3. Arsenic and its compounds toxicity

Arsenic is extremely poisonous for multicellular life, although several types of bacteria are capable of using arsenic compounds as respiratory metabolites. Pollution of groundwater with arsenic is a problem that affects millions of people around the world. Worldwide, up to 100 million people are at risk of exposure to arsenic from excess arsenic in drinking water in countries such as Argentina, Bangladesh, Chile, China, India, Mexico, and the USA. The US Environmental Protection Agency classifies arsenic as a carcinogen of group A due to the evidence of its adverse effects on health [17]. Exposure to 0.05 mg L<sup>1</sup> can cause 31.33 cases of skin cancer per 1000 inhabitants. For this reason, the maximum acceptance limit of 0.050 mg L<sup>1</sup> of arsenic was lowered to 0.010–0.020 mg L<sup>1</sup> . However, it was found that a daily intake of 12–15 μg arsenic as a microelement from meat, fish, vegetables, and cereals maintains the immune system activity. The WHO warns that the maximum safe arsenic concentration for health is as low as 10 ppb, but limit values for arsenic species are not established [17, 18].

Arsenic can be found as a pollutant in water or food, especially in shells and other seafood, and often polluting fruits and vegetables, especially rice. Today arsenic poisoning occurs through industrial exposure, from contaminated wine or smuggled spirits, or due to intentional use. The possibility of arsenic contamination of herbal preparations and food supplements should also be taken into account.

Inorganic forms of arsenic are more toxic than the organic ones. Arsenic oxides are the most common threat because arsenite and arsenate salts are the most toxic. These forms are components of geological formations and are extracted into groundwater.

The two forms of inorganic arsenic reduced (trivalent arsenic) and oxidized (five valent arsenic) can be absorbed and accumulated in tissues and body fluids. The trivalent form is more toxic and reacts with thiol groups. Very few organs and systems are not affected by the toxic effects of arsenic. The arsenic compound toxicity decays in the following order: As(III) > monomethylarsine oxide > dimethylarson > monomethylarsenate > As(V). The toxicity of As(III) is 10 times greater than that of As(V) and the lethal dose for adults is 1–4 mg kg<sup>1</sup> .
