Middle Pastaza River basin.

<div><p>One of the most toxic metals is mercury, which exhibits high toxicity during short exposure periods. This study aimed to determine the concentration of total mercury (THg) in fish muscle tissue from various species captured from two locations in the middle basin of the Pastaza River in Ecuador, which the locals use in their weekly diet. The individuals captured belong to the following families: Loricariidae, Cetopsidae, Heptapteridae, Cichlidae, Parodontidae, Characidae, Prochilodontidae, Curimatida, Siluriformes, Cichliformes, Characiformes, Erythrinidae and Curimatidae. Carnivorous species <i>Charax</i> sp. and <i>Cetopsis plumbea</i>, had THg concentrations were 0.241± 0.018 and 0.116 ± 0.045 mg kg<sup>-1</sup>, respectively. Herbivorous species <i>Hypostomus</i> sp. had a lower of THg. Carnivorous species <i>Hoplias malabaricus</i> exhibited THg concentration of 0.160±0.033 and 0.020±0.007 mg kg<sup>-1</sup> for the omnivorous species <i>Creagrutus</i> sp. Carnivorous species accumulated higher levels of Hg compared to non-carnivorous species. Concentration of total mercury in the collected fish did not exceed the maximum permissible limits set by legislative standards (Ecuadorian Institute of Standardization (INEN as per the acronym in Spanish), FAO/WHO and European Commission); and the objective hazard quotient was less than 1, indicating that the consumption of this fish may pose no risk to human health. Considering the mean concentrations of methylmercury, for all the fish species analysed, the results for daily consumption rate were between 6–199 g and 29–928 g for children and adults, respectively.</p></div>