Functions and uses

All life is inseparably linked to salt as a raw material and commodity. Its taste is unique, and the effects it produces are extremely diverse. However, dosage is the critical factor in all the many applications for salt. This is why controlled and careful handling of salt as a natural substance is vital to survival.

1. Humans and salt

Salt is life
Salz ist LebenWhen life was first stirring on the earth, salt was already playing its part. Salt and other basic chemical substances combined with water in the primordial oceans to form a “primeval broth” in which the first micro-organisms were able to develop.
Multi-cellular man has also retained something of the primordial ocean within himself since the start of his three million years of development, in the form of what is known as the extracellular fluid that surrounds our cells. One litre of this fluid contains 9 grammes of common salt.
Salt is a special substance with a unique taste and a diverse range of effects. Fine food can only take a few pinches of salt, but it can be added generously to the water for an invigorating bath, while the pain of “rubbing salt in a wound” is not only proverbial but a literal fact.
Blood (in our arteries), sweat (on our brows) and tears (of joy on our cheeks) make it clear that salt is the food of life. Water, heat and salt buoy our heavy bodies up in a brine bath to relax our minds, care for our skin and activate our circulation.

A natural medicine
Medical science accorded a position of universal importance to salt in days gone by. Salt was also a medicine. It played its part in hygiene and was regarded as an effective diet. Even in those days, the therapeutic effects of sea water and brine baths were appreciated.
One example is the 0.9% common salt solution that is essential in case of accidents involving blood loss or as a carrier fluid for other drug solutions in infusions. This physiological and isotonic solution of common salt helps to save lives.
However, salt is also put to successful use in naturopathy and for home remedies. Saltwater solutions in specified concentrations can reduce swelling in inflamed mucous membranes, and they are helpful with colds or inflammations of the throat and pharynx. Knowledge about the therapeutic effects of brine springs has also been handed down to modern times. Brine baths are used for a whole series of complaints, in particular those affecting the musculoskeletal system (gout, rheumatism and sciatica). Warm brine baths are also popular as a form of post-operative treatment after orthopaedic or neurological interventions, for injuries due to accidents, consequences of paralysis, cardiovascular disorders and diseases of the respiratory tract. Many renowned spas came into being during the Roman era.
Skin diseases are treated successfully with salt, light and heat, either directly on the seashore or in clinics. People suffering from psoriasis find relief in the spas of the Dead Sea. Over 200 years ago, the particularly bracing climate of the North Sea was already known for its beneficial influence on respiratory tract diseases.

The roles of sodium (Na) and chlorine (Cl)
Natrium-chlorverteilung-43Sodium also plays a key part in transmitting stimuli along the pathways of our nervous system. When at rest, nerve cells contain potassium ions and their cell membranes are impermeable to sodium ions. But when the cell is stimulated, the membrane suddenly becomes permeable and sodium ions flow in, causing a change in the cell’s electrical condition. The nerve fibres pass this on as an electrical signal. If the body’s potassium-sodium ratio is disrupted due to a lack of salt, symptoms such as fatigue, enervation, sluggish reactions and muscular cramps may occur. However, sodium cannot be replaced by potassium. Dietary recommendations are often misunderstood in this regard.
das-Salz-im-körper-46Sodium ions perform their main task in the nervous system, whereas chloride ions are crucially important for the digestive function. In addition to mucus and enzymes, the gastric juices also contain hydrochloric acid which makes them strongly acidic (pH value: 1.0–1.5). This acidity is important because it kills pathogens contained in food and prepares food protein for further digestion.
The taste of tears and sweat makes us aware that we have salt in our bodies. For a body weight of 70 kilograms, the salt content is in fact 125 grams (see the NaCl distribution chart). However, this is not a constant value because we excrete salt every day through sweat and urine. Humans and animals feel compelled to replace lost salt. Going without salt for lengthy periods results in deficiency symptoms, illnesses and even death in extreme cases. However, there is a risk of salt deficiency with unbalanced diets, thirst sensation disorders in elderly people, extreme diarrhoea and endurance sports.

How much salt does a person need?
Salt requirements are highly individual and they vary according to weight, physical activity and state of health. Adults need 4 to 6 grammes of common salt per day. With balanced nutrition, these quantities are contained in meals. In Germany, Austria and Switzerland, statistics indicate that this guidance figure is exceeded by one to two grammes per day.

