Toxicological and histopathological effects of lead and zinc on juveniles of <i>Aporrectodea giardia</i> in northeast of Alegria

Abstract

Most studies investigating the effects of heavy metals on soil communities have focused on using earthworms such as Lumbricus terrestris and Aporrectodea giardia as efficient bioindicators of soil health. Therefore, the present study was aimed to assess the toxicological and histopathological effects of four different concentrations of lead and zinc (0, 100, 200, 500 and 1000 ppm) on Juveniles of A. giardia for four exposure periods (24, 48, 72 and 96 hours). The physicochemical analysis proved the soil as an appropriate living environment for earthworms due to its richness in organic matter (OM = 8.93 > 4), neutral pH, and the sandy-silty texture owed to the capacity in the field (19.37) and in the interval (12 – 14). Moreover, a reduction in earthworms survival rate confirmed by a proportional increase of lethality rate with the increase concentrations of lead and zinc (Lead: LC₅₀ = 893.27; LC₉₀ = 12394.42; Zinc: LC₅₀ = 785.22; LC₉₀ = 92348.13). The histological findings of earthworms exposed to 100 and 200 ppm of Zn and Pb for 96 hours showed a dispersion or loss of junctions and cohesions of the chloragogen cells, while serious alterations at the level of the epidermal and intestinal cells (chloragogen) characterized by the formation of vacuoles and detachment of cellular fibres were noticed in the concentrations of 500 and 1000 ppm of the two metals.