Effect of Zn, Cd, and Pb on the growth of food crops and bioassimilation of metals in rabbits from contaminated vegetation

Abstract

Pot and field experiments were conducted to determine the effect of cadmium (Cd) lead (Pb) and zinc (Zn) on the growth of spinach (Spinacea oleracea). The metals contaminated vegetable was fed to the test animals and their bioassimilation in the body was investigated. The wire house and field experiments were conducted to monitor the effect of environmental conditions on difference in uptake of Cd, Pb and Zn in spinach. Both experiments were started at the same time to compare the metal concentrations in the leaves of spinach. The metal concentrations in all treatments decreased in the field experiment and the highest concentration of metals under study were found in 5 kg soil followed by 10 kg soil in wire house and the lowest in the field plots. Application of phosphorus (P1) to these treatments significantly (p ≤ 0.05) decreased the concentration of these metals in the leaves of spinach. Shoot and root fresh matter yield reduced with the increase of heavy metals but the application of P significantly (p ≤ 0.05) increased fresh matter yields and ultimately decreased the uptake of these metals. Furthermore, spinach grown in the field plots contaminated with Pb (1000 mg kg-1 soil) and Zn (150 mg kg-1 soil) without application of phosphorus (P0) was fed to the rabbits for assessment of bioassimilation in the blood, essential organs (liver and kidney) and bones of rabbits. The study investigated the bioavailability of Zn and Pb in soil-plant-animal system. This involved an investigation of the connection between the total volume and the mobile forms of Pb and Zn in soils; the translocation of these metals into spinach; and their ingestion by rabbits fed with spinach leaves. It was found that these metals from spinach feeding were assimilated in the bones and essential organs of the rabbit. Bioassimilation of Pb in the body of rabbits was in order of bone > kidney > liver > blood while for Zn a decreasing order of bone > liver > kidney > blood was observed. Bioaccessibility of Pb and Zn from spinch leaves grown in these field plot spiked with Pb (1000 mg kg-1 soil) and Zn (150 mg kg-1 soil) fed to the rabbits was also determined. Overall, the bioaccessibility of Pb and Zn was 6.53 and 7.64 % of the total metal contents in the spinach leaves respectively. In next study, spinach was repeatedly grown in the field plots contaminated with Zn (150 mg kg-1 soil) and Pb (1000 mg kg-1 soil) without P (P0) after the harvest of first crop to determine the bioavailability of these metals with time. The concentration of Pb in the soil (after the first spinach crop) has no significant effect on the shoot fresh biomass of the spinach. However, Zn concentration has increased the fresh weight of shoot. The concentration of the heavy metals under study, i.e. Pb and Zn decreased in successive spinach crop. At the end, effect of Zn nutrition on the uptake of Cd was studied 2 in spinach in soil contaminated with Cd:Zn ratio of 1:10 (Cd @ 3 mg kg-1 and Zn @ 30 mg kg-1) and 1:100 (Cd @ 3 mg kg-1 and Zn @ 300 mg kg-1). Due to similarities in different chemical properties, an antagonistic relation between Cd and Zn was observed in the present study. Lower level of Zn @ 30 mg kg-1 with 3 mg kg-1 Cd has no significant effect on the shoot and root dry matter yields of spinach. A higher level of Zn @ 300 mg kg-1 in the 1:100 ratio of Cd:Zn caused a greater decrease in the Cd concentration in spinach leaves compared to Cd:Zn ratio of 1:10. Through these experiments it was found that leafy vegetable such as spinach accumulated high concentrations of Cd, Pb and Zn in its leaves. These metals entered in the food chain and after the consumption of contaminated vegetable got assimilated in the body of rabbits. Bioavailability of these metals decreased with the application of phosphorus (P1) and from the interaction with other ion, i.e. Zn. The result of these experiments showed that the vegetables such as spinach, grown on metal contaminated soil should be consumed with care because spinach has the tendency to accumulate higher concentration of these metals in its edible part. However, amendment like phosphate treatment or other interacting ion like Zn can reduce the uptake of metals and therefore contributes to safe food production on metal contaminated soils.