University of Manchester scientists have discovered significant concentrations of microplastics in the male reproductive system of sea turtles.
The scientists also found slightly less, but still significant levels of microplastics in other organs of both male and female turtles, including the heart, kidney, liver and spleen, as well as skeletal muscle, subcutaneous fat, stomach and intestines.
They studied the bodies of 10 stranded loggerhead sea turtles, recovered by the Oceanogràfic Foundation of Valencia, that suffered drowning and exhaustion when they were accidently caught up in commercial fishing nets.
The findings, published in the journal Marine Environmental Research, could spell disaster for the majestic creatures already found in declining numbers in the world's oceans.
It is the first study to show that microplastics from the gut can translocate in sea turtles, opening up the possibility of different organs especially the reproductive system - being directly affected.
The scientists believe microplastics may also lead to systemic inflammation in the animals.
The largest median particle size of around 25 microns was found in the intestines and fat, and the smallest median particle size - of around 15 microns was found in the stomach and reproductive organs.
Lead author Leah Costello, a PhD researcher from The University of Manchester was funded under a Biotechnology and Biological Sciences Research Council Doctoral Training Studentship.
She said: "Microplastics are a pervasive marine environmental pollutant, on a par with other global threats such as climate change and ozone depletion.
"Our study is the first to show direct evidence of the presence of microplastics in the reproductive and other organs of loggerhead sea turtles.
"Sea turtles already face many pressures from human activity and although we have been aware that they ingest plastic throughout their range, the finding of microplastics in almost every tissue sample was quite shocking.
"These findings show that even seemingly healthy individuals could be under physiological stress, impacting the reproductive success of vulnerable and recovering populations."
Foreign microparticles were identified in 98.8% of all samples, of which around 70% were microplastics.
Analysis revealed that polypropylene, polyester fibres, and polyethylene were the most common microparticle types.
Polypropylene is used in include food packaging, clothing, bottle caps, ropes, personal care products, fishing gear and twine.
Loggerhead turtles are regularly reported to ingest plastic bags - made from polyethylene - who misidentify them as jellyfish and algae.
Polyester is another dominant microfiber releasing large numbers of microfibres into the oceans and seas.
And further analysis provided direct visualisation of cotton microfibres embedded in loggerhead heart tissue.
Three million tonnes of primary microplastics are released into environment every year, with a further 5.3 million tonnes of larger plastic items that can degrade into secondary microplastics over time.
Because plastics can remain in the gut for up to four months in sea turtles, the scientists speculate that microplastics can cross biological barriers from the gut to organs via the circulatory system contributing to a suite of adverse biological effects.
Co-author Professor Holly Shiels from the University of Manchester added: "Microplastic accumulation is likely to be associated with organ damage and toxicity in these incredible marine reptiles that can live for 70 years.
"Of particular concern is the impact on reproduction, with implications on growth, development and viability of offspring which could spell trouble for the stability of these already vulnerable sea turtle populations.
"However, further studies are required to more broadly assess the biological and health impacts of microplastic on sea turtle reproduction."
- Image: fibre lodged in sea turtle heart
- Microplastics accumulate in all major organs of the Mediterranean loggerhead sea turtle (Caretta caretta) is publushed in Marine Environmental Research https://doi.org/10.1016/j.marenvres.2025.107100
