 Hijiki and Arsenic
Hijiki ( Hijiki
photos ) Hijiki is an uncommon kind of seaweed harvested mainly from seas off
Japan and Korea . It is generally sold in dry and shredded form (short
coarse strips) and is almost black in colour. Because of these appearances,
dried hijiki seaweed is physically distinct from other varieties of seaweed
such as arame, kombu, wakame and nori . It is commonly used as starter
or appetiser in Japanese and Korean cuisines. Hijiki can also be used
as an ingredient in salad, soup and vegetarian dishes. Unlike nori seaweed
which is usually sold in dried, thin sheets, hijiki is not used in rolling
sushi. In Hong Kong , hijiki seaweed is usually sold in Japanese supermarkets
and restaurants. Hijiki may contain arsenic naturally in high levels, especially the more
toxic inorganic form. On the other hand, overseas studies show that arsenic
contents in other seaweed varieties such as kombu are mainly in the less
toxic organic form and the levels are much lower than those found in hijiki.
Moreover, one of these studies also reveals that none of the other varieties
is found containing detectable level of inorganic arsenic. Based on these
findings, seaweed other than the hijiki variety is safe to eat with respect
to its arsenic content. Arsenic Arsenic is a metalloid present naturally in the earth's crust and is
found in trace amounts in rock, soil, water and air. It exists in both
organic and inorganic forms in foods. Primary route of exposure in humans
to arsenic is mainly through ingestion of foods, especially aquatic foods,
which contain relatively high levels of arsenic. Scientific evidence shows that low dosage of arsenic as low as a few
grams could cause acute or sub-acute toxicity. In general, inorganic arsenic
is more toxic than the organic form. In acute toxicity, the patient will
suffer from severe inflammation of gastrointestinal tract, resulting in
vomiting and diarrhoea, followed by more serious consequences such as
multi-organ failure of the body. Other signs and symptoms include fever,
emaciation, increased irritability, hair loss, etc. Chronic toxicity due to arsenic may lead to skin lesions, nerve damage,
skin cancer and diseases of the blood vessels. The Joint Food and Agriculture
Organization / World Health Organization Expert Committee on Food Additives
(JECFA) has evaluated arsenic and established a provisional tolerable
weekly intake (PTWI) of 15 £gg/kg bw/week to inorganic arsenic. PTWI is
an estimate of the amount of a contaminant that can be ingested over a
lifetime without appreciable risk. An intake above the PTWI does not automatically
mean that health is at risk. Transient excursion above the PTWI would
have no health consequences provided that the average intake over long
period is not exceeded as the emphasis of PTWI is a lifetime exposure.
The International Agency for Research on Cancer, which is part of WHO,
has classified arsenic as carcinogenic to humans. Local situation Samples of hijiki taken under the Food Surveillance Programme of the
Food and Environmental Hygiene Department (FEHD) in November 2004 found
that the arsenic levels of the samples exceeded the statutory limit. Offenders
upon conviction are liable to a fine of $50,000 and to imprisonment for
6 months. All the products in question have been withdrawn from the market.
Close surveillance over any sale of hijiki seaweed in local market will
continue. Due to the high level of inorganic arsenic present, consumption of a
relatively small amount of hijiki can significantly increase the dietary
exposure to arsenic. Further safety assessment showed that occasional
consumption of small amount of hijiki is unlikely to cause adverse health
effect. However, vegetarians and people who are fond of hijiki are at
greater risk. Considering the highest level of inorganic arsenic detected in our samples,
i.e. 130 mg/kg (expressed as As2O3), for a 60-kg person, consumption of
as little as 9 grams per week would lead to inorganic arsenic exposure
reaching the PTWI. For children with a lower body weight, consumption
of a smaller amount of hijiki may still result in exposure exceeding the
PTWI. Advice to public
- To avoid consumption of hijiki and avoid choosing hijiki as food ingredient.
- To choose foods from markets carefully in particular prepackaged ones
by reading their labels to make sure they do not contain hijiki.
- Except the hijiki variety, there is no need to stop eating other varieties
of seaweed as they contain high levels of minerals and trace elements
such as iron and iodine that are beneficial to health.
Advice to trade
- To avoid sourcing hijiki as food ingredient .
- T o check the seaweed supply and its label carefully to ensure it
is not hijiki.
- To avoid using hijiki as ingredient in any kind of foods such as starters,
appetisers in Japanese or Korean cuisines, etc, and to use other safe
food ingredients as substitutes for hijiki.
Risk Assessment Section, FEHD
January 2005 |
