This week, the canton of Vaud said that eggs and pumpkins produced in a zone covering much of Lausanne should not be eaten.
The areas affected are shown by shading in the image above. The darkest shaded zones are the most polluted. Eggs grown in the three central zones should not be eaten, along with cucurbit vegetables (pumpkins, courgettes and cucumbers) from the two darkest zones, warned the canton. In addition, in the two darkest zones, root vegetables must be peeled, said the canton. From the two lightest shaded zones the canton recommends not eating more than 100 grams of cucurbit vegetables a week.
In addition, the ingestion of soil from gardens and parks in these areas should be avoided and vegetables and hands should be washed after contact with the soil – see full advice from canton here.
So what is the pollution?
The pollution is dioxins that were discovered in the area at the beginning of this year after testing at 126 sites. Dioxins are environmental pollutants belonging to the so-called “dirty dozen”. They are both toxic and persistent, which means they are very slow to degrade, reducing by half every 7 to 11 years.
Because dioxins are persistent they accumulate in the animal food chain. As a protective measure animals offload dioxins into their own fat tissue, eggs and milk. This means dioxin levels are higher in these foods. Mothers also offload dioxins to foetuses and newborns via their milk, so they need to be extra careful.
Long-term exposure to dioxins is linked to impairment of the immune system, the developing nervous system, the endocrine system and reproductive functions. It is also associated with some cancers – more information on dioxins from the World Health Organisation can be found here.
Dioxins are found everywhere and cannot be completely avoided so the focus is on reducing exposure to them. The best way for individuals to do this is by reducing the consumption of food produced in polluted regions, in particular animal products where dioxins concentrate.
The level of dioxin pollution discovered in Lausanne ranges from 20 nanograms/kilogram to more than 200 nanograms/kilogram. The map can be viewed directly here.
The safe soil dioxin limit set by the canton of Vaud is 100 nanograms/kilogram. This is low compared some other nations, such as France and Germany, which set the limit at 1,000 nanograms/kilogram. 26 of the 126 sites tested in Lausanne exceeded the 100 nanograms/kilogram limit.
How did they get there?
Based on investigations so far it appears that the pollution in Lausanne came from the exhaust of the old Vallon waste incineration plant situated east of Lausanne. The plant was closed in 2005.
Many of the toxic emissions from such plants date from 1960s to the beginning of the 1990s. After that better exhaust cleaning systems were fitted.
Dioxins travel well in the air, binds to soil and from there passes to plants and animals. However, dioxins are not very soluble in water. This means food is the main vector for transmission to humans, not water, according to the canton.
What about other Swiss cantons?
The discovery of dioxins in Lausanne has spurred other cantons to check their soil. Zurich, Glarus, St. Gallen and Neuchâtel are among the cantons planning dioxin soil tests. Zurich started testing when suspicions were first reported in Lausanne, according to SRF, with a focus on identifying pollution from waste incineration plants. Zurich has six of these.
Some cantons have a clean bill of health. The canton of Schaffhausen examined its soils for dioxin two years ago and contamination levels there were low, according the canton’s environmental department. The canton of Schaffhausen closed its last waste incineration plant in the 1970s.
For cantons that still run incinerators like Zurich, pollution has fallen sharply due to improved exhaust gas cleaning systems.
Wolfgang Bollack, the spokesperson for the department of waste, water, energy, air and nature in Zurich, told SRF he is confident that the situation in the canton of Zurich differs from that in Lausanne. However, there will only be certainty when the measurements are completed at the beginning of next year.