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Consequences of the use of thawing salt on our roads

With this article we would like to inform and to contribute our standpoint to an on-going discussion. It concerns the use of thawing salt for the roads of Kiev and other cities with the goal to facilitate the traffic. Road thawing salt consists predominantly of common salt (chemical name sodium chloride or NaCl) sometimes with admixtures of calcium chloride and (toxic) potassium ferrous cyanide. To road thawing salt there are hardly alternatives (e.g. snow removal, sand) and therefore it is not pretended here that it is possible to maintain the traffic completely without the use of salt. But how much salt must be? For the answer of this question, also its negative effects must be evaluated apart from the usefulness of salt. Since the disadvantages are by far less known, they are briefly described here.
Salt does not only thaw ice and snow. It attacks the road surface, cars and even reinforced concrete (buildings). Along the roads (according to literature data up to 80 m!) salt is deposed on the soil, changes the soil structure and thus reduces its permeability for rain water. Trees take up the chloride through the roots, a part will be deposited in the leaves and let them get brown already in the spring. Rain can wash out the salt from leaves, but finally this salt comes again in contact with the roots. After several years the tree is attacked by parasites and dies. Often salt was the cause but this is not always recognised.
Salt, which seeped into the soil, either reaches the groundwater and sometimes possibly the drinking water or is enriched in the soil. Both effects are not desired. With the melting water salt comes into the rainwater drains and a substantial part flows into the brooks. The salt concentration in the brooks reaches its maximum already short time after the beginning of the thawing process. One day later the concentration can already drop to nearly normal values. In order to catch the biologically relevant maximum, automatic samplers must be set up, which take samples regularly also at night, or one measures continuously the electrical conductivity (which depends from the salt concentration).
ILES has performed several control measurements on the 14th and 15th of February2005. On the 14th water collected from the streets and the storm water drains was strongly loaded with salt as expected. In three different places of the brook Libid the electrical conductivity was about 1050 mS/m (roughly 10 times more than usual). The maximal load was probably even higher. Our laboratory analyses have shown that 1000 mS/m correspond to a chloride concentration of approximately 2500 mg/L. Such concentrations occur otherwise only in mines drainage water. They are deadly for stream organisms. Most freshwater organisms tolerate only 1000 up to 2300 mg/L chloride (literature data, KOPPE and STOTZEK 1999). Most macrophytes (water plants) tolerate not more than 150 mg/L chloride.
The same risk is given for the ecologically more valuable streams Siretz and Darnitza because both receive storm water runoff. They also showed increased conductivity after snow melting.
The river Nivka is an exception: it seems to receive less storm water and flows through several ponds. The ponds dilute the inflowing water and reduce the current velocity. Salt water is heavier than freshwater and sinks down to the bottom, where it can cause problems as well. Downstream of the ponds water did not show obvious signs of salinisation or increased pollution.
The following day, 15 February, conductivity has fallen already down to between 400 – 500 mS/m in the first mentioned streams.

Former investigations have already shown that only a reduced number of organisms live in Kievs’ brooks. Salinisation is possibly one of the main reasons for that. If we want that our brooks reach a better ecological status then we should include this aspect into our considerations and balance advantages and disadvantages of salt use.
In our mind, the damage to material and nature is substantial. To quantify this damage and to put it into relation with the advantages of thawing salts is unfortunately not possible for us. Nevertheless, following the precautionary principle, we mean that the use of salt should be minimised as far as possible. The employment should be limited to the main connecting roads. On side streets, sand must be strewn in the case of need. The most important is however that the drivers and the inhabitants understand the needs and accept measures if taken by the city administration

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Ukr.-American Environmental Association has published the following article about chestnut trees that are suffering from salt, air pollution and soil loads:

V.) KYIV CHESTNUT TREES NEED TREATMENT:

 National Radio Company of Ukraine, February 12, 2007

 <http://www.nrcu.gov.ua/index.php?id=148&listid=41097> 

Kyiv boasts two million chestnuts, scientists of the National Academy Of Sciences inform. The majority of them, however, experience some bad condition, especially those, located in the Kyiv downtown. 

Scientists of the Hryshko National Botanical Gardens are engaged in carrying out a research of the state of Kyiv chestnuts. The scientists agree Kyiv chestnuts need treatment, at least this proves to be cheaper than planting new chestnuts, evaluated at 100 M. US$.


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