COMMENT:

We have all seen those heartbreaking photos showing sea-turtles eating plastic bags, and environmental campaigners have used them to make us rethink our reliance on single-use plastics.

Although eating ocean plastic can indeed be fatal to turtles, new research shows that much smaller plastics may have a more serious effect on the world's turtle population.

Microplastics are tiny pieces of plastic, typically 5mm or smaller. They are grouped into two categories: primary and secondary microplastics.

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Primary microplastics are designed and created by manufacturers for a specific purpose, such as microbeads in facial washes and toothpastes to provide abrasion.

Secondary microplastics are formed from the breakdown of large pieces of plastic over time.

Litter such as plastic drink bottles and food containers can end up in our oceans and eventually break up into smaller pieces as they are exposed to sunlight or physical stress from the ocean's waves.

Due to their small, round size, this increasing volume of microplastics typically goes unnoticed by most. However, next time you go to the beach, grab a handful of sand and look carefully at each grain, it's likely that you will find a few pieces of microplastic in there too.

There are several challenges with microplastics – their small size means that when humans use products containing microplastics, they pass through our filtration systems and into the ocean. They are then easily consumed by fish, and eventually end up on our dinner plates.

Another challenge is that plastics hold and retain much more heat than a regular grain of sand.

As the ratio of microplastics to sand grains steadily shifts - our beaches are gradually becoming more plastic, and the ambient temperature of the beach will increase.

As egg layers, turtles dig out large nests in the sand. They lay their eggs and cover them, leaving their clutch buried for around two months to develop. Turtle eggs are thermosensitive - the final sex of the offspring is controlled by the ambient temperature surrounding the eggs during a critical period of development of the embryo. Warmer temperatures result in female turtles and colder temperatures in males.

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A study published in the journal Current Biology earlier this year already showed that due to rising air temperatures around the Great Barrier reef, 99 per cent of young green turtles that hatch there are female.

This week a new study published in the journal Marine Pollution Bulletin looked at the concentration of microplastics on the beaches in Cyprus where loggerhead and green turtles are known to lay their eggs.

Taking over 1200 samples from 17 different turtle nesting beaches the researchers found that the top 2cm of sand contained up to 130,000 fragments of plastic per cubic metre.

Digging deeper to a the lowest depth of a turtle nest at around 60cm, the scientists found an average of 5300 particles of plastic per cubic metre.

These results indicate that the high concentration of microplastics in the sand has the potential to increase the temperature surrounding the turtle nests, resulting in even more of an imbalance in the gender ratio of the offspring produced.

Worldwide, six of the seven sea turtle species are classified as threatened or endangered. Successful breeding of turtles is crucial for their survival. These subtle but important changes to our beaches have the potential to affect the future reproductive success of the species if colder environments producing more male turtles can't be found.

As we strive to understand and reduce our impact on the world around us, it's important to think beyond the campaign images we see online. Our waste can have far more subtle and widespread impact, over long time periods and long distances.