Use of Brassica Oleracea var. Acephala as a vegetal monitor for metals in the atmosphere

The possibility to use Brassica Oleracea var. Acephala (kale) as a vegetal monitor for metals dispersed in the atmosphere was evaluated. For this purpose, two experiments were conducted. i) "Nursery experiment": specimens were planted in a mould contaminated with known metal concentrations and they were exposed in the very likely unpolluted atmosphere of a nursery, with the aim of monitoring the root uptake. ii) "City experiment": some plants were planted in an unpolluted mould and exposed in flower beds in three different sites in the city of Turin (north west of Italy) in order to favour leaf uptake; given the different vehicle traffic, the sites in the city were considered to have various levels of atmospheric pollution. After four and eight weeks, some leaves were collected in the nursery and in the city sites and their content in Cr, Cu, Ni, Pb and Zn was determined. The nursery experiment demonstrated that metal concentration in the mould did not influence significantly metal contents in the leaves. On the contrary, the experiments conducted in the city showed abundant accumulation of metals in the leaves, which was proportional to the different levels of atmospheric pollution in the three sites. To distinguish the fraction of metals merely deposited on the leaves from that more tightly bound, the leaves sampled in the city sites were subdivided into two sub-samples: i) leaves were analysed as is; ii) leaves were carefully washed with water to eliminate any deposit. The washing procedure resulted in a lower concentration of metals, but it allowed for a correct correlation between the deposit accumulation and the exposure time as the results were unrelated to atmospheric precipitation.