Research investigates the concentration of chemical elements in commercial species
Marine fish are considered a source of high-quality protein and are rich in essential amino acids, fats, vitamins and many essential chemical elements such as calcium, iron and selenium. However, the presence of potentially toxic inorganic elements can cause everything from neurological and endocrine problems to increased cancer incidence. Metals such as mercury, lead and cadmium are toxic even when consumed at low concentrations, and their adverse effects are magnified by accumulating in animal tissues. On the other hand, even elements like zinc and chromium, which play important roles in metabolism, can cause toxic effects if consumed in excess.
The accumulation of chemical elements in organisms depends on several factors, such as the type of element, the form of assimilation, the species and the metabolism in different tissues. For example, tissues with high metabolic rates, such as liver and kidney, may have a high concentration of metals, especially those with potential toxic effects.
Thus, to understand the potential risk of marine fish consumption, Márcia Cardoso et al.  assessed the concentration of multiple chemical elements in three species frequently consumed on the southeastern Brazilian coast: Sphyraena guachancho (Barracuda), Priacantus arenatus (Common bigeye) and Genidens genidens (Guri sea catfish).
Muscle is the major part of fish used for human consumption. As such, it is essential that this tissue is evaluated for monitoring the concentration of chemical elements in these animals. However, taking muscle samples can damage the appearance of the product and lower its market value. Therefore, a secondary objective of the group was to evaluate the use of low market value tissues to monitor fish quality. Fins, for example, are a commonly discarded part during the cleaning process in fish markets. Hence, using samples of this tissue may be an alternative in monitoring elemental concentrations.
Using the facilities of the XRF X-ray fluorescence beamline of the Brazilian Synchrotron Light Laboratory (LNLS), the researchers quantified in muscle and fin tissue samples the concentration of various chemical elements: zinc, silver, barium, mercury, titanium, nickel, copper, chromium, manganese, iron, phosphorus, potassium, sulfur, calcium, bromine and chlorine.
Potentially toxic elements such as silver, barium, cadmium, chromium and mercury were detected in the samples. The concentration of the various chemical elements showed differences between each species, affected by the fish’s trophic level, feeding habits and morphological characteristics. Thus, according to the researchers, this study confirmed earlier evidence that fish that occupy higher trophic levels have higher concentrations of various elements in the muscle, especially metals with potential toxicity such as mercury.
Finally, the different muscle samples presented greater variation in elemental concentration than the fin samples. This apparent lack of consistence between the two tissues suggests that fins are not a viable alternative for monitoring the concentration of chemical elements in fish.
Source:  Márcia Cardoso, Renata de Faria Barbosa, Gislene Torrente-Vilara, Gabriela Guanaz, Edgar Francisco Oliveira de Jesus, Eliane Teixeira Mársico, Roberta de Oliveira Resende Ribeiro, Felipe Gusmão; Multielemental composition and consumption risk characterization of three commercial marine fish species, Environmental Pollution 252 (2019) 1026 – 1034. DOI: 10.1016/j.envpol.2019.06.039.