Repeated Land Application of Biosolids in Quebec: Impacts on Soils, Dairy Milk Quality and Greenhouse Gas Emissions
Abstract:In the Saguenay region (Quebec, Canada), a field study was done to evaluate metal accumulations of the soil surface layer (0–20cm) with 26 farm fields that received a mean of 7 annual spreadings of municipal biosolids between 1991 and 2006. This corresponds to a cumulative mean loading of 20 t/ha (d.w.b.). Spreadings were in conformity with Quebec regulations and criteria. Metal accumulations were evaluated by comparing the surface layer to the 40–60 cm layer, as a control, and by using loading calculations.
Cumulative spreadings of biosolids on soils had no impact on cadmium and aluminium contents, but they caused a significant increase in the upper layer with total mercury and with extractable copper, lead and zinc (Mehlich 3). However, final soil contents were well below agricultural soil reference criteria used in the province of Quebec, even soils that received up to 12 applications. Because lead and mercury contents of Saguenay biosolids are decreasing since 1990, further accumulations of these metals in receiving soils are likely to be lower in the future.
Repeated land application of biosolids also increased the phosphorus saturation index of soils (P/Al), still most final values remained low (< 4 %). This increase in soil P fertility will tend to reduce further biosolids loadings to soils, in order to respect nutrient regulations. Hence, biosolids quality, field results and trends suggest that metal quality criteria for agricultural soils will not be exceeded over the long term (100 years), with possible exception for Cu, as it is the case with hog manure. A new approach has been published to prevent excessive soil Cu accumulations with the use of these organic fertilizers. However, further sampling of 14 dairy farms receiving biosolids in the Saguenay region, indicate no impact on Cu and Mo contents in milk, as compared to control farms. A resumÉ of concentrations of inorganic trace elements and PBDE in dairy milk will be presented at the conference, as well as results of a survey on greenhouse gaz emission reductions associated with the Saguenay biosolids program.
Document Type: Research Article
Publication date: January 1, 2011
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