Heavy metal contents in green spears of asparagus (Asparagus officinalis L.) grown in Southern Italy: Variability among farms, genotypes and effect of soil mycorrhizal inoculation

The concentration of sixteen different heavy metals (HMs) [arsenicum (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), selenium (Se), tin (Sn), uranium (U), vanadium (V) and zinc (Zn)] were determined in green asparagus spears produced in an intensively cultivated area of Southern Italy. The level of the HMs was analysed in the most common cultivar in the area (‘Grande’), along with the variability in HM contents on four different farms within this area. The effect on HM levels of soil inoculation with arbuscular mycorrhizal fungi (AMF) and of three different genotypes (‘Atlas’, ‘Italo’ and ‘Purple passion’) was also evaluated. Asparagus spears had greater amounts of Fe (29.3 mg kg−1 fresh weight – fw), Zn (3.1 mg kg−1 fw) and Mn (2.0 mg kg−1 fw) than the other micronutrients. As a whole the observed values were within the range reported in the literature and in food composition databases for asparagus and other vegetables, being even richer in iron and lower in As, Cd, Hg and Pb. The principal component analysis underlined a larger HM concentration in both plant essential (Fe, Mn), beneficial (Co, Se and V) and non-essential (As, Cr, Pb) elements in the product obtained from two out of the four farms investigated, likely to be due to the larger application of organic amendments. Between the less intensively fertilized farms, a lower content of Cu and Ni and an improved Mo level further seems to result from the non-application of mineral phosphorus and of guano-based fertilizers. The product from AMF inoculated soil was distinctively richer in almost all the elements, particularly in non-essential ones, but also in several important micronutrients for humans health (e.g.: Cu, Fe, Mn). Compared with the standard cultivar (‘Grande’), ‘Atlas’ and ‘Italo’ had a greater concentration of As, whereas no changes or lower levels were detected for the other HMs. The violet type (‘Purple passion’) stood out for the highest Se content along with a generally lower level of other HMs.