Iodine in salt – fighting off gout
Illustration-deSalt contributes to good health as an ideal carrier medium for trace elements. The human body needs iodine to regulate the thyroid function. The daily requirement for an adult is between 100 and 150 microgrammes (0.00015 g). This is an infinitesimal quantity, and yet the consumption of food or beverages will not guarantee that we receive it. Lack of iodine leads to goitre and other deficiency symptoms.
The consequences of iodine deficiency were already known at the start of the last century. After local trials, iodisation of salt was introduced throughout the country for the first time in 1922. Switzerland was therefore a pioneer in this field. Since then, the Swiss Saltworks have added potassium iodide to table salt on behalf of the authorities. There is no doubt that the decline in cases of goitre and iodine deficiency diseases can essentially be attributed to this measure. Iodisation of table salt is now a key factor in the global healthcare programmes of the World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF).

Fluoride in salt – for the sake of our teeth
fluor_zaehneSwiss JuraSel® table salt is available not only with iodine but also with fluorine. At an early stage, dental medicine discovered that regular rinsing of the tooth enamel with even very low concentrations of fluoride helps to conserve and harden the enamel. Fluorine is not only effective during the growth phase but also in elderly people. Fluoride in table salt is therefore a suitable and (moreover) inexpensive means of preventing tooth decay for the entire population.

2. Biology

Plants that tolerate salt
Salt and its world have many surprises in store – but sometimes a second look is needed to discover them. Plants that tolerate salt or halophytes are a good example. They populate sea coasts, saltmarshes and marshland, salt deserts and saliniferous springs. These masters of survival still flourish in salt concentrations of over 0.5% thanks to various physiological strategies. Glands that excrete salt, extreme water storage (succulence) and filtration in the roots are typical examples of how these plants have adapted. An opportunistic lifestyle can also be successful. Plants of this sort complete their life cycle and form seeds before the salt concentration in their tissue reaches the lethal level.
Intense sunshine, major fluctuations in temperature and droughts create harsh living conditions for littoral plants, similar to those in high mountain areas, deserts and polar regions. Many salt-tolerant plants are therefore dwarfed, or they may grow in clumps with small, leathery, fleshy or hairy leaves.
These examples will give you more insights into the variety of halophytes. Each of these plants is representative in its own particular way.

Gold coin or Mediterranean beach daisy (Asteriscus maritimus L.)
Strandstern-89The perennial gold coin or Mediterranean beach daisy (Asteriscus maritimus L.) becomes conspicuous when it blooms in spring and its vibrant yellow blossoms carpet the coastal rocks of the Mediterranean Sea. Otherwise, this plant (a member of the composite or asteraceae group of plants) is unremarkable. The dwarf shrub is woody at the base with narrow leaves and rough hairs in the upper part. These features enable it to withstand wind, heat, radiation and dryness.

Spiny rush (Juncus acutus)
Binse-92Grasses, sedges and rushes number among the typical flora found on beaches, in swamps and flat areas near coasts. They are often utilised as “pioneer” plants for land reclamation, for fodder or litter in agriculture, or as building materials (reeds are an example of this). Seen from a distance, they resemble one another. However, grasses, sedges and rushes are not related. For our illustration, we have selected the spiny rush (Juncus acutus). Like the very similar Juncus maritimus, it populates the Mediterranean coasts.

Sea grape (Coccoloba uvifera)
Meertraube-95The sea grape (Coccoloba uvifera), a member of the knotweed family, is often the only source of shade on desolate sand beaches in Central and South America, and in the Caribbean. It grows into an evergreen tree with multiple trunks and can reach heights of up to 8 metres. The sea grape is resistant to wind and salt, and it is both useful and decorative. It provides fruits that can be eaten and utilised, as well as firewood and dye. Popular medicine makes use of the roots to treat diarrhoea, and the bark is a remedy for throat inflammations.

Buck’s horn plantain (Plantago coronopus)
Dickblättriger-Wegerich-98The buck’s horn plantain (Plantago coronopus) likes to populate sandy and rocky areas on central European coastlines. Its appearance and distribution mark it out as a plant that tolerates salt. However, even laymen will recognise that it is related to the native ribwort and broad-leaved plantain.

Mangrove forests (Rhizophora mangle)
Mangovenwälder-101Mangrove forests (Rhizophora mangle) lend a special fascination to tropical coasts and river estuaries, not only as unique habitats but also as backdrops for adventurous filming and travel. Mangroves flourish in salty and brackish water, and they have no problems in coping with alternating tidal movements. We have selected R. mangle, the most widespread and important species. It supplies reddish wood from which tanning agents can be extracted, or which can be used to produce charcoal. The seeds are propagated in a very unusual way. They germinate on the parent plant, fall into the water and remain caught in holes in the silt (as if they were planted with a dibble).

