National monitoring study in Denmark finds increased and critical levels of copper and zinc in arable soils fertilized with pig slurry

The increasing consumption of copper and zinc in modern farming is linked to their documented benefit as growth promoting agents and usefulness for controlling diarrhoea. Copper and zinc are inert and non-degradable in the slurry and the environment and thereby introducing new challenges and concern. Therefore, a follow-up to pervious national soil monitoring programs on heavy metals was initiated in 2014 with special focus on the historical trends in soil concentrations of copper and zinc in Danish arable soils. Hereby it is possible to analyse trends for a 28 year period. Data shows that: 1) Amendment of soils with pig slurry has led to a significant increase in soil concentrations of copper and zinc, especially in the latest monitoring period from 1998 to 2014; 2) Predicted no-effect concentrations for soil dwelling species published by the European Union is exceeded for zinc in 45% of all soil samples, with the highest proportion on sandy soils; 3) 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. - Highlights: • The study follow-up to pervious national soil monitoring programs to analyse trends for a 28 year period. • Amendment of soils with pig slurry has led to a significant increase in soil concentrations of copper and zinc. • Predicted no-effect concentrations for soil dwelling species is exceeded for zinc in 45% of all soil samples. • The use of zinc in pig production may lead to leaching posing a risk to aquatic species. - This study addresses the use of zinc and copper in modern pig farming and demonstrates an unsustainable trend in soil concentrations within the last 28 years.