Concentrations and compositions of metallic elements in commercially important marine species

Abstract

Metals have been in our environment since the genesis of the world and are ubiquitous in all environments. We as humans mine, utilize, and release these metals from the environment to a level that may affect chronically or acutely environment and human health. To that sense, information on metal concentrations are valuable in commercially marine species as they are an important food source to many communities. Fish and molluscs are also good bioindicators and biomonitors as they can indicate the health of the environment, they are found in. There is, however, an information gap about metal concentrations in the marine environment off the coast of South Africa. In this study, sardines (Sardinops sagax) and chokka (Loligo reynaudii) from the Indian and the South Atlantic oceans, and hake (Merluccius capensis), kingklip (Genypterus capensis), and monkfish (Lophuis vomerinus) from the South Atlantic Ocean were analysed for metals using an inductively-coupled plasma mass spectrometry. These species, representing two trophic levels, are exploited in large quantities for human consumption. More knowledge on metal composition will shed light on the biological relationships between the species, possible impacts elevated metal concentrations might have on the fish, and on human and predator consumer health. Metal concentrations and compositions of each species were established and compared. Significant differences in metal concentrations were found between sardine, chokka and the demersal species (hake, kingklip, and monkfish). As was expected, higher trophic levels (hake, kingklip and, monkfish) contained significantly higher concentrations of metals than lower trophic levels such as sardines. Chokka contained significantly lower concentrations of vanadium, cobalt, molybdenum, and manganese than sardines, hake kingklip, and monkfish, but significantly higher concentrations were found for boron, titanium, zinc, cadmium, rubidium, and strontium. These patterns could be caused by physiological regulation or lack of regulation of these metals in chokka. Demersal predators’ metal concentrations and compositional patterns did not differ significantly between each other, probably due to a trophic overlap in diet. Metal compositions or fingerprints were distinct between sardines and chokka from different oceans. This indicates metal compositional patterns could be used as a possible stock discrimination tool. Sardines and chokka metal compositions were distinct from the demersal predators. Demersal metal compositions overlapped, once again possibly caused by diet similarity. The effect of physical parameters (length and mass) on metal concentration was assessed for chokka, hake, kingklip, and monkfish. Negative regressions were found for most metals. However, a positive regression was found for chromium with kingklip length that could be cause for consumer (animal and human) concern. Compared with other studies from around the world cadmium, lead, and mercury concentrations were lower or on par in all species. Cadmium, lead, and mercury concentrations in the muscle tissue of all species were assessed for human consumer safety. Concentrations were found to be below the limits set by South Africa and the European Union for these fish. Estimated daily intake and the total hazard quotient (for South African adults) was calculated for cadmium, lead and mercury. All values were below the quotient of unity. Based on my study it can be concluded that the species studied would be safe for human consumption, but data from more fish from more sites would be needed for confirmation. For the first time, sardines, chokka, hake, kingklip, and monkfish metal concentrations and compositions are compared. Also for the first time, metal concentrations and compositions are compared between sardine and chokka sampled from the South Atlantic and Indian oceans. This study provides valuable information on these commercial species and narrows the information gap currently present on commercial marine species off the South African coast. I also stress the need for more samples from more sites, the need to sample more species, the need to sample higher predators such as dolphins