Quantitative and Qualitative Assessment of Heavy Metal Risk in a Peri-Urban Area of Central Portugal

Abstract

Peri-urban areas are characterized by a variety of types of housing, transport infrastructure and multifunctional agriculture, covering extensive areas (ca. 48,000 km2) within the European Union (EU). These areas provide a diverse range of recreation sites and ecosystem services, such as food production. Food security is one of the first priorities for the EU, and there is a critical interface between agriculture and peri-urban land use change. The proximity between urban pollution sources and agricultural areas raises concerns regarding the possible adverse effects of heavy metals contamination on crop quality, and consequent impact on both food security and human health. A field study was performed to assess the risk of soil contamination in a peri-urban area in central Portugal. The total amount and the bioavailable and water-soluble fractions of heavy metals (Cd, Cr, Cu, Pb and Zn) were quantified in the soil samples The results show that heavy metals concentrations were lower than the standard values for soil assessment. However, the bioavailable fraction of Pb was quite variable, depending upon the sampling site. Since only the soluble, exchangeable and chelated metal species in the soils represent the labile fractions available to plants, there is doubt as to how to properly apply the standard values categorized by land utilization to estimate a potential risk relative to metal bioavailability in a multifunctional peri-urban area. It is recommended to standardize a reliable methodology in terms of assessing the risk in soil-crop-human transfer of heavy metals, especially in multifunctional peri-urban areas.