Dust palliatives are used to control fugitive dust originating from unpaved surfaces. There are dozens of types and brands of dust palliatives. The most common types range from plain water, surfactants, chlorides, synthetic polymers, vegetable oils (soybean oil, sugar beet oil), bentonite clays, lignosulfonates, paraffinic (mineral) oils, petroleum resins, engineered modified asphalt emulsions (Earthbind®), etc.
Most dust control palliatives claim to control dust by keeping the soil/aggregate surfaces wet or wet longer (water, surfactants), draw moisture from the air (magnesium and calcium chlorides), “encapsulate” the dirt particles (paraffinic oils), and/or chemically bind the dust particles together (lignosulfonates, petroleum resins, vegetable oils, synthetic polymers, Earthbind, etc.).
Of all the dust control product types currently used in the United States, it appears that the most common are calcium chloride and magnesium chloride. The reason why the chlorides are used extensively is because they are abundant and relatively cheap.
Chlorides are often used as a dust control agent since they are hygroscopic and deliquescent – the ability to absorb moisture from the humid air. This absorbed moisture helps limit dust by keeping the surface of the road damp enough to hold the dust particles down and reduces blow-off as fugitive dust.
Although chlorides are considered to be less expensive than other dust control agents, the potential negative impact of using salt may outweigh any positive aspects. There are numerous reasons why using chloride is less than desirable for dust control on unpaved roads1 and incidentally, one of the biggest reasons not to use chlorides is that it can readily wash off with rainwater.
A big issue with chlorides being water-soluble and easily washed off with rainwater and/or snowmelt is its potential effect on the environment. Since chlorides do not chemically attach (bind) on soil particles, they can be readily mobile. Once the chloride gets into the soil it can be taken up by plant roots. High concentrations of chlorides in soil can affect plant growth and survival both indirectly and directly. At lower chloride concentrations, a reduction in plant growth may be due to osmotic effects that disrupt normal water and nutrient uptake. At high concentrations, chlorides can accumulate at the margins of transpiring leaves or the tips of needles which can cause foliar necrosis and leaf abscission through dehydration and/or specific metabolic disruptions. These could lead to branch and tree die-back. In addition, during dry conditions, water stress and dehydration may aggravate chloride toxicity and cause even more extensive damage2.
Research has shown that injury can occur when the needle/leaf chloride content reaches 5,000-ppm (dry weight) in conifer trees and 10,000-ppm to deciduous species. This may sound like a lot of chloride, but it may not be on a roadside that was treated with magnesium chloride. For example, if you apply a normal typical application of ½-gallon of a 30% solution of a magnesium chloride solution, you are applying approximately 1.2-pounds or 544,311 milligrams of chloride per square yard of road. The amount of chloride is staggering when a typical one-time application of magnesium chloride may contribute 11,358 pounds of chloride per mile on a 16’ wide road! Obviously, roads treated more than once a year will greatly increase the chloride concentration. And since magnesium chloride is highly water soluble, 54,200 milligrams per liter, it is easy to understand why it can leach and run-off a treated road so easily2.
Also, chlorides are not the only dust palliative that can be affected by rainwater. Other dust control products such as the lignosulfonates can wash off with rainwater or in the case of paraffinic oils, can become “dislodged” from the surfaces due to their density (lighter than water) and float away.
It is very important to apply a water-resistant dust control palliative, not just for the environment but also for longevity. It does not make a whole lot of sense to apply a product that can possibly wash away with the first rainfall event.
While the ease of availability and the lower cost of magnesium chloride maybe attractive, a much better choice is to use an environmentally-friendly dust control product that can efficiently and effectively bind soils and aggregates together and that does not wash off with rainwater. With this in mind, Earthbind® 100 is an exceptionally good choice. Earthbind® not only can control fugitive dust, they can at the same time help mitigate stream sedimentation during the rainy season. In addition, as long as the Earthbind treated surface material is not motor-graded off or snow plowed off, you should expect to see a residual “build up” over time with subsequent maintenance applications. This will lead to great dust control longevity while using less and less Earthbind for maintenance. This translates to significant cost savings.
If you would like to know more about how Blue Line Transport Company can help you get the products you need for a better road, you should call our office at 503-279-2600 to speak to one of the representatives at our headquarters in Portland, Oregon. We will be happy to serve you!