Framework for Modelling Chemical Residuals of Polychlorinated Dibenzo-p-dioxins, Polychlorinated Dibenzofurans (PCDD/Fs) and Polychlorinated Biphenyls (PCBs) in Australian Ranched Southern Bluefin Tuna (Thunnus maccoyii)

Abstract

Southern Bluefin Tuna (SBT) is an economically important ranched marine finfish in South Australia. It is exported for the premium Japanese sushi and sashimi markets. Japanese consumers are demanding increased accountability because of concerns over food safety - especially chemical residues that include PCDD/Fs (dioxins) and PCBs. Dioxins and PCBs bioaccumulate in the fatty tissue of fish and other aquatic animals because of high lipophilicity. Although current results exhibit low residue levels in SBT feed, baitfish is believed to be the major source of dioxins and PCBs. Substantial testing of SBT in Australia and Japan has shown low levels by international standards. However, industry aims to further reduce levels from dietary sources, to meet current and future consumer expectations. Therefore, a quantitative through-chain predictive model for dioxins and PCBs in tuna will be developed. Here the steps necessary for developing a framework for modelling dioxins and PCBs in ranched SBT are developed from a quantitative risk assessment - this is a first step to documenting residue traceability for ranched SBT. The framework consists of five steps. The first defines the chemical residue(s) of interest and the purpose of the model. The second addresses the biochemical, physiological and toxicological aspects of the toxin(s) and SBT. The third is a mathematical formulation of the predictive bio-chemical model with information from Step Two. The fourth requires integration into suitable computing software for data input and evaluation. The fifth step is validation of the model against independent data. A validated model can be used to develop scenarios to inform industry on baitfish selection and feeding practices to ensure minimal residue levels in harvested fish. The validated model derived from this framework will provide increased confidence in international market acceptance and can be adapted for ranched marine finfish elsewhere in the future.