Reza Vahidzadeh said recent studies show that the factories and brick-making furnaces in the region produce acids and particulates which deposit soot on the structures of the ancient complex.

The black smoke and air pollution are a great threat to the brick structures, changing their color and causing erosion, he added.

Experts believe that the use of cheap fuels and the old method of burning the farm fields are the main reasons for the air pollution. They have suggested that converting to high-quality fuel and teaching new strategies to farmers to encourage them to abandon their old practices would be the best way to protect the ancient structures from further damage.

The only surviving ziggurat in Iran, Chogha Zanbil is a major remnant of the Elamite civilization. It is located near Susa, the ancient capital of Elam, and was registered on the UNESCO World Heritage List in 1978.

Built about 1250 BC under the direction of the Elamite ruler Untash-Gal during the Middle Elamite period (c. 1500–c. 1000 BC), the complex was dedicated to Inshushinak (Insusinak), the bull-god of Susa. The square base of the ziggurat, 344 feet (105 meters) on each side, was built principally of brick and cement. It now stands 80 feet (24 meters) high, less than half its estimated original height.