What’s your poison? For sperm – it’s chemical cocktails
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What’s your poison? For sperm – it’s chemical cocktails

Sperm quality is declining, and one of the culprits – you guessed it – is toxic chemicals. But it’s not enough to look at the effects caused by individual substances. A new study shows that the broad mixtures of chemicals, which most humans are exposed to on a regular basis, pose a much greater threat to male fertility.

Human sperm quality is decreasing. This has been reported several times over the past few years. The trend is evident among men in the Western world, where studies have shown that men’s sperm counts have more than halved in the last 40 years.

Well-known endocrine-disrupting chemicals, such as phthalates, flame retardants, and bisphenols, have previously been linked to the decreasing sperm quality. And it’s true that these toxic substances all have a severe negative effect on men’s fertility. Individually, however, these chemicals cannot explain the dramatic decline.


The secret is in the mixture

Instead, studies show that the explanation lies in the mix of chemicals we are all exposed to. This is the so-called cocktail effect – the principle that exposure to a mixture of several chemicals might cause greater harm than the summed-up effects of the individual substances.

A recent study performed within the European Human Biomonitoring project (HBM4EU) has shed light on this issue. The study shows that looking at one chemical at a time will result in underestimated exposure risks.

It’s not even enough to look at groups of related chemicals, such as phthalates. Therefore, a mixture risk assessment needs to focus on broader groups of chemicals, to really reveal the risks posed to humans.

“A mixture risk assessment needs to focus on broader groups of chemicals, to really reveal the risks posed to humans”

This study on chemical effects on semen quality was carried out by a team of researchers led by Andreas Kortenkamp at Brunel University in London. Professor Kortenkamp and his team first looked at combined risks for phthalates, and found that most of them fell below the safety threshold.


Common painkillers increase the combined risk

They then added bisphenol F and S, which showed a higher combined risk. And when they added paracetamol and 20 background chemicals, the image shifted to reveal a combined risk way over the safety threshold for every single person participating in the study.

“A mixture of a large enough number of chemicals will in fact push all of them way over the safety threshold”

“The field has been obsessed mainly with doing mixture risk assessments for phthalates. You see that if you do this you only see a segment of the problem. The contours of the problem only become apparent when we widen the net and think seriously about which chemicals we should consider together”, said Andreas Kortenkamp at the HBM4EU conference, where his study was presented.

According to professor Kortenkamp, this means that even if the chemicals seem to be under the safety threshold when viewed one at a time, a mixture of a large enough number of chemicals will in fact push all of them way over the safety threshold. We’re basically talking about the worst possible kind of synergy, where the combined result is greater than the sum of the individual components.


Widen the picture and take mixtures into account

So, what do we learn from this? The conclusion from professor Kortenkamp is that as of now, there is no regulation to protect us against mixture exposure. Single-chemical assessments underestimate risks, and even a consideration of chemical groups, such as phthalates, is not enough.

A mixture assessment factor, MAF, to better account for the combined risks of chemicals is currently being considered as an option under REACH. The data from professor Kortenkamps semen quality study supports this approach. However, the proposed MAF of 10 is probably too low.

According to Chemical Watch, a consultancy group is currently assisting the European Commission on the best way to introduce a MAF under REACH. A final report is expected in June.