HOW LAB REVEALED COD AND SALMON ARE TAINTED
WE bought cod and salmon fillets from the open fishmonger counters of Sainsbury’s, Asda, Morrisons, Tesco and Waitrose in London. We also purchased packaged fillets from Lidl, Aldi and M&S, which do not have such counters.
The samples were hand-delivered the same day to the Institute of Marine Sciences at the University of Portsmouth.
In a laboratory proofed against air pollution, researchers extracted 5g from each fillet using a device like a hole punch. The samples were placed in potassium hydroxide, which dissolved the flesh and all biological matter.
Scores of microplastics were found when the remaining mixture was put through filter paper 8 hours later. As the pictures below show, most were tiny fibres or fragments.
Because the samples were fillets, rather than whole fish, the microplastics must have come from airborne pollution. They were too large to have passed into the fish muscle tissue from the gut after having been ingested in the ocean. The fillets from fishmonger counters were more contaminated than those from closed packets.
Microplastics are created when manmade materials break down through friction or the effect of heat or light. But instead of disintegrating completely they accumulate in the oceans, the earth and in the air.
The plastic fibres and fragments found on our fish samples came from a variety of airborne sources including clothing and cleaning materials. The contamination is thought to have taken place at some stage during the handling, filleting, packing and display process.
The air also contains microplastics from litter, tyres and packaging such as water bottles. Another source is the fibre from synthetic clothing. It is estimated that 1,800 plastic particles can be produced every time such garments are washed.
Research shows that plastic fibres that float around in the air come down to the ground either through rainfall or as plain dust.