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Pesticides found in mothers’ breast milk – so what?

Pesticides - where do they end up? Deigo Azubel/EPA

A recent study by the organisation Moms Across America claims to have found a pesticide at harmful levels in human breast milk and urine.

Moms Across America is an organisation concerned with the use of pesticides and genetically modified (GM) foods. Through tests carried out by its members across the US, the organisation assessed the level of the common pesticide glyphosate (sold in products such as Roundup) in urine and breast milk of nursing mothers.

While it accepts it has not conducted the equivalent of a full scientific study, it found what it calls “high” levels of glyphosate in 30% of the samples it analysed: between 76-166 microgrammes per litre (µg/L) in breast milk. This is 760-1,600 times higher than the current maximum level allowable under the European Drinking Water Directive of 0.1µg/L, but is up to nine times lower than the current maximum contaminant level (MCL) for water set by the US Environmental Protection Agency.

Limited data yields limited results

For their testing programme, Moms Across America enlisted a commercial firm to measure glyphosate levels in 35 urine and breast milk samples from women in several states. Levels of glyphosate in water from 21 areas were also tested. The study used a common laboratory test called an enzyme-linked immunosorbent assay, or ELISA, to compare glyphosate levels to known standards. The organisation did not publish the full results, but did provide a partial data set.

Unfortunately, the usefulness of this study is limited. Two of the three positive tests in breast milk were within 25 microgrammes per litre (µg/L) of the ELISA test’s detection limit, indicating that the results could be within the margin of error. Likewise, for the urine analysis, six of the 13 positive test results were within 2µg/L of the detection limit. The safe level as set by the EPA is 0.7 milligrammes per litre (mg/L), equivalent to 700µg/L, or 700 parts per billion (ppb); a difference of 2µg/L or 2ppb is unlikely to indicate a cause for concern.

While this was not meant to be a full scientific study, the random distribution of breast milk from ten women across ten states makes it difficult to assess whether the results are due to local increases in glyphosate levels or, as the article claims, due to contamination from brands of food that are distributed nationally. No mention is made of the time of year the studies were taken nor of the participants’ diet, which could greatly affect the results as glyphosate levels should be higher during application in the field.

Big words with selective support

In short, the survey and accompanying article is short on scientific rigour and uses little more than scare tactics to make its point. Some of it shows clear misunderstandings of topic – for example, highlighting that glyphosate is both a pesticide and a herbicide. This is redundant; the term “pesticide” refers to anything used to kill “pest” species, generally broken down into insecticide, fungicide, and herbicide.

The function of glyphosate is to inhibit an enzyme in plants known by the unwieldy name of 5-enolpyruvyl shikimate 3-phosphate synthase, shortened to EPSP. Blocking this enzyme prevents plants manufacturing the essential amino acids phenylalanine, tyrosine, and tryptophan, causing them to wither and die. But as this enzyme is only found in plants – animals must supply themselves with these amino acids from their diet – the effects of glyphosate on animals is unknown.

Unfortunately, much of the literature focuses upon correlative studies, where an association is made between a human condition and an environmental concern. Results that may indicate toxicity in a laboratory study, such as work by Egberto Barbosa on glyphosate and Parkinson’s disease, do not corroborate the human clinical studies that show no link between glyphosate poisoning and Parkinson’s.

Many other studies are funded by agro-chemical research organisations like Monsanto, manufacturer of Roundup, which has a vested interest in showing the safety of its products. Alternatively, grassroots or campaigning organisations have an interest in proving the opposite. Thus it can be difficult to tease out the inherent bias in the presented results from what the data really says.

A perfect example of this research by Channa Jayasumana et al, which argues that glyphosate is responsible for chronic kidney disease in Sri Lanka by binding to heavy metals such as lead. But further examination of the research presented beyond the abstract clearly shows that the researchers were unable to detect such glyphosate-metal complexes within humans to support the claim. This study was funded in part by Hela Suwaya, an organization with a focus on promoting organic farming practices.

It has to go somewhere

It’s not unexpected to find these types of chemicals in fluids in our body and those our body is excreting. The purpose of the kidney is after all to filter out toxins from the blood and remove them from the body via urine. Nursing mothers are continually warned about drug and alcohol ingestion as many of these compounds can be detected in breast milk.

Similarly, as the concentration of a substance in the urine is related to how much urine is produced, it would be more relevant to discuss the rate at which the body clears glyphosate rather than amount excreted. One frequently cited study by Acquavella and colleagues states that the rate of glyphosate excreted by farmers increases after they have applied glyphosate to their fields.

This is to be expected – we should be concerned if there were low levels of excretion, which would indicate that the chemical was being retained in the body with potentially detrimental effects. A more concerning report would be if levels of glyphosate were being found in body fat or liver tissues – it would make more sense to measure levels of glyphosate in blood or tissue samples rather than that removed from the body.

This is not to say that the concerns of Moms Across America are invalid. Whenever we are exposed to a chemical that is designed to cause death of a species, we should pause and identify if that chemical is toxic to us as well. However, we need to exercise caution and not jump to conclusions based on limited preliminary data that show no short- or long-term negative side effects.

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