Bioaccumulation of Heavy Metals by Grasshoppers and a Mantid Along a Pollution Gradient

The concentrations of Cd, Cr, Cu, Fe, Ni, Pb, and Zn were studied in soil, plants, three grasshopper species (Aiolopus thalassinus (Fabricius, 1781), Calephorus compressicornis (Latreille, 1804), and Acrotylus patruelis (Herrich-Schäffer, 1838)), and a mantid (Miomantis paykullii Stål, 1871), to estimate the scale of spatial influence of a point pollution source, to investigate metal bioaccumulation up the soil–plant–grasshopper–mantid food chain, and to assess these insects as ecologica l bioindicators. Plant, insect, and soil sampling was undertaken simultaneously from grass margins of an arable farmland near an industrial complex in Al-Tebbin. Correlation analyses revealed a pollution gradient, with samples closest to the industrial activities having the highest concentrations of heavy metals. Sigmoid curves indicated that the influence radius of the industrial zone for heavy metal contamination in soil, plants, and grasshoppers was in the range of 3.0–4.0 km. The average concentrations of Cd, Cr, Cu, Fe, Ni, Pb, and Zn in the three grasshopper species were 4.9, 4.0, 73.9, 210, 5.2, 12.0, and 224.2 mg/kg, respectively, while those in the predaceous mantid were 9.0, 7.9, 106.4, 400, 14.8, 23.0, and 463.7 mg/kg, respectively. The metal content did not increase from soil to grasses, but at plant–primary consumer level, Cd, Cu, Pb, and Zn were biomagnified, and, in general, all metal concentrations increased with an increase in the trophic level (i.e., secondary consumer). In light of this site-dependent accumulation of heavy metals and their biomagnification patterns, the investigated acridids can be considered bioindicators of Cd, Cu, Pb, and Zn pollution.