In Summary
- Whilst this tools focusses on microbial risks in smoking fish, some important chemical risks are outlined below, including relevant regulations connected to them and risk factors for them arising in fish products.
- These risks include; polycyclic aromatic hydrocarbons, heavy metals, histamine, and polybrominated diphenyl ethers.
In addition to the microbiological hazards, there are also chemical contaminants that should be considered by a comprehensive HACCP scheme for the manufacture of food. Important chemical hazards associated with seafood and smoked fish includes:
- Polycyclic aromatic hydrocarbons (PAHs); derivatives of PAH, such as nitro-PAH or oxygenated PAH, and to a lesser extent also N-nitroso compounds and heterocyclic aromatic amines are carcinogenic molecules generated during the combustion of wood during the traditional smoking of fish (Varlet et al. 2007). A comprehensive listing of the issues with PAH in smoked foods generally, and strategies to reduce their concentrations has been compiled by the Codex Alimentarius Commission of the UN Food and Agriculture Organisation, and is available here. Although unprocessed fish muscle can contain trace quantities of PAHs, most of the PAHs in smoked foods comes from wood smoke (Stołyhwo and Sikorski, 2005). Different PAHs and their derivatives differ in carcinogenic potency, but even those that are regarded as not highly carcinogenic, may act synergistically with other PAHs, effectively increasing their carcinogenicity (Stołyhwo and Sikorski, 2005). There are a number of research publications that have acknowledged PAHs as a public health hazard and that have sought to decrease the concentrations of PAH in smoked fish and other foods (Varlet et al. 2007; Nithin et al. 2020). In general, liquid smoked fish will generate a product with lower PAHs compared with smoke from combusting wood (Stołyhwo and Sikorski, 2005; Nithin et al. 2020). Liquid smoke can be applied as a vapour from heated plates. Varlet et al. (2007) compared different smoking methods and concluded that vapour application gave the lowest levels of PAHs in fish at low cost, with good application control and with good between batch reproducibility. The protection of public health from the carcinogenic properties of PAHs are covered by food safety regulations. For example, regulation 1334/2008 limits the concentration of benzopyrene to 0.03 μg kg−1 in liquid smoke flavourings. There is currently a derogation in EU law in regard to PAH concentrations in traditional products, e. g. Arbroath smokies that still applies in the UK. The derogation is part of Commission Regulation (EU) No 1327/2014. The derogation means that tolerated PAH levels may be different in traditionally smoked fish products intended for domestic consumption. Processors should check with their local authorities if they are unsure whether their product falls into this category.
- Heavy metals. In polluted aquatic ecosystems such as freshwater lakes used for industrial purposes, there can be an accumulation of metals that increases with ascension of the food chain (Dallinger et al. 1987). In some cases, the elevated concentration of metals can be high enough to make the consumption of fish harmful to humans (Dallinger et al. 1987). The accumulation and transfer of a selection of metals in blue mussels farmed in a polluted river was studied to determine the amount of bioaccumulation of metals in rainbow trout by an Irish study (McEneff et al. 2017). The trout were fed muscles from either a contaminated, or an unpolluted source. Fourteen different metals were detected in the mussels collected from both sources. However, the mussels collected from the contaminated site contained three times more Co, Mo, Sn and V compared with the mussels collected from the unpolluted site. After the rainbow trout were fed the respective mussels for 28-days, the concentrations of As and Se in the trout muscle, and Pb, Se and Zn in the fish skin, were significantly greater in the fish feeding on contaminated mussels. The main human dietary exposure to toxic heavy metals is the consumption of fish (Dadar et al. 2016). However, aside from a few studies of the type undertaken by McEneff et al. (2017) there is a lack of information that quantitatively describes how metals accumulate through the food chain, although the toxicity of heavy metals and how they impact human metabolism is well established (Jaishankar et al. 2014; Zafarzadeh et al. 2017). FBOs should be aware there are criteria contained within regulation EC 1881/2006 and other legislation that set the maximum permitted concentrations in fish for some heavy metals such lead, mercury, and tin in fish.
- Scombrotoxin (Histamine). Scombroid poisoning in humans occurs after the ingestion of fresh, canned or smoked fish with high histamine concentrations (Visciano et al. 2020). Some species of fish have naturally high levels of free histidine, which is converted to histamine by a bacterial enzyme called histidine decarboxylase (Hungerford, 2010). Thus, scombroid poisoning is likely the result of product mishandling, including inadequate refrigeration, that allowed bacterial growth (Visciano et al. 2020). In contrast to L. monocytogenes, histidine and histamine are not destroyed by cooking or other heat treatments (Hungerford, 2010) and so scrombrotoxin is a good example of why a multi-pronged approach to food safety is required for robust consumer protection. There are food safety criteria for scrombrotoxin (histamine) under regulation EC 2073/2005, which are not greater than 200 and 400mg/kg histamine for dry salted and brined fish of stipulated species, respectively. Thus, regular histamine testing of some fish with the potential for high histamine concentrations is a legal requirement for processors.
- Poly Brominated Diphenyl Ethers (PBDEs). In addition to the hazards listed above, seafood is a potential source of persistent environmental contaminants such as pesticides and dioxins. Poly brominated diphenyl ethers have also become a cause of attention in seafood (Cruz et al. 2015). These compounds were used as coatings for manufactured flammable objects to reduce their combustibility. PBDEs are not readily degradable and historical imperfect recycling that allowed leaching from landfill, means PBDEs are now common contaminants of terrestrial soil and surface water (Cruz et al. 2015). The lipophilic nature of PBDEs promotes their concentration in cell membranes and in the organs of eukaryotic organisms, including seafood (Cruz et al. 2015; 2018). In humans and wildlife, PBDEs mimic thyroid hormones, and can cause gender, reproduction, and neurological alterations. As a prophylactic safety precaution, EU directive 2013/39 defined a new quality standard of ≤8.5 pg g−1 wet weight for total PBDEs in the biota of an environment.
References
Hungerford, J. M. (2010) Scombroid poisoning: a review. Toxicon 56, 231-43.
