• Fish soup has been regarded as a nutritious food and is considered by the Chinese traditionally to be particularly good for lactating women as part of the postpartum confinement diet. Public concern has been raised that the contaminants present in the fish may leach into the soup which may pose risk to their foetus and infant if the pregnant or lactating women drink fish soup frequently.
• Fish contain high quality proteins and many essential nutrients, such as long-chain n-3 polyunsaturated fatty acids (LCn3PUFAs) (i.e. omega-3 fatty acids). On the other hand, fish may also contain higher levels of contaminants such as methylmercury, and dioxins and dioxin-like polychlorinated biphenyls (PCBs).
• In recent years, the risks and benefits of consuming fish have aroused public debates and drawn attention of the scientific community. According to the assessment conducted in January 2010 by the Joint FAO/WHO Expert Consultation on the Risks and Benefits of Fish Consumption, it concluded that moderate consumption of a variety of fish is recommended. However, risks and benefits assessment of fish soup consumption has not been reported. Hence, the Centre for Food Safety (CFS) conducted a study to evaluate the risks and the benefits of fish soup consumption in a limited scale and is going to submit the results to World Health Organization.

Safety and Public Health Significance

• Methymercury, an organic form of mercury, is the most toxic form of mercury. The primary health effect of methylmercury is impaired neurological development of foetuses, infants and children. Methylmercury can cross the placenta into the foetus in pregnant women and build up in the foetal brain and other tissues. In addition, infants may be exposed to methylmercury through breast milk but its transport from blood to milk is less efficient than transport across the blood-brain and blood-placenta barriers. Therefore, methylmercury exposure of infants through lactation is lower than exposure of foetues.
• Dioxins and dioxin-like PCBs are persistent organic pollutants (POPs) ubiquitous in the environment. Dioxins occur naturally and as by-products of combustion and various industrial processes, in contrast, PCBs were manufactured in the past for a variety of industrial uses, and their uses have been banned by most countries since 1970s. Concerns on dioxins and dioxin-like PCBs are mainly due to their toxic effects on a number of systems, including endocrine and immune systems, the developing nervous system and their cancer-causing potentials. Dioxins and dioxin-like PCBs can excrete from breast milk.

Risks and Benefits Assessment

• The study on the risks and the benefits of fish soup consumption focused on five kinds of fish, which are considered common for preparing fish soup for women after childbirth or lactating women in Hong Kong. They are small snakehead, grass carp tail, flat-head, crucian carp and catfish. The levels of dioxins and dioxin-like PCBs, methylmercury, and LCn3PUFA including eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) in the fish soup were determined ( see Table ). In general, a higher level of methylmercury / dioxins and dioxin-like PCBs was found in fish soup with a higher LCn3PUFA content.
• Our dietary exposure assessment suggests that adverse effect of the local population including the women of childbearing age due to the exposure of methylmercury or dioxins and dioxin-like PCBs from the fish soup alone is unlikely.
• The effects of prenatal exposure to DHA and EPA versus methylmercury on child IQ were compared. The risk and benefit comparison was conducted with reference to the approach recommended by the Joint FAO/WHO Expert Consultation on the Risks and Benefits of Fish Consumption (January 2010). The findings suggested that the benefits gained from consumption of fish soup outweighed the risks. For example, consumption of catfish soup, which was found containing the highest methylmercury level and also the highest DHA and EPA content, resulted in an estimated net gain of 4.6 – 5.5 IQ points if the child's mother consumed four bowls of catfish soup per day.

Advice to public

• The public is advised to maintain a balanced and varied diet, including a variety of fruits and vegetables.
• Since fish contain many essential nutrients, such as omega-3 fatty acids and high quality proteins, moderate consumption (including pregnant women and young children) of a variety of fish is recommended. In addition, fish soup can be a source of nutrients such as omega-3 fatty acids.
• Pregnant women, women planning pregnancy and young children should avoid eating predatory fish and the types of fish that may contain high levels of methylmercury (e.g. tuna, alfonsino, shark, swordfish, marlin, orange roughy and king mackerel) ( For reference of study report on methylmercury in different types of fish, please click here).

Risk Assessment Section
December 2013