Glasswort (Salicornia perenne)
Ausdauernder-Queller-104The glasswort (Salicornia perenne) is known as a plant used in salads. This popular member of the goosefoot family of shrubs is related to spinach. The glasswort is a fleshy, salt-tolerant plant that resembles asparagus; it is frequently native to European coastlines, mud flats and saltmarshes. It is also planted for land reclamation purposes.

Saltmarsh sand spurry (Spergularia salina)
Salz-Spärkling-107The sea spurry or saltmarsh sandspurry (Spergularia salina) is a member of the carnation (or pink) family. This inconspicuous low-growing plant flourishes on sea coasts and saliniferous ground in Europe, North Africa and the Near East. It produces white or pale pink blossoms between April and September.

Tamarisk (T. africana Poir.)
Tamariske-110The genus of tamarisks includes some 80 species of deep-rooted trees and bushes that produce foliage. Their native territory stretches from the Mediterranean to China and they are often found in desert regions. They are planted along coastlines as windshields. Some of them are medicinal plants or sources of dye. Desert peoples have valued manna (Tamarix mannifera) since biblical times. The illustration shows the African tamarisk (T. africana Poir.) which flourishes along rivers, on flat coasts and in the sand dunes of the Mediterranean region, North Africa and the Canaries. It is also cultivated as a decorative plant and a roadside tree.

Beach morning glory (Calystegia soldanella L.)
Strandwinde-113The beach morning glory (Calystegia soldanella L.) is a relative of our own field bindweed. It seeks out warm coastal regions around the world for its habitat. It creeps across sand, rocks and dunes. Its vibrant evergreen and fleshy foliage and its clusters of bright pink- and white-striped flowers make it a favourite of beachcombers.
Illustrations: Heinrich Bäbler

Animals, water and salt
The sea is the cradle of life, and its rhythm still beats in our arteries. There is no life without water, and no life without salt. In seas or rivers, in the dripping rain forest, on red-hot desert sand or in the Antarctic pack ice – the evolution of organisms and the struggle for survival are also a constant fight to achieve the right balance between water and salt. Organisms that can bypass diffusion and exploit the principle of osmosis will win through.
All living things need salt, but they can only tolerate it in small quantities. We use various vertebrates as examples to show you how nature succeeds in solving this problem. Our selection is not entirely random, because the creatures’ desalination strategies are best illustrated by their contrasting living conditions.
The evolution of vertebrates has enabled various organs to perform osmoregulation. Examples include skin and gills. They are the external interfaces that are in direct contact with the surrounding medium: seawater, freshwater or air. Glands that actively excrete salt are widespread in the animal kingdom. In reptiles and birds, they can be found near the eyes, nose and mouth. The kidneys are equally efficient participants in regulating the water-salt balance.

Atlantic salmon (Salmo salar)
Atlantischer-Lachs-60The salmon is far more than an excellent fish to eat. Its migrations are legendary. The fry leave their native waters, migrate downstream and disappear into the mythical Sargasso Sea. On attaining sexual maturity, they embark on the return journey to fresh waters, guided by their phenomenal sense of smell and an overpowering compulsion to spawn.
The salmon is simultaneously a freshwater and seawater fish, which makes it even more interesting.
In freshwater, its body has a higher concentration of salt than the surrounding water, which therefore enters continuously through the skin and gills. The salmon is at risk of swelling. The kidney must excrete water and retain salt. For this purpose, it produces large quantities of heavily diluted urine. In seawater, on the other hand, the salmon’s body has a lower salt concentration than the surrounding water. The saltwater constantly removes bodily fluid from the fish through its skin and gills. Paradoxically, the salmon is at risk of dying of thirst due to dehydration. The fish therefore keeps drinking large quantities of saltwater; the kidney retains the freshwater and excretes the salt. It produces small amounts of heavily concentrated urine. The gills of sea fish can also excrete salt.

Roadrunner (Geococcyx californianus, G. velox, American roadrunner)
Rennkuck-Geococcyx-californianus-G.-velox-amerik.-Roadrunner-63The roadrunner or earth cuckoo is originally a desert bird that is excellently able to thrive in its habitat. Two American species are known. They occur in the western USA, e.g. in the Sonora and Mojave deserts, and in Central America, and they are known for their spectacular turns of speed. They can reach almost 30 km/h. Roadrunners are omnivores, but they mainly chase reptiles and insects. They do not disdain colibris or rattlesnakes. The roadrunner’s exuberance has also made it popular as a comic character (The Road Runner by Chuck Jones (Warner Brothers)).
Roadrunners are very sparing in their consumption of water. Water retention in the rectum is extreme, so the faeces are bone dry. In the searing midday heat, the roadrunner reduces its activity by one half. Excess salt is excreted through a salt gland in its nose, but the kidney plays no part in salt regulation.

