Iced (1988)

[Flocka Bilodeau]

Its Episode 35! And Dan dives deep into the 35th minutes of Blood Lake (1987) and Iced (1988).In Blood Lake, Rebecca offers those two guys that I keep calling Steve lunch. Do they accept?And in Iced, Jeanette shows John and Diane their room in the chalet/ lodge/ cabin. Do they like it?Please, listen and find out.

An estimated 365,000 tons of road salt is applied in the Twin Cities Metropolitan Area (TCMA) each year. The chloride in road salt flows into our lakes, streams, and groundwater, potentially harming our environment.

Several different types of deicing chemicals exist. Those covered in this section include chloride-based deicers, acetate-based deicers, and carbohydrates. A list of the chemicals approved for use by the MNDOT can be found here. This article summarizes environmental effects of de-icing chemicals. Other effects (e.g. on infrastructure) are discussed elsewhere in this manual.

The chloride-based deicers discussed in this section are sodium chloride (NaCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2). Deicers can enter into the environment during storage, transport, and application. The distribution of the deicer is a complex process, an overview of which is provided in the figure to the right. When chloride deicers are dissolved in runoff, the anion and cation dissociate. The following section separately describes the environmental effects of anions (i.e. chloride) and cations (i.e. sodium, calcium, or magnesium).

The chloride component of chloride-based deicers does not easily precipitate, is not biodegradable, is not readily involved in biological process, and does not adsorb significantly to mineral/soil surface (Levelton Consultants Ltd., 2008). As such, chloride is highly mobile and can impact the soil, vegetation, groundwater, surface water, and air. Stefan et al. (2008) found around 30 percent of the salt applied to the roads in the TCMA makes its way to the Mississippi River. This suggests that the remaining 70 percent is either blown away, transported into the ground water, or stays within the soil, lakes, or wetlands.

Deicers reach the soil via runoff, splashing, spraying, or plowing. In general, chloride concentrations are the greatest within 2 to 3 meters from the road edge (Berthouex and Prior, 1968). Others, such as Norrstrom and Bergstedt (2001) have found salts as far out as 10 meters from the road edge, with the highest concentration within 6 meters. The distance that the salts will be transported through the soils depends on subsurface conditions. Long-term accumulation of chloride can result in reduced soil permeability and fertility, as well as increased soil alkalinity and density. As a result, there could be negative effects on the chemical properties of the soil and its ability to retain water, both of which are important to plant growth and erosion control (National Research Council, 1991). Another adverse effect of chloride in soil is its potential to release the metals sorbed to the soil particles (National Research Council, 1991; Amrhein et al., 1992; Backstrom et al., 2004).

Since chloride does not bind to soils, chlorides that enter the subsurface with infiltrating water may reach the groundwater table. Howard and Haynes (1993) found that 55 percent of salt applied to a catchment in Toronto enters temporary storage in shallow sub-surface waters. Cusack (n.d.) estimated that approximately 45 percent of chlorides applied as road salt will be carried to the groundwater. Chloride entering groundwater systems is likely to persist for a long time since there is no significant removal mechanism and groundwater moves slowly.

Chloride concentrations in surface waters tend to follow a seasonal distribution. Concentrations usually increase in the winter and decrease in the summer (Novotny et al., 2007). The chronic chloride pollution standard has been set at 230 mg/L and the acute standard at 860 mg/L by the MPCA in Minnesota Rules Chapters 7050 and 7052. These limits are based on the findings that chronic concentrations of 230 mg/L are harmful to aquatic life, while concentrations above the acute standards are lethal and sub-lethal to aquatic plants and invertebrates. Stefan et al. (2008) reported that to date there are no documented exceedances of the acute standard in the Twin Cities. However, there are 21 lakes, 22 streams, and 4 wetlands that are impaired for chloride.

Salt-containing water has a higher density than non-salt-containing water and will sink to the bottom of the water body. This can result in chemical stratification and disrupt the lake mixing patterns (New Hampshire Department of Environmental Service, N.D.; Novotny et al., 2007). Effects on surface waters may be minimized by the dilution of the deicers as they are transported to the surface water. Dilutions of 1:100 to 1:500 are estimated to mitigate negative impacts of the deicer (Fischel, 2001). Small ponds and slow streams are estimated to be most impacted by deicers because the likelihood of dilution and dispersion is lower in those environments (Fischel, 2001).

