Community Garden Heavy Metal Study
Halifax Regional Municipality (HRM), Canada
Environment Canada Science Horizon Youth Internship Program, Nova Scotia Agricultural College (NSAC), and the Halifax Regional Municipality (HRM). Ecology Action Centre (EAC)
This study was conducted to assess the level of heavy-metal contamination in the soils of urban gardens in the HRM. Four elements were chosen, and their concentrations in existing and potential urban gardens were measured. Soil samples were taken from specified locations following standard protocols. The following issues were addressed:
Development of survey design, sampling and analytical protocols; Identification of potential and existing urban gardens in the HRM; Selection of heavy metals of concern;
Collection, preparation and analysis of soil samples;
Comparison of the results of this study to studies conducted in other Canadian cities, and to background levels for native soils in Nova Scotia; and Investigation of potential spatial pattern for contamination occurrence within the HRM.
A principle objective was to develop preliminary recommendations for existing and future gardens for managing and mitigating heavy metal contamination in the urban garden soil. This is a preliminary study and it provides only an indication of soil’s heavy- metal contamination in the sampled gardens, rather than an absolute assessment of heavy- metal contamination of the soils of HRM.
Chapter 5: Conclusion and Recommendation
The concentration of lead, arsenic, copper and zinc was measured in samples collected from current and potential gardens in the HRM. Within each site, random samples were collected to obtain a representative estimation of heavy metal contamination in each garden. Partial digestion of soil samples was carried out to estimate the bioavailable concentration of heavy metals. Soil heavy metal concentrations were compared to the CCME soil quality guidelines for agricultural lands in order to assess the level of contamination and potential risk to human and ecological health. The results of this study indicate that more than one third of samples had higher concentration of lead than the CCME guideline. Arsenic contamination was also seen widely in the sampled sites, with a concentration higher than the CCME guideline in almost half of the sampled locations. This was expected due to the high background concentration of arsenic in Nova Scotia soils and bedrock. Copper and zinc were also measured for this study and only a few sampled locations had higher concentration of these elements than the CCME guideline. However, the concentration of zinc and copper might have been underestimated due to the selection of the digestion method.
Following the correlation analysis, it was concluded that the occurrence of lead, zinc, and copper are related. There were no obvious patterns for spatial distribution of these heavy metals in the HRM. By comparing the results of this study with similar studies conducted in other Canadian cities, it was concluded that the lead concentration in the HRM was lower than Sydney, NS, Trail, BC, and St. John’s, NL, and higher than Sudbury, Ottawa, and Iqaluit. It is important to keep in mind that concentrations of heavy metals between cities might not be directly comparable, as some studies use different sampling strategies and analytical methods.