SEGH Articles

An historical reconstruction of atmospheric heavy metals deposition from a peat bog record on the North Shore of the St. Lawrence Estuary, Quebec

01 October 2013
Peat bogs were used to reconstruct the history of atmospheric heavy metal deposition along the St. Lawrence Valley. Results from one of the study sites were presented at the 29th SEGH held in July 2013, Toulouse.

Steve Pratte is currently a Ph.D. student at the Department of Earth and Atmospheric Sciences of Université du Québec à Montréal (UQAM, Canada) and the National Polytechnical Institute of Toulouse (INPT, France). The research presented at the 29th SEGH Conference in Toulouse won the Hemphill prize for best poster presentation in July.  The research was carried out during his Master’s degree in Earth and Planetary Sciences at McGill University in Montreal, under the supervision of Dr. Alfonso Mucci and Dr. Michelle Garneau.

Human activities, especially since the Industrial Revolution, have left a legacy of trace metal contamination that is potentially harmful for natural ecosystems and human health (e.g. As, Cd, Pb) and affected their geochemical cycles. Atmospheric metal pollution is recorded in different environmental archives such as lake and marine sediments, snow and ice and peat bogs. Among these archives, peat bogs have proven to be effective in reconstructing the history of atmospheric metal deposition throughout Europe, but few studies have been carried out in North America or in Quebec. Being an important natural wind corridor, oriented from south-west to north-east, the St. Lawrence Valley is affected by long-range transport of contaminants.

The present study focuses on the reconstruction of the history of atmospheric As, Cd, Ni, Pb and Zn deposition in surface cores (<100 cm) from three peat bogs along the St. Lawrence Valley (Fig.1). Core chronologies were established using 210Pb for the upper horizons and 14C dating for the deeper sections. Metal accumulation rates were computed from measured concentrations and core chronologies. Stable lead isotopes (204, 206, 207 and 208) were also analysed to distinguish natural and anthropogenic sources of Pb. Arsenic, cadmium, lead and stable lead isotopes results from one of the study sites (Baie bog) were presented at the 29th SEGH conference.

Metal accumulation rates (AR) and concentrations start increasing from the beginning to mid-19th century and increase more sharply from early 20th century. At the same time, Pb isotopic values diminish from 1850 AD probably from deposition of coal burning particle, and stabilise from the 1920’s likely due to contributions from leaded gasolines. Lead accumulations rates peak in 1951 AD, which is earlier than other studies undertaken in the region. Maximum Pb AR (24 mg m-2 yr-1) are in good agreement with other studies, while As and Cd AR are much lower than accumulation rates obtained in the southwestern part of the St. Lawrence Valley. This is likely explainable by the more remote location of the site which allow more particles to settle before reaching the site. This is also reflected in lead isotope values which fall closer to Canadian aerosols values, the site further away from the US Mid-west, receives proportionally more contributions from Canadian leaded gasolines. A sharp decrease in metal accumulation rates and concentrations from the mid-60’s and increase in Pb isotopic ratios from the mid-1970’s is observed, which reflect the phasing out of leaded gasoline and the implementation of other mitigation policies (i.e. Clean Air Act). However, values are still an order of magnitude higher than pre-industrial values and other less radiogenic sources of Pb must be invoked (likely coal consumption and smelting activities) to explain the recent decrease in isotopic values.

Study site locations

In short, the Baie bog recorded the main trends in industrial activities since the Industrial Revolution. The site receives more pollution from Canadian than US sources in reason of its greater distance from the main industrial and urban sources. Mitigation policies (phasing-out of leaded gasoline, Clean Air Act) have been effective in reducing metal emissions and deposition in the environment. Nevertheless, other sources than leaded gasolines are still contributing to Pb and other metal emissions.

Link to an article in Atmospheric Environment arising from this study.

Steve Pratte

Department of Earth and Atmospheric Sciences of Université du Québec à Montréal (UQAM, Canada) and the National Polytechnical Institute of Toulouse (INPT, France).

Keep up to date

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

  • Characteristics of PM 2.5 , CO 2 and particle-number concentration in mass transit railway carriages in Hong Kong 2016-06-20


