Pig manure pollutes Danish waterways with heavy metals

Nearly four out of five Danish waterways are contaminated with zinc, while almost half exceed safe levels of copper, according to a DR analysis of Environment Ministry data covering nearly 6,700 stream segments.

Authorities identify pig manure as the primary source, as zinc and copper added to pig feed pass through the animals and enter the slurry spread on fields. The metals, used for decades to prevent diarrhoea in piglets and promote growth, then leach into waterways.

“This makes copper and zinc one of the major challenges for chemical water quality,” said John Jensen, senior researcher in ecotoxicology at Aarhus University. He called the scale of contamination “a clearly enormous task ahead of us.”

Excess zinc and copper can harm the growth and reproduction of aquatic plants and animals. While most streams show only minor exceedances, Jensen noted that even small disruptions to microscopic organisms can reduce food sources for fish.

Environment Ministry and Environmental Protection Agency figures cited by DR estimate that 70–75% of zinc and copper in waterways originate from agricultural fertiliser, with pig manure the chief contributor.

Danmarks Naturfredningsforening said the findings underscore the need to reduce pig production. “It shows we have a system our nature and environment simply cannot sustain,” said Anna Bak Jäpelt, the group’s agricultural policy advisor.

Industry group Landbrug & Fødevarer acknowledged the environmental impact but said producers had followed existing rules on feed additives. “We’ve all focused on what was best for the animals in terms of production and growth, without considering the environmental side effects,” said chief consultant Bent Ib Hansen.

A 2022 ban on medicinal zinc in pig feed is expected to reduce zinc pollution over time, though the latest assessments—based on data through 2022—do not yet reflect this. The Environmental Protection Agency anticipates fewer zinc-contaminated streams in its next report, due late 2027, but offered no estimate on the scale of improvement. Jensen doubts the ban alone will eliminate all zinc pollution without further action.

Copper restrictions in feed were tightened in 2019, and industry representatives expect contamination to decline, though authorities have not predicted the extent of future reductions.