Oysters sold in São Paulo and Santa Catarina contain toxic bacteria and metals, study says

Resistant bacteria and toxic metals were found at high levels in ready-to-eat oysters sold in markets in São Paulo and Santa Catarina, according to research by the University of São Paulo (USP) in partnership with the Federal University of Santa Catarina (UFSC) and the Fisheries Institute.

The research published in the scientific journal Food Research International analyzed oysters in markets in São Paulo and Santa Catarina between September 2022 and March 2023 and took the mollusks for laboratory analysis.

The analyses detected the heavy metal arsenic (Ar) at levels considered high by scientists, with up to 1.95 mg for each kilogram of mollusk — the maximum concentration authorized by the National Health Surveillance Agency (Anvisa) is almost half, 1 mg/kg.

The metal is considered toxic to the human body and can cause everything from nausea and diarrhea to kidney and heart damage. Scientists are warning about the mollusks' ability to bioaccumulate.

Organisms called primary consumers, such as bivalve mollusks and filter-feeding fish like sardines , filter seawater in search of microscopic food. As they filter the water, they accumulate metals and toxins in their bodies.

The oysters also showed resistant bacteria. At least five multidrug-resistant bacteria were detected, including Escherichia coli, a priority antibiotic by the World Health Organization (WHO).

The study states that oysters are a public health problem that requires surveillance and appropriate management strategies. CNN contacted the governments of São Paulo and Santa Catarina and has not yet received a response.