**4.2 Chromium**

Depending on its degree of oxidation, chromium can be a trace element or a toxic element. According to Cotte and Duret, 2011 [46], trivalent chromium (III) is implicated in the action of insulin. Although, the human body is highly exposed to chromium through ingestion, a small percentage of ingested chromium enters the body through the digestive tract [47]. In fact, chromium (VI) is more absorbed in the small intestine than chromium (III) because of the structural similarity between chromium VI and sulphates. In humans, the adsorption of chromium III does not exceed 1%, whereas that of chromium VI can be around 10% [48, 49]. Moreover, once absorbed, chromium VI represents the real danger for the human body. It can enter many cells and be reduced by hydrogen peroxide (H2O2), glutathione (GSH) reductase and ascorbic acid to produce reactive intermediates including chromium (V), chromium (IV), thiyl radicals, hydroxyl radicals, which can disrupt cellular functions by attacking DNA, membrane proteins and lipids [50, 51]. This ability to produce oxidants makes chromium VI responsible, according to the French National Institute for Occupational Safety and Health, for gastric corrosion and renal failure [52, 53]. Also, according to the Agency for Toxic Substances and Disease Registry, chromium (VI) is responsible for ulcer and anaemia. These different actions of chromium VI on the body make chromium one of the eight metals present in the top 50 toxic substances in the world [47]. The World Health Organization (WHO) has classified chromium as carcinogenic to humans [54].
