Microplastic pollution has been found in all human semen samples tested in a study, and researchers say further research on the potential harm to reproduction is “imperative”. Sperm counts in men have been falling for decades and 40% of low counts remain unexplained, although chemical pollution has been implicated by many studies. The 40 semen samples were from healthy men undergoing premarital health assessments in Jinan, China. Another recent study found microplastics in the semen of six out of 10 healthy young men in Italy, and another study in China found the pollutants in half of 25 samples. Recent studies in mice have reported that microplastics reduced sperm count and caused abnormalities and hormone disruption. Research on microplastics and human health is moving quickly and scientists appear to be finding the contaminants everywhere. The pollutants were found in all 23 human testicle samples tested in a study published in May. Microplastics have also recently been discovered in human blood, placentas and breast milk, indicating widespread contamination of people’s bodies. The impact on health is as yet unknown but microplastics have been shown to cause damage to human cells in the laboratory. Millions of tonnes of plastic waste are dumped in the environment and much is broken down into microplastics. These have polluted the entire planet, from the summit of Mount Everest to the deepest oceans. People are known to consume the tiny particles via food and water as well as breathing them in. “As emerging research increasingly implicates microplastic exposure as a potential factor impacting human health, understanding the extent of human contamination and its relation to reproductive outcomes is imperative,” said Ning Li, of Qingdao University in China, and colleagues. “[Mouse studies] demonstrate a significant decrease in viable sperm count and an uptick in sperm deformities, indicating that microplastic exposure may pose a chronic, cumulative risk to male reproductive health.” The research, published in the journal Science of the Total Environment, detected eight different plastics. Polystyrene, used for packaging, was most common, followed by polyethylene, used in plastic bags, and then PVC. The particles may be causing inflammation in tissue, as air pollution particles do, or the chemicals in the plastics could cause harm. In March, doctors warned of potentially life-threatening effects after finding a substantially raised risk of stroke, heart attack and earlier death in people whose blood vessels were contaminated with microscopic plastics. Luigi Montano, of the University of Rome, who led the Italian study, said: “Intervention is necessary to stop the exponential increase in plastic waste.” More than 180 nations are negotiating a UN treaty to regulate plastic and cut pollution. “In particular, there is a need for action to avoid additional permanent damage to the planet and the human body,” Montano said. “If microplastic pollution impacts the critical reproductive process, as evidenced in particular by the decline in seminal quality recorded in recent decades globally, it may prove to be [even worse] for our species in the not too distant future.”