Action must be taken to curb the use of plastic additives linked to plummeting sperm counts, a leading reproductive scientist has warned, as splits over chemical regulation contributed to the collapse of a crucial treaty on plastic pollution.

Across the world, sperm counts have been declining at a rate of about 1% a year for the past 50 years, and human fertility has been diminishing at a similar rate, studies have shown.

Increasing levels of obesity, sedentary lifestyles and ageing populations have all been held up as possible causes. But according to Dr Shanna Swan, professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai in New York City, environmental factors play the most significant role.