Priority Substances List Assessment Report for Road Salts

Environment Canada
Health Canada
2001
ISBN: 0-662-31018-7
Cat. No.: En40-215/63E

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(1,535K)

Canadian Environmental Protection Act 1999

Table of Contents

• List of Acronyms and Abbreviations
• Synopsis
• 1.0 Introduction
• 2.0 Summary of Background Information for the Assessment of Road Salts
  • 2.1 Identity, properties, production and sources
    • 2.1.1 Substance characterization
    • 2.1.2 Physical and chemical properties
    • 2.1.3 Production and use
      • 2.1.3.1 Sodium chloride
      • 2.1.3.2 Calcium chloride
      • 2.1.3.3 Mixture of sodium chloride and calcium chloride
      • 2.1.3.4 Magnesium chloride
      • 2.1.3.5 Mixture of sodium chloride and magnesium chloride
      • 2.1.3.6 Potassium chloride
      • 2.1.3.7 Brines
      • 2.1.3.8 Ferrocyanide
    • 2.1.4 Sources and releases
      • 2.1.4.1 Natural sources
      • 2.1.4.2 Anthropogenic sources
  • 2.2 Road Salt loadings
    • 2.2.1 Surveys
      • 2.2.1.1 Provinces
      • 2.2.1.2 Municipalities and regional governments
      • 2.2.1.3 Salt industry data
      • 2.2.1.4 Municipal estimates
      • 2.2.1.5 Provincial and municipal use of dust suppressant salts
    • 2.2.2 Results
      • 2.2.2.1 Sodium chloride
        • 2.2.2.1.1 Recommended application rates
        • 2.2.2.1.2 Loadings
      • 2.2.2.2 Calcium chloride
      • 2.2.2.3 Total chloride loadings
      • 2.2.2.4 Historic trends
    • 2.2.3 Reliability of loadings data
    • 2.2.4 Summary
  • 2.3 Snow disposal
    • 2.3.1 Characterization of snow from roadways
    • 2.3.2 Volumes of snow in Canadian cities
    • 2.3.3 Snow clearing and snow disposal methods
      • 2.3.3.1 Methods not involving snow removal
      • 2.3.3.2 Methods involving release into waterways after processing or treating meltwater
      • 2.3.3.3 Methods involving release to surface water without water treatment
    • 2.3.4 Use of disposal methods by Canadian municipalities
    • 2.3.5 Summary
  • 2.4 Patrol Yards
    • 2.4.1 Number of patrol yards and quantity of materials stored
    • 2.4.2 Patrol yard design and management
    • 2.4.3 Estimation of releases of salts from patrol yards
    • 2.4.4 Salt concentrations at different areas around patrol yards
      • 2.4.4.1 Concentrations at surface points around patrol yards
      • 2.4.4.2 Concentrations in patrol yard well water
      • 2.4.4.3 Concentrations in shallow groundwater
      • 2.4.4.4 Concentrations in patrol yard soils
    • 2.4.5 Off-site concentrations at patrol yards
  • 2.5 Environmental fate and pathways
    • 2.5.1 Fate/transport
      • 2.5.1.1 Chloride
      • 2.5.1.2 Sodium and potassium
      • 2.5.1.3 Calcium
      • 2.5.1.4 Magnesium
      • 2.5.1.5 Sodium ferrocyanide
    • 2.5.2 Environmental pathways
      • 2.5.2.1 Roadway applications
      • 2.5.2.2 Snow disposal sites
      • 2.5.2.3 Storage sites/patrol yards
  • 2.6 Chloride concentrations in surface waters across Canada
    • 2.6.1 Mapping of chloride concentrations in watersheds across Canada
    • 2.6.2 Environmental concentrations: Lakes and rivers
      • 2.6.2.1 Atlantic region (Newfoundland, Nova Scotia, New Brunswick and Prince Edward Island)
      • 2.6.2.2 Central region (Ontario and Quebec)
      • 2.6.2.3 Prairie region (Manitoba, Saskatchewan and Alberta)
      • 2.6.2.4 Pacific region (British Columbia)
      • 2.6.2.5 Yukon, Northwest Territories and Nunavut
