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TECHNICAL REPORTS

Heavy Metals in the Environment

Risk Indicator for Agricultural Inputs of Trace Elements to Canadian Soils

^a ECOMatters Inc., 24 Aberdeen Ave., Pinawa, MB, Canada R0E 1L0
^b Agriculture and Agri-Food Canada, Brandon Research Centre, 18th St. and Grand Valley Rd., P.O. Box 1000a, R.R.#3, Brandon, MB, Canada R7A 5Y3
^c Agriculture and Agri-Food Canada Environmental Health, 960 Carling Ave., Ottawa, ON, Canada K1A 0C6

^* Corresponding author (sheppards{at}ecomatters.com).

Received for publication April 27, 2008. Trace elements (TEs) are universally present in environmental media, including soil, but agriculture uses some materials that have increased TE concentrations. Some TEs (e.g., Cu, Se, and Zn) are added to animal feeds to ensure animal health. Similarly, TEs are present in micronutrient fertilizers. In the case of phosphate fertilizers, some TEs (e.g., Cd) may be inadvertently elevated because of the source rock used in the manufacturing. The key question for agriculture is "After decades of use, could these TE additions result in the deterioration of soil quality?" An early warning would allow the development of best management practices to slow or reverse this trend. This paper discusses a model that estimates future TE concentrations for the 2780 land area polygons composing essentially all of the agricultural land in Canada. The development of the model is discussed, as are various metrics to express the risk related to TE accumulation. The elements As, Cd, Cu, Pb, Se, and Zn are considered, with inputs from the atmosphere, fertilizers, manures, and municipal biosolids. In many cases, steady-state concentrations could be toxic, but steady state is far in the future. In 100 yr, the soil concentrations (Century soil concentrations) are estimated to be up to threefold higher than present background, an impact even if not a problematic impact. The geographic distribution reflects agricultural intensity. Contributions from micronutrient fertilizers are perhaps the most uncertain due to the limited data available on their use.

Abbreviations: BMP, best management practice • CCME, Canadian Council of Ministers of the Environment • CR, plant/soil concentration ratio • C_SS, steady state soil concentration • C₁₀₀, soil concentration after 100 years, or Century soil concentration • GIS, geographic information system • GSD, geometric standard deviation • ICP–MS, inductively coupled plasma–mass spectroscopy • Kd, soil solid/liquid partition coefficient • NAHARP, National Agri-environmental Health Analysis and Reporting Program • RQ, risk quotient • SLC, soil landscape classification • TE, trace element