Maize pollen travels a long way

January 2015

Field of corn. CC photo by Joel Dinda on Flickr

German scientists have come up with a large and well-controlled data-set which suggests that the management of 'Bt' insecticidal maize (the only GM crop grown on any scale in Europe) is fundamentally flawed.

Europe has created a legal obligation for GM and GM-free agriculture to co-exist. Minimum separation distances between crops have therefore been defined to prevent GM pollen from contaminating GM-free crops.

 

Based on an average height maize plant, average size and weight maize pollen grains, and average wind-speed in maize-growing Germany, risk-assessors determined that maize pollen would be deposited an average of 20-40 meters from the parent plant, reducing exponentially with distance to become vanishingly small beyond this zone.

 

However, readings of actual GM maize pollen deposition from 216 sites in Germany, Switzerland and Belgium during 2001-2010 has shown this separation distance to be out by a factor of at least 100.

 

The model of exponential decrease in pollen deposition once it leaves the parent plant is wrong. Substantial quantities of pollen continue to travel away from the parent plant for distances measured in kilometres. For example, readings ranging from nearly 3000 to over 10,000 pollen grains per square meter were recorded over 4 kilometres from the nearest maize crop.

 

Although its pollen grains are relatively large and heavy, maize is a grass and very well adapted for wind pollination: the plants are tall (2.5-3.0 meters) with the pollen-producing 'tassel' at the top; one plant can release up to 50 million pollen grains in a season. 

 

Add to this that pollen release is triggered by dry, warm, windy weather conditions: perfect for turbulence and heat-induced up drafts to keep the pollen in the air, plus stronger than average winds to blow the pollen further. Unless the air is still (which means never), the pollen won't drop to the ground at anything like an exponential rate, but will move away from the parent plant in a very long tail.

 

The authors concluded that

"The exponential curve used in the EU risk assessment underestimates deposition and, thus, underestimates exposure of non-target organisms, especially over a longer distance range. Consequently, previous risk assessments and conclusions regarding distances, potential exposure, and effects on non-target organisms should be revised in the light of these findings."

 

 

OUR COMMENT 

 

 

It seems that 'non-target' organisms are likely to be getting a hefty dose of GM maize pollen due to this severe underestimation of its dispersal distance and the required buffer zones. Non-target organisms include: 

• Conventional maize, including that grown for seed stocks and that grown in non-GM refuges to slow the emergence of pest-resistance, plus their offspring grown from gene-polluted kernels.
• Susceptible insects, for which ingestion of as few as 4 - 9 pollen grains can be fatal
• Air-breathing animals (including humans) will have GM pollen and its toxin in their lungs.

At the moment we're talking about 'Bt' GM maize which produces an artificial bacterial insecticidal protein, but GM crops of the future may produce industrial chemicals or drugs.

 

In light of this single study, the EU needs to rethink its policies on the use of non-GM refuges, GM related allergy testing, GM toxin inhalation, GM-related environmental damage, seed purity control, the increased risk of accidentally stacked genes, and the wisdom of putting GM chemicals into food crops. EU regulators also needs to check out how much science vs. assumption has gone into their risk-assessments. Have a word with you MEP. 

 

SOURCE: 

• Frieder Hofmann, et al., 2014, Maize pollen deposition in relation to distance from the nearest pollen source under common cultivation - results of 10 years of monitoring (2001 to 2010), Environmental Sciences Europe 26:24