    • 2.6.3 Environmental concentrations: Benthic sediments
    • 2.6.4 Environmental concentrations: Wetlands
    • 2.6.5 Environmental concentrations: Urban lakes and ponds
    • 2.6.6 Chloride concentrations based on mass balance calculations
      • 2.6.6.1 Calculation of watershed chloride concentrations resulting from the use of road salts
      • 2.6.6.2 Calculation of chloride concentrations in roadway runoff
    • 2.6.7 Summary
• 3.0 Assessment of Critical Information and Assessment of "Toxic" under CEPA 1999
  • 3.1 CEPA 1999 64(a): Environment and CEPA 1999 64(b): Environment on which life depends
  • 3.2 Groundwater
    • 3.2.1 Introduction
    • 3.2.2 Groundwater principles
      • 3.2.2.1 Hydrological cycle
      • 3.2.2.2 Unsaturated flow and groundwater recharge
      • 3.2.2.3 Saturated flow and contaminant migration
    • 3.2.3 Impacts of road salts on groundwater quality
      • 3.2.3.1 Factors controlling the migration of road salts
      • 3.2.3.2 Predicted road salt concentrations in groundwater
      • 3.2.3.3 Plume migration and impact assessment
    • 3.2.4 Case studies
    • 3.2.5 Conclusions
  • 3.3 Aquatic ecosystems
    • 3.3.1 Scoping and assessment approach
    • 3.3.2 Laboratory studies
      • 3.3.2.1 Short-term or acute toxicity studies
      • 3.3.2.2 Chronic toxicity
    • 3.3.3 Assessment of toxicity to aquatic ecosystems
      • 3.3.3.1 Quotient-based risk characterization
      • 3.3.3.2 Tier 1 and Tier 2 assessments
        • 3.3.3.2.1 Estimated Exposure Values (EEVs)
        • 3.3.3.2.2 Critical Toxicity Values (CTVs)
        • 3.3.3.2.3 Conclusions for Tier 1 and Tier 2 assessments
      • 3.3.3.3 Tier 3 assessments with field validation
        • 3.3.3.3.1 Case 1: Road salt runoff and urban creeks, streams and small rivers in densely populated areas
        • 3.3.3.3.2 Case 2: Road salt runoff and creeks, streams and rivers in less densely populated areas
        • 3.3.3.3.3 Case 3: Road salt runoff and urban ponds and lakes
        • 3.3.3.3.4 Case 4: Highway runoff and rural ponds and lakes
        • 3.3.3.3.5 Case 5: Salt storage depots and aquatic ecosystems
        • 3.3.3.3.6 Case 6: Snow dumps
      • 3.3.3.4 Other effects
      • 3.3.3.5 Conclusions for aquatic ecosystems
  • 3.4 Soils
    • 3.4.1 Soil salinization resulting from road salt application
      • 3.4.1.1 Definitions and equations
      • 3.4.1.2 Case studies
      • 3.4.1.3 Discussion
      • 3.4.1.4 Conclusions
    • 3.4.2 Biological effects of road salts on soils
      • 3.4.2.1 Ecological role of soil biotic communities
      • 3.4.2.2 Effects on soil biota
      • 3.4.2.3 Exposure of soil organisms to road salt
      • 3.4.2.4 Environmental assessment
      • 3.4.2.5 Conclusions
  • 3.5 Terrestrial vegetation
    • 3.5.1 Conservative environmental assessment
      • 3.5.1.1 Effects threshold values
      • 3.5.1.2 Estimated Exposure Values (EEVs)
      • 3.5.1.3 Quotient estimation
    • 3.5.2 Detailed environmental assessment - threshold-based analysis
      • 3.5.2.1 Response to sodium in soil
      • 3.5.2.2 Response to chloride in soil
      • 3.5.2.3 Response to sodium chloride in soil
      • 3.5.2.4 Response to sodium and chloride by aerial dispersion
      • 3.5.2.5 Detailed environmental assessment - summary of threshold-based analysis
    • 3.5.3 Detailed environmental assessment - reference site analysis
      • 3.5.3.1 Spread of halophytic plant species
      • 3.5.3.2 Community changes in a bog impacted by road salts
