Breathing sharp, freshlycut sand dust, such as silica at sand mining and processing sites, carries a greater risk of pulmonary disease than breathing older, smoother particles weathered by heat, wind, and moisture – such as silica dust blown from cropland. There is no federal standard for ambient air exposure to silica outside the workplace.
Health Effects of Dusts, Gases and Vapours: Nuisance dusts are relatively inert and, by definition, cause no serious health effects although they may be irritant to the upper airways. Examples include chalk, limestone, and titanium dioxide (provided they are free of toxic impurities). They may cause radiographic changes without disease.