Roundup is an endocrine disruptor and is toxic to human cells in vitro (tested in culture dishes in the laboratory) at levels permitted in drinking water in Australia, a new study has found.

This is the first study to examine the effects of glyphosate and Roundup on progesterone production by human female cells in an in vitro system that models key aspects of reproduction in women.

Glyphosate alone was less toxic to human cells than glyphosate in a Roundup formulation; both glyphosate and Roundup caused cell death which resulted in decreased progesterone levels – a form of hormone/endocrine disruption. Endocrine disruption did not precede the toxicity to cells but occurred after it. The decreases in progesterone concentrations were caused by reduced numbers of viable cells.

A 24h exposure to a concentration of glyphosate (in Roundup) similar to that recommended as an acceptable level for Australian drinking water caused significant cytotoxicity in vitro, which supports a call for long-term in vivo (in live animals) studies to characterise the toxicity of Roundup.

The possibility that Roundup has endocrine disrupting activity independent of its ability to kill or disable cells needs further study.