high-resolution study provides compelling evidence of the significant contribution of lead-sheathed telecommunication cables to lead pollution in Portland, in addition to the continuing impact of historical leaded gasoline emissions. The study underscores the importance of high-resolution sampling techniques in identifying localized pollution sources and highlights the need for further research to quantify the impact of these cables and develop effective remediation strategies. Future work should focus on detailed analysis of cable composition and leaching rates to better understand the extent and persistence of this pollution source.
Limitations
The study focused on moss as a biomonitor, and results may not fully represent all pathways of human exposure to lead. The identification of lead-sheathed cables relied on Google Street View imagery, which may not be completely comprehensive. While soil samples were collected in some areas showing elevated lead concentrations near cables, more extensive soil analysis is needed for a complete picture. The study focused on Portland, and findings may not be generalizable to all urban environments.
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