Sea snakes (Hydrophiidae)
Seeschlange-Hydrophiidae-66Sea snakes inhabit tropical waters from the Persian Gulf to the south-west Pacific Ocean. All of them are poisonous. They usually grow to lengths of about 1.5 metres. In most cases, young sea snakes already hatch inside the female’s body, so they are born live. Most species never leave the water. They are excellent swimmers but they need to obtain air as a basic requirement. They can also remain underwater for several hours by swallowing water, absorbing the oxygen it contains and expelling the water again. Sea snakes feed on fish. Unless they feel threatened, sea snakes do not usually attack humans. Sea snakes excrete excess salt through glands located under their tongue.

Camel (Camelidae)
Kamel-Camelidae-69The single-humped camel (Camelus dromedarius) and the two-humped camel (Camelus ferus) live in the desert regions of Asia and North Africa. Both species have been domesticated since time immemorial, and are highly valued as mainstays of livelihood or as racing camels. Camels are able to withstand long periods of drought and great heat without consuming water. They display an extreme version of control over the water and salt balance. The fatty tissue in their humps is both an energy reserve and a water store. As the fat is reduced, water is released into their metabolism. The quantity of urine is small but with high concentrations of urea and salt.
Nowadays, the two-humped camel is only found in the wild in south-western Mongolia and north-western China. Less than 1000 of these animals remain. At the start of 2001, the discovery of an allegedly unknown species of camel that could drink salt water hit the headlines. 600 specimens were still said to be living in the remote Kum-Tagh dunes in the Chinese province of Xinjiang, on the edge of the Tibetan mountains. There were no photographs and so far, there has been no confirmation of this report.

Penguin (Spheniscidae)
Pinguin-Spenescidae-spez.-72This comical bird has won the hearts of adults and children alike. Their “morning dress” and upright waddling gait may seem ungainly, but in water penguins display superb swimming skills. They are also very resilient: after all, most of the 18 species of penguin live in the Antarctic or on sub-Antarctic islands. Other species are native to the coasts of Australia, South Africa and South America, as well as the Galápagos and Falkland Islands. If penguins are denied access to fresh water, their salt glands begin to function in order to regulate the salt concentration in their bodies (as happens with other birds). Penguins’ salt glands are located behind their eyes and they open into the nasal cavities. The concentrated salt solution exits through their nostrils and drips off their beaks.

Flamingos (Phoenicopteridae)
Flamingos-Phoenicoterus-spez.-75An impressive spectacle can be seen when thousands of shrieking flamingos rise into the air from the lagoons, making the sky shimmer in hues of pink and white. But these birds with their long legs, long necks and curved bills are also fascinating to watch in a zoo as they majestically scout for food, as if walking on stilts. Flamingos breed in various regions of the earth, mostly in still bodies of water or on low-lying islands in flat ponds, salt lakes and lagoons. The perfect way they adapt to habitats that are usually very salty is not so well known. They are not even deterred by the all-engulfing soda lakes of East Africa. Flamingos excrete excess salt through salt glands in their noses. Some species of flamingo drink fresh water from geysers and hot springs.

Marine iguana (Amblyrhynchus christatus)
Meerechse-Amlirhynchus-christatus-78This ancient reptile belongs to the unique fauna of the Galápagos archipelago. Charles Darwin developed his fundamental ideas on evolution and the development of species here because he witnessed live evidence before his very eyes. The marine iguanas live on the surf-swept cliffs, and their dull coloration and gnarled appearance give the impression that they have emerged directly from the lava. However, they are harmless herbivores that feed on algae and various types of seaweed. They use salt glands to regulate the concentration of salt in their bodies. These glands are located in front of their eyes, and they open into the nasal cavity. The concentrated salt solution exits from their nostrils in the form of fine droplets.

Hawksbill sea turtle (Eretmochelys imbricata)
Echte-Karettschildkröte-Eretmochelys-imbricata-80This sea turtle inhabits all warm seas and oceans. Its shell can reach lengths of up to 90 centimetres. The shape of its upper jaw resembles the beak of a bird of prey. Hawksbill sea turtles feed on fish, molluscs, crustaceans and various marine plants. They are hunted and decimated to obtain their shells. To detach the horny plates (“scutes”) from the turtle’s carapace, the creatures are often exposed to a source of heat while they are still alive. The turtles can survive this procedure, after which they form new scutes which are no longer suitable for decorative purposes because they are of lesser quality. Like other marine creatures, the hawksbill sea turtle must constantly excrete excess salt in strong concentrations. Special salt glands perform this function. Their opening is located in front of the turtle’s eye, and the trickling fluid becomes encrusted here when exposed to air. This is why turtles and other creatures with salt glands appear to weep.

