**5. Results and discussion**

One of the main characteristics of the different bioindicator species is, among other things, the ability to respond in an observable and measurable way to disturbances or to accumulate the pollutant. The distribution of invertebrates in all types of terrestrial and aquatic makes them excellent for ecotoxicological analysis and are efficient biomarkers in detecting environmental pollution. However, the internal study of the compartment of metals in different subcellular fractions, allows us to better interpret the mechanisms of accumulation of toxic elements in organisms and their transfer through trophic chains [12]. In general, toxic metals, even at low

### *Effect of Heavy Metal Pollution on Invertebrates DOI: http://dx.doi.org/10.5772/intechopen.109905*

concentrations, have a polluting nature with harmful effects for living organisms. Heavy metals have a cumulative effect. Their selective attachment to sensitive organs and tissues can be dangerous when their concentrations are high [57]. It is also likely that heavy metal ions act on Ca2+ receptors [58] and metal ions enter the interior of the cell, from where they initiate free radical oxidation [59]. An oxidative stress reaction then develops which in turn influences the lysosomes. Furthermore, variation in the concentration of heavy metals affects the susceptibility of insects to entomopathogenic fungi [60, 61]. According to [62], the humoral immunity of invertebrates could be affected by the stress of toxic elements, and the response of the humoral immunity of insects was found to affect the susceptibility of insects to entomopathogenic microorganisms [62, 63]. In addition, insects reduce their feeding or decrease their digestion and absorption as a result of heavy metals accumulated in food [64]. Referring to [65], a reduction in intermediate carbohydrate metabolism, was observed in chironomid (*Chironomus tepperi*), including glucose 6-phosphate, fructose 6-phosphate and disaccharides following exposure to Zn stress. Thus, to better understand the effect of heavy metal stress on insect disease resistance and their corresponding regulatory mechanisms, studies on several insect species and different types of toxic elements should be done [66].
