Parental plastic exposure harms offspring through multiple biological rout

Microplastics and nanoplastics are increasingly found throughout aquatic environments, raising concern about whether these tiny particles can move from exposed parents into their offspring. But a new critical review warns that harm observed in the next generation should not automatically be interpreted as evidence that plastic particles were directly transferred from mother to offspring.

Published in New Contaminants, the review examines evidence from aquatic organisms including water fleas, rotifers, copepods, fish, and bivalves. The researchers propose an evidence classification framework that separates true maternal particle transfer from intergenerational, multigenerational, and transgenerational toxicity.

"When offspring show developmental or reproductive changes after their parents were exposed to microplastics, it is tempting to conclude that the particles themselves were inherited," said corresponding author Neng Yan. "But similar effects can arise through several very different biological routes. Distinguishing these routes is essential if we want to understand the real environmental risks."

The distinction matters because parental exposure can affect offspring even when plastic particles never enter an egg or embryo. Micro(nano)plastics may damage reproductive organs, alter egg quality and energy supply, disrupt hormones, trigger oxidative stress, or change the parental gut microbiome. Embryos may also encounter particles externally after spawning.

The review found that direct evidence for maternal particle transfer remains surprisingly limited. In the water flea Daphnia magna, for example, studies suggest that nanoparticles can reach embryos through both the brood chamber and an internal gut to ovary to oocyte pathway. One study estimated that about 88% of embryo exposure occurred through the brood chamber, while only around 12% was associated with the internal transfer route.

Evidence is less clear in many other organisms. In fish, parental exposure has been linked to altered hatching, growth, heart rate, reproduction, and behavior in offspring, yet direct entry of maternal particles into offspring tissues has rarely been demonstrated using multiple independent analytical methods.

To strengthen future research, the authors propose several minimum requirements for claiming true maternal transfer. Particles should be directly localized inside eggs, embryos, or offspring tissues using complementary techniques, while experiments should rule out surface contamination, dye leakage, and particles carried over in the surrounding water. Studies claiming effects across unexposed generations should also include clean-generation experiments.

The review further maps biological mechanisms that may connect parental exposure with offspring effects, including oxidative and mitochondrial stress, inflammation, apoptosis, endocrine disruption, epigenetic changes, microbiome disturbances, and interactions between plastics and other contaminants.

The authors argue that environmental risk assessment should move beyond asking whether particles can cross from mother to offspring. A more important ecological question is whether parental exposure ultimately reduces reproductive success, offspring fitness, and population renewal.

Future studies should therefore use more environmentally realistic particles, strengthen particle identification, follow unexposed generations, and track outcomes from parental reproduction through offspring growth and reproductive capacity. Such evidence could help transform microplastic research from a collection of toxicity observations into a more reliable framework for predicting ecological risk.