      • 3.5.3.3 Effects of salt spray from a four-lane highway on peach and plum orchards in Grimsby, Ontario
      • 3.5.3.4 Effects of salt spray from a four-lane highway on peach and plum orchards near St. Catharines, Ontario
      • 3.5.3.5 Effects of salt spray from a two-lane highway on blueberries in western Nova Scotia
      • 3.5.3.6 Concentrations in soil and woody plants adjacent to highways in interior British Columbia
      • 3.5.3.7 Concentrations in soil and woody foliage adjacent to a two-lane highway in British Columbia
      • 3.5.3.8 Concentrations in woody foliage directly adjacent to a two-lane highway in Connecticut
      • 3.5.3.9 Concentrations in soil and woody and herbaceous foliage along roadsides in Massachusetts
      • 3.5.3.10 Concentrations in soil and woody plants downslope from a four-lane highway in British Columbia
      • 3.5.3.11 Concentrations in soil and woody foliage adjacent to a patrol yard
    • 3.5.4 Changes in application rates and current injury in Canada
    • 3.5.5 Estimate of area of potential injury
    • 3.5.6 Risk assessment summary and conclusions
  • 3.6 Terrestrial wildlife
    • 3.6.1 Exposure characterization
      • 3.6.1.1 Mammals
      • 3.6.1.2 Birds
    • 3.6.2 Effects characterization
      • 3.6.2.1 Acute toxicity of sodium chloride
      • 3.6.2.2 Sublethal effects of excess salt ingestion in birds and mammals
    • 3.6.3 Risk characterization
      • 3.6.3.1 Estimating the contribution of salt toxicity to vehicle strikes
      • 3.6.3.2 Conclusions and discussion of uncertainty
  • 3.7 Ferrocyanides
    • 3.7.1 Exposure characterization
      • 3.7.1.1 Soil
        • 3.7.1.1.1 Non-illuminated ferrocyanide
        • 3.7.1.1.2 Illuminated ferrocyanide
      • 3.7.1.2 Water
      • 3.7.1.3 Air
      • 3.7.1.4 Biomagnification
    • 3.7.2 Measured and estimated environmental concentrations
    • 3.7.3 Effects characterization
      • 3.7.3.1 Aquatic biota
        • 3.7.3.1.1 Microorganisms
        • 3.7.3.1.2 Plants
        • 3.7.3.1.3 Invertebrates
        • 3.7.3.1.4 Vertebrates
      • 3.7.3.2 Terrestrial biota
        • 3.7.3.2.1 Microorganisms
        • 3.7.3.2.2 Plants
        • 3.7.3.2.3 Invertebrates
        • 3.7.3.2.4 Vertebrates
    • 3.7.4 Risk characterization
      • 3.7.4.1 Tier 1 risk characterization
        • 3.7.4.1.1 Cyanide concentration in water
        • 3.7.4.1.2 Cyanide concentration in soil: Case I
        • 3.7.4.1.3 Cyanide concentration in soil: Case II
        • 3.7.4.1.4 Cyanide concentration in air
        • 3.7.4.1.5 Quotient calculations
        • 3.7.4.1.6 Tier 1 conclusions
      • 3.7.4.2 Tier 2 risk characterization
        • 3.7.4.2.1 Cyanide concentration in water
        • 3.7.4.2.2 Cyanide concentration in soil: Case I
        • 3.7.4.2.3 Cyanide concentration in soil: Case II
        • 3.7.4.2.4 Cyanide concentration in air
        • 3.7.4.2.5 Quotient calculations
        • 3.7.4.2.6 Tier 2 conclusions
      • 3.7.4.3 Tier 3 risk characterization
        • 3.7.4.3.1 Assumptions
        • 3.7.4.3.2 Estimation of the frequency of occurrence of toxic events
        • 3.7.4.3.3 Tier 3 results and conclusions
    • 3.7.5 Conclusion for ferrocyanides
  • 3.8 Overall conclusions
    • 3.8.1 Considerations
      • 3.8.1.1 Environment
      • 3.8.1.2 Harmful effects
      • 3.8.1.3 Weight of evidence
    • 3.8.2 Summary of assessment
    • 3.8.3 Uncertainties
    • 3.8.4 Conclusions
  • 3.9 Considerations for follow-up (further action)
• 4.0 References

