**3.2 Toxic effects of Hg**

Various Hg species, as Hg°, methyl-Hg ore ethyl-Hg, accumulates in the central nervous system (CNS) and has extremely neurotoxic effects, including the appearance of well-known clinical symptoms and signs. In case of occupational exposure to Hg°, the most frequent symptoms and signs include "erethism", increased irritability, depression and other neurobehavioral changes, sleep disturbances, oral disturbances, gingivitis and stomatitis with excessive salivation, intentional tremor, peripheral neuropathy (lower sensor and motor conduction velocities), and renal impairment. In vitro and in vivo studies showed that Hg can stimulate free radical generation as a catalyst in Fenton-type reactions and through some other mechanisms, and can promote oxidative stress, peroxidation of lipids and DNA bases, disturbances in cell membrane permeation and calcium homeostasis in cells, impairment and even apoptosis of monocytes, T cells, glial cells and neurons, disturb the functioning of neurotransmitters, and cause immune disorders (Aschner, 2000; ATSDR, 1999; Castoldi et al., 2001; Clarkson & Magos, 2006; Kobal et al., 2004; Kobal-Grum et al., 2006; Lund et al., 1993; Magos, 1997; Pollard & Hultman, 1997; Schara et al., 2001; WHO, 1991).
