The main pollutant of leather tanneries in the wastewater is ?

Explanation

Chromium is commonly used in the tanning process of leather, and it can exist in several oxidation states. Among these states, chromium IV, also known as chromium (IV) oxide of chromium dioxide, is a particularly problematic pollutant in the wastewater from leather tanneries.(a) chromium III: Chromium III, also known as trivalent chromium, is a less toxic form of chromium compared to chromium IV. While chromium III can also be present in tannery wastewater, it is not typically considered the main pollutant. Instead, it is often used in the tanning process itself.(c) chromium V: Chromium V, also known as chromium (V) oxide or chromium trioxide, is another oxidation state of chromium. While it can be present in tannery wastewater, it is less common than chromium IV and generally less problematic in terms of pollution.(d) chromium VI: Chromium VI, also known as hexavalent chromium, is a highly toxic and carcinogenic form of chromium. It can indeed be found in tannery wastewater, but it is usually present in smaller quantities compared to chromium IV. Chromium VI is a significant concern due to its harmful effects on human health and the environment, but it is not typically considered the main pollutant in tannery wastewater.(Environmental chemistry,Introduction and Types of Pollution Factors affecting Water Quality)