Excerpted from: Profile of Dust Suppressants Used in Canada

For a full copy of this report, contact Road Salts Working Group:
Tel: (819) 953-6065
Fax: (819) 994-0007

1.1	Introduction

Dust from unpaved roads can be a significant source of particulate matter in the atmosphere, and can have numerous environmental and socio-economic implications such as air pollution, impairment of driver vision, health impacts, and impacts to aesthetics. Road deterioration can increase because of loss of fines (i.e., <0.075 mm), since they act as road surface binders. This can lead to road safety issues, increased economic cost to vehicles and increased road maintenance needs. The use of dust suppressants has been shown to lower road maintenance requirements and associated costs as well as mitigate the environmental and health impacts associated with road dust.

There are numerous products/techniques that can be used for dust suppression. Various road salts make up the main chemical-based dust suppressants currently used in Canada. However, in 1995 road salts were placed on the Federal Government’s Priority Substances List 2 for assessment to determine its toxicity under theCanadian Environmental Protection Act(CEPA). The science assessment concluded that because of the high releases around storage and snow disposal sites and through run-off and splash from roadways into soils, streams and rivers, road salts pose a serious threat to the aquatic environment, plants and animals.

1.2	Overview of Dust Suppressant Alternatives

The main use of dust suppression products is to minimize dust emissions from unpaved roads and unpaved shoulders of paved roads. Loss of aggregate and subsequent road surface deterioration (e.g. ruts, potholes, and corrugations) with the loss of road surface fines results in dust generation. There are two major alternatives employed to achieve desired dust control results. The first general method to control dust generation is to apply good construction and maintenance practices on unpaved roads. The second general method is the application of chemical methods of dust suppression. Other methods of dust suppression include changes to speed limits, encouraging the use of alternative routes, restricting heavy traffic, paving roads, or changing the timing of road construction and maintenance activities (i.e., to occur during wet weather).

Seven categories of chemical dust suppressants have been identified and described in the report, specifically:

1. Chloride (e.g. calcium chloride and magnesium chloride) salts and brines. These chemicals are either mixed in place with the top few centimeters of surface material, or they are topically sprayed. Water-attracting chemical dust suppressants are recognized for providing the best combination of application ease, durability, cost, and dust control for semi-arid, semi-humid, and humid climates. They can have significant impacts on the reduction of dust (e.g. 30 to 80%) but require frequent re-application to maintain long-term dust suppression performance. Environmental impacts of chlorides include metal corrosion, degradation to nearby vegetation, surface water, groundwater and aquatic species.
2. Organic non-bituminous chemicals (which include lignosulfonates, sulphite pulp mill liquors, tall oil pitch, pine tar, vegetable oils, and molasses) adhere to the soil particles or physically bind the soil particles together to increase particle mass and cohesion. They tend to require frequent application. Environmental impacts include being sticky, odorous and visually unappealing. They are also slow to biodegrade, contribute to deoxygenation of surface water (i.e., from spills) and may cause the road to becomes slippery when wet.
3. Petroleum waste oils are insoluble and create a sealed surface on the road. They can be very effective. However, there is significant sealed surface leakages associated with hazardous components that may contaminate surface and groundwater.
4. Electro-chemical stabilizers attract positively charged fine dust particles and bind ionically to them. They also expel adsorbed water from the soil and increase compaction. These stabilizers are considered environmentally acceptable, but vegetation does not easily establish on compacted sites where sulphonated petroleum products have been used.
5. Polymers, most effective in lightly trafficked surfaces, are composed of long-chained molecular structures. These dust suppressants can stick to more particles and bridge greater gaps between particles.
6. Enzyme slurries promote compaction, which reduces dust generation. They have been effective under highly specific trafficked surface and aggregate conditions.
7. Cementitious binders work by chemically and permanently binding soil particles together.

1.4	Regulatory Restrictions of Dust Suppressants in Canada

There were no nation-wide prohibitions on the use of chloride-based dust suppressants in Canada, the U.S. or Europe. Individual jurisdictions have developed restrictions with respect to the application of chloride-based dust suppressants. Ontario and Quebec are the dominant users of chloride-based dust suppressants in Canada. Currently, Ontario has prohibited used oil and another lignosulfonate-based dust suppressant prohibited in 2002. Quebec has banned used oil as well as calcium, lignosulfonate for use as dust suppressants in the entire Province.

Source: Industry interviews, Cheminfo estimates. Statistics Canada, Industry interviews