The round up on Roundup

Advice from Dr Belinda Cridge, programme leader and lecturer in toxicology at the University of Otago:

The Monsanto case is based on some relatively new evidence. In 2016, the International Agency for Research on Cancer (IARC) re-classfied glyphosate – the active ingredient in Roundup – as a “probable human carcinogen”.

However, the IARC does not generally conduct a full risk assessment, judging where and how contact with the chemical may occur. These additional factors are important in determining the overall risk. For comparison, the IARC has also classified red meat consumption as a probable carcinogen.

The case in the US cited that adjuvants – additives in Roundup beyond the active glyphosate compound – may have had a synergistic effect to cause the cancer. Synergistic effects occur when two chemicals that are relatively benign separately act together to make a small effect much worse. “This means there is a very real possibility that adjuvants in the Roundup mixture accelerated any carcinogenic effects, but to the best of my knowledge this is hypothesised rather than proven.

The plaintiff in the Monsanto case did not need to demonstrate conclusively that glyphosate caused the cancer, only that it was a plausible contributing factor. Also, Monsanto is unable to prove that glyphosate definitely did not cause the cancer. There is still no proof either way.

Roundup isn’t, and has never been, a safe panacea for all weed control. However, Roundup has been used extensively worldwide for a long time, it has a reasonably good safety record and has limited environmental effects – compared to the alternatives.

“My standard advice is for people to not use chemicals where they don’t need to (hand pulling weeds is much safer than any chemical alternative), know what chemicals you are using and be rigorous about safety equipment. This applies to all the chemicals we use, from home cleaners to agrochemicals such as Roundup.”