Varying concentrations of microplastics have been discovered in the vital organs of both male and female sea turtles, including the heart, kidney, liver, and spleen, with the highest levels found in the male reproductive system – sparking major concern among scientists over the future survival of the species.

Studying the bodies of ten stranded loggerhead sea turtles that had suffered drowning and exhaustion when they were accidentally caught up in commercial fishing nets, researchers from the University of Manchester believe the findings “could spell disaster” for a species already suffering a stark decline in numbers.

While microplastics were found in all vital organs of both male and female loggerhead sea turtles, as well as within their skeletal muscle, subcutaneous fat, stomach, and intestines, the highest concentrations – by far – were found in the male reproductive system.

Published in the journal Marine Environmental Research, this 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 largest particle size of around 25 microns was found in the intestines and fat, while the smallest particle size – around 15 microns – was found in the stomach and reproductive organs. The researchers working on the project believe microplastics could lead to systemic inflammation in the animals.

“Microplastics are a pervasive marine environmental pollutant, on a par with other global threats such as climate change and ozone depletion,” said lead author, Leah Costello, a PhD researcher from The University of Manchester.

“Our study is the first to show direct evidence of the presence of microplastics in the reproductive and other organs of loggerhead sea turtles.”

A species that already faces mounting pressure from human activity, the loggerhead sea turtle has been known to ingest plastic throughout their range. The discovery that microplastics are present in almost every tissue sample examined in this study, said Costello, 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,” she added.

Foreign micro-particles were identified in 98.8% of all samples, of which around 70% were microplastics. Analysis revealed that the most common micro-particle plastics were polypropylene, polyester fibres (from synthetic clothing), and polyethylene – the most commonly produced plastic used across plastic bags, bottles, and other packaging types.

Polypropylene meanwhile is used in food packaging, clothing, bottle caps, ropes, fishing gear, and twine. Loggerhead turtles are reported to routinely ingest plastic bags – made from polyethylene – having misidentified them as jellyfish and algae.

Further analysis even identified cotton microfibres embedded in loggerhead turtle heart tissue. 

It speaks volumes for the infrastructure crisis we face when it comes to waste and waste management. Three million tonnes of primary microplastics are released into the environment every year, with a further 5.3 million tonnes of larger plastic items that can degrade into secondary microplastics over time.

What’s more, because plastics can remain in the gut for up to four months in sea turtles, scientists at the University of Manchester speculate that microplastics can cross biological barriers from the guts to organs via the circulatory system, contributing to a suite of adverse biological side effects.

“Microplastic accumulation is likely to be associated with organ damage and toxicity in these incredible marine reptiles,” said co-author, Professor Holly Shiels from the University of Manchester. 

“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. 

“Further studies are required, however, to more broadly assess the biological and health impacts of microplastic on sea turtle reproduction.”

The study – ‘Microplastic accumulate in all major organs of the Mediterranean loggerhead sea turtle’ – has been published in the journal Marine Environmental Research.

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