I had the fortune to be invited to collaborate on a large-scale study by my Egyptian colleague – Prof Amr Mohamed. In the project the Amr and another Egyptian colleague had collected data on how heavy metals (Chromium and Nickel) accumulate across a wide range of organisms in an Egyptian agri-industrial from grasshoppers to the common kestrel. My involvement primarily focussed on adding ecological context to the invertebrates used in the study (grasshopper, mantis and wolf spider), but I was also able to provide input on the writing, figures and data analysis. The main results of the study is that while significant bioaccumulation occurs in the invertebrate food chain, less accummulation occurs higher up in the food chain with some vertebrate groups such as birds and mammals even showing sign of biodilution (while others such as amphibians and lizards showed biomagnification). In general, we found that heavy metal concentrations generally decreased in the trophic chain with distance from the pollution source.
Soliman, M. M., Hesselberg, T., Mohamed, A. A. And Renault, D. (2022). Trophic transfer of heavy metals along a pollution gradient in a terrestrial agro-industrial food web. Geoderma 413, 115748. https://doi.org/10.1016/j.geoderma.2022.115748
Abstract
Heavy metal contamination across the food web is a growing concern because of increasing environmental discharges in industrial zones, atmospheric transport, and deposition and erosion during rainfall events. We examined the transfer pathways of chromium (Cr) and nickel (Ni) through a terrestrial trophic web and investigated the potential for their bioaccumulation along the trophic chain. Soil, plants, arthropods, and vertebrates were sampled from different localities in the south of Cairo (El-Tebbin, Egypt) and the amounts of Cr and Ni from these samples were measured. We also computed a body condition index (BCI) for vertebrates to estimate individual health and fitness levels in relation to heavy metal concentrations in the liver. The levels of Cr and Ni varied significantly among the samples. Lower trophic levels showed a tendency for biomagnification, while higher trophic levels showed possible biodilution of the two heavy metals: arthropods, amphibians, and lizards concentrated more Cr and Ni than the other taxonomic groups; conversely birds and small mammals generally showed lower levels of Cr and Ni. A negative relationship was obtained when the concentrations of Cr in the soil, plant, and arthropods, and the concentrations of Ni in the wolf spider were plotted as a function of the distance to the industrial area. A significant inverse relationship was found between the Ni concentration of liver and body length, while body mass had no significant effect. Our study thus highlights the varied effects of heavy metal concentrations across a complex food web at different distances from the pollution source, and the need for further studies of their effect on multiple species in an ecosystem.
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