Metal concentrations and toxicity in South African snoek (Thyrsites atun) and yellowtail (Seriola lalandi).

The concentrations of 16 metals were assessed in snoek(Thyrsites atun; n=20) and yellowtail (Seriola lalandi; n=37) sampled from the West and South-East coasts of South Africa. Variability was observed at both small (Al, Cr, Hg, Pb, Mn and Cu) and large (As and Cu) spatial scales while inter-specific examination revealed diverse metal concentrations in snoek (Higher levels: Cr, Mn, Co, Hg and Pb) and yellowtail (higher levels: Fe and Cu). Zn, As and Hg were positively correlated with yellowtail size with no such correlations in snoek. Mean concentrations of As (0.61mg·kg-1; 0.98mg·kg-1), Cd (0.008mg·kg-1; 0.004mg·kg-1), Hg (0.27mg·kg-1; 0.16mg·kg-1) and Pb (0.009mg·kg-1; 0.005mg·kg-1) for snoek and yellowtail respectively were within regulatory guidelines. However, 10% (n=2) of snoek exceeded Hg maximum allowable limit, suggesting caution and further investigation. Overall, two meals (150g) per week of snoek or larger yellowtail (12-15kg) can be safe for human (adult) consumption.

Mercury accumulation in Yellowfin tuna (Thunnus albacares) with regards to muscle type, muscle position and fish size.

The concentrations and relationships between individual mercury species and total mercury were investigated in different muscle parts and sizes of Yellowfin tuna (Thunnus albacares). Fourteen Yellowfin tuna caught in the South Atlantic off the coast of South Africa had an average total Hg (tHg) concentration of 0.77 mg/kg wet weight. No differences were detected (p > 0.05) in tHg, MethylHg (MeHg) or inorganic Hg (iHg) accumulation among the four white muscle portions across the carcass, but both tHg and iHg were found in higher concentrations (p < 0.001) in dark muscle than white muscle. Positive linear correlations with fish weight were found for both tHg (r = 0.79, p < 0.001) and MeHg (r = 0.75, p < 0.001) concentrations. A prediction model was formulated to calculate toxic MeHg concentrations from measured tHg concentrations and fish weight (cMeHg = 0.073 + 1.365 · tHg-0.008 · w). As sampling sites and subsampling methods could affect toxicity measurements, we provide recommendations for sampling guidelines.

Heavy metal accumulation and toxicity in smoothhound (Mustelus mustelus) shark from Langebaan Lagoon, South Africa.

Together with several health benefits, fish meat could introduce toxins to consumers in the form of heavy metal contaminants. High levels of mercury (Hg), especially, are frequently detected in certain predatory fish species. Mustelus mustelus fillets were analysed for 16 metals and three individual Hg species (inorganic Hg, ehtylmercury, methylmercury) with inductively coupled plasma mass spectrometry (ICP-MS) and HPLC-ICP-MS respectively. Eleven of the 30 sharks had total Hg levels above the maximum allowable limit with toxic methylmercury found as the dominant mercury species with a strong correlation (r = 0.97; p < 0.001) to total mercury concentrations. Limited correlations between metals and shark size parameters were observed; therefore metal accumulation in M. mustelus is mostly independent of size/age. Average values for arsenic (28.31 ± 18.79 mg/kg) exceed regulatory maximum limits and Hg (0.96 ± 0.69 mg/kg) is close to the maximum limit with all other metals well below maximum limits.

Heavy metals in marine fish meat and consumer health: a review.

The numerous health benefits provided by fish consumption may be compromised by the presence of toxic metals and metalloids such as lead, cadmium, arsenic and mercury, which can have harmful effects on the human body if consumed in toxic quantities. The monitoring of metal concentrations in fish meat is therefore important to ensure compliance with food safety regulations and consequent consumer protection. The toxicity of these metals may be dependent on their chemical forms, which requires metal speciation processes for direct measurement of toxic metal species or the identification of prediction models in order to determine toxic metal forms from measured total metal concentrations. This review addresses various shortcomings in current knowledge and research on the accumulation of metal contaminants in commercially consumed marine fish globally and particularly in South Africa, affecting both the fishing industry as well as fish consumers.

The effects of gender, size and life-cycle stage on the chemical composition of smoothhound shark (Mustelus mustelus) meat.

BACKGROUND: Knowledge on the chemical composition of foods, and on the variation in such components as influenced by endogenous factors, is required for nutritional labelling, dietetic planning and food processing. This study examined the effects of endogenous factors (gender, size and life-cycle stage) on the chemical components (proximate, amino acid, fatty acid, mineral and mercury contents) of smoothhound shark (Mustelus mustelus) meat. RESULTS: Levels of moisture, protein, lipids, ash, amino acids and most minerals were not affected (P > 0.05) by the gender, size or life-cycle stages of the sharks. The fatty acid content was higher in females than in males, as well as in non-pregnant females compared to pregnant females. Certain fatty acids decreased in quantity in medium-sized sharks (prior to maturity). Pregnant females had higher aluminium (Al) and copper (Cu) levels than non-pregnant females and mercury (Hg) levels were highest in large male sharks. CONCLUSION: This study has, for the first time, established that endogenous factors have minimal influence on the chemical composition of M. mustelus meat, demonstrating the feasibility of describing an average composition for this species. Additionally, new insights have been obtained on potential safety concerns (mercury) associated with consumption of the meat that require further investigation.