    Fine particulate matter (PM2.5) levels, carbon dioxide (CO2) levels and particle-number concentrations (PNC) were monitored in train carriages on seven routes of the mass transit railway in Hong Kong between March and May 2014, using real-time monitoring instruments. The 8-h average PM2.5 levels in carriages on the seven routes ranged from 24.1 to 49.8 µg/m3, higher than levels in Finland and similar to those in New York, and in most cases exceeding the standard set by the World Health Organisation (25 µg/m3). The CO2 concentration ranged from 714 to 1801 ppm on four of the routes, generally exceeding indoor air quality guidelines (1000 ppm over 8 h) and reaching levels as high as those in Beijing. PNC ranged from 1506 to 11,570 particles/cm3, lower than readings in Sydney and higher than readings in Taipei. Correlation analysis indicated that the number of passengers in a given carriage did not affect the PM2.5 concentration or PNC in the carriage. However, a significant positive correlation (p < 0.001, R 2 = 0.834) was observed between passenger numbers and CO2 levels, with each passenger contributing approximately 7.7–9.8 ppm of CO2. The real-time measurements of PM2.5 and PNC varied considerably, rising when carriage doors opened on arrival at a station and when passengers inside the carriage were more active. This suggests that air pollutants outside the train and passenger movements may contribute to PM2.5 levels and PNC. Assessment of the risk associated with PM2.5 exposure revealed that children are most severely affected by PM2.5 pollution, followed in order by juveniles, adults and the elderly. In addition, females were found to be more vulnerable to PM2.5 pollution than males (p < 0.001), and different subway lines were associated with different levels of risk.

  • Excessive fluoride consumption increases haematological alteration in subjects with iron deficiency, thalassaemia, and glucose-6-phosphate dehydrogenase (G-6-PD) deficiency 2016-06-18


    Excessive fluoride consumption leads to accelerated red blood cell death and anaemia. Whether that increases the haematological alteration in subjects with haematological disorders (iron deficiency, thalassaemia, and G-6-PD deficiency) is still unclear. The fluoride in serum and urine and haematological parameters of students at Mae Tuen School (fluoride endemic area) were analysed and compared to those of students at Baan Yang Poa and Baan Mai Schools (control areas). Iron deficiency, thalassaemia, and G-6-PD deficiency were also diagnosed in these students. The students at Mae Tuen School had significantly (P < 0.001) higher levels of mean fluoride in the serum and urine than those in control areas. In both control and fluoride endemic areas, students with haematological disorders had significantly lower levels of Hb, Hct, MCV, MCH, and MCHC than those without haematological disorders. Moreover, the lowest levels of Hb, MCH, and MCHC were observed in the students with haematological disorders who live in the fluoride endemic area. Thus, the excessive fluoride consumption increased haematological alteration in subjects with iron deficiency, thalassaemia, and G-6-PD deficiency and that may increase the risk of anaemia in these subjects.

  • Health risk assessment of potentially harmful elements and dietary minerals from vegetables irrigated with untreated wastewater, Pakistan 2016-06-18


    In the developing world, vegetables are commonly grown in suburban areas irrigated with untreated wastewater containing potentially harmful elements (PHEs). In Pakistan, there is no published work on the bioaccessibility aspect of PHEs and dietary minerals (DMs) in sewage-irrigated soil or the vegetables grown on such soils in Pakistan. Several industrial districts of Pakistan were selected for assessment of the risk associated with the ingestion of vegetables grown over sewage-irrigated soils. Both the total and bioaccessible fraction of PHEs (Cd, Co, Cr, Ni, and Pb) and DMs (Fe, Cu, Mn, Zn, Ca, Mg, and I) in soils and vegetable samples were measured. The concentrations of these PHEs and DMs in sewage-irrigated and control soils were below published upper threshold limits. However, compared to control soils, sewage irrigation over the years decreased soil pH (7.7 vs 8.1) and enhanced dissolved organic carbon (1.8 vs 0.8 %), which could enhance the phyto-availability of PHEs and DMs to crops. Of the PHEs and DMs, the highest transfer factor (soil to plant) was noted for Cd and Ca, respectively. Concentrations of PHEs in most of the sewage-irrigated vegetables were below the published upper threshold limits, except for Cd in the fruiting portion of eggplant and bell pepper (0.06–0.08 mg/kg Cd, dry weight) at three locations in Gujarat and Kasur districts. The bioaccessible fraction of PHEs can reduce the context of dietary intake measurements compared to total concentrations, but differences between both measurements were not significant for Cd. Since the soils of the sampled districts are not overly contaminated compared to control sites, vegetables grown over sewage-irrigated soils would provide an opportunity to harvest mineral-rich vegetables potentially providing consumers 62, 60, 12, 104, and 63 % higher dietary intake of Cu, Mn, Zn, Ca, and Mg, respectively. Based on Fe and vanadium correlations in vegetables, it is inferred that a significant proportion of total dietary Fe intake could be contributed by soil particles adhered to the consumable portion of vegetables. Faecal sterol ratios were used to identify and distinguish the source of faecal contamination in soils from Gujranwala, Gujarat, and Lahore districts, confirming the presence of human-derived sewage biomarkers at different stages of environmental alteration. A strong correlation of some metals with soil organic matter concentration was observed, but none with sewage biomarkers.