Water-absorbing magnesium chloride (deliquescent) attributes include • Absorbing water from the air at 32%
relative humidity, almost independent of temperature • Treated roads can be regraded and re-compacted with less concern for losing moisture and density However, limitations include • Minimum humidity level • Better suited for drier climates • Concentrated solutions become very
corrosive, • Moisture attraction, thereby prolonging the active period for corrosion • High fines content in treated material may become slippery when wet • When less than 20% solution it has performance effectiveness similar to water The use of magnesium chloride on roads remains controversial. Advocates claim (1) cleaner air, which leads to better health as
fugitive dust can cause health problems in the young, elderly, and people with respiratory conditions; and (2) Greater safety through improved road conditions, including increased driver visibility and decreased risks caused by loose gravel, soft spots, road roughness, and flying rocks. It reduces foreign sediment in nearby surface waters (dust that settles in creeks and streams), helps prevent stunted crop growth caused by clogged pores in plants, and keeps vehicles and property clean. Other studies show the use of salts for road deicing or dust suppressing can contribute substantial amounts of chloride ions to runoff from the surface of roads treated with the compounds. The salts MgCl2 (and CaCl2) are very soluble in water and will dissociate. The salts, when used on road surfaces, will dissolve during wet weather and be transported into the groundwater through infiltration and/or runoff into surface water bodies. In addition, the chloride concentration in the surface water also depends on the size or flow rate of the water body and the resulting dilution achieved. In a chloride concentration study carried out in Wisconsin during a winter de-icing period, runoff from roadside drainages was analyzed. All studies indicated that the chloride concentration increased as a result of de-icing activities, but the levels were still below the MCL of 250 mg/L set by the EPA. Nevertheless, the long-term effect of this exposure is not known. Although the U.S. EPA has set the maximum chloride concentration in water for domestic use at 250 mg/L animals can tolerate higher levels. At excessively high levels, chloride is said to affect the health of animals. As stated by the National Technical Advisory Committee to the Secretary of Interior (1968), "Salinity may have a two-fold effect on wildlife; a direct one affecting the body processes of the species involved and an indirect one altering the environment making living species perpetuation difficult or impossible." One major problem associated with the use of de-icing salt as far as wildlife is concerned is that wildlife is known to have "salt craving" and therefore are attracted to salted highways which can be a traffic hazard to both the animals and motorists. Regarding the accumulation of chloride salts in roadside soils including the adverse effects on roadside plants and vegetation physiology and morphology, documentation dates back to the World War II era and consistently continues forward to present times. However, recent research and updates indicate biological toxicity in the environment in plants is an ongoing problem. Since 2001, truckers have complained about "killer chemicals" on roads and now some states are backing away from using salt products. A small percentage of owners of indoor arenas (for example, for horse riding) may apply magnesium chloride to sand or other "footing" materials to control dust. Although magnesium chloride used in an equestrian (horse) arena environment is generally referred to as a dust suppressant it is technically more accurate to consider it as a water augmentation activity since its performance is based on absorbing moisture from the air and from whatever else comes in contact with it. To control or mitigate dust, chlorides need moisture to work effectively so it works better in humid than in arid climates. As the humidity increases the chloride draws moisture out of the air to keep the surface damp and as humidity decreases it diffuses and releases moisture. These naturally occurring equilibrium changes also allow chlorides to also be used as a dehydrating agent including the drying out of and curing and preservation of hides. As a road stabilizer, magnesium chloride binds
gravel and
clay particles to keep them from leaving the road. The water-absorbing (hygroscopic) characteristics of magnesium chloride prevent the road from drying out, which keeps gravel on the ground. The road remains continually "wet" as if a water truck had just sprayed the road. ==See also==