Manganese concentrations in Scottish groundwater.

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• Groundwater is a vital resource in Scotland for public and private supplies.
• Elevated manganese (Mn) concentrations in groundwater are a growing concern, frequently exceeding the Scottish drinking water limit of 0.05 mg l⁻¹.

Purpose of the Study:

• To assess the prevalence and magnitude of high Mn concentrations in Scottish groundwater.
• To identify the key factors controlling Mn levels in these water sources.

Main Methods:

• Compiled and analyzed a dataset of 475 high-quality groundwater samples from Scotland.
• Utilized statistical analysis on a subset of 137 samples from Devonian aquifers to determine controlling factors.

Main Results:

• Mn concentrations ranged up to 1.9 mg l⁻¹, with 30% of samples exceeding the Scottish limit (0.05 mg l⁻¹) and 9% exceeding the WHO guideline (0.4 mg l⁻¹).
• Highest concentrations were found in Carboniferous, Devonian, and superficial aquifers.
• Redox potential (Eh), pH, and dissolved oxygen explained 58% of the variance in Mn concentrations in Devonian aquifers.
• A strong correlation between iron (Fe) and Mn suggests Fe oxides influence Mn solubility.

Conclusions:

• Widespread elevated Mn concentrations across various Scottish aquifer types necessitate broader monitoring.
• Sorption of Mn onto iron (Fe) oxides, released under reducing conditions, is the likely primary mechanism for high Mn levels.
• Recommendations include increased monitoring of Mn in both public and private groundwater supplies in Scotland and potentially other regions.