The Lake Ortaa body of water of glacial origin squeezed between hills and mountains in the region of Cusio in Piedmontis certainly not among the most famous in Italy despite its strong tourist vocation. Its story, however, is an important testimony of the effects of industrialization on the Italian territory, but also of success in damage repair caused by man. The waters of this lake, once rich in life and a source of subsistence for the inhabitants of the area, were rapidly polluted by the arrival of the first industries, leading to the disappearance of the fish fauna already at the end of the 1920s.
The studies of academic experts such as Rina Monti they identified in poor water exchange and in concentrations of heavy metals the main cause of the decline. Since the 1980s, interventions to control discharges and, in particular, the reclamation of water through the spreading of carbonate have made it possible to restore natural habitat. The tormented history of the lake therefore has a happy ending, and represents an example of international importance for the redevelopment of heavily polluted water basins.
Lake Orta and the Bemberg textile industries
Lake Orta, located in the Piedmont region of Cusioat the beginning of the twentieth century famous for its abundance of fishas well as for the picturesque views of its banks and the small island of San Giulio, home to an abbey built on the foundations of an old castle and the Basilica of the same name.
Fed only by a few streams, the lake has only one emissary stream (which comes out of the lake): for this reason, the exchange of water in the basin is decidedly slow and the major source of water is rainwater. Its waters therefore presented few dissolved mineral salts (a low fixed residue), constant seabed temperature and a “purity” of drinking water.
Thanks to this particular ecosystem, it was rich in fish fauna and plankton, as demonstrated by the analyzes conducted in 1925 by the Swiss Hans Bachmann. Bachmann had been in charge of the company Bemberg, a German textile company to find a suitable location for a production plant Rayonsilk-like cellulose-based fibre. The production required very pure water, in which to dissolve the cellulose, which, reacting with a copper compound, the copper tetramino (Cu(NH3)42+), could polymerize and be processed by extrusion forming the textile fibre.
How in just a few years industry has destroyed the fish flora of Lake Orta
Given the promising results, Bemberg founded a plant in Gozzanoa town at the southern tip of the lake. Production began in September of 1926 and just two years later, analyzing new samples sent by the company, Bachmann found the disappearance of the plankton population in water drawn from the area.
The studies of Rina Montifirst woman to obtain a professorship in the Kingdom of Italy in 1909 in Sassari and established in those years at the University of Milan, confirmed in 1929 the tragic situation. In publishing the results, it will state at the outset that:
Lake Orta, which was famous for its wealth of fish, especially its beautiful salmon trout, has now become barren and deserted. All the flora and fauna of the upper lake has already completely disappeared (…)
The analyses, carried out by experts from the Universities of Milan and Pavia, demonstrated the water and sediment toxicitywhich were able to strongly reduce the bacterial population in test cultures. The decantation and recovery procedures of the Bemberg company’s reagents led in fact to the release of copper and iron compounds, capable of rapidly consume dissolved oxygen and remain suspended in the water for a long time. The first to suffer the consequences were unicellular organisms and plankton, followed by fish which more slowly facedlocal extinctiondue to lack of food and for the toxic effects of copper on the gill apparatus.
Industrial pollution of the lake
Bemberg was not the only company to cause damage to Lake Orta: after the Second World War numerous companies producing taps spread across the area (hence the name “Tap District“). In addition to iron and copper compounds, the discharges from Bemberg and the discharges from the faucet plating companies also released heavy metals such as chrome And nickel and acidifying compounds such asammonium sulfate.
Ammonium is oxidized into nitrate (NH4+ + 2O2 → NO3– + 2H+ +H2O), consuming even more dissolved oxygen in the water and increasing the concentration of hydrogen ions in solution. The more this concentration increases, the more acidic the solution becomes. The concentration of hydrogen ions is measured via pH, a scale of values that tells us how basic or acidic a solution is: pH 7 is neutral, pH values lower than 7 indicate an acidic solution, while higher pHs indicate a basic solution. At the end of the 1980s, the pH of the water reached values Between 3.9 and 4.4very far from the original 7.2 (neutral pH) measured in the pre-industrial period, making Orta the “largest acidified lake in the world”
Normally, the presence of mineral salts and other species in solution can slow down pH variations thanks to equilibrium reactions, via a chemical process called “effect swab”but the characteristic natural scarcity of mineral salts dissolved in the lake reduced the capacity of the waters resist acidification.
The restoration of Lake Orta thanks to calcium carbonate
Over the next decades, progressive improvements in the management and reduction of discharges and pollution by industries led to reappearance of life in the lake: a 1958 publication of the Italian Institute of Hydrobiology, while acknowledging these efforts and the return of some species like diatoms, however, he noted the persistence of copper in the waters, with little precipitation of salts on the seabed. Interventions followed treat sewage water residential, but the poor water exchange due to the particular geography of the lake forced more incisive actions to recover the ecosystems.
For this reason, in the two-year period 1989-1990 it was decided to spread 14900 tons of limestone, a process called liming (from English limestone“limestone”).
The calcium carbonate (CaCO3) contained in limestone is soluble in water and in an acidic environment it reacts with the hydrogen ions present to form carbonic acid, which quickly decomposes into carbon dioxide (CO2) and water (H2OR). This reaction allows the concentration of hydrogen ions (which are consumed by reactions with the carbonate) to be lowered and therefore increase the pH bringing it back to pre-industrial values: in the 2000s the pH values thus reached i 6.8-6.9restoring the neutral nature of the body of water. Having eliminated uncontrolled discharges from industries or homes, the residual ammonium was completely consumed and this variation also led to the reduction of the concentration of metals suspended in solution or dissolved in the lake waters, thanks to the increase in precipitation on the seabed.
The success of the ei operation repopulations have brought several fish species back to Lake Orta, and have also allowed theseaside use favoring the influx of tourists: as with the Lake Maggiore area, Cusio has also become a holiday destination for Swiss, French and Germans.
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