A study of 755 fish caught off three ports in Mexico found an average of 20% of them had micro-plastics in their guts.
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The report by researchers from several universities and conservation groups studied grey snapper, red grouper, white mullet and king mackerel.
The fish were caught off the Gulf coast port of Veracruz, Puerto Morelos on the Caribbean, and La Paz on the Sea of Cortez or Gulf of California.
Plastic was found in over one-third of the Veracruz fish, but only 8% of those in La Paz and 23% in Puerto Morelos.
The Center for Biological Diversity said Veracruz’s bigger population may be sending more waste into the ocean around the port.
Tests found much of the plastic came from cellophane tape and cling wraps.
Micro-plastics are generated as plastic products break down in ocean water. The tests also found fibers used for textiles, and some plastics that apparently came from food containers, fishing gear, bottles and bags.
The study did not test to determine whether micro-plastics had made their way into the flesh of the fish, but scientific studies suggest that could happen.