The use of weedkillers in gardens could be causing bacteria to become more resistant to antibiotics.
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New research from Canterbury University has found ingredients in a number of every day herbicides can cause antibiotic resistance at even low level application rates.
He said the study focused on the use of herbicides in urban areas, which could create problems for pets and children.
He said pets and children could unwittingly track the herbicide into the home and indirectly into the mouth after walking through lawns and gardens that had been sprayed.
"And in rural areas we think that spray drift and direct contact with feed stuff that has been sprayed may be affecting livestock."
Professor Heinemann said exposure to the herbicides may increase antibiotics' resistance to bacteria and undermine their effectiveness.
He said 8 million chemicals were used commercially, and very little was known about how they may be affecting microbes.
"Every human being is host to 100 trillion micro organisms, so these exposures are universal and they may be very important in understanding how to maintain the effectiveness of antibiotics."