**4. Effect of heavy metal pollution on invertebrates**

Metallic elements are considered systemic toxins known to induce neural and multi-organ damage, and contribute to cancer in animals and humans, even at low levels of exposure. Their toxicity depends on several factors, including dose, route of exposure and chemical species, as well as the age, sex, genetics and nutritional status of those exposed. However, in some invertebrates, physiological and ecological changes following pollution by heavy metal can be detected by neurological dysfunctions and sensory, endocrine or metabolic disturbances [28]. Following exposure to a series of soils contaminated with different concentrations of cadmium and zinc on the talitrid amphipod species *Orchestia gammarellus*, [29] detect significant changes in the morphology and in the ultrastructural organization of hepatopancreatic cells as well as the rhythm of locomotor activity. However, the results show that the damage observed at depends on the concentration at which the individuals were expressed. Concerning the behavioral response, a great intervariability of the locomotor rhythm was observed. Patterns were in majority bimodal for the uncontaminated individuals and became unimodal and multimodal when exposed under Cd and the Zn respectively. In addition, the circadian period lengthened after Zn exposure. Referring to [30] pollution intensities could have negative effects on the restriction of the distribution area or even the disappearance of certain species. In a polluted environment morphological, behavioral, tissue or physiological alterations, as well as the abundance, reproductive success and mortality of animal species are observable and measurable variables reflecting the state of their habitat [12, 24, 25]. In line with that, toxic metals interfere with cytoplasmic membranes and lead to pathological results [31, 32]. These pathological ramifications contain the nuclear

and cytoplasmic corruptions. The follicular epithelial cells showed signs of damage which is a remarkable appearance seen in the ovarian cells from the polluted site. This can delay oocyte maturation and result in imperfect yolk deposition [33, 34]. The distorted brush borders of the microvilli may block the passage of the materials toward the oocyte. Also, the deformity of yolk granules could obstruct vitellogenesis and result in a lower fecundity and egg viability [34].

Referring to [12], following pollution by Cd, Ni and Zn, the response of invertebrate species of *Pterostichus oblongopunctatus* (ground beetles) results in severe intestinal degeneration. In the case of Zn pollution, a decrease in the number of eggs laid by *Poecilus cupreus* has been observed [35]. Furthermore, the results obtained by [36] indicate an increase in egg production and a reduction in egg quality (hatching) in zones polluted by metals compared to unpolluted areas. In [37], it was shown that in polluted areas the body weight of *P. oblongopunctatus* is higher compared to unpolluted areas. It was explained by advanced metal tolerance [38]. Several publications have appeared in recent years documenting that exposure of invertebrates to toxic elements causes sublethal consequences, sometimes difficult to evaluate, such as impaired fertility observed in (grasshoppers: [39]; springtail: [40]; earthworm: [41], resistance to pathogens; ant: [42]; honey bee: [43]), developmental abnormalities fly [44]; moth: [45]; ant: [46]) and similarly altered feeding behavior (aphid: [47]; honey bee: [48]). In addition, metal pollution can cause cell damage or death in the brains of invertebrates, as their nervous systems are small in size and contain relatively few neurons [49, 50]. According to [51], toxic elements, particularly zinc, can disturb molting cycles, alter the digestive glands in isopods and can affect food consumption, reproduction and the composition of the community. Previous studies indicate that metal pollution has severe consequences on pollinator behavior by affecting foraging activity, food perception and memory abilities necessary for energetic foraging [5, 48, 52, 53]. The results obtained by [54] on tenebrionid beetles (*Blaps polycresta* and *Trachyderma hispida*) inhabiting polluted soil shows several abnormalities in oocytes and trophocytes. These baseline abnormalities included exfoliation and vacuolation of follicular epithelium, vacuolated trophocyst, nuclear abnormalities, and morphological changes in cytoplasmic organelles. Co-exposure of honey bees (*A. mellifera*) to cadmium and copper resulted in increased developmental time, high mortality, and decreased food intake and response to sucrose [55]. Referring to [56], the study of the impact of Cadmium on species of Tenebrionidae, reveals a decrease in population density, a reduction in body weight, an increase in the mortality rate and an increase in the sex ratio insects. Moreover, the results also revealed a striking decrease in the body length of polluted insects with a marked increase in the percentage of deformed gonads and digestive tract.
