Soil Physicochemical Properties, Metal Deposition, and Ultrastructural Midgut Changes in Ground Beetles, Calosoma chlorostictum, under Agricultural Pollution

Abstract

Unsustainable agricultural practices that minimize soil organic matter can promote the removal of heavy metal pollutants into the food chain. Such polluted soils can release contaminants into the groundwater, which leads to accumulation in plant tissue that is transferred to animals, birds, insects, and humans. Biomonitors of soil pollution with heavy metals can be identified by the ground beetles Calosoma chlorostictum (Coleoptera: Carabidae) as bioindicators of soil quality and its yield sustainability. The experiment was performed on two sites in Zagazig City (30.62° N, 31.44° E), Egypt. The physicochemical parameters indicated that soil moisture and organic matter had the highest differences in the polluted agricultural soil compared to the reference soil. However, there were no significant differences in chloride content. The atomic absorption analysis exhibited the highest concentration recorded for arsenic (As) and the lowest for selenium (Se) in the polluted soil and the insect’s midgut. Meanwhile, the differences between heavy metal concentrations in the total soil and midgut of C. chlorostictum from current sites indicated that the highest differences were in aluminum (Al) and mercury (Hg), while arsenic (As) and cadmium (Cd) were the lowest. Furthermore, the correlation between heavy metal concentrations in the soil and insect midgut was highest in As, while the lowest correlation was noticed in Al. We used transmission electron microscopy (TEM) that showed a more considerable disturbance in the C. chlorostictum midgut epithelial layer collected from the agricultural area than in the insects collected from the reference area. Evident ultrastructural alterations showed a rupture and distortion of microvilli, destruction of the columnar and regenerative cells, large separation between epithelial cells, and stretching of the cellular axis, as a result of which the lumen became very narrow. Moreover, a lot of vacuoles with little enzyme secretion were observed in the columnar epithelial cells. In addition, other manifestations due to pollution with heavy metals such as a pyknotic nucleus with abnormal chromatin, cytoplasmic vacuolization, disruptions, and vacuolation of mitochondria were detected, as well as the appearance of electron-dense vesicles, a lot of lysosomes, large myelin figures, and dilation of the rough endoplasmic reticulum on account of soil contamination. Potential counteractive health influence in such applications could be avoided if the soil was adequately treated.