View report page

The Metallic Contaminants Sub-Committee appointed by the Food Standards Committee consider
and recommend as to the limits for any metals or other injurious elements, and whether
they should be applied to foods generally, to any particular food, or groups of foods.
Shellfish appear to have been excluded from food standards legislation because of the high
levels of metallic elements naturally encountered and because even at those levels there is no
apparent hazard to health.
Shellfish may ingest and absorb lead compounds present in sea and estuary waters. Some of
these sources are uncontrollable but others are attributable to human agency and can be regulated.
The Lead in Food Regulations 1961 do not apply to crustacea and molluscs for which a natural
lead content in excess of 2 p.p.m. has been established. The Regulations permit up to 5 p.p.m.
in canned fish.
In view of the high natural copper content of shell fish and crustacea, a limit has not been
specified but the Sub-Committee recommend that the sale of shellfish containing copper in
excess of 20 p.p.m. should be permitted if it can be shown that the copper is of natural occurrence.
Traces of copper in food is a less serious problem than is the case of lead and arsenic. The
Arsenic in Food Regulations, 1959, do not apply to crustacea and molluscs or edible seaweed
for which a natural arsenic content in excess of 1 p.p.m. has been established.
P.C.Wood (11) has reported that Copper and Zinc in concentrations in excess of 250 and 1,200
m.g/l respectively, have been found in oysters from estuaries polluted by waters from old mine
workings. These oysters are unacceptable because of the green coloration of the tissues and
the bitter metallic flavour imparted by the metals.
The following table of emetic and toxic doses (12) can be related to shellfish in order to
arrive at a decision as to fitness on the basis that 1 p.p.m. is approximate to 1 mgm. per kilo -
Copper: Emetic dose 300 mgm. of copper sulphate.
Arsenic: Fatal dose about 100 mgm. Arsenious oxide.
Zinc: Emetic dose 1 -2 gms. of zinc sulphate.
Tin: An unofficial tolerance of 250 p.p.m.
The presence of methyl mercury in imported Japanese tinned oysters was discovered by the
Port of London Health Authority in 1961. The amount, when present, was considered to be of no
great hazard to health. However, methyl mercury in tuna fish imported into the United Kingdom
was confirmed by the Government Chemist and resulted in a statement by the Minister of Agriculture,
Fisheries and Food and Press Notices (13).
The Bacteriological Examination of Imported Shellfish
The bacteriological examination of imported live shellfish from Denmark (mussels) and imported,
cooked, peeled, frozen shellfish from Japan, Korea, Canada and Bahrein has been a
regular feature of imported food inspection. In 1967 the Association of Sea and Air Port Health
Authorities agreed a "recommended standard" which has been faithfully applied by the Authorities
since that date. From time to time additional and more specific sampling has had to be carried out
as was the case in 1969 arising from the blooming of dino-flagellates which caused shellfish
food poisoning in Northumberland and Denmark (14).
The Public Health (Shellfish) Regulations, 1934, places responsibility on a local authority,
through their Medical Officer of Health, for ensuring that the health of the public is safeguarded
from the consumption of oysters, mussels and cockles derived from layings in prescribed areas.
There is nothing in the law to prevent the public from eatinq shellfish derived from locations outside
the prescribed areas. However, a Medical Officer, on becoming aware of a possible danger
to public health, is obliged to report his findings to the local authority with a view to an order
being made.
There are various ways whereby a Medical Officer of Health may become aware of a danger
to public health. This may be on notification of food poisoning attributed to the consumption of
shellfish derived from the district, from intermittent sanitary inspections of the district or from
planning and development applications through the close and friendly liaison which should
exist between a port or harbour authority, river authority and sea fisheries committee. Information
will also be derived from the Ministry of Agriculture, Fisheries and Food and the Department
of Health and Social Security. It is significant that in the case of the Port of London, the Health
Authority for the Port have made two orders prescribing areas and one joint Public Health Shellfish
Regulation. At present they are carrying out a survey and research in the estuarial waters in
order that they may consider the making of new orders or modifying or extending original orders.
The polluted condition of ports, rivers and estuaries is also of concern to port health
authorities in the advice sought by ship owners in relation to the filling of water ballast tanks
which may ultimately contaminate the ship's potable water by accidental contamination. Advice
is increasingly sought in relation to the use on board ship of distillation plants whilst in port.
A pin hole in the condenser section can have disastrous results.