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No: 159: Content of copper and zinc in soil

Bak, J.L., Jensen, J. & Larsen, M.M.2015. Belysning af kobber- og zinkindholdet i jord. Indhold og udvikling i kvadratnettet og måling på udvalgte brugstyper. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 72 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 159


This study is a targeted follow-up study to previous monitoring activities on heavy metals in Danish soils as reported in e.g. Bak et al. (1997) and Gräber et al (2005).

The study has focused on pig farms because it has been expected that use of zinc and copper in pig production can lead to elevated concentrations in soils fertilized with pig slurry. The study has used two levels of data collection and both statistical analysis and dynamic models for data analysis

One level of data collection has been fields, which are part of a national 7 x 7 km2 grid-net established in 1987 by SEGES primarily to be used for regular monitoring of nitrogen balances. The concentrations of copper and zinc for a subset of points in this net belonging to pig farms have been monitored with soil samples collected in 1986, 1992, 1998, and 2014 (this study). Information on land-use and farming systems is available for all sites. The size of the sampling programs has varied in the specific sampling years, but measurements for two years or more exist for more than 100 points. It has thereby been possible to analyze trends for a 28 year period. A second level of data collection has been at 22 selected farms covering farms with weaner production, fattening pigs as well as farms with only crop production. For 12 of these farms, detailed historic information about agricultural practice on both farm and field level, e.g. fertilizer use, crop production etc., is known. Soil samples for all fields on these farms have been analyzed for copper and zinc. Dynamic model calculations have been used to make projections of the metal content in soils based on nationwide data for slurry application, soil types, net precipitation, crop rotations and crop yield.

The results are summarized in the Tables and Figures of this report, with table and figure texts in English. Furthermore, a short summary of the major conclusions are listed below.

  • In summary, it is concluded that the study gives a good foundation for describing the actual level and trend in soil concentrations of copper and zinc, especially on farms with pig production. The study also permits an analysis of the relationship between the soil concentrations of copper and zinc and land-use and agricultural practices. Furthermore, data enables a comparison of current and (modelled) future soil concentrations with predicted no-effect concentrations (PNEC) for soil dwelling organisms. EU recommended PNEC values for soil organisms evaluated and published by ECHA are used.

The major conclusions of the report are:

  • The agricultural use of pig slurry has led to a significant increase in soil concentrations of copper and zinc. A considerable variation of the increase in soil concentrations is observed from field to field as a result of differences in agricultural practice, soil type, crop, net precipitation etc., and, to a lesser degree, due to uncertainties in sampling and analysis.
  • The predicted no-effect concentrations for soil dwelling species is exceeded for zinc in 45% of all soil samples, with the highest proportion on sandy soils. For copper, only one sample exceeding the PNEC value has been found.
  • The use of copper and zinc in animal feed and veterinary medicine has, in average over the period 1986-2014, increased soil concentrations in the range of 21-28 % for copper and 2-5 % for zinc. The increase in soil concentrations has, however, been markedly higher for zinc over the last sampling period (1998-2014), i.e. on average 24 %, whereas the increase in copper concentrations from 1998-2014 is comparable to the increase over the entire sampling period.
  • A continuation of current agricultural practice is predicted to increase the number of fields exceeding the PNEC value for zinc significantly, although the current number is already relatively high. For copper, the PNEC value is in the future predicted to be exceeded on 30-50 % of the fields receiving pig slurry. A quarter of these within 80 years from now.
  • The current use of zinc and copper in pig production may lead to leaching of metals, especially zinc, from fields fertilized with pig slurry in concentrations that may pose a risk to aquatic species. This aspect has not been an objective of the current study and should be investigated further.