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

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

  • Alterations in antioxidant defense system of workers chronically exposed to arsenic, cadmium and mercury from coal flying ash 2016-02-01

    Abstract

    Humans are exposed to different stress factors that are responsible for over-production of reactive oxygen species. Exposure to heavy metals is one of these factors. The aim of the study was to analyze the effect of chronic exposure to heavy metals through coal flying ash on the efficiency of antioxidative defensive mechanisms, represented by the activity of superoxide dismutase, glutathione peroxidase and ascorbic acid. Nonessential elements such as arsenic and mercury levels showed a significant increase (p > 0.001) in the power plant workers rather than in the control subjects. There were no significant differences of blood cadmium between power plant workers and control subjects. We found a significant positive correlation (p < 0.05) between BAs/SZn (r = 0.211), BAs/BSe (r = 0.287), BCd/SCu (r = 0.32) and BHg/BSe (r = 0.263) in the plant workers. Red blood cell antioxidant enzymes and plasma ascorbic acid were significantly lower in power plants workers than in the control group (p < 0.002). We can conclude that levels of mercury, arsenic and cadmium in blood, despite their concentration within the reference values, significantly affect plasma ascorbic acid concentration, superoxide dismutase and glutathione peroxidase activity, which are able to increase the risk of oxidative stress.

  • Increase in platinum group elements in Mexico City as revealed from growth rings of Taxodium mucronatum ten 2016-02-01

    Abstract

    Tree rings may be used as indicators of contamination events providing information on the chronology and the elemental composition of the contamination. In this framework, we report PGEs enrichment in growth rings of Taxodium mucronatum ten for trees growing in the central area of Mexico City as compared to trees growing in a non-urban environment. Concentrations of PGE were determined by ICP-MS analysis on microwave-digested tree rings. The element found in higher concentrations was Pd (1.13–87.98 μg kg−1), followed by Rh (0.28–36.81 μg kg−1) and Pt (0.106–7.21 μg kg−1). The concentration trends of PGEs in the tree-ring sequences from the urban area presented significant correlation values when comparing between trees (r between 0.618 and 0.98, P < 0.025) and between elements within individual trees (r between 0.76 and 0.994, P < 0.01). Furthermore, a clear increase was observed for rings after 1997, with enrichment of up to 60 times the mean concentration found for the sequence from the non-urban area and up to 40 times the mean concentration for the pre-1991 period in the urban trees. These results also demonstrate the feasibility of applying T. mucronatum ten to be used as a bioindicator of the increase in PGE in urban environments.

  • Heavy metals and parasitic geohelminths toxicity among geophagous pregnant women: a case study of Nakuru Municipality, Kenya 2016-02-01

    Abstract

    Geophagia is defined as deliberate consumption of earths’ materials, e.g. soil, clay and soft stones. The practice is widespread among pregnant women, and there are conflicting views as to whether it is beneficial to health or not. Geophagic materials may be a source of micronutrients though the materials may bind the micronutrients thus reducing or hindering their bioavailability in the body. Geophagia is closely associated with geohelminthic infections among pregnant women and heavy metal poisoning, which constitute significant public health problem in many developing countries such as Kenya. In our research, the geophagic materials consumed by the pregnant women were studied. A total of 38 geophagic materials in the possession by different pregnant women were analysed. The collected samples were subjected to standard digestion procedures and analysed for zinc, lead and iron by atomic absorption spectroscopy. Results indicated that the geophagic materials contained elevated levels of Fe at mean concentration value of 80.10 ppm, Pb at 3.28 ppm and Zn 1.81 ppm for a 1.00 g sample. An average of 20 g of the geophagic materials was being consumed per day. Based on the average consumption, the pregnant women were exposed to 65.52 ppm Pb per day, 36.2 ppm Zn per day and 1602 ppm Fe per day. Lead exceeded the WHO-lead exposure limits of 25 ppm/day for pregnant women. The materials were also subjected to microscopic examination for Ascaris lumbricoides, Trichuris trichiura, Taenia Spp., Necator americanus and Ancylostoma duodenale. In conclusion, the women were exposed to heavy metals—iron, zinc and lead, but there was no observable eggs, larvae or adult species of the geohelminths. The key recommendation was that there is need to integrate public health education on geophagia, lead screening and testing with antenatal support care systems. This will enhance maternal and child health, thus reducing infant and maternal morbidity and mortality rates.