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Unraveling the multi-source history of lead contamination in North America’s oldest city St John’s, Newfoundland

P. Sylvester R. Magalios Marc Poujol 1
1 Terre, Temps, Traçage
GR - Géosciences Rennes
Abstract : Lead isotopes were used to determine sources of high quantities of lead in soilsin urban St. John’s, Newfoundland. Highest lead levels are found near roads(mean=674 ppm) and along the drip line of houses built prior to 1945(mean=2107 ppm) and are an order of magnitude higher than background levelsfrom C-horizon tills (40 ppm). In many cases values exceed national guidelines(CCME, 140 ppm). Sources likely include atmospheric precipitation, coal ashwastes and deposition of lead-based paints along drip lines of buildings. Leadwas likely contributed to the atmosphere from burning of coal for home heatingand from leaded gasoline.Previous measurements of lead isotopes in lake sediments in and aroundthe city suggested that the sources of lead used in the manufacture of dispersedcontaminants changed in about 1960 from ores with low 206Pb/207Pb ratios(~1.064 in the Sullivan mine in Trail, British Columbia or ~1.037 in Broken Hill,Australia) to ores with much higher 206Pb/207Pb ratios (~1.16 in Bathurst, NewBrunswick or 1.28-1.33 from southeastern Missouri, U.S.A.). This studydetermined lead isotopes ratios in 27 soils, 7 C-horizon tills, 2 exterior paints anda piece of archived coal to constrain the sources of lead and their relativecontributions.A linear trend from bedrock-derived lead in tills with high 206Pb/207Pb(~1.18-1.20) and low 208Pb/206Pb (~2.06-2.08) ratios to leads from clapboard driplines and paint from >100 year-old houses with low 206Pb/207Pb (~1.12-1.13) andhigh 208Pb/206Pb (~2.13-2.14) ratios is apparent. Coal and paint from a 50 yearoldhouse fall mid-way along the trend (as do ratios from ores from Bathurst).Soils with moderate lead levels from vacant lots and parks plot toward higher206Pb/207Pb values, whereas lead-rich soils from residential settings plot towardlower 206Pb/207Pb. Contamination of open spaces is dominated by lead fromCape Breton coal and/or gasoline residues and <50-year-old paint derived fromBathurst ores. Contamination of urban residential sites also includes asignificant component of >50 year-old paint derived in part from Sullivan leads.Lead isotope compositions of some soils collected along roads and open spacesin the city trend away from the main data array toward a lead source with higher206Pb/207Pb and lower 208Pb/206Pb than the natural background source. Theseareas may be contaminated by residues of gasoline lead from SE Missouri ores.Anthropogenic lead in St. John’s soils thus appears to be derived from up to fourexotic sources.
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Conference papers
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Submitted on : Monday, November 17, 2014 - 2:13:06 PM
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P. Sylvester, R. Magalios, Marc Poujol. Unraveling the multi-source history of lead contamination in North America’s oldest city St John’s, Newfoundland. GAC-MAC conference, May 2006, Montréal, Canada. pp.145. ⟨insu-01083537⟩

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