Variation in groundwater manganese in Finland

Abstract

Increasing evidence has emerged that Mn derived from drinking water could be a health risk, especially for children. This study aimed to provide more information on the variation in Mn concentrations in well water and factors that affect manganese concentrations in groundwater in the natural environment. The geochemical data consisted of analyses of single water samples (n = 5311) that were taken only once and data from monitoring sites where water samples (n = 4607) were repeatedly taken and analyzed annually from the same wells. In addition, the well-specific results from six wells at monitoring sites were described in detail. We obtained the data on water samples from the groundwater database of Geological Survey of Finland. In single samples, Mn concentrations varied from < 0.02 µg/l to 5800 µg/l in bedrock well waters and up to 6560 µg/l in Quaternary deposit well waters. Results from single water samples from bedrock wells and Quaternary deposit wells indicated that the dissolved oxygen content has an inverse association with the Mn concentration. When the dissolved oxygen O₂ levels were lower, the Mn concentrations were higher. No clear association was found between the Mn concentration and the pH or depth of the well for single samples. Part of Mn was particle bound, because total Mn was higher than soluble Mn in most measured samples. In the monitoring survey, large variation in Mn concentrations was found in bedrock well water in Kemijärvi, 114-352 µg/l, and in dug well water in Hämeenkoski, 8.77-2640 µg/l. Seasonal and spatial variability in Mn concentrations in water samples from two bedrock wells was large at monitoring sites in northern Finland. Variability in the Mn concentrations in groundwater can be large, even in the same area. These data suggest that single measurements of the Mn concentration from a water source may not reveal the Mn status, and measurement of both the total and soluble Mn concentrations may be recommended.

Keywords: Bedrock; Groundwater; Manganese; Medical geology; Quaternary deposit.

Fig. 1

Locations of sampled monitoring sites and index map

Fig. 2

Locations and distribution of Mn concentrations in single water samples from bedrock wells in 1992–2013

Fig. 3

The percentage of single water samples with a Mn concentration above 100 µg/l in each depth class of bedrock wells

Fig. 4

a and b Annual and monthly variation in manganese concentrations in water from bedrock wells at the monitoring sites in Kemijärvi (min = 114, max = 352 µg/l) and Inari (min = 173, max = 472 µg/l), northern Finland, in 1993–2006

Fig. 5

Annual and monthly variation (1994) in the Mn concentration of water from an artesian bedrock well at the Pori monitoring site (min = 119 µg/l, max = 135 µg/l) in southern Finland between 1993 and 2000

Fig. 6

The variation in Mn concentrations in bedrock well water during spring and summer 2005 at the Lempäälä monitoring site (min = 109 µg/l, max = 164 µg/l)

Fig. 7

The cumulative percent distribution of manganese concentrations in water for each bedrock well in which the concentration exceeded 100 µg/l at four monitoring sites in southern and northern Finland in 1992–2006

Fig. 8

Sampling locations and distribution of Mn concentrations in water samples from Quaternary deposit wells in 1992–2009

Fig. 9

Manganese concentrations in single samples of water from Quaternary deposits wells (Mn > 100 µg/l) according to depth

Fig. 10

The cumulative percent distribution of manganese concentrations in water from six Quaternary deposit wells where the Mn concentration exceeded 100 µg/l. The Sodankylä monitoring site is located in northern Finland and the others in the southern part of the country

Fig. 11

Annual median Mn concentrations in water from Quaternary deposit wells (Mn > 100 µg/l) at monitoring sites in 1992–2009

Fig. 12

a Annual and monthly variation in Mn concentrations in dug well water from the Hämeenkoski monitoring site (min = 8.77 µg/l, max = 2640 µg/l) b Annual variation in Mn and O₂ concentrations in dug well water from the Hämeenkoski monitoring site in 1992–2008

Fig. 13

Annual variation in the Mn concentration in dug well water from a till area at the monitoring site in Enontekiö in 1991–1995

Fig. 14

Total Mn (µg/l) concentrations in relation to soluble Mn (µg/l) in groundwater according to the water source in 2005–2013 (n = 31)