A cocktail of chemical pollutants measured in people’s bodies has been linked to lower sperm quality by new research.
Chemicals such as bisphenols and dioxins are thought to interfere with hormones and damage sperm quality, and the study found that combinations of these compounds are present in ‘astonishing’ levels, up to 100 times those considered safe.
Bisphenol A (BPA) was responsible for the highest risks, the scientists said. The chemical is found in milk and canned foods when it leaks out of the packaging liners. Key milestones in healthy male sexual development occur during pregnancy, making the study findings particularly relevant to pregnant women, the researchers said.
Sperm count and concentration have suffered an alarming decline in Western countries for decades, the scientists said, with sperm counts halving in the past 40 years. Other male sexual disorders such as penile malformation, breast cancer and undescended testicles have increased. Hormone-disrupting chemicals are a prime suspect, and the study sheds new light on the potential for chemical cocktails to cause harm.
The study team, led by Professor Andreas Kortenkamp, of Brunel University London, said they were “astonished by the magnitude of the Danger Index”, the measure of risk from cocktails chemicals. The team was also surprised that BPA was the chemical of greatest concern, as previous work had focused on phthalates, which are used in plastics.
Kortenkamp told the Guardian that the research would allow for better epidemiological studies of people to assess the impacts. “But personally, I think with the evidence we have produced, there is no reason to delay any regulatory action.”
The research, published in the journal Environment Internationalassessed measurements of nine chemicals, including bisphenol, phthalates and paracetamol (known in some countries as acetaminophen), in urine samples from nearly 100 Danish men aged 18 to 30. It also used existing data, mainly from the European Food Standards Agency, to estimate people’s exposures to 20 other chemicals.
These data were compared with acceptable exposure levels, also taken from the scientific literature. This gave a measure of the potential impact of each chemical, which was then summed using an established method to produce an overall measure of risk for the cocktail of chemicals in each of the men.
All the men were exposed to dangerous combined exposures and the most exposed in the study had levels 100 times higher than acceptable values, the average being 17 times. “Our assessment reveals alarming exceedances of acceptable combined exposures,” the researchers concluded.
The researchers were also able to rank the chemicals, with BPA being the main risk factor, followed by dioxins, paracetamol and phthalates. However, eliminating BPA did not bring the combined exposure back to acceptable levels.
Paracetamol has been shown to cause a decline in sperm quality in laboratory animals and to increase the risk of non-descending testicles in boys born to mothers using the painkiller during pregnancy. In 2021, a journal supported by 90 scientists said: “We recommend that pregnant women be warned early in pregnancy to desist [paracetamol] unless its use is medically indicated, and consult a doctor or pharmacist if in doubt.
The researchers admitted that there were uncertainties in their analyses. For example, the data used concerned the years 2009-2010 and, while exposure to BPA has decreased slightly since then, exposure to other bisphenols has increased. It is also possible that the young women were not exposed to the same chemicals as the young men in the study.
But the researchers said: “Given the multitude of chemicals to which humans are exposed, these constraints almost certainly mean that we have underestimated the risks of mixing.” So-called “eternal chemicals”, PFAS compounds, can harm sperm, but were excluded from the study because data is limited. Air pollution can also affect sperm quality.
Apart from the impact of chemicals, other causes of declining sperm quality have been proposed by scientists, with research suggesting links to body weight, lack of physical activity and smoking.
“We’re not saying chemicals are the only factor,” Kortenkamp said. “Nutritional epidemiologists say eating lots of fatty foods – cheese, butter, cheap fats, lots of fatty meat – is not good for sperm quality.”
Professor Hagai Levine, from the Hebrew University School of Public Health, Israel, said: “This is a unique study that adds to the growing evidence of the negative impact of certain chemicals on human reproduction. We need to step up global efforts to study the causes of male reproductive disruption.
Professor Richard Sharpe, from the University of Edinburgh, said: “Unlike the authors of the new study and many members of the scientific community, I am still not convinced that exposure to environmental chemicals at Low endocrine activity plays an important causative role in the drop in sperm count He said direct evidence was lacking that most of the chemicals assessed by the study harm human testicular development, although there is good evidence for paracetamol.
Sharpe said he was convinced the drop in sperm count must have an environmental cause, most likely impacting the onset of pregnancy. But he said a high-fat, processed diet was both harmful in itself and the main source of the chemicals, making it hard to tell which might be to blame. Still, Sharpe said it remains possible that certain chemical cocktails negatively affect sperm count in men.