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 µg/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.
Last
revision date: 20-01-2005