Whitefish (Coregonus spec.)
Felchen-Coregonus-spez.-83This famous game fish (edible fish) is one of the species that most resembles salmon. It is primarily native to the cold, deep lakes of the northern hemisphere. It is a typical freshwater fish which feeds on plankton and invertebrates.
Its body tissue has a higher concentration of salt than freshwater, so it continuously takes water in through its skin and gills. The whitefish does not drink water and it must retain salt. Its kidney actively filters the salt out. Consequently, it produces large quantities of heavily diluted urine.

Seals (Pinnipedia)
Robben-Pinnipadia-86These mammals populate all marine regions in the cold and temperate climate zones. Monk seals are the only species found in tropical regions. Seals consist of three families: eared seals (sea lions, fur seals), walruses and earless seals (elephant seals). The ancestors of the seals used to live on land and they retreated into the water in the course of the evolutionary development of their species. They are almost perfectly adapted to life in the water, although they return to the coast or drift ice in order to mate and raise their young. As predators, they feed on fish, crabs, molluscs and other marine creatures. They regulate their salt balance via the renal function. Their urine is heavily concentrated.

3. Salt and the environment

Salt is everywhere
salz-und-umwelt-baeumeSalt is a natural mineral. Vast quantities of it occur as rock salt (halite) in geological strata, or in dissolved form as sodium and chloride ions in seas, lakes and rivers. Living creatures contain small quantities of salt.
Life and salt are inseparably linked. A small pinch of just 4 to 6 grammes per day is enough for us. However, too much salt in drinking water or agricultural soil can prevent all forms of life. This is why salinisation and desertification (whether natural or man-made) are often equated. Although salt was described as a curse in the Bible, is is also a blessing when it comes to preserving food. This is why – in both senses – the controlled and careful handling of salt as a natural substance is vital to survival.

Salt: a Swiss commodity, naturally available and ecological
Salt is a Swiss commodity and our supplies will suffice for many 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 the Jura and the Swiss Plateau. The salt layers have been overlaid by younger rocks.
The principle of the evaporation method, as practised at the 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 heated up again 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 after packaging. 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
salz-im-wasser-waldbachSalt dissolves very easily in water, so virtually all bodies of water naturally contain salt, or sodium and chloride ions. Sources of water 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 through the discharge of wastewater, fertilisation and winter services, so strict monitoring of groundwater and flowing waters is needed in order to assess 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 for about 70% of Switzerland! See for yourself that 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 EDP-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. Full snow clearance down to the blacktop is eliminated where this is a responsible choice. 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 also unpredictable. The quantities of de-icing salt sold per year by Swiss Saltworks fluctuate between about 100,000 and 300,000 tonnes, 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 weapon
For a long time, grit was seen as the ecological alternative to de-icing salt. But grit performs poorly when it comes to safety for traffic. Blunting agents actually have no effect on slippery frost and black ice. Accident analyses prove this point clearly.
Based on a comparison of quantities, grit also comes off worse because ten to twenty times more grit than de-icing salt must be spread to achieve the same effect; after 300 to 500 vehicles have driven over the grit, it is already thrown off the carriageway and needs to be spread again.
The costs of grit are therefore high as regards 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 trees, bushes and stretches of grass alongside roads. Now that the many stress factors for plants in urban and roadside habitats are better known and are systematically combated, this allegation is groundless. Take a look for yourself.
Compared to humans and animals, plants only need small quantities of salt and they react more sensitively to it. Plants in lagoon and beach areas by the sea have adapted well to the change in salt concentration.
Where there is a large supply of chloride in a roadside location, the trees absorb more of it. However, they can store chloride in their wood, thereby keeping it away from the active metabolism.
A study conducted over several years on roadside trees in Hanover showed that the chloride content is subject to heavy fluctuations over the course of a year, and the maximum limits of 0.3% which are associated with damage were never attained either in the plants or in the soil. Most de-icing salt is carried into the sewer system and into flowing bodies of water by rain and meltwater, so it does not reach the root zone of plants (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 sewer ducts

Contamination (e.g. from engine oil, dog excrement)
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

“Acid rain” *Saltwater