For the past 70 years, humanity has become more and more reliant on plastic materials for a variety of functions. In this time, an estimated 6 billion tons of plastics have ended up being deposited in the environment where they gradually degrade and fragment into micrometer- and nanometer-sized particles. These micro- and nanoplastics (MNPs) have become widely distributed throughout the environment and the food chain, and have been found in the tissues of humans and other mammals.
Previous studies have confirmed that MNPs entering in food can cross the intestinal barrier into the blood stream, and MNPs have been found in the tissues of laboratory rats and fish. Furthermore, pregnant rats fed plastics in their food had offspring that suffered an array of unhealthy outcomes affecting the brain, testicles, liver, immune system and metabolism. Placental tissues in humans, both maternal and fetal have also been shown to contain these tiny particles of plastic, but there has never been a study confirming that MNPs can cross the placenta from mother to offspring.
In a new investigation by Rutgers scientists, pregnant rats were fed specially marked nanoscale plastics to determine whether these could cross the placenta and infiltrate the tissues of their unborn pups. The researchers hypothesized that the carboxylated red fluorescent 25 nm (PS25C) polystyrene spheres would cross the intestinal barrier of the mother rats and then also cross the placenta and enter the blood stream and tissues of the unborn pups.
The five experimental rats were fed liquid containing the 25 nm polystyrene balls on day 19 of their pregnancy. Control rats were not fed in this way. After 24 h, the rats were sacrificed and images were made of their tissues, and of the tissues of their pups. The results, published in the journal Nanomaterials, showed that the MNPs had not only crossed the intestinal and placental barriers within 24 h, but they had permeated the livers, kidneys, hearts, lungs and brains of the unborn offspring.
“Much remains unknown, but this is certainly cause for concern and follow-up study,” said Philip Demokritou, the Henry Rutgers Chair and professor in nanoscience and environmental bioengineering at the Rutgers School of Public Health.
“The use of plastics has exploded since the 1940s due to their low cost and versatile properties. From 9 billion metric tons produced over the last 60 years, 80 percent ended up in the environment, and only 10 percent was recycled,” said Demokritou, who also holds appointments at Rutgers’ School of Engineering and directs the Nanoscience and Advanced Materials Research Center at the Environmental and Occupational Health Sciences Institute.
“Petroleum-based plastics are not biodegradable, but weathering and photooxidation break them into tiny fragments. These tiny fragments, called micro-nano-plastics, are found in human lungs, placentas and blood, raising human health concerns. As public health researchers, we are trying to assess the health risks from such an emerging contaminant to inform policymakers and develop mitigation strategies. The goal is also to increase the reuse and recycling of plastics and even replace them with biodegradable, biopolymer-based plastics. This is part of our bigger societal goal towards sustainability.”
The results confirm the hypothesis of the researchers, that MNPs can cross the placental barrier and permeate the tissues of the unborn offspring. They also suggest the potential for the maternal–fetal transfer of nanoscale polystyrene MNPs.
The researchers acknowledge that the investigation involved only polystyrene MNPs, of a single specific size, and that this is not representative of the variety of environmental MNPs to which animals and humans are exposed. However, they were able to prove, for the first time, that plastics of this size can cross the placental barrier and affect the tissues of the offspring.
It is estimated that the average human ingests and inhales around 5 g of MNPs a week, a quantity that is equal to the mass of a credit card. It hasn’t yet been shown whether this amount, ingested unavoidably by a pregnant woman, will have similar effects on an unborn child, although some studies suggest plastics do affect human embryonic development, said Demokritou.
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