ARSENIC LEVELS IN DANISH GROUNDWATER AND DRINKING WATER: HISTORICAL DATA ASSESSMENT 2001-2013

Arsenic is according to WHO one of the 10 chemicals/elements of major public health concern as it has well-known carcinogenic effects and as µg l^-1levels may have adverse effects on public health. Drinking water in Denmark is solely of groundwater origin which generally is considered of high quality with low arsenic levels. Danish drinking water quality is routinely monitored and all analyses are added to a public geological and hydrological database, denoted Jupiter.

Here we present a national-scale overview on natural-occurring arsenic concentrations in ground- and drinking water for the last decade. More specifically our goals are: 1) to compare the arsenic concentrations from ground- and drinking water, both at the consumer and at the exit of the water treatment facilities; 2) to find and describe the proportion of samples exceeding the quality criteria; and 3) to visualize the spatial variation. In order to do that, two datasets including all quality-checked water samples containing arsenic data were selected for the period 2001-2013, consisting of respectively groundwater samples (n=29676) and drinking water samples (n=16498).

Our data analysis revealed geographical patterns with naturally occurring arsenic-rich groundwater with the highest density in the eastern part of the country. Table 1 presents a summary with the drinking water samples exceeding the criteria (1.89%); for the last decade only a small fraction of the Danish waterworks have distributed water with elevated arsenic levels to consumers.

In addition, analyses on the spatial distribution of groundwater arsenic levels with respect to the redox water type, depth of extraction, and type of predominant sediment will be presented and discussed in relation to both aqueous chemistry and public health.

Table 1.

Type	Threshold value [µg l-1]	Number samples exceeding criteria (incl.)	Number of affected waterworks	Number of affected municipalities	Sum of abstraction volumes 20105 [mio m3]
Drinking water1 (n=2762)	5	311	78	28	23.47
Pipe system2 (n=11965)	(10)4	87	38	17	3.8
Tap water3 (n=1771)	10	10	8	8	3.1

¹after treatment before leaving the waterworks

²in the pipes between the waterwork and the consumers tap

³at consumers tap

⁴no specific criteria - the tap water criteria has been adopted

⁵ annual abstractions (2010) from the waterworks with exceeding samples