Through a long-standing collaboration with Prof Abida Butt from the University of the Punjab in Pakistan, I have had the opportunity to be involved in an interesting project on the accumulation of heavy metals in an agro-ecosystem in the berseem plant (a clover used as cattle feed) -> grasshopper and berseem plant -> aphid -> ladybird food chains. Most of the heavy metals investigated (cadmium, lead and zinc) showed transfer to all trophic levels, but that the rate varied for both metals and insects depending on feeding style, retention and toxicity. My main contributions consisted of assisting in data analysis and in writing the paper.
Butt, A., Qurat-ul-Ain, Rehman, K., Khan, M. X. and Hesselberg, T. (2018). Bioaccumulation of cadmium, lead, and zinc in agriculture-based insect food chains. Environmental Monitoring and Assessment 190, 698. doi.org/10.1007/s10661-018-7051-2
Abstract
Globally, the metal concentration in soil is increasing due to different anthropogenic and geogenic factors. These metals are taken up by plants and further transferred in the food chain through different routes. The present study was designed to assess the transfer and bioaccumulation of the heavy metals, cadmium (Cd), lead (Pb), and zinc (Zn), in food chains from soil to berseem plants (Triofolium alexandrinum), to insect herbivores (the grasshopper Ailopus thalassinus and the aphid Sitobion avenae) and to an insect carnivore (the ladybird beetle Coccinella septempunctata). The soil of studied berseem fields were slightly alkaline, silty loam in texture and moderate in organic matter. In soil, the concentration of Zn and Pb were under permissible level while Cd was above the permissible level. The accumulation of metals in T. alexandrinum were found in the order Zn > Cd > Pb. Grasshoppers showed higher accumulation of Pb than of Cd and Zn. In the soil-berseem-aphid-beetle food chain, metal enrichment was recorded. However, aphids did not show bioaccumulation for Cd. Metals accumulation in beetles showed that translocation of Zn, Cd, and Pb was taking place in the third trophic level. Our study highlights the mobility of metals in insect food chains and showed that insect feeding style greatly influenced the bioaccumulation. However, different metals showed variable bioaccumulation rates depending on their toxicity and retention.
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