However, government regulators say the best-available science shows these chemicals are not having an effect on humans. Other experts say a link is possible but that the evidence is a long way from settled. Some plastics can release chemicals, known as endocrine disruptors, that can mimic human sex hormones. In animal studies, exposure when pregnant can have profound effects on an animal's offspring, including infertility, undescended testes and hypospadia. There is no strong evidence about what they do to humans. But we all have observable levels in our blood because they are so common in everyday life. Dr Pask points to several chemicals that may have an effect on humans: BPA, phthalates (both used in plastics), parabens (used in toothpastes and beauty products) and atrazine (herbicide). Despite a large number of studies overseas, Dr Pask and his Melbourne University colleague Dr Mark Green believe they are Australia’s only scientists studying the chemicals’ effect on male reproduction.

A 2007 study found the rate of severe hypospadia had almost doubled between 1980 and 2000 in Western Australia, with one in 118 male babies born with the birth defect. A Victorian study from 1998 reported similar findings. But a review of studies around the world reported the data was too inconsistent to draw strong conclusions. A small French study in 2015 found a “strong” link between exposure to endocrine-disrupting chemicals during pregnancy and hypospadia, as did another in Italy. “No one likes to talk about this. Often parents don’t even like to tell their kids they had it – it gets surgically repaired but often the surgeries don’t work very well,” says Dr Pask. “When it’s doubling, it cannot be genetic defects – it takes years for that to spread through a population. So we know it has to be environmental in origin.” Lecturer Mark Green and Associate Professor Andrew Pask think chemicals in plastics may be linked to shrinking penis size and penis birth defects. Credit:Justin McManus

Pask also points to studies showing exposure to EDCs that mimic the female sex hormone oestrogen can shorten penis length. However there is no population-level data to back this claim. Hypospadia causes the urethra, which is supposed to exit at the the tip of the penis, to do so anywhere from the shaft to the scrotum, causing a range of functionality problems including difficulty urinating. In his lab, Dr Pask says it is remarkably easy to give a baby mouse hypospadia: infuse the pregnant mother’s drinking water with atrazine (his findings have not yet been published). In animals, the damage intensifies over subsequent generations, he says. It becomes particularly acute by the third generation. “Humans have been exposed to these since the 1950s, so about two generations,” says Dr Green. Professor Peter Sly, director of the World Health Organisation Collaborating Centre for Children’s Health at the University of Queensland, says there is strong evidence exposure to the chemicals reduces sperm count and quality, and could possibly be reducing penis size.

“There is a lot of evidence out there. There is human-level data.” Associate Professor Frederic Leusch, a senior environmental scientist at Griffith University, says while there is no scientific consensus about the chemicals' effect on humans, the evidence is clear in animals. “We have clear, indubitable, mechanistic-linked evidence from animals this can happen. Humans are animals. And we know these chemicals are in our bodies. So it’s absolutely possible. But we still cannot be sure,” Dr Leusch says. Loading Replay Replay video Play video Play video A Food Standards Australia New Zealand survey of BPA in foods concluded the average consumer’s exposure levels were far below safe limits.

“The weight of scientific evidence indicates that exposure to BPA in food does not present a significant human health and safety issue at current exposure levels,” the agency noted. At the Royal Children’s Hospital in Parkville, paediatric urologist Aurore Bouty is in charge of operating on hypospadia. “The patients cannot stand to pass urine. The only option is to have surgery. And the surgery of course has complications,” Dr Bouty says. “The prognosis depends on the form. The further away from the tip of the penis, the higher the risk of complications after surgery. Complication rates run from 5 to 70 per cent for more proximal forms.” A spokesperson for the National Industrial Chemicals Notification and Assessment Scheme, which regulates the introduction of industrial chemicals, said it closely monitored scientific literature on endocrine-disrupting chemicals.