Proceedings of the 4 th World Congress on New Technologies (NewTech'18) Madrid, Spain – August 19 – 21, 2018 Paper No. ICEPR 163 DOI: 10.11159/icepr18.163 ICEPR 163-1 Determination of Soluble/Exchangeable Metals in Peri-urban Farmland (Ribeira dos Covões) of Central Portugal Ryunosuke Kikuchi 1 , Carla S. S. Ferreira 2 , Fábio L. P. Viela 3 1 Faculty of Science & Technology, Ryukoku University Seta, Yokotani 1-5, Otsu, Japan kikuchi@rins.ryukoku.ac.jp 2 Centro de Recursos Naturais, Ambiente e Sociedade, Escola Superior Agrária de Coimbra Bencanta, Coimbra, Portugal cferreira@esac.pt 3 Faculdade de Ciências, Universidade Agostinho Neto Av. 7 de Fevereiro, Luanda, Angola fabioviela1988@gmail.com Abstract - Heavy metal contamination of soil is widespread, and there is a potential risk of transferring toxic metals to agricultural crops, animals and humans. The total heavy metals content can indicate the extent of contamination, but this measure is not usually an accurate indication of the phyto-toxicity; therefore, a number of recent studies have investigated the bioavailable heavy metal fractions in soils and evaluated the phyto-toxic risks for humans. Soluble and exchangeable forms of metals in the soil are the fractions available for plants. The main purpose of the present study is to quantify the total and soluble/exchangeable fractions of heavy metals (Pb, Cr, Cu and Zn) in soils of peri-urban farmland in Portugal (Ribeira dos Covões). The results show that the total heavy metals content is greater than the soluble/exchangeable content, but no clear correlations were recorded: Pb ‒ 70.8 mg/kg vs. 16.7 mg/kg, Cr ‒ 25.0 mg/kg vs . 0.0 mg/kg, Zn ‒ 383.3 mg/kg vs. 0.0 mg/kg, Cu ‒ 183.3 mg/kg vs. 0.0 mg/kg in a horticultural garden (site 10), and; Pb ‒ 270.8 mg/kg vs. 79.0 mg/kg, Cr ‒ 25.0 mg/kg vs. 0.0 mg/kg, Zn ‒ 12.5 mg/kg vs. 0.0 mg/kg, Cu ‒ 33.3 mg/kg vs. 29.2 mg/kg in a backyard (site 18). It is possible that the use of a single extraction procedure, in the laboratory, may not provide a proper assessment of heavy metal forms, and it is therefore advisable to combine different extraction methods in order to correctly perform a risk-based evaluation. Keywords: Bioavailable Fraction, Farmland, Heavy Metal, Peri-Urban, Portugal. 1. Introduction Heavy metal contamination of soils is widespread and there is a risk of transfer of toxic and available metals to agricultural crops, animals and humans [1]. Heavy metals can induce toxicity in wildlife if the level in the soil reaches critical concentrations; accumulation in above-ground tissues of plants can also result in an increase of metal accumulation in top- soil, via leaf deposition, or can create an exposure pathway for metal introduction into the food chain [2]. Two main sources of heavy metals in soils can be considered: the natural pedo-geochemical background, which represents the heavy metal concentration inherited from the parent rock [3] and anthropogenic contamination, which can be directed via wastes [4], compost [5], or sewage sludge [6] or may diffuse via aerosol deposition [7]. The total heavy metal contents can indicate the extent of contamination, but is not usually an accurate indication of the phyto-toxicity [8 & 9]. Many recent studies investigated the bioavailable heavy metal fractions of mine soils [8 & 9] and evaluated the phyto-toxic risk for human receptors. Bioavailability is the proportion of total metals that are available for incorporation into biota (bioaccumulation). Total metal concentrations do not necessarily correspond with metal bioavailability [10]. However, the determination of heavy metal fractions is a more complex task than the determination of the total contents of heavy metals [11]. Several analytical methods have been used to quantify heavy metals in the soil; for example, the soil extraction with strong acids is commonly carried out to assess total heavy metals, and X-ray fluorescence spectrometry is used to determine the content of total elements (review in [12]). Soluble and exchangeable forms of metals in the soil are the fractions available