Plastic is everywhere.
Significant concentrations of microplastics have been found in human testicles, raising concerns they may be adding to the global decline in sperm quality.
Researchers from the University of New Mexico analysed testicular tissue from both humans and dogs, and found every sample included microplastics. In total, they found 12 different types of material.
The team also revealed a correlation between certain microplastics and reduced sperm count in the canine samples.
Across Europe, North America, Australia and New Zealand, sperm counts are falling at around 1.5% per year. Globally, around one in six people have trouble conceiving.
Microplastics have already been found in human placentas.
Team leader Professor Xiaozhong ‘John’ Yu has previously studied the effects of heavy metals, pesticides and endocrine-disrupting chemicals on reproductive health. He said said he began exploring the relationship between microplastics and fertility following a conversation with his colleague, Professor Matthew Campen.
‘He said, “Have you considered why there is this decline [in fertility] more recently? There must be something new”,’ said Professor Yu.
To investigate, the team obtained human testicular samples from the New Mexico Office of the Medical Investigator, and canine tissue from City of Albuquerque animal shelters and private veterinary clinics that perform spay-neutering operations.
Extracting the microplastics began by using chemicals to dissolve the fat and proteins in the tissue samples, which were then spun in an ultracentrifuge, leaving all the microplastics in a nugget at the bottom of the tube.
To keep it simple: microplastics are tiny particles of plastic.
US-based organisation NOAA – aka the National Oceanic & Atmospheric Administration – defines microplastic as being 5mm in diameter or less, or ‘the size of a sesame seed’.
There are also two types of microplastics: primary and secondary.
Primary microplastics are those produced directly as microparticles, such as microbeads – the little plasticky balls you used to get sometimes in toothpaste and cosmetics like exfoliating skincare gels and scrubs.
These have already been banned in the UK, US and Canada.
Another example is a microfibre from polyester, nylon or acrylic clothing.
Secondary microplastics refer to larger plastic products that have broken down into smaller pieces – such as plastic bottles, food packaging and tyres.
Microplastics are harmful to both the environment and humans. They have been found across the planet and throughout our bodies, with a growing number of scientific studies revealing the harm they can cause.
They are also almost impossible to avoid. Plastic production has increased enormously since the 1950s, and plastics take hundreds of years to decompose.
This was then heated to 600C, as different plastics emit different gases at certain temperatures, allowing the researchers to determine which plastics were present.
In dogs, the average concentration of microplastics was 122.63 micrograms per gram of tissue – a microgram is a millionth of a gram.
In humans, the concentration was almost three times higher at 329.44 micrograms per gram.
The most common plastic in both human and canine tissues was polyethylene (PE), commonly used to make bottles, food containers and plastic bags.
‘At the beginning, I doubted whether microplastics could penetrate the reproductive system,’ said Professor Yu. ‘When I first received the results for dogs I was surprised. I was even more surprised when I received the results for humans.’
In dogs, the second most common microplastic was PVC, used in a wide range of products including bank cards, packaging, bottles and flooring. Further analysis revealed that the higher the concentration of PVC, the lower the sperm count.
Similar analysis was not possible in the human tissue because it did not contain sperm cells.
‘The plastic makes a difference – what type of plastic might be correlated with potential function,’ said Professor Yu. ‘PVC can release a lot of chemicals that interfere with spermatogenesis [the production of sperm] and it contains chemicals that cause endocrine [hormone] disruption.’
When it comes to studying reproduction and lifestyle, dogs are more closely associated with humans than rats or mice – particularly because they live alongside each other and share the same environment.
‘Physically, their spermatogenesis is closer to humans and the concentration has more similarity to humans,’ said Professor Yu, adding that canine sperm counts also seem to be dropping.
‘We believe dogs and humans share common environmental factors that contribute to their decline.’
Professor Yu also noted that the average age of men sampled was 35, meaning their exposure to microplastics began decades ago. He warned that the impact might be greater for the younger generation, with more plastic than ever in the environment.
Further research is needed to determine whether microplastics have the same impact on human sperm as in dogs and whether they are playing a role in the global decline in fertility.
However, he added that he doesn’t want anyone to panic.
‘We don’t want to scare people,’ said Professor Yu. ‘We want to scientifically provide the data and make people aware there are a lot of microplastics. We can make our own choices to better avoid exposures, change our lifestyle and change our behavior.’
The study is published in the journal Toxicological Sciences.
