Influence of ferrous-metal production on mercury contamination and fractionation in farmland soil around five typical iron and steel enterprises of Tangshan, China

Iron and steel production is one of the main anthropogenic sources of mercury (Hg) emission and release. Oxidized and particulate Hg discharged from iron and steel enterprises deposit into the surrounding soil, which accumulate and introduce environmental risks. Therefore, it is important to assess Hg pollution in the soil surrounding iron and steel enterprises. In this study, the Hg pollution, Hg distribution from steel plants and Hg fractionation in farmland soil around five typical steel plants were analysed in Tangshan of China. The Hg pollution indexes (Pi) of more than 90% soil samples were greater than 3 by the single factor pollution index method, which showed that most soil samples around the five steel plants were strongly contaminated by Hg. The Hg contents in soil increased first and then decreased, and the maximum content presented at 250–300 m away from the boundary of the steel plants. The order of Hg fraction proportion in the soil samples was extractable (35%–43%) > volatile (24%–36%) > residual (10%–26%) > reducible (0–15%) > oxidizable (0–12%). The distribution of Hg fraction in farmland soil had no regular trend with the distance from the steel plants. The volatile Hg and extractable Hg were dominant in farmland soil, and their combined proportion was greater than 60%. These two fractions of Hg are at risk of re-volatilization into the atmosphere or potential absorption by plants. •More than 90% of soil samples around steel plants were seriously polluted by Hg.•Steel plant was the main Hg source of soil based on the elevated point source model.•Volatile Hg and extractable Hg were dominant in farmland soil.