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A thresher shark poached by fishermen in the stretch of sea between the island of Ponza and the coast of Terracina (Lazio, Central Italy, Mediterranean Sea) and confiscated by the Italian health authorities was evaluated for the presence of chemical contaminants. Hg mean concentration of 2.1 mg kg -1 was found in muscle; speciation analysis confirmed it was almost in the toxic organic form of MeHg (2.0 mg kg -1 ). The Se:Hg molar ratio was <1 not protective against the toxic effect of Hg. 137 Cs was detected at a mean concentration of 0.53 Bq kg -1 , and 40 K, radioisotope of natural origin was found at 91 Bq kg -1 . Dioxins and PCBs were found in the common thresher shark at mean concentrations of 0.012 and 0.088 pg TEQ-WHO g -1 w.w. while NDL PCBs at 4.5 ng g -1 w.w., lower than limits set by European Regulation. The major concern is constituted by the presence of Hg twice the maximum limit set by EU Regulation, then the consumption of thresher shark flesh should be strongly discouraged., (Copyright © 2021 Elsevier Ltd. All rights reserved.)