A small percentage of the total applied chloride is evidenced to be transported by air. Blomqvist and Johansson (1999) found some deicing road salts can be transported by air 40m from the application site. Kelsey and Hootman (1992) found that sodium chloride was detected at a height of 49 feet (15 meters) within 220 feet (67 meters) of the highway. Kelsey and Hootman (1992) also found evidence of a positive correlation between plume height, and the travel distance of the constituent. The Connecticut DOT found road salt powder could travel as far as 300 feet laterally under heavy traffic conditions. Chloride transported by air can affect soil and surface/groundwater, but deposition on the vegetation is the primary concern (Levelton Consultants Ltd., 2008).

The cation components of chloride-based deicers (i.e. sodium, magnesium, and calcium) can also impact the environment. Sodium ions can change the structure of soil, causing a decrease in permeability, and infiltration (Davis et al., 2012). Sodium can also reduce the amount of calcium, magnesium, and other nutrients in the soil by raising the alkalinity of the soil and reducing the ion exchange capacity (National Research Council, 1991). Magnesium and calcium can improve soil structure by causing soil particles (particularly clays) to form aggregates, resulting in improved drainage (Amrhein, and Strong, 1990). The presence of chloride, magnesium, and calcium may also result in the mobilization of heavy metals sorbed to soil particles (Amrhein, and Strong, 1990; Backstrom et al., 2003)

Sodium, magnesium, and chloride in surface and groundwater can affect the hardness of water. The hardness of water will be reduced if there are elevated levels of sodium and will be increased if there are elevated levels of calcium and magnesium (Cheng and Guthrie, 1998). An increase in water hardness has shown evidence of decreasing the toxicity of heavy metals (Lewis, 1997).

In order to reduce the corrosive effects of some of the chloride-based deicers, corrosion inhibitors can be added. Corrosion inhibitors can include heavy metals, inorganic ions, and organic substances (Levelton Consultants Ltd., 2008). The toxicity and environmental effects of corrosion inhibitors vary greatly and are dependent on the composition (Pilgrim, 2013). In general, the inhibitors that contain organic components consume oxygen during decay. The oxygen consumption can lead to anoxic conditions in the soil, groundwater, or surface water (Fischel, 2001). At colder temperatures, the rate of decomposition will decrease and there will be an increased potential for the inhibitors to reach the groundwater (Cheng and Guthrie, 1998).

Much of the information on the environmental impacts of acetate-based deicers is based on studies regarding calcium-magnesium acetate (CMA) Therefore, much of the information presented in this section is related specifically to CMA. Modeling studies have estimated that the concentrations of CMA in the runoff from highways is between 10 and 100 mg/L, with a maximum concentration of 5,000 ppm. The typical annual mass loading is estimated to be 10 tons/linear-mile (Horner, 1988). Despite high mass loading, runoff and receiving water are predicted to dilute the concentration.

The characteristics of acetate suggest it would be absorbed to the soil surface and not carried away with the runoff. Once in infiltrating water, acetate can be mobile, however Horner (1988) found that less than 10 percent of the acetate applied to test plots were found in the underlying soil and groundwater. The sodium and potassium contained in other types of acetates are less likely to adsorb to the soils and therefore have a greater potential to leach into groundwater (Cheng and Guthrie, 1998).

Acetate-based deicers dissociate when in water. The metal ion persists, but the acetate ion will degrade (Fortin et al, 2014). Degradation of the acetate ion consumes oxygen, which is one of the biggest environmental concerns associated with the use of acetate-based deicers. At temperatures between 10C and 20C, the biological oxygen demand (BOD) was fully applied within 5 to 10 days of the acetate being deposited into the water. At a water temperature of 2C decomposition took 100 days (Horner, 1992).

Modeling studies have predicted CMA concentrations in the highway runoff range from 10 to 100 ppm, with a maximum concentration of 5,000 ppm. Evidence has shown that at a concentration of 100 ppm and a temperature of 20C, CMA will completely deplete the oxygen in the water. At concentrations of 10 ppm the dissolved oxygen in ponds was reduced by approximately 50% (Brenner and Horner, 1992).

Carbohydrate-based deicers are often made from the fermentation of grains or the processing of sugars such as cane or beet sugar (Rubin et al., 2010). Small quantities of carbohydrates are sometimes used with other deicers. Alone carbohydrates do not aid in melting ice or snow; however, their use can help reduce the freezing point of ice further than salt and can help salt stick better to the road surface (Fortin et al, 2014; Rhodan and Sanburn, 2014). Carbohydrates are not corrosive to steel, and at high concentrations, carbohydrates can act as a corrosion inhibitor for salt brines.

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