The last kilometer of the stage took us along the Meurthe River in Nancy. Like other urban rivers in industrial regions, the Meurthe has a significant history of pollution. The Meurthe’s big problem is salt, a byproduct of the soda ash factories established upstream of Nancy.
Soda ash is another name for sodium carbonate, which is an important industrial chemical. It is used, for instance, to make soda-lime glass, which is made into glass bottles. Soda ash was originally made by burning a plant called saltwort. But demand for soda ash incentivized several efforts to manufacture soda ash that culminated in the work of the Belgian chemist Ernst Solvay. His process combines sodium chloride, in the form of a brine solution, with carbon dioxide, generated by heating limestone, in the presence of ammonia. In 1864, Solvay built a factory just outside Charleroi to make with his process. By 1874, the Solvay company was looking to expand, and they decided to situate their new factory in Lorraine, where extensive salt deposits could be mined to supply the brine they needed. They chose Dombasle for their new location, right on the Meurthe upstream of Nancy.
The first reaction in the Solvay Process produces ammonium chloride as a byproduct. This ammonium chloride is then reacted with the lime (calcium oxide) left over from heating the limestone to make ammonia, which is reused in the first step, and calcium chloride, which is disposed of by discharging it into the river through a set of settling basins, which are the most visible aspect of the soda ash production along the Meurthe.
There was initially some opposition to the Solvay factory, as some were concerned about the effects of the calcium chloride discharges into the Meurthe, which supplied Nancy’s drinking water. However, Nancy found other sources of drinking water and began to discharge sewage into the Meurthe in the 1880s (Garcier 2007), so that the chloride discharges were no longer of much concern to the citizens of Nancy.
Salinization of freshwater rivers is a global issue that significantly affects the integrity of these ecosystems (Cañedo-Argüelles et al. 2013). The salinity gradient along the Meurthe formed by the accumulation of chloride from the soda ash plants has been shown to decrease the diversity of macroinvertebrate communities (Piscart et al. 2005).