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In order to interpret the predicted contribution of Mg emissions from industry to local environmental concentrations and the predicted no effect concentrations (PNEC), it is important to evaluate these values in view of natural background reference concentrations. Therefore, a detailed overview of the background concentrations of magnesium in the environment (aquatic, terrestrial and sediment compartment) was made, based on the baseline background concentrations for dissolved magnesium in European stream waters and total magnesium levels in topsoil and stream sediment reported by the FOREGS Geochemical Baseline Mapping Program (see attached report). The FOREGS (Forum of European Geological Surveys) Geochemical Baseline Mapping Programs main aim was to provide high quality, multi-purpose environmental geochemical background data for stream water, stream sediment, floodplain sediment, soil, and humus across Europe. A baseline background concentration was defined as the concentration of an element in the present or past corresponding to very low anthropogenic pressure (i.e., close to the natural background).

The typical median or 90th percentile of baseline background concentration of magnesium in the freshwater, sediment and soil is computed as the median value of all the country-specific 50th or 90th percentiles of the measured magnesium concentration in the investigated samples for the EU-27 and Norway.

Magnesium is the third most abundant ion in seawater, behind sodium and chloride. In contrast to the varying Mg concentration in freshwater systems, the Mg concentration in seawater is rather constant, with an average concentration of 1290 mg Mg/L

 Compartment Unit  Typical median baseline background concentration  Typical 90th percentile of baseline concentrations 
Fresh surface water  mg Mg/L  7.1  22.0 
Marine water  mg Mg/L  1290   
Soil (0 -25 cm)  mg Mg/kg dw  3930  11051 
Stream sediment  mg Mg/kg dw  6918  19041 

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