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The following year, further more detailed sampling was carried out to investigate how this has come about.
Like many transport routes, both the rail and port areas are regularly treated with glyphosate herbicide. Add to this that seed spillage during unloading and transport is a fact of life. Plants arising from spilled glyphosate-resistant GM rape seed in a glyphosate-sprayed area will be the only ones to survive.
However, oilseed rape is an annual or biennial plant and local populations don't, as a rule, persist unless there are fresh inputs.
The Swiss permitted GM contamination level of 0.5% (in line with EU standards) suggests the original population may well have come directly from 'non-GM' consignments.
This can't be the whole story because company records show that only small shipments of crushed rapeseed transitted through the port during 2012 and 2013, and the freight station hasn't handled seed since 2009. Multiple other sources of the contamination must be active.
Oilseed Rape seeds can lie dormant in the soil for up to 17 years, and could contribute to feral GM populations for decades.
Most worryingly, the authors were suspicious of a role for Canadian wheat imports. Wheat is the major seed handled by the Basel port, and because there's no GM wheat cultivation anywhere in the world, consignments are not tested for GM content. One fifth of Switzerland's wheat imports come from Canada where almost all the oilseed rape now grown is GM. Mixing of grains during their journey round the globe could well be a cause of GM contamination.
Surprisingly, glufosinate-herbicide-resistant GM oilseed rape was also found at several sites during the latest sampling at the Basel port. Since these will succumb to glyphosate, it suggests that either there's a very regular fresh flow of GM oilseed rape onto the site, or that spraying is not being carried out appropriately, or both.
Note that vegetation control on railway lines is necessary for worker safety and for the stability of railway gravel beds. The progression of feral GM oilseed rape through the European landscape due to hybridisation with wild and cultivated relatives therefore presents a physical risk to the public.
Clearly, banning GM import and cultivation in your own country isn't enough, especially if the 'ban' allows low-level contamination and turns a blind eye to crops imported from countries which are heavily GM-contaminated.
In the meantime, GM bans or no bans, we may have already lost our conventional oilseed rape forever.
- Juerg Schulze, et al., 2014, Unexpected Diversity of Feral Genetically Modified Oilseed Rape (Brassica napus L.) Despite a Cultivation and Import Ban in Switzerland.