Doctoral Degrees (Food Science)

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Browsing Doctoral Degrees (Food Science) by Author "Bosch, Adina Cornelia"

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    Status of mercury and other heavy metals in South African marine fish species
    (Stellenbosch : Stellenbosch University, 2015-12) Bosch, Adina Cornelia; Hoffman, Louwrens C.; Sigge, G. O.; Kerwath, Sven E.; O’Neill, Bernadette; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Fish is an important food source in South Africa as it is globally, thus the importance of determining and monitoring its safety in terms of metal contaminants and consumer safety. Effective methodology for analysing total metal concentrations and toxic metal components together with representative sampling protocol for sampling individual fish and larger catches are therefore required for accurate assessment of meat safety. Both inductively coupled plasma mass spectrometry (ICP-MS) and high pressure liquid chromatography coupled to ICP-MS was validated as effective methods for accurately determining concentrations of total metals and individual Hg species, respectively. Consequently, it was found that total mercury loads in fish meat consisted mainly of toxic methylmercury (MeHg) components with a minor addition of an inorganic Hg (iHg) component and ethylmercury concentrations being negligible. This proportion of MeHg to iHg varied between muscle types in yellowfin tuna (Thunnus albacares), with higher iHg concentrations in dark muscle than in white muscle, whereas the toxic MeHg concentrations did not vary across the carcass. The MeHg to tHg relationship was caused to vary with variation in fish weight, being described by the following prediction model: 𝑐𝑀𝑒𝐻𝑔=0.073+1.365∙𝑐𝑡𝐻𝑔−0.008∙𝑤; taking into account fish weight as covariate. For the eight other fish species studied [blacktail (Diplodus sargus capensis), hottentot (Pachymetopon blochii), yellowtail (Seriola lalandi), snoek (Thyrsites atun), blue shark (Prionace glauca), shortfin mako (Isurus oxyrinchus), soupfin (Galeorhinus galeus) and smoothhound (Mustelus mustelus)], the relationships between MeHg and tHg were constant even with varying fish sizes as iHg components were considered an insignificant portion of tHg (ctHg = cMeHg). The tHg measurements could therefore be used as accurate indicators of MeHg concentrations without requiring addition speciation analyses. Sampling from the cephalic region of the dorsal white muscle tissue proves representative of the entire edible portions (white muscle) of larger fish (tuna and sharks spp.) for determining both total metal concentrations and toxic Hg components. Where Hg concentrations are positively correlated to fish size (yellowfin tuna, yellowtail and soupfin), subsamples should include individuals representing the entire size range present per catch. A summary of metal concentrations in all eight species studied indicate that Hg is the main metal of concern where a single portion of certain fish (yellowfin tuna, shortfin mako, soupfin and smoothhound shark) consumed per week could exceed regulatory limits for safe Hg intake, whereas other fish species (hottentot) could be consumed daily without concern of Hg toxicity. Information provided by this study will prove useful to both the fishing and processing industry as well as to health authorities providing information for dietary exposure assessments.