Exposure to even low doses of microplastics hit fertility
The main discovery of the Chinese doctors was how exactly exposure to low levels of polystyrene microplastics affects the quality of male sperm and the number of offspring born. In addition, the researchers were able to discover a factor that exacerbates the damage being done.
Urologists from Shanghai Jiaotong University and Beijing Tongzhen Hospital at Capital Medical University (China) conducted experiments with mice and found that exposure to low levels of polystyrene particles - either alone or in combination with a high-fat diet - significantly reduces sperm quality and the number of offspring. The researchers reported their findings in a paper published in the journal Environmental Pollution.
Since the second half of the 20th century, people have been using plastic products everywhere. However, not even 60 years passed, as mankind began to fight with plastic: it turned out that made of it glasses and bottles decompose for 450 years, and toothbrushes - as much as 500. Small plastic fragments (usually less than five millimeters) constantly get into the soil and oceans, and eventually end up in the human and animal body through air, water and food.
Many studies have been devoted to the problem of microplastic pollution and its impact on reproductive health. For example, in 2022, scientists from the Chinese province of Henan calculated that the minimum dose of microplastics for humans, leading to abnormal sperm quality, is 0.016 milligrams per kilogram of body weight per day. Based on this, the experts concluded that such particles can affect sperm quality and likely serve as one of the reasons for the decline in male fertility over the past 80 years.
A team of physicians from Shanghai and Beijing undertook to supplement the conclusions of colleagues. The authors of the new experiment explained that until now scientists have not figured out how the reproductive function of males is affected by low levels of polystyrene - a polymer of amorphous type, which is obtained after processing vinylbenzene, is not characterized by high strength, but can perfectly transmit light. Today, it is produced in the world for about 15.6 million tons each year, and volumes continue to grow. This plastic is used to create signs, signage, window displays, decorative and design elements, various building materials (e.g. sandwich panels, laminate, blocks, formwork, partitions), jewelry, greenhouses and much more, among other things.
The 12-week study involved 30 male and 30 female laboratory mice of the C57 line, two months old and weighing approximately 20 grams each. The males were divided into six groups: the first was a control group; the second was exposed to low doses of polystyrene particles - 0.6-0.7 micrograms per day; the third was on a high-fat diet. The scientists chose this condition because obesity is an important factor affecting fertility, but until now it was not known whether exposure to plastics could exacerbate the effects of excess weight on fertility.
A fourth group of mice survived both the effects of microplastics and a special diet. The fifth group first gained weight and then lost weight; the rodents in the sixth group were treated the same way, but were also exposed to polystyrene. In addition, each male was mated with five different females over a period of three weeks.
After all the tests, the test subjects were weighed, put to sleep, their blood samples were taken, and their testicles, prostate and fat deposits were frozen and studied under a microscope.
"The results showed that a single exposure to low doses of polystyrene particles, as well as a high-fat diet alone, significantly reduced sperm quality and number of offspring born, while exposure to low doses of polystyrene together with a high-fat diet enhanced the above effects. Their combination led to a marked increase in the level of inflammation in the prostate of the mice, triggered apoptosis (physiological cell death. - Ed.) of the prostate epithelium and decreased levels of nutrients such as zinc and citrate in the seminal fluid," said the urologists.
They recalled that the prostate is an exocrine tubular alveolar gland of the male body of mammals, which plays an important role in ejaculation and reproduction. Its secretion, being one of the main components of seminal fluid, provides nourishment for mature spermatozoa and promotes sperm liquefaction, activation and capacitation of male germ cells.
Nevertheless, the harm caused by obesity could be significantly offset by avoiding high-fat diets and losing weight. Thus in the mice involved in the experiment, it was possible to reduce apoptosis of the prostate epithelium, increase the levels of zinc and citrate in the seminal fluid and increase the number of calves born.
"We found for the first time that exposure to low doses of polystyrene microparticles is toxic to the male reproductive system because it causes decreased sperm quality, inflammation and apoptosis in the prostate. <...> Also, our results may provide valuable information to better understand the effects of low-dose microplastics on fertility in metabolic disorders and help develop preventive measures," the Chinese researchers concluded.