Heavy metals in seafood: maximum allowable limits

Seafood, in particular fish are a good source of protein and omega 3 fatty acids. As well these beneficial nutrients, seafood can contain trace amounts of different metals. Heavy metals present in water both naturally and introduced to the water system are absorbed by animals living in that environment. While trace elements are found in most seafood, much higher levels are found in predatory sea animals, due to the cumulative effect of their consumption. Analysis of trace metals is important to remain compliant with different countries food laws.

The Australian Food Standards Code: Schedule 19-4 provides the maximum allowable limits for metal contaminants. In crustacea and fish Arsenic is permitted up to 2.0mg/kg and at 1.0mg/kg for molluscs.  Cadmium only has a specified limit in Molluscs (excluding dredge/bluff oysters and queen scallops) of 2.0mg/kg. Mercury limits are covered by Schedule 19-7: Mean and maximum levels of mercury in fish, crustacea and molluscs. Schedule 19-7 has a maximum and mean level of allowable mercury. For gemfish, billfish (including marlin), southern bluefin tuna, barramundi, ling, orange roughy, rays and all species of shark the mean level can’t exceed 1.0mg/kg. If there are ten or more sample units, the maximum permitted level is 1.5mg/kg. For five sample units there is no maximum set as long as the mean level is met and if there are insufficient units to sample, there is no mean level set, but a maximum of 1.0mg/kg. The number of samples required are dependent on catch size and is specified in subsection S19—7(2). For other fish, fish products, crustacea and molluscs similar sampling unit rules apply. For ten or more sample units, the mean level is 0.5mg/kg and the maximum is 1.5mg/kg. There isn’t a maximum for five unit samples, but the mean level must not exceed 0.5mg/kg. Again, if there are insufficient unit samples the maximum is 1.0mg/kg.

In China the maximum levels are outlined in GB 2762-2012:  National Food Safety Standard Maximum Levels of Contaminants in Food. Arsenic is permitted in fish and their products at 0.1mg/kg while other aquatic animals and their products are permitted up to 0.5mg/kg. Lead and cadmium in seafood is more specifically defined. Lead is allowed in fish and crustaceans at 0.5mg/kg while bivalves are limited to 1.5mg/kg. Fresh and frozen aquatic animals (excluding fish, crustaceans, bivalves) and Aquatic products (excluding jellyfish products) can have a maximum of 1.0mg/kg and jellyfish are permitted a maximum of 2.0mg/kg lead. Cadmium is permitted in fresh and frozen fish at 0.1mg/kg and in fresh and frozen crustaceans at a maximum of 0.5mg/kg. Fresh and frozen bivalves, gastropods, cephalopods, echinoderms are permitted a maximum of 2.0mg/kg. Preserved products have different permissible levels of cadmium. Canned fish (excluding canned anchovies, swordfish) has a limit of 0.2mg/kg and canned anchovies and swordfish have a maximum of 0.3mg/kg. Finally, for cadmium, there is another category called other fish products. Other fish products (except anchovy and swordfish products) have a limit of 0.1mg/kg while anchovy and swordfish products are permitted up to 0.3mg/kg. Mercury is set at a maximum of 0.5mg/kg in aquatic animals and their products, except for predatory fish which have a maximum of 1.0mg/kg.

The European Union specifies maximum levels in The European Food Safety Authority (EFSA), Regulation (EC) No 629/2008 3.2.13. Cadmium is permitted in the muscle meat of bonito (Sarda sarda), common two-banded seabream (Diplodus vulgaris), eel (Anguilla anguilla), grey mullet (Mugil labrosus labrosus), horse mackerel or scad (Trachurus species), louvar or luvar (Luvarus imperialis), mackerel (Scomber species), sardine (Sardina pilchardus), sardinops (Sardinops species), tuna (Thunnus species, Euthynnus species, Katsuwonus pelamis), wedge sole (Dicologoglossa cuneata) at a maximum of 0.1mg/kg. In muscle meat of bullet tuna (Auxis species), the limit is 0.2mg/kg, the limit for muscle meat of anchovy (Engraulis species) and swordfish (Xiphias gladius) is 0.3mg/kg and for the muscle meat of all other fish the limit is 0.05mg/kg. Crustaceans, excluding brown meat of crab and excluding head and thorax meat of lobster and similar large crustaceans (Nephropidae and Palinuridae) have a maximum cadmium level of 0.5mg/kg while bivalve molluscs and cephalopods (without viscera) have a limit of 1.0mg/kg. Mercury has a maximum limit of 1.0mg/kg in the muscle meat of anglerfish (Lophius species), Atlantic catfish (Anarhichas lupus), bonito (Sarda sarda), eel (Anguilla species), emperor, orange roughy, rosy soldierfish (Hoplostethus species), grenadier (Coryphaenoides rupestris), halibut (Hippoglossus hippoglossus), kingklip (Genypterus capensis), marlin (Makaira species), megrim (Lepidorhombus species), mullet (Mullus species), pink cusk eel (Genypterus blacodes), pike (Esox lucius), plain bonito (Orcynopsis unicolor), poor cod (Tricopterus minutes), Portuguese dogfish (Centroscymnus coelolepis), rays (Raja species), redfish (Sebastes marinus, S. mentella, S. viviparus), sail fish (Istiophorus platypterus), scabbard fish (Lepidopus caudatus, Aphanopus carbo), seabream, pandora (Pagellus species), shark (all species), snake mackerel or butterfish (Lepidocybium flavobrunneum, Ruvettus pretiosus, Gempylus serpens), sturgeon (Acipenser species), swordfish (Xiphias gladius), tuna (Thunnus species, Euthynnus species, Katsuwonus pelamis).

To analyse trace amounts of metals in seafood Inductively Coupled Plasma Mass Spectrometry (ICP-MS) can be used as it can quantify extremely low concentrations of different elements. Before being introduced to argon plasma causing ionisation, nitric acid alone or in combination with hydrochloric is used to digest samples. Ionised samples can then be quantified in the mass spectrometer component of the unit.

While many countries have very specific legislation on the concentration of trace metals in seafood, knowledge of the legislation and analysis makes it possible to conform with your product.

U.S. Food and Drug Administration (04/11/2018) What You Need to Know About Mercury in Fish and Shellfish, Available at: https://www.fda.gov/food/foodborneillnesscontaminants/metals/ucm351781.htm (Accessed: 20/08/2018).

European Commission (02/07/2008) Commission Regulation (EC) No 629/2008 of 2 July 2008 amending Regulation (EC) No 1881/2006 setting maximum levels for certain contaminants in foodstuffs, Available at: https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32008R0629 (Accessed: 20/08/2018).

Australia New Zealand Food Standards (25/03/2015) Australia New Zealand Food Standards Code – Schedule 19 – Maximum levels of contaminants and natural toxicants, Available at: http://www.foodstandards.gov.au/code/Documents/Sched%2019%20Contaminant%20MLs%20v157.pdf (Accessed: 20/08/2018).

National Standard of the People’s Republic of China: GB 2762-2012 ( 01/06/2013) National Food Safety Standard Maximum Levels of Contaminants in Food, http://www.seafish.org/media/publications/china_max_levels_of_contaminants_in_food.pdf