Assessment of biotransfer and bioaccumulation of cadmium, lead and zinc from fly ash amended soil in mustard–aphid–beetle food chain

The present study investigates the extent of biotransfer and bioaccumulation of cadmium (Cd), lead (Pb) and zinc (Zn) from fly ash amended soil in mustard (Brassica juncea)-aphid (Lipaphis erysimi)-beetle (Coccinella septempunctata) food chain and its subsequent implications for the beetle. The soil was amended with fly ash at the rates of 0, 5, 10, 20 and 40% (w/w). Our results showed that the uptake of Cd, Pb and Zn from soil to mustard root increased with the increase in fly ash application rates, but their root to shoot translocation was relatively restricted. Increase in chlorophyll content and dry mass of mustard plant on treatments ≥ 20% even at elevated accumulation of Cd (1.67 mg kg^− 1), Pb (18.25 mg kg^− 1) and Zn (74.45 mg kg^− 1 dry weight) in its shoot showed relatively higher tolerance of selected mustard cultivar to heavy metal stress. The transfer coefficient (TC¹ Transfer coefficient.) of Cd from mustard shoot to aphid was always > 1, indicating that Cd biomagnified in aphids at second trophic level. But, there was no biomagnification of Cd in adult beetles at third trophic level. Zinc accumulation was 2.06 to 2.40 times more in aphids than their corresponding host shoots and 1.26–1.35 times more in adult beetles than their prey (aphids) on which they fed. Lead was only metal whose TC was < 1 at both second and third trophic levels. The elimination of Cd via honeydew of aphids was most efficient as the ratio of metal in honeydew to aphid (ranging from 0.21 to 0.26) was higher than the Pb (0.16 to 0.20) and Zn (0.07 to 0.09). The statistically consistent (p > 0.05) biomass and predation rate of predatory beetles indicated that all levels of soil amendments with fly ash did not have any lethal or sub-lethal effects on beetles.