Effects of heavy metal contamination

Abstract

Spiders successfully survive in heavy metal-polluted environments. They are generally classified as heavy metal macro-concentrators. Bioaccumulation of heavy metals in their body depends on their load in the prey, hunting behaviour, activity, gender, age and intensity of exposure to metals. In their active form, potent toxic metals generate oxygen stress and lipid peroxidation and accumulate intracellularly by binding to cytosolic and nuclear material, thus forming complexes with nucleophilic ligands of target molecules that may lead to cell death. In the body, metals are deposited mainly in the midgut glands. Gonads are protected and are relatively free of nonessential metals. In cells, metals are stored in an inactivated form of mineral granules, as bound to metallothioneins, or metallothionein-like proteins. The defence against the harmful effects requires significant changes in energy allocation and trade-off strategies, leading to a shift in energy expenditures from development, growth and reproduction to detoxification. This results in reproductive strategy changes where females may lay fewer eggs but of higher weight. The allocation of less energy for growth and development may disturb these processes and demonstrate itself as fluctuating asymmetry of the spider body. This fluctuating asymmetry is therefore a measurable symptom of environmental pressure. Nevertheless, the number of spiders inhabiting polluted areas is often similar as in unpolluted habitats, but the composition of species differs: sensitive species are replaced by more tolerant or better physiologically adapted species.