Manganese (Mn) in Scottish Groundwater

Background

Excessive Mn concentrations can result in metallic tasting water, staining of clothes, dishes, and products such as paper or plastics, and reduced water pressure and flow in pipes from accumulation of Mn oxides (Sly et al., 1990). They have also been found to have an adverse effect on human health. In adults, exposure to elevated Mn concentrations in drinking water has been associated with manganism, a Parkinson-like disorder, and in children, intellectual function and hyperactive behaviour. Because of the association between Mn intake and neurological effects the World Health Organisation(WHO) current guideline concentration for Mn in drinking water is 0.4 mg l-1 (World Health Organisation, 2008).

Controls of Mn in groundwater

Figure 1: Mn concentrations in Scotland

Figure 2: Bedrock aquifer units

Figure 3: Manganese concentrations in groundwater and geology in Scotland

The occurrence and concentration of Mn in groundwater are controlled by many factors, the main ones being rock geochemistry, water chemistry and microbiological activity. Some rock types, such as mafic and ultramafic rocks, shale, greywacke and limestone, contain high concentrations of Mn, which can lead to elevated concentrations in soil and sediment through weathering processes. Water chemistry, in particular pH, redox potential (Eh), dissolved oxygen (DO), and dissolved organic carbon (DOC), is instrumental in mobilising Mn and controlling its speciation and concentration in the water environment.

Recent Research on Mn in Scotland

Recent research using data by Baseline Scotland (Hominik et al. 2010) assessed the concentrations of Mn in Scottish groundwater, between different aquifer types, and examined the controls on elevated Mn concentrations in groundwater.

This research developed a quality-controlled dataset of groundwater Mn concentrations across Scotland with data for 475 sites.

Results

  • Analysis of this dataset showed that elevated Mn concentrations (> 0.05 mg/L) occurred in 30% of the groundwater samples (Figure 1), particularly in superficial, Carboniferous, and northern Devonian aquifers (Figures 2 and 3); and 9% of sites had concentrations above the WHO health drinking water limit (0.4 mg/L).
  • The principal controls on Mn concentrations in groundwater in Scotland are redox conditions and pH, with some influence from Fe behaviour. Redox conditions exercise the strongest control.
  • The results highlight the potential risk of exposure to excessive Mn in drinking water for consumers using private water supplies and indicate the need for appropriate methods for sampling and testing groundwater for Mn not only in Scotland but worldwide.

References and resources

Homoncik, S, MacDonald, A M, Heal, K V, Ó Dochartaigh, B É, and Ngwenya, B T. 2010. Manganese concentrations in Scottish groundwater, Science of the Total Environment, 408; 2467–2473.

MacDonald, A M and Ó Dochartaigh, B É. 2005. Baseline Scotland; an overview of available groundwater chemistry data for Scotland, British Geological Survey Commissioned Report, CR/05/239N, British Geological Survey, Keyworth, Nottingham.

MacDonald, A M, Robins, N S, Ball, D F and Ó Dochartaigh, B É. 2005. An overview of groundwater in Scotland, Scottish Journal of Geology, 41; 3–11.

Robins, N S. 2002. Groundwater quality in Scotland: major ion chemistry of the key groundwater bodies, Science of the Total Environment, 294; 1–3; 41–56.

Sly, L J, Hodgkinson, M C and Arunpairojana, V. 1990. Deposition of manganese in a drinking water distribution system, Applied Environmental Microbiology, 56; 628–639.