Microplastics have been discovered inside every single sample of seafood bought at a market as part of a scientific study.
Researchers cut open oysters, prawns, crabs, squids and sardines and studied them for any sign of microplastics.
Sardines were found to be the worst affected and had ingested the largest amount of plastic, up to 30mg per serving – the same weight as a grain of rice.
Microplastics are tiny particles which are less than five millimetres (0.2 inches) in length.
The health impact of humans ingesting these particles remains a concerning mystery.
The study was led by the University of Exeter and the University of Queensland and has been published in the journal Environmental Science & Technology.
Academics report plastic levels of 0.04 milligrams (mg) per gram of tissue in squid, 0.07mg in prawns, 0.1mg in oysters, 0.3mg in crabs and 2.9mg in sardines.
‘Considering an average serving, a seafood eater could be exposed to approximately 0.7mg of plastic when ingesting an average serving of oysters or squid, and up to 30mg of plastic when eating sardines, respectively,’ said lead author Francisca Ribeiro, a PhD student who led the research.
‘For comparison, 30mg is the average weight of a grain of rice. Our findings show that the amount of plastics present varies greatly among species, and differs between individuals of the same species.
‘From the seafood species tested, sardines had the highest plastic content, which was a surprising result.’
The researchers wanted to see if and how plastic was affecting a wide range of ocean-dwelling creatures so bought five wild blue crabs, ten oysters, ten farmed tiger prawns, ten wild squid and ten wild sardines.
While they were still raw and fresh, the animals were analysed for five different types of known plastic pollution,: polystyrene, polyethylene, polyvinyl chloride, polypropylene and poly(methyl methacrylate).
All of these polymers are commonly used in plastic packaging and textiles and previous studies have found they make up a lot of marine litter.
Researchers used chemicals to dissolve any plastics in the tissues of the samples and the liquid produced was then put into a machine to determine what type of plastic it was.
‘We found polyvinyl chloride – a widely used synthetic plastic polymer – in all samples we tested, but the most common plastic in use today – polyethylene – was the highest concentrate we found,’ Ms Ribeiro said.
‘Another interesting aspect was the diversity of microplastic types found among species, with polyethylene predominant in fish and polyvinyl chloride, the only plastic detected in oysters.’
Microplastics are being increasingly found around the world, with evidence of them now seen at the bottom of the deepest ocean as well as in the Alps and Antarctica.
They are created when plastics degrade, are washed or broken up, and are hard to catch and destroy.
Due to their prevalence, researchers are desperately trying to understand how harmful they are to human and animal health.
A report commissioned by the United Nations last year found microplastics in drinking water.
This was the first attempt by the WHO to examine the potential human health impacts of exposure to microplastics.
Some of the key findings include the revelation that larger microplastic particles, bigger than 150 micrometres, are likely to be passed out of our bodies without harm.
Smaller particles could potentially be absorbed into our organs, however.
It also suggests microplastics have the potential to both carry disease-causing bacteria and help bacteria become resistant to antibiotics.