Appendices

• Appendix A Search Strategies Employed for Identification of Relevant Data
• Appendix B Supporting Documents Prepared for fhe PSL Assessment of Road Salts

List of Tables

• Table 1 Physical and chemical properties of road salts
• Table 2 Total loading of sodium chloride road salt, winter 1997-98 (from Morin and Perchanok, 2000)
• Table 3 Estimated quantities of calcium chloride used on roadways in a typical year (from Morin and Perchanok, 2000)
• Table 4 Total loadings of chloride (from Morin and Perchanok, 2000)
• Table 5 Total volume of waste snow and quantity of salt used in certain Canadian cities, winter 1997-98 (from Delisle and Dériger, 2000)
• Table 6 Snow disposal methods used in certain Canadian cities, winter 1997-98 (from Delisle and Dériger, 2000)
• Table 7 Number of provincial patrol yards and sodium chloride and abrasive use, by province (from Snodgrass and Morin, 2000)
• Table 8 Estimate of magnitude of salt loss at patrol yards (from Snodgrass and Morin, 2000)
• Table 9 Chloride concentrations in various streams in the Toronto Remedial Action Plan watershed for 1990-96 (from Toronto and Region Conservation Authority, 1998)
• Table 10 Toxicity responses of organisms to sodium chloride for exposures less than 1 day (from Evans and Frick, 2001)
• Table 11 Toxicity responses of organisms to sodium chloride for exposures of 1 day (from Evans and Frick, 2001)
• Table 12 Four-day LC₅₀s of various taxa exposed to sodium chloride (from Evans and Frick, 2001)
• Table 13 Seven- to 10-day LC₅₀s and EC₅₀s of various taxa exposed to sodium chloride (from Evans and Frick, 2001)
• Table 14 Summary of Tier 2 calculations (from Evans and Frick, 2001)
• Table 15 pH, total phosphorus and chloride optima for selected diatom species in the northeastern United States (from Dixit et al., 1999)
• Table 16 Sodium chloride tolerance of selected plant species in the salt-impacted mat zone of Pinhook Bog, Indiana (from Wilcox, 1982)
• Table 17 Predicted cumulative percentage of species affected by chronic exposures to chloride (from Evans and Frick, 2001)
• Table 18 Modelled electrical conductivity values and chloride concentrations for Corbett Brook, downstream from Fredericton's salt depot
• Table 19 Species list of roadside trees and shrubs rated for their resistance to airborne highway salt spray (from Lumis et al., 1983)
• Table 20 Species list of native forest tree species rated for their resistance to highway salt spray
• Table 21 Range of threshold values estimated for soil and water for various forms of plants (from Cain et al., 2001)
• Table 22 Range of threshold values estimated for herbaceous tissue concentrations following soil or water solution exposure (from Cain et al., 2001)
• Table 23 Range of threshold values estimated for woody tissue concentrations following aerial exposure (from Cain et al., 2001)
• Table 24 Calculation of the number of particles of salt that need to be ingested in order to reach CTVs assuming a model 28-g house sparrow consuming particles at the upper end of its known preference range
• Table 25 Calculation of the number of particles of salt that need to be ingested in order to reach CTVs assuming a model 28-g house sparrow consuming particles of average size
• Table 26 Quotient calculation results for aquatic biota - Tier 1 (from Letts, 2000a)
• Table 27 Quotient calculation results for terrestrial biota - Tier 1 (from Letts, 2000a)
• Table 28 Quotient calculation results for aquatic biota - Tier 2 (from Letts, 2000a)
• Table 29 Quotient calculation results for terrestrial biota - Tier 2 (from Letts, 2000a)

