A common ingredient used to make plastics such as baby bottles causes birth defects in mice — defects that could also occur in people, U.S. researchers said on Monday.

They urged more research into the potential effects of bisphenol A, a chemical long criticized by environmentalists as being a hormone disruptor that could cause defects in embryos.

The defects they found, when they occur in humans, can cause miscarriages or mental retardation such as Down Syndrome — and they seem to be caused at what were considered to be low levels of exposure, the researchers report in the journal Current Biology.

The discovery came by accident, Patricia Hunt and colleagues at Case Western Reserve University in Ohio report.

Her team first noted a higher than normal increase in abnormalities in developing egg cells in female mice.

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