Environmental protection

Although salt was described as a curse in the Bible, it is also a blessing when it comes to preserving food. This is why the controlled and careful handling of salt as a natural substance – in both senses – is vital to survival.

The natural resource salt in Switzerland, naturally available and ecological

Salt is a Swiss natural resource which will serve us for centuries to come. Our salt was gifted to us by the primordial ocean that evaporated 200 million years ago, leaving behind layers of salt up to 100 metres thick in North-western Switzerland, the Jura and the Swiss Midllands. The salt layers are overlaid by younger rocks.

The principle of the evaporation method, as practised at Swiss Saltworks, is simple. We drill into the salt layers at depths of 140 to 400 m, and pump drinking water into them. The salt dissolves, while clay, fine sand and insoluble minerals are left behind. We pump the salt solution (saturated brine) into huge tanks. Firstly, the brine is softened by precipitating calcium sulphate and calcium carbonate, and then it is heated in evaporators. The water evaporates and pure, fine salt is crystallised. The steam is re-heated and re-used. We feed condensed, mineral-free residual water into the Rhine. The salt then enters the economic cycle in bulk (loose) form or in packs. Gypsum and other minerals obtained as sludge during the brine softening process are compacted back into the subsoil from which they originally came.

Thanks to heat recovery, fifteen times less energy is needed to produce one tonne of salt nowadays than in the past.

Salt in water

Salt dissolves very easily in water, so virtually all bodies of water naturally contain salt, or sodium and chloride ions. Water springs containing salt and minerals have been used for drinking and therapeutic purposes for generations, and it would be impossible to imagine the sea without salt.

However, many industrial processes release common salt and other salts into nature from sewage, fertilisation and winter services, so strict monitoring of groundwater and flowing waters is needed in order to assess their quality and potential health risks. The identification, assessment and tracking of sodium and chloride in bodies of water have become routine and transparent procedures (at least in Switzerland).

Switzerland is a member of the International Commission for the Protection of the Rhine (ICPR), and so it shares responsibility for the quality of the water in this major European river system. Values measured at Basel highlight the status of our water protection activities and, in fact, they are representative of about 70% of Switzerland. See for yourself that the salt contamination of bodies of water in Switzerland gives no cause for concern.

De-icing salt – ecologically beneficial

Winter services using de-icing salt have improved substantially in recent years due to economic and ecological requirements. Contributory factors include damp (pre-wetted) salt technology, infrared and IT-controlled spreading methods, networked road condition diagnosis, improved weather information and optimised operational planning. The concept of "differentiated winter service" sets clear priorities for high-capacity roads and hazardous sections. Where this is a responsible option, snow is not fully cleared down to the blacktop. Depending on weather conditions, only 5 to a maximum of 20 grammes of salt are now spread per m2.

The weather has the greatest influence on salt consumption, but this influence is unpredictable. The quantities sold per year by Swiss Saltworks fluctuate between about 100,000 and 300,000 tonnes of de-icing salt, with a long-term average of some 150,000 tonnes.

Salt is indisputably the most effective and economical means of making icy roads safer for traffic. However, road safety, costs and environmental pollution always have to be kept in balance. This is why the principle for winter services is: "As much as necessary, but as little as possible".

Grit: a blunt instrument

For a long time, grit was seen as the ecological alternative to de-icing salt. However, grit performs poorly on traffic safety: blunting agents have no effect on slippery frost and black ice. Accident analyses prove this point clearly.

Grit also comes off worse in terms of quantity, because ten to twenty times more grit than de-icing salt has to be spread to achieve the same effect; by the time 300 to 500 vehicles have passed, all the grit has been churned off the carriageway and the spreader needs to go over it again.
The costs of grit are therefore high in terms of purchasing, transport, storage and spreading. Moreover, compaction (which generates dust), complex recycling or disposal as special waste all prove to be costly procedures.

Source: Salz- und Splittstreuung im Winterdienst, neue Forschungserkenntnisse [Salt and grit spreading for winter services, new research results], Dr. Beatrice Ruess, Strasse und Verkehr 1998.

Salt and roadside trees

Salt spread on the roads in winter used to be held solely responsible for the pitiful condition of stands of trees, bushes and stretches of grass along the roadsides. Now that the many stress factors for plants in urban and roadside habitats are better known and systematically addressed, this allegation is groundless. Take a look for yourself.

Compared to humans and animals, plants only need small quantities of salt and react more sensitively to it. Plants in lagoon and beach areas by the sea have adapted well to the change in salt concentration.

Where chloride is in plentiful supply in roadside locations, the trees absorb more of it. However, they can store chloride in their wood, thereby isolating it from the active metabolism.

A study conducted over several years on roadside trees in Hanover showed that the chloride content fluctuates sharply over the course of a year, and the maximum limits of 0.3% where damage begins were not reached either in the plants or in the soil. Most de-icing salt is carried into the sewerage system and into flowing bodies of water in rain and melt water, so it does not reach the plants’ root zone (see the chart: "Damaging factors").

Stress factors for roadside trees

• Soil conditions on the roadside
• Soil compaction
• Constriction of the root zone
• Lack of water, nutrients and oxygen
• Salinisation of the soil by de-icing salt
• Mechanical damage to roots
• Work on pipes and sewerage ducts
• Contamination (e.g. from engine oil, dog excrement)
• Soil conditions on the roadside

Stress factors with overground impact

• Typical conurbation climate with "oven effect"
• Air pollution in the form of gases and dusts (immissions)
• Mechanical damage to the trunk, branches and twigs