Abstract
Emissions of manganese (Mn), lead (Pb), iron (Fe), zinc (Zn), copper (Cu) from ferro-alloy operations has taken place in Valcamonica, a pre-Alp valley in the province of Brescia, Italy, for about a century until 2001. Metal concentrations were measured in the soil of local home gardens and in the cultivated vegetables. Soil analysis was carried out using a portable X-Ray Fluorescence (XRF) spectrometer in both surface soil and at 10 cm depth. A subset of soil samples (n = 23) additionally was analysed using the modified BCR sequential extraction method and ICP-OES for intercalibration with XRF (XRF Mn = 1.33 * total OES Mn - 71.8; R = 0.830, p < 0.0001). Samples of salads (Lactuca sativa and Chichorium spp.) were analyzed with a Total Reflection X-Ray Fluorescence (TXRF) technique. Vegetable and soil metal measurements were performed in 59 home gardens of Valcamonica, and compared with 23 gardens from the Garda Lake reference area. Results indicate significantly higher levels of soil Mn (median 986 ppm vs 416 ppm), Pb (median 46.1 ppm vs 30.2 ppm), Fe (median 19,800 ppm vs 13,100 ppm) in the Valcamonica compared to the reference area. Surface soil levels of all metals were significantly higher in surface soil compared to deeper soil, consistent with atmospheric deposition. Significantly higher levels of metals were shown also in lettuce from Valcamonica for Mn (median 53.6 ppm vs 30.2) and Fe (median 153 vs 118). Metals in Chichorium spp. did not differ between the two areas. Surface soil metal levels declined with increasing distance from the closest ferroalloy plant, consistent with plant emissions as the source of elevated soil metal levels. A correlation between Mn concentrations in soil and lettuce was also observed. These data show that historic ferroalloy plant activity, which ended nearly a decade before this study, has contributed to the persistence of increased Mn levels in locally grown vegetables. Further research is needed to assess whether this increase can lead to adverse effects in humans and plants especially for Mn, an essential element that can be toxic in humans when exceeding the homeostatic ranges.
Highlights
Metal contamination of the environment raises concern for the possible impact on human health, and the occurrence of heavy metals in soils, of both natural and anthropogenic origin, is well-recognized as a potentially important source of human exposure [1,2]
Near total Mn levels measured with the BCR and inductively coupled plasma-optical emission spectrometry (ICP-OES) were highly significantly correlated with Mn levels measured by X-Ray Fluorescence (XRF) (XRF Mn = 1.33*OES Mn – 71.8, R = 0.830, p < 0.0001)
Chemically labile Mn levels measured with the BCR and ICP-OES (BCR fractions 1 + 2) were significantly correlated with Mn levels measured by XRF (XRF Mn = 1.43*OES Mn – 14.7, R = 0.826, p < 0.0001)
Summary
Metal contamination of the environment raises concern for the possible impact on human health, and the occurrence of heavy metals in soils, of both natural and anthropogenic origin, is well-recognized as a potentially important source of human exposure [1,2]. Where metals in soil are increased by anthropogenic disposal and emission, the measure of metal concentrations provide useful information on potential human cumulative exposure. Anthropogenic processes recognized as potential sources of soil contamination with heavy metals include: 1) agricultural activities with the use of metal-containing fertilizers, pesticides, sewage sludge, and irrigation water; 2) emissions from energy and fuel production activities; 3) mining and smelting operations, such as tailing, smelting, refining and transportation; 4) vehicle traffic and combustion of petroleum fuels containing metal additives; 5) emissions from waste incineration; and 6) metal recycling operations like scrap melting [5]
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