*3.3.1 Effects of chromium on human health*

Chromium is one of the heavy metals considered a major pollutant. It has been widely used in industrial processes for leather tanning, dyes and paint preparation,


#### **Table 3.** *Physical and chemical properties of chromium, lead and nickel.*

textile manufacturing, paper mills, wood preservation, stainless steel production, and photography [111]. Chromium exists in several oxidation states. The most stable and common forms are trivalent chromium, Cr(III), and hexavalent chromium, Cr(VI), which exhibit contrasting biochemical properties and toxicokinetics [112, 113]. Cr(III) compounds occur naturally in the form of oxides, hydroxides or sulfates, and they are nutritionally necessary to humans for glucose, fat and protein metabolism [114]. In contrast, Cr(VI) compounds are mainly anthropogenic and highly toxic; its mutagenic and carcinogenic nature and high oxidation state enhances its ability to move into living cells [114]. Cr(III) and Cr(VI) interchangeability depends on their concentration in solution, pH, the redox potential (Eh) of the medium, and the presence or absence of a strong oxidant or reductant [111, 115].

The toxicity of chromium is directly dependent on the valence state, with hexavalent chromate Cr(VI) and trivalent chromate Cr(III) being of the greatest interest [112]. Oral bioavailability varies with valence state, with Cr(VI) being more readily absorbed. Cr(VI) can be broken down into Cr(III) within the acidic environment of the stomach [111]. Acute exposure to chromium is indicated by immediate irritation of the eye, nose, throat, and respiratory tract, which results in burning, congestion, epistaxis, and cough. Ulceration, bleeding, and erosion of the nasal septum mark chronic exposure. Cough, chest pain, dyspnea, and chromiuminduced asthma indicate exposure to soluble chromium products [113]. If chronic exposure is suspected, in conjunction with weight loss, cough, and hemoptysis, this suggests the development of bronchogenic carcinoma. Dermatological manifestations include painless, slow-healing ulceration of the fingers, knuckles, and forearms. Ingestion is marked by nausea, vomiting, abdominal pain, prostration, and death associated with uremia [114].
