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Environmental fate & pathways

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Natural background in surface waters

Data on natural background of zinc in surface waters in the EU were discussed in the RAR (ECB 2008). Based on values reported for a number of EU countries, incl. NL, D, F, SF and others, two values were selected for total background concentration, to be used in the risk characterisations:

-3µg Zn/l which is the lower limit of the range reported by the member states in the risk assessment process,

-12µg Zn/l which is the geometric mean value of an extensive EU database on Zn concentrations in lowland brooks in unpolluted areas in N-Europe, (10P and 90P in this review are 4 and 35 µg totalZn/l resp. - Zuurdeeg 1999).

-Using a Kpsuspof 110,000 l/kg (RA; ECB 2008) and a default particulate matter content of 15 mg/l, these values are equivalent to 4.44 µg dissolved Zn/l, and 1.11 µg dissolved Zn /l, respectively.

 

Due to geochemical differences, the natural background concentrations in surface waters will differ throughout Europe. It is thus not appropriate to set one value for the whole of the EU. Recently, an extensive database has become available on a.o. zinc background values in surface waters, covering the whole of the EU (FOREGS 2005). The 10P and 90P values for dissolved zinc following from this analysis performed also on non-polluted head waters (cfr Zuurdeeg 1999) are 0.7 and 18 µg dissolved zinc /l, resp. (http://www.gtk.fi/publ/foregsatlas/maps/Water/w_icpms_zn_edit.pdf);the median value of 2.7 µg dissolved Zn/l corresponds well with the one used in the RAR (ECB 2008).

 

The FOREGS study thus confirms the data reported in the EU RAR and the Zuurdeeg (1999) analysis. It confirms that the value of 12µg total Zn/l – 4.44 µg dissolved Zn/l can be seen as the median value for zinc background in European freshwaters. 

 

Regarding the sediment, the RAR concluded, based on reported data from a number EU countries, incl NL, D, F, N, SF, SW, that the range of the background data for sediment was more or less in the same order of magnitude (range 70-175 mg/kg dwt). Based on the data from several EU-regions the value of 140 mg/kg dwt was set for use as a natural background for correcting the EU sediment monitoring data.

 

It was noted that, if available monitoring data can unequivocally be linked with a particular natural background value in an area, preference should be given to that specific background value (ECB 2008).

For comparison, FOREGS (2005) reports for zinc in sediments 10P and 90P values of 18 and 270 ppm, resp., demonstrating the big variation, due to local geology. The median value is 65 ppm. Because of the great variability, more localised assessments are preferred.

 

Natural background in the terrestrial compartment

The natural zinc concentrations in soils are highly variable and dependent on soil type and soil properties. The EU RAR concluded from the available soil data for a number of EU countries that there is a large variation in the natural zinc background concentrations. This variation is related to the native soil material and the present soil characteristics like humus and lutum. The RAR observed a clear relationship between natural background levels and various soil parameters, but noted that a quantification of the exact natural background level for a specific EU soil type is at present still an extremely difficult and complex issue. The RAR mentioned zinc backgrounds usually in the range 50-100 mg Zn/kg DW, which is confirmed by data from the more recent FOREGS database, reporting 10P, 50P and 90P zinc concentrations of 8, 52, and 140 mg/kg DW, respectively in unpolluted soils throughout Europe. Important to note is that, due to the high variability on the data, the RAR concluded that it was only possible to use monitored soil data for risk characterisation when it was possible to make a correction with the natural zinc background concentration(s) typical for that soil type.

Monitored data

Recent monitored data on zinc concentations in water, sediment and soil in the EU member states are reported under IUCLID section 5.5.1.