by Professor Jack Heinemann
New studies published by Nature’s journal Scientific Reports are questioning the basis of how to determine the safety of products used in agriculture and at home.
The first of these featured reports is on the application of ‘omics’ techniques to a long familiar GM maize line called NK603. The second featured report is on the application of omics to rats that eat Roundup, one of the glyphosate-based herbicides used on NK603.
Where is the science in scientific risk assessment?
The basis for most risk assessments of genetically modified plants is ‘comparative’. The GM product is compared to something already assumed to be safe. The risk assessment is informed by scientific tests that measure the similarity or otherwise of the engineered product to, usually but not always, the closest parent that has not been genetically engineered.
The comparative method is informed by science but isn’t scientific data. For starters, someone has to decide what constituents of the GM and non-GM plant will be isolated for comparison. What could be important might not be known at the time this decision is made. In addition, even what constituents can be detected can vary as scientific instrumentation and methodologies change.
After measurements are made, the crop developer and regulators decide whether they believe that any detected dissimilarities are worrisome and whether the sum of similarities is reassuring enough to consider the new product ‘as safe as’ non-GM alternatives. That step is often referred to as the standard of ‘substantial equivalence’.
Determining substantial equivalence is an action of experts, including scientists, but is not itself ‘science’ or the data that comes from a particular scientific experiment. In technology risk assessment, the public deserves to know where the science ends and expert scientific judgment begins.
A GM plant is intended to be different in at least one important way, such as in tolerating a herbicide. A decision on product safety follows considering potential adverse effects of both the intended change in traits and the unintended differences. Substantial equivalence to a non-GM relative implies that there were no important unintended changes in the GM plant.
NK603 was engineered to live after being treated with herbicide (e.g. Roundup). Regulatory approvals for cultivation of NK603 date back 17 years and it is approved for cultivation in 13 countries. It is one of the oldest and most widely adopted GM products in history. There should be no surprises from this maize if substantial equivalence is being used effectively to evaluate safety.
Challenge to substantial equivalence
Using methodologies that were not reasonably available when this product was developed in the late 1990s, the first featured study found previously undetected changes in the proteome and metabolome of NK603 compared to its non-GM relative. The proteome is the collection of proteins and the metabolome is the collection of small molecule biochemicals, in each case taken from specific tissues at a particular time.
Importantly, the study also compared herbicide sprayed NK603 to unsprayed NK603. Differences were found in maize seeds from sprayed and unsprayed plants too.
Differences per se may not make the product harmful to people, animals or the environment. However, identifying differences is a critical first step for constructing specific hypotheses about how those differences could cause harm. If this first step in a comparative risk assessment is compromised, then the final risk assessment might be too.
A critic of the study asked: “How equivalent does it need to be [to be safe]?” This is a reasonable question. Because the answer is a judgment, not the outcome of an experiment, it is contestable, a point made by the authors of this study. In whose judgment do we rely, and how might that judgment change depending on the context of how the product is used or who benefits from its use?
For example, pharmaceuticals have side-effects and don’t always work. The decision to use a particular drug is affected by both the health and history of the patient and the patient’s assessment that the side-effects and other risks are less important than the benefits the drug promises to deliver.
GM crop plants neither have safety trials equivalent to drug testing nor is their use as controlled as prescriptions. GM products may be distributed in much more varied ways, for example, through inhalation of flour or ingested as complex cooked mixtures that vary from country to country or by babies to adults.
Substantial equivalence works best when significant differences have been found, but is marginal as a method to ensure safety because it may not be informed by a full description of relevant differences.
Challenge to pesticide safety
The second featured study describes some important physiological changes in rats that have chronically ingested herbicide at and below legally allowed levels in food and drinking water.
This study used livers from rats fed Roundup in an earlier study that reported significant changes to blood and urine biochemistry, histological alterations reflective of structural damage, functional disturbances in liver and kidneys and tumour formations, especially those of the mammary gland. While the latter observation was contested, the former findings, to my knowledge, have received little challenge.
Significant differences were seen between the proteome and metabolome profiles of the livers of female treated and control rats. The changes caused by low levels of herbicide exposure were consistent with the manifestations of non-alcoholic fatty liver disease and its progression to non-alcoholic steatohepatosis.
These liver diseases are important and growing in frequency. The study makes no claim that all or even most occurrences are due to herbicide residues, leaving this to future investigations. However, when symptoms of these diseases in rats are linked to herbicide exposures it makes sense to reconsider the risk assessment for Roundup and other herbicides based on glyphosate.
While much time is devoted to carcinogenicity, the glyphosate-based herbicides have been associated with a variety of other health effects, from inducing antibiotic resistance to endocrine system disruption. Were these herbicides obscure formulations used in specialist factories, such concerns might not be of such great public interest. But they are used worldwide more than any other kind of pesticide, and herbicides are some of the most common chemicals released into food and the environment.
Concerns about glyphosate-based herbicides are often countered by threats that their elimination would cause greater use of more toxic alternatives. This threat rings hollow, both because excessive use is leading to resistant weeds that is already driving farmers to use other herbicides, and because it is a false choice.
Let’s not swap glyphosate-based herbicides for those that have different toxic effects. Rather, let’s use science to reduce the use of herbicides and the products of technology that are dependent upon them.
Professor Jack Heinemann is a lecturer in genetics at the University of Canterbury.