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.

http://www.sciencedirect.com/science/article/pii/S1352231013005943


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

SEGH Events

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

  • Biochar-based constructed wetlands to treat reverse osmosis rejected concentrates in chronic kidney disease endemic areas in Sri Lanka 2017-12-01

    Abstract

    The objectives were to investigate the potential remedial measures for reverse osmosis (RO) rejected water through constructed wetlands (CWs) with low-cost materials in the media established in chronic kidney disease of unknown etiology (CKDu) prevalent area in Sri Lanka. A pilot-scale surface and subsurface water CWs were established at the Medawachchiya community-based RO water supply unit. Locally available soil, calicut tile and biochar were used in proportions of 81, 16.5 and 2.5% (w/w), respectively, as filter materials in the subsurface. Vetiver grass and Scirpus grossus were selected for subsurface wetland while water lettuce and water hyacinth were chosen for free water surface CWs. Results showed that the CKDu sensitive parameters; total dissolved solids, hardness, total alkalinity and fluoride were reduced considerably (20–85%) and most met desirable levels of stipulated ambient standards. Biochar seemed to play a major role in removing fluoride from the system which may be due to the existing and adsorbed K+, Ca+2, Mg+2, etc. on the biochar surface via chemisorption. The least reduction was observed for alkalinity. This study indicated potential purification of aforesaid ions in water which are considerably present in RO rejection. Therefore, the invented bio-geo constructed wetland can be considered as a sustainable, economical and effective option for reducing high concentrations of CKDu sensitive parameters in RO rejected water before discharging into the inland waters.

  • Medical geology of endemic goiter in Kalutara, Sri Lanka; distribution and possible causes 2017-12-01

    Abstract

    This study assesses the distribution of goiter in the Kalutara District, Sri Lanka in order to find causative factors for the occurrence of goiter even after the salt iodization. A questionnaire survey was conducted at the household level and at the same time iodine and selenium levels of the water sources were analyzed. Questionnaire survey results indicated the highest numbers of goiter patients in the northern part where the lowest were found in the southern sector which may be due to the presence of acid sulfate soils. Females were more susceptible and it even showed a transmittance between generations. Average iodine concentrations in subsurface water of goiter endemic regions are 28.25 ± 15.47 μg/L whereas non-goiter regions show identical values at 24.74 ± 18.29 μg/L. Surface water exhibited relatively high values at 30.87 ± 16.13 μg/L. Endemic goiter was reported in some isolated patches where iodine and selenium concentrations low, latter was <10 μg/L. The formation of acid sulfate soils in the marshy lands in Kalutara district may lead to transformation of biological available iodine oxidation into volatile iodine by humic substances, at the same time organic matter rich peaty soil may have strong held of iodine and selenium which again induced by low pH and high temperature were suggested as the instrumental factors in the endemic goiter in Kalutara district. Hence, geochemical features such as soil pH, organic matter and thick lateritic cap in the Kalutara goiter endemic area play a role in controlling the available selenium and iodine for food chain through plant uptake and in water.

  • Nickel accumulation in paddy rice on serpentine soils containing high geogenic nickel contents in Taiwan 2017-12-01

    Abstract

    We investigated the extractability of nickel (Ni) in serpentine soils collected from rice paddy fields in eastern Taiwan to evaluate the bioavailability of Ni in the soils as well as for demonstrating the health risks of Ni in rice. Total Ni concentrations in the soils ranged were 70.2–2730 mg/kg (mean, 472 mg/kg), greatly exceeding the natural background content and soil control standard in Taiwan. Available Ni concentration only accounts for <10% of total soil Ni content; 0.1 N HCl-extractable Ni was the more suitable index for Ni bioavailability in the soil to rice than was diethylenetriaminepentaacetic acid (DTPA)-extractable Ni. The accumulation ability of rice roots was much higher than that of its shoots; however, compared with those reported previously, our brown and polished rice samples contained much higher Ni concentrations, within the ranges of 1.50–4.53 and 2.45–5.54 mg/kg, respectively. On the basis of the provisional tolerable Ni intake for adults recommended by the World Health Organization (WHO), daily consumption of this rice can result in an excessive Ni intake.