List of Figures

• Figure 1 Provincial road network area fraction (from Morin and Perchanok, 2000)
• Figure 2 Recommended provincial application rates for sodium chloride road salts, 1998 (from Morin and Perchanok, 2000)
• Figure 3 Average recommended municipal application rates for sodium chloride road salts, 1998 (from Morin and Perchanok, 2000)
• Figure 4 Total amount of sodium chloride used, by maintenance district (from Morin and Perchanok, 2000)
• Figure 5 Historical salt use by provincial agencies (based on surveys conducted by the Salt Institute, 1964-1983, and Morin and Perchanok, 2000)
• Figure 6 Average daily concentration of leachate from salt-treated sand pile, 1975-76 (from NB DOE and DOT, 1978)
• Figure 7 Chloride concentrations in Heffley Creek municipal wells (from AGRA, 1999)
• Figure 8 Road salts transport pathway
• Figure 9 Observed chloride concentrations in Canadian watersheds (from Mayer et al., 1999)
• Figure 10 Estimated road salt chloride concentrations by watershed, calculated from average annual road salt loadings and average annual runoff (from Mayer et al., 1999)
• Figure 11 Chloride concentrations in runoff for provincial roads in Canada
• Figure 12 Estimated chloride concentrations in groundwater for various chloride application rates and a groundwater recharge rate of 10 cm/year (from Johnston et al., 2000)
• Figure 13 Estimated chloride concentrations in groundwater for various chloride application rates and a groundwater recharge rate of 20 cm/year (from Johnston et al., 2000)
• Figure 14 Estimated chloride concentrations in groundwater for various chloride application rates and a groundwater recharge rate of 40 cm/year (from Johnston et al., 2000)
• Figure 15 Chloride concentrations in groundwater from municipal production wells in southern Ontario (from Johnston et al., 2000)
• Figure 16 Species diversity across a salinity and chloride gradient (from Wetzel, 1983)
• Figure 17 Experimental acute toxicity and predicted chronic toxicity for aquatic taxa (from Evans and Frick, 2001)
• Figure 18 Representative short-term chloride concentrations in the Canadian aquatic environment associated with contamination by road salts and concentrations causing adverse biological effects following brief exposures
• Figure 19 Representative long-term chloride concentrations in the Canadian aquatic environment associated with contamination by road salts and concentrations causing adverse biological effects following prolonged exposures
• Figure 20 Areas with low to medium to high road salt application hazards, based on product of soil clay content with exchangeable sodium ratio (from Morin et al., 2000)
• Figure 21 Box plot showing 10th, 25th, 75th, and 90th percentile plus individual data above and below the 10th and 90th percentile for ditch water electrical conductivity and chloride concentrations along two highways near Fredericton's salt depot, outside the depot's catchment area for representative days in June, July, October 1999, and January 2000. "Well-drained", "cross-flow", and "stagnant" refer to three conditions: ridges from which water drains, stream/road crossings, and ditch depressions with no visible outflow, respectively (from Arp, 2001)
• Figure 22 Estimates for total dissolved solids (TDS) and electrical conductivity (EC) of average soil solution and surface waters, by level 2 watersheds and by municipal boundary, Ontario and Quebec (from Morin et al., 2000)
• Figure 23 Exchangeable sodium percentage (ESP) along roadsides, by provincial road maintenance district (from Morin et al., 2000)
• Figure 24 Salt tolerance and crop yield relative to soil salinity (electrical conductivity, EC) and the estimated percentage of roadsides with corresponding levels of electrical conductivity (from Bresler et al., 1982)