Assessment of total soil and plant elements in rice-based production systems in NE Italy

Abstract

Macro- and micronutrients concentrations and PTEs contents in soils and plants (rice) fromthe rice district in the Venetian territory (NE Italy) have been determined by Inductive Coupled Plasma Optical Emission Spectrometry (ICP-OES), with the following aims: - to determine the background levels of macro- and microelements in the study area; - to assess possible contamination of soils and plants; - to calculate the Translocation Factor (TF) of metals from soil to plant, and the possible hazard for human health. Four rice plots with different rotation systems were investigated from seedling time to harvesting; sampling of soils (0–30 cm) and plants was carried out 4 times during growing season (three replicates). Rice plants were separated into the roots, stems, leaves and grains, and then oven-dried. Chemical and physical analyses were carried out at the Soil Science Lab of the University of Bologna and Venice, respectively. The results obtained point to a land with high soil contamination by Li and TI. The total concentrations of most studied metals (Al, As, Be, Cd, Co, Cr, Cu, Fe, Ni, Pb, Sb, Sn, Sr, V, Zn) in the soil samples fell in the natural geochemical background concentration levels, even though the concentration levels of some of them (e.g. Sn) overcame the Italian threshold limits for green areas (DM 152/2006). Most elements are likely associated with the geochemistry of the parent material. Antimony and Ti contents in soils are positively correlated with soil pH, while As, Be, Fe, Li, Sb, Ti, Tl and Zn are negatively correlated with organic matter content. With the exception of strontium, soil metals are always correlated between variable couples. Heavy metals in plants vary according to the sampling season, texture and moisture, and soil pH. Most non-essential trace elements are accumulated in rice roots and, only in cases of essential micronutrients, in leaves. Therefore, rice can be assumed as an excluder plant (i.e. metal in the roots b metal in soil) for Li, Sn, Tl. The results of multiple linear regression analysis showed that soil extractable P and total Ca played an important role in predicting annual grain yield of rice. The average translocation of metals from the soil to the root was found to be N1, irrespective of the essential/not essential function; conversely, only essential elements (Cu, Fe, Mn, Zn) are translocated rather easily from the roots to leaves (TF ≤ 1) via xylem, and very little are translocated to grains (TF ≪1). Rice plants were able to accumulate non essential metals in their tissues especially in the roots, but not in the edible part, and this could be useful for the restoration of contaminated sites with a very limited hazard for human population consuming rice crops