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A culture of denial over the horizontal spread of genetically modified nucleic acids prevails in the face of direct evidence that it has occurred widely when appropriate methods and molecular probes are used for detection.

by Dr Mae Wan Ho

This article has been sent to Dr Kaare Nielsen in his capacity as a member of the European Food Safety Authority GMO Panel and he is given the right to reply.

A fully illustrated and referenced version of this article is posted on ISIS members website and is otherwise available for download here.

A culture of denial over the horizontal spread of GM nucleic acids

The first genetically modified (GM) crop was commercially approved and released into the environment 20 years ago. From the beginning, some of us have been warning repeatedly of hidden dangers from the unintended horizontal transfer of GM DNA (transgenes). A comprehensive review [1] (Gene Technology and Gene Ecology of Infectious Diseases, ISIS scientific publication) and successive updates were submitted to the World Health Organization (WHO) and regulatory agencies in the US, UK and European Union (see [2] Ban GMOs Now, ISIS Report); all to no avail.

The position taken by regulators and their scientific advisors today is perhaps best represented in a recent publication [3] with lead author Kaare Nielson at Norwegian University of Science and Technology, who both advises Genøk-Centre for Biosafety and serves as member of the EFSA (European Food Safety Authority) GMO panel.

The paper, entitled “Detecting rare gene transfer events in bacterial populations”, recognizes that horizontal gene transfer is part of the risk assessment for GMOs, and that the large-scale cultivation of GM-plants on more than 170 m ha worldwide results in “multitudinous opportunities for bacterial exposure to recombinant DNA and therefore opportunities for unintended horizontal dissemination of transgenes.” It admits that horizontal gene transfer has indeed been demonstrated in the laboratory. “But in natural settings, negative or inconclusive evidence has been reported from most sampling-based studies of agricultural soils, runoff water and gastrointestinal tract contents.”

It tells us that horizontal gene transfer research “suffers from significant methodological limitations, model uncertainty and knowledge gaps.” In particular, on account of the “low mechanistic probability of horizontal transfer… in complex environments”, it would take “months, years, or even longer for the few initially transformed cells to divide and numerically out-compete non-transformed members of the population” for them to be “detectable.” The rest of the paper mentions a mathematical model based on those very assumptions, the most important being the very low probability of horizontal transfer; which has been contradicted by empirical evidence, most decisively from a study in China reported in 2012 [4].