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Posts tagged ‘Road salt’

Environmental Impacts of Road Salt


I see that john Gormely the environment Minster is in charge of the country’s road De-icing operations

Baring in mind that this man is a Green Minster I would ask him to take notice of this article!

Having lived in Germany for many years I know all too well the destruction Salt does to the environment

There are alternatives available!

Mr Gormely

This article can be read in full at the following link

http://www.newyorkwater.org/downloadedArticles/ENVIRONMENTANIMPACT.cfm

By William Wegner and Marc Yaggi

Chloride salts are composed of approximately 60% chloride and 40% positive ion. De-icing operations use calcium, potassium, and magnesium chlorides, but to a lesser degree than NaCl. These salts may be applied in liquid or crystalline form, either of which can be used in conjunction with abrasives. Liquid salt solutions provide immediate deicing upon application to roads and foothpaths. Crystalline forms are slower and longer acting than liquid solutions. Sodium ferrocyanide is added to chloride salts to prevent clumping during storage and application. In water, sodium ferrocyanide can be photolyzed to release approximately 25% cyanide ions (EPA, 1971).
Runoff to surface waters and percolation to groundwater are the most common mechanisms for road salts to enter water supplies. Infiltration is more common for groundwater-based supplies. Chloride concentration in groundwater supplies exhibits a relatively linear relation to road-salt application rate or two-lane road density throughout the year. In surface-water supplies, chloride concentration depends on salting intensity, soil type, climate, topography, and water volume, with larger water bodies exhibiting lower concentrations through the process of dilution. Deicing salts applied to roads during winter are the primary source of solutes to groundwater,).

NaCl dissociates in aquatic systems into chloride ions (CL) and sodium cations (Na+). While sodium may bond to negatively charged soil particles or be taken up in biological processes, chloride ions are less reactive and can be transported to surface waters through soil and groundwater. Road salts applied to roadways can enter air, soil, groundwater, and surface water from direct or snowmelt runoff, release from surface soils, and/or wind-borne spray. These salts remain in solution in surface waters and are not subject to any significant natural removal mechanisms). Their accumulation and persistence in watersheds pose risks to aquatic ecosystems and to water quality. Approximately 55% of road-salt chlorides are transported in surface runoff with the remaining 45% infiltrating through soils and into groundwater aquifers
Vegetation

Soils

Soil biotic communities cycle nutrients, decompose organic matter, and increase soil aeration and water-holding capacity. EC (2000) reported soil chloride concentrations exceeding 200 mg/l as far as 200 m from roadsides. EPA has set the Secondary Maximum Contaminant Level (SMCL) for chloride at 250 mg/l in drinking-water supplies.

Exposure to NaCl inhibits some soil bacteria at concentrations as low as 90 mg/l, which ultimately compromises soil structure and thereby inhibits erosion control. Federal standards for turbidity require that a drinking-water supply not exceed 5 nephelometric turbidity units;.

 

Elevated sodium and chloride levels in soils create osmotic imbalances in plants, which inhibit water absorption and reduce root growth. Salt also disrupts the uptake of plant nutrients and inhibits long-term growth. EC (2000) cites numerous studies attributing tree injury and decline to road-salt application, concluding that NaCl can cause severe injury to the flowering, seed germination, roots, and stems of roadside plant species. Damage to vegetation can occur up to 200 m from roadways that are treated with deicing salts. Up to 50.8% of woody plant species are sensitive to NaCl, and many of these have disappeared from Canadian roadsides. Of the 15 principal tree genera occurring in Canadian forests, 11 have been rated as sensitive to road salt. Threshold values for woody and herbaceous plant forms can be as low as 67.5 ppm in soils, with pine seedlings being the most sensitive; 280 ppm in herbaceous tissues; and 200 ppm in woody tissues. Plants may be sensitive to concentrations of either or both salt ions present in soil. An Ontario study reported a soil chloride concentration of 1,050 ppm in soil taken from a highway median and 890 ppm in soil sampled 10 m from the highway NaCl exposure as low as 100 ppm in soil inhibits seed germination and root growth rates for grasses and wildflowers. As a result of salt concentrations in roadside soils, salt-tolerant halophytic plant species, formerly endemic to coastal wetlands, now colonize inland roadsides (EC, 2000). These species include cattails and Phragmites, both of which can be indicators of degraded wetlands subject to excessive nutrient loading and/or salt contamination.

Damage to vegetation can amplify adverse impacts on drinking-water quality Degradation of soils and vegetation in buffer areas between roads and watercourses compromises the retention and processing of pollutants transported in stormwater runoff and diminishes the beneficial value of buffer zones to groundwater sources and reservoirs. Impacts to water quality can be particularly acute when high level-of-service roads are adjacent to drinking-water reservoirs insulated by narrow buffers,

Wildlife


Damage to vegetation degrades wildlife habitat by destroying food resources, habitat corridors, shelter, and breeding or nesting sites. Behavioral and toxicological impacts to wildlife also are associated with road salts. Sodium-deficient wildlife sometimes travel great distances to ingest road salt. Many animals tend to overshoot their salt deficit and then drink salty snow melt to relieve thirst, which increases salt toxicity in blood and tissues

While wildlife impacts might not be construed as directly relating to water-quality impacts, kills and population declines among salt-sensitive species can be indicators of salt toxicity in aquatic ecosystems.

Birds.

12 reports of bird kills associated with road salt in the US, Canada, and Germany. Two reports involved kills in excess of 1,000 birds. Seed-eating birds may not be able to distinguish between road-salt crystals and the mineral grit their diets require. Laboratory studies of sparrows consuming salt particles at the upper limits of their known preference range reveal that ingestion of 0.25 NaCl particles (266 mg/kg) results in a breach of homeostasis; ingestion of 1.4 particles (1,500 mg/kg) may result in death (median lethal dose = 2.8 at 3,000 mg/kg). This means behavioral abnormalities can occur in small bird species with ingestion of a single salt particle and death can occur with ingestion of two particles. Salt toxicosis in birds increases their vulnerability to car strike. The local human inhabitants near Mount Revelstoke Park, BC, refer to winter finches as “grille birds” because of the large numbers that collect on the grilles of moving vehicles. Although there is a high correlation between the distribution of winter finches and the Canadian road system receiving salt, risk characterization is difficult to assess in terms of kill frequency because of the various mechanisms–fatal attraction, toxicosis-induced car strike, lethal ingestion–that contribute to mortality. Nevertheless, EC concluded that transportation officials probably underestimated the contribution of road salt to wildlife kills.

Aquatic Biota.
Road-salt loadings in surface waters vary with regional climate conditions, season, and air temperature fluctuation. Snowmelt may proceed gradually overall, but it increases dramatically following application of road salt. Shock loads of salt to aquatic ecosystems might last less than a day following application, with concentration decreasing thereafter. Salt held in solution in snow or deposited on surface soil layers is readily dissolved by rain and can be transported to receiving waters in runoff. Prolonged retention of salt in streambeds or lakebeds decreases dissolved oxygen and can increase nutrient loading, which in turn promotes eutrophication.


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