Arsenic-Contaminated Soils in the Urban Area of Ouro Preto, Minas Gerais, Southeastern Brazil

Arsenic (As) is a toxic and carcinogenic element. Numerous As compounds are present in the environment and in biological systems. The most common exposure routes of humans to As are consumption of polluted water, gas inhalation or ingestion of soil dust, causing toxic and acute effects in tens of millions of victims all over the planet. In the Brazilian city of Ouro Preto, in the urban districts Piedade, Antônio Dias, Padre Faria, Taquaral and Alto da Cruz, 21 soil samples were collected at sites spaced about 200 m apart, in a 2 km2 area, to analyze the physical properties, chemical constitution, mineralogy and presence of As. Of all samples, 15 had a predominantly clayey texture, and in 12 of these, As levels of > 250 mg.kg-1 were detected. In general, the As levels ranged from 6 to 925 mg.kg-1. No primary or secondary As minerals were found, suggesting that As had been retained and adsorbed by Fe, Al and oxides and hydroxides and by clay minerals. The predominant minerals were quartz, muscovite, kaolinite, goethite, hematite, illite and gibbsite.