A cocktail of chemical contaminants, measured in human bodies, has been linked to deteriorating sperm quality in a new study.
Chemicals such as bisphenols and dioxins are thought to interfere with hormones and damage sperm quality, and studies have found that combinations of these compounds are present at “amazing” levels, up to 100 times higher than those considered safe.
Bisphenol A (BPA) is responsible for the highest risks, scientists said. The chemical is found in milk and canned foods, as it is extracted from the packaging. The key steps to healthy male sexual development occur during pregnancy, making the results of the study particularly relevant for expectant mothers, the researchers said.
Sperm counts and concentrations have declined alarmingly in Western countries for decades, scientists said, with sperm counts halving in the past 40 years. Other male sexual disorders such as penile malformations, breast cancer and undescended testicles are on the rise. Hormone-disrupting chemicals are a prime suspect, and the study sheds new light on the potential of chemical cocktails to cause harm.
The research team, led by Prof. Andreas Kortenkamp of the University of Brunel in London, said they were “amazed by the size of the hazard index”, a measure of the risk of chemical cocktails. The team was also surprised that BPA is the most worrying chemical, as previous work has focused on phthalates used in plastics.
Cortencamp told the Guardian that the study would allow better epidemiological studies in humans to assess the effects. “But I personally think that with the evidence we have provided, there is no reason to postpone any regulatory action.”
The study, published in the journal Environment International, evaluated the measurements of nine chemicals, including bisphenol, phthalates and paracetamol, in urine samples from nearly 100 Danish men aged 18 to 30. It also uses existing data, mainly from the European Food Standards Agency, to assess human exposure to 20 other chemicals.
These data were compared with acceptable exposure levels, also derived from the scientific literature. This gave a measure of the potential impact of each chemical, which was then added together using an established method to create a common risk measure for the cocktail of chemicals in each of the men.
All men were exposed to dangerous combined exposures and the most exposed in the study had levels 100 times higher than acceptable values, with an average of 17 times. “Our assessment reveals alarming exceedances of acceptable combined exposures,” the researchers concluded.
Researchers have also been able to rank the chemicals, with BPA being the biggest driver of risk, followed by dioxins, paracetamol and phthalates. However, the elimination of BPA did not reduce the combined exposure to acceptable levels.
Paracetamol has been shown to cause deterioration in sperm quality in laboratory animals and increase the risk of non-descending testicles in boys born to mothers who use painkillers during pregnancy. In 2021, a review supported by 90 scientists said: “We recommend that pregnant women be warned to give up in early pregnancy. [paracetamol] unless its use is medically indicated, and consult a doctor or pharmacist if you are unsure. “
The researchers acknowledged that there was uncertainty in their analysis. For example, the data used are for the years 2009-2010, and while BPA exposure has decreased slightly since then, exposure to other bisphenols has increased. It is also possible that young women do not have the same chemical exposure as the young men in the study.
But researchers said: “Given the many chemicals that humans are exposed to, these restrictions almost certainly mean that we have underestimated the risks of mixing. The so-called “forever chemicals”, PFAS compounds, can harm sperm, but were excluded from the study because the data are limited. Air pollution can also affect sperm quality.
In addition to the effects of chemicals, scientists have suggested other reasons for the deterioration of sperm quality, such as studies suggesting links with body weight, lack of physical activity and smoking.
“We’re not saying chemicals are the only factor,” Kortenkamp said. “Nutrition epidemiologists say that eating a lot of fatty foods – cheese, butter, cheap fats, a lot of fatty meat – is not good for sperm quality.
Prof. Haggai Levine of the School of Public Health at the Hebrew University of Israel said: “This is a unique study and complements the growing evidence of the adverse effects of certain chemicals on human reproduction. We need to step up global efforts to investigate the causes of male reproduction disorders. “
Professor Richard Sharp of the University of Edinburgh said: “Contrary to the authors of the new study and many in the scientific community, I remain unconvinced that exposure to low endocrine-active chemicals in the environment plays an important causal role in sperm counts.” He said there was no direct evidence that most of the chemicals evaluated by the study had harmed human testicular development, although there was good evidence for paracetamol.
Sharpe said he was convinced that the falling sperm count must have an environmental cause, most likely to affect early pregnancy. But he said a high-fat, processed diet is harmful in itself and a major source of chemicals, making it difficult to tell who could be to blame. However, Sharpe said it remains possible that some chemical cocktails could negatively affect sperm counts in men.
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