Fig. 4

Sensitivity analysis of aluminium concentration for sample K-28. The value was varied from 0.009 to 0.117 mmol/kg in increments of 0.006 mmol/kg. The figure shows an extract of the data, where the aluminium concentration ranges from 0.021 to 0.057 mmol/kg in increments of 0.006 mmol/kg. The statistical minimum of the boxplot comparison is reached for a concentration of 0.039 mmol/kg highlighted in a darker blue colour