Salt PollutionAs awareness for pollution increases, other forms of pollution aredefined. Almost everyone knows about toxic waste and carbon dioxide pollution,but not many people have heard of salt pollution. Salt pollution has been onthe increase since the evolution of the automobile. With more pressure ongovernment agencies to keep the highway clear and safe, an increase in the useof salt has developed. It is important to understand why salt is used and howit work as well as the environmental effects to understand the salt pollutionproblem.
Salt is a necessary and accepted part of the winter environment. Itprovides safety and mobility for motorists, commercial vehicles and emergencyvehicles. Salt is used as the principal deicer because it is the most availableand cost-effective deicer. Rock salt is preferred because it is cheap andeffective. It costs 20 dollars a ton where as an alternative like calciummagnesium cost around 700 dollars a ton. Some 10 million tons of deicing salt isused each year in the U.S. and about 3 million in Canada.
Salt is used to keep snow and ice from bonding to the pavement and toallow snowplows to remove. When salt is applied to ice and snow it creates abrine that has a lower freezing temperature than the surrounding ice or snow.
Salt is the ideal deicing material because it is:the least expensive deicereasy to spreadeasy to store and handlereadily availablenon-toxicharmless to skin and clothingSalt pollution is broken into two main groups. Water, which includesthe effects on ground water, surface water and aquatic life and land.
Most of the salt applied to the roadways eventually ends up in theground water. It is estimated that 30% to 50% of the salt used travels into theground water. Salt effect two areas of ground water, chloride concentration andsodium concentration. Chlorides may be present in the form of sodium chloridecrystals or as a ion in a solution. Normal concentrations in the water areaverage around 10 mg/litre. Concentrations found in ground water near majorhighways have been recorded as high as 250 mg/litre which is around thethreshold of taste.
The main factor with ground water pollution is the risk to human health.
The raised level in sodium in water can cause high blood pressure andhypertension. With people who already suffer from these problem it is necessaryto keep their salt intake relatively low, they should not drink water above 20mg/liter. Although this is recommended, a study of private well water inToronto showed that half the wells exceeded this limit, twenty percent exceeded100 mg/litre and six percent exceeded 250 mg/litre. This increase in sodium andchlorine can also cause problem with water balance in the human body.
As well as surface water, ground water is also affected by road salting.
Although the effects are not as great as ground water, they still pose problemsto the environment. The problems are based on the salt ions. The salt ionsinteract with heavy metal that fall to the bottom of the body of water. Anexample of this is when sodium and chlorine ions compete for mercury to bondwith. This cause the release of mercury into the water system. The risk ofmercury poisoning is far greater than that of sodium or chlorine. This increaseof sodium and chlorine as well as mercury and other heavy metal also causechanges in the pH of water.
The increase of salt around bodies of water also effect aquatic life inthe area. Two main areas that are effected are osmotic regulation in fish andthe death of micro-biotic life in ponds and lakes. Most fish life can onlytolerate a narrow range of salt content in the water. The increase of salt inthe water produced by road de-icing cause freshwater fish to swell up with water.
The increased salt cause a lower concentration of water in the fishes cells.
To compensate, the fishes body takes in water to restore equilibrium. This cankill fish if the salt concentration becomes to high.
Just as important as fish, microorganisms are also effected in adetrimental way. Microrganisms are tiny organism that sustain aquatic life inall bodies of water. They are more susceptible to the effect of salt pollutionthan fish. These microorganism are at the bottom of the food chain, when theydie, it doesn’t take long for the rest of the food chain to follow. Largeincrease in salt concentration can cause 75% – 100% death for thesemicroorganisms, The effect of salt is almost immediate. Most of the organismare only one cell big and blow up in contact with increased amounts of salt.
Water insects are also effected by the increase in salt in theenvironment. The number of insects lowers because the inability for waterinsects to reproduces in the presence of high salt concentrations. With thedecreasing numbers in microorganisms, insects and fish, it is easy to see theeffect it would have on the rest of the food chain even though other animal maybe more salt tolerable.
Salt pollution also is a major factor to land. It can also be broken upinto the effects on soil, vegetation and animals.
The effect of salt on soil may seem relatively less important than theother topics mentioned so far, but it leads up to more important things. Theeffect salt has on soil is that it alters the soil structure. Sodium chlorideactually deteriorates the structure of the soil. This cause a decrease in soilfertility. In most cases calcium in the soil is replaced by sodium in a anionexchange. The make the soil less usable by vegetation. This also occurs withmagnesium. This depletion of calcium and magnesium also causes the soil toincrease in alkalinity with pH of nearly 10. Normal pH for the soils testedwere between 5.4 and 6.6.
High concentrations of sodium in the soil also makes the soil lesspermeable. In some case soil may be encrusted in a layer of salt. As a result,moisture content in the soil may be drastically decreased. High concentrationsof salt may also cause clay to have a decreased concentration of water. Thismakes the clay harder and vegetation is less likely to grow.
Although salt already effects the soil vegetation grows in, it also candirectly effect vegetation itself. Vegetation can be dehydrate to the point ofdeath when in contact with high levels of salt. This occurs because the osmoticstress put on the plant make it react like it was in a drought. A decrease inroots production and burns to leaf tips cause the plant to go into shock.
Salt injury will also occur when plants come into contact with increasedlevels of salt. Salt injury is when foliage damage is present by leaf burn,die-back, defoliation and brooming. It can also cause fruit trees to havereduced quantity and quality of fruit. This occurs with only a small amount ofsalt comes in contact with the plant. It only take 0.5% of the plants tissuedry weight to become salt before the plant reach toxic levels. Increasedchlorine levels can also cause salt injury to a plant in the same way. Saltinjury also effect trees as well as small plant life. Growth of plants in alsoeffected by the presence of sodium and chlorine.
Animal are also greatly effected by roadway de-icing. Although animalstolerance to salt intake is quite high using salt for de-icing road presentsunusual dangers. Moose and deer become susceptible to salt pollution because oftheir attraction to salt. Deer and moose are know to drink the salty wateraround roads. It becomes an addiction to them and reduces the level of fearwhen in contact with cars and people. They have also been found licking thegravel and the side of the road and even the road itself in search for salt.
Small animals are effected more by the toxicity of high levels of salt.
Increased levels of salt in small wildlife caused kidney hemorrhaging,depression, excitement, tremors, incoordination, coma and death. Rabbits seemto be the most susceptible because their inability to stop consuming salt.
Household pets are also effected. once outside, salt collects on their feet.
Pets consume a lot salt when cleaning their feet. This causes cats and dogs toget inflamed stomachs.
As one can see, the effect of roadway de-icing on the environment aretremendous. The use of salt causes a great burden to both land and water. Onemust weigh the pro’s and con’s of de-icing when learn about the effects of salton the environment.