Zeolites Reduce the Transfer of Potentially Toxic Elements from Soil to Leafy Vegetables

Abstract

The ability of natural zeolite amendment to reduce the uptake of potentially toxic elements (PTEs) by lettuce, spinach and parsley was evaluated using pot experiments. PTE concentrations in roots and shoots, as well as the pseudo total (PT), water soluble (WS) and bioavailable (BA) PTE fractions in the amended soils, were assessed. Although the PT PTE concentration was high, the WS fraction was very low (<0.4%), while the BA fraction varied widely (<5% for Cr, Mn and Co, <15% for Ni, Pb and Zn, >20% for Cd and Cu). PTE concentration decreased in both roots and shoots of all leafy vegetables grown on zeolite amended soils, especially at high amendment dose (10%). The uptake of PTEs mainly depended on plant species, PTE type and amendment dose. With the exception of Zn in spinach, the bioaccumulation factor for roots was higher than for shoots. Generally, lettuce displayed the highest PTE bioaccumulation capacity, followed by spinach and parsley. Except for Zn in spinach, the transfer factors were below 1 for all PTEs, all plant species and all amendment doses. Our results showed that the natural zeolites are promising candidates in the reclamation of contaminated soils due to their ability to immobilize PTEs.

Zeolite Properties, Methods of Synthesis, and Selected Applications

“…In contrast, in the roots of sunflowers, zeolite application to soil contributed to a decrease in chromium and zinc content by 15% and 4%, respectively. The beneficial effect of zeolite application on the immobilization of trace elements in contaminated soil was also demonstrated by Cadar et al [ 79 ]. They showed that a 10% addition of this material to the soil reduced the bioaccumulation of Co, Cr, Cu, Mn, Ni, Pb, and Zn in the roots and shoots of spinach, parsley, and lettuce, with the exception of Cd in the spinach roots.…”

Modification of natural zeolites and their applications for heavy metal removal from polluted environments: Challenges, recent advances, and perspectives

“…Natural zeolites received significant attention due to their unique physicochemical properties, such as high ion exchange capacity without any structural modification, large void volume, reversible dehydration, adsorption of molecules, catalytic activity, etc. [ 30 , 33 , 50 ]. Since the cation exchange ability is expressed as the cation exchange capacity (CEC), depending on the substitution of Si by Al, the natural zeolites display a CEC value in the range 1–4 mmol M + /g zeolite [ 50 ].…”

“…These adsorbents can remove heavy metals from polluted waters by ion exchange, chemisorption or mechanical removal [ 79 ]. Also, they were successfully applied for the remediation of the polluted soils by diminishing the mobility of the metals in soil, thus decreasing the heavy metals transfer to the plants, by the so-called “stabilization” process, without significantly altering the natural function of soils [ 33 , 43 , 80 ]. Efficiency in the environmental remediation is contingent on the type, quantity and porosity of used natural zeolites, particle size and initial concentration of contaminants, pH and ionic strength of the solution, contact time between zeolite and solution, pressure, temperature, and presence of other organic and inorganic contaminants [ 35 , 48 ].…”

“…About 70 types of natural zeolite occur worldwide, and more than 250 zeolites similar to the natural ones have been synthesized. The main natural zeolite sources are in Slovakia, Bulgaria, Greece, Italy and United States of America [ 32 , 33 ]. Natural zeolites were produced by conversion of volcanic glass under various geochemical settings [ 34 ], their chemical formula being (M + x , M 2+ y )[Al (x+2y) Si n−(x+2y) O 2n × mH 2 O, where M + x and M 2+ y are monovalent or divalent metal ions, [Al (x+2y) Si n−(x+2y) O 2n ] is basic structure, and m is the number of molecules of water [ [35] , [36] , [37] ].…”

“…These cations can be involved in ion-exchange processes and replaced in the zeolite structure by other cations [ 41 , 42 ]. Natural zeolites are commonly used in many areas, including industry, medicine, cosmetics, agriculture, animal husbandry, biotechnology, waste management and pollution control [ 33 , [43] , [44] , [45] , [46] ]. Due to the presence of impurities, the specific area of natural zeolites is smaller than that of synthetic zeolites, which is unfavorable for environmental remediation.…”