Glyphosate linked to antibiotic resistance
The controversial key ingredient in a common weedkiller is contributing to antibiotic resistance, research shows.
Scientists from the University of Canterbury found glyphosate, the active ingredient in Roundup, caused antibiotic resistance at concentrations well below the application rates given on their labels.
UC molecular biology and genetics professor Jack Heinemann said the study’s key finding was that ‘‘bacteria respond to exposure to the herbicides by changing how susceptible they are to antibiotics used in human and animal medicine’’.
Two other herbicides, Kamba and 2,4-D, which contain dicamba and 2,4-D, respectively, were also studied and found to cause antibiotic resistance.
The trio of weedkillers were among the most widely used in the world, including New Zealand, Heinemann said.
‘‘They are among the most common manufactured chemical products to which people, pets and livestock in both rural and urban environments are exposed,’’ he said. ‘‘These products are sold in the local hardware store and may be used without training, and there are no controls that prevent children and pets from being exposed in home gardens or parks.’’
The UC study also found that other ingredients commonly used in some herbicide formulations and processed foods caused antibiotic resistance.
An antibiotic resistance response was caused by both the tested surfactants, Tween80 and CMC, both of which are used as emulsifiers in foods like icecream and in medicines. Both caused antibiotic resistance at concentrations allowed in food and food-grade products.
Heinemann, an expert in genetic engineering, bacterial genetics and biosafety, said regulators needed to consider the ‘‘sub-lethal’’ effects of chemical products when deciding whether they were safe for their intended use.
‘‘More emphasis needs to be placed on antibiotic stewardship compared to new antibiotic discovery,’’ he said. ‘‘Otherwise, new drugs will fail rapidly and be lost to humanity.’’
Scientific opinion is split over the safety of glyphosate with debate hotting up in the wake of a landmark court case in the United States earlier this year. A California jury awarded terminally ill former groundsman Dewayne Johnson US$289 million ($440m) in damages, after it determined Roundup caused his cancer and the manufacturer failed to warn him of the health hazards from exposure.
While a 2015 study by the World Health Organisation’s International Agency for Research on Cancer (IARC) concluded the chemical was ‘‘probably carcinogenic to humans’’, the US Environmental Protection Agency said the chemical was safe for use when directions on the label were followed.
New Zealand’s Environmental Protection Authority (EPA) classifies glyphosate as a low-risk chemical and safe to use as instructed on the label. The EPA said last week that it would reassess the safety of 40 chemicals from over 700 on a chemicals priority list but glyphosate was not included because it ‘‘did not meet priority criteria’’.
‘‘When compared directly to other chemicals we have screened using the same methodology and criteria, there are a large number currently being used in New Zealand, which present a greater risk to human and environmental health,’’ the EPA said.
UC professor of toxicology Ian Shaw was in favour of categorising the chemical as hazardous and reassessing its regulatory status in New Zealand. He said the US court ruling was clearly based on an acceptance of the IARC classification and the evidence behind it. However, while the courts required a balance of probabilities (51 per cent) for a guilty verdict, scientists usually required more statistical security.
‘‘I do not think we should base our regulatory decisions on a US court case, but I do think that the evidence that glyphosate is possibly a carcinogen in humans is robust.’’
New Zealand’s arable industry, which is worth about $1.2 billion a year, and exports $180m worth of seeds and cereals, is highly dependent on the chemical, as is horticulture (export value $5.1b).