From Mark Simmonds, Whale and Dolphin Conservation Society
Bath
Christopher Williams emphasised the importance of not taking a
“single-substance approach” to the threat posed by pollution to human
intelligence
(Letters, 13 December, p 56). Another, related consideration that
arises from the study in the Faeroes, linking mercury in diet to problems in
mental development
(This Week, 22 November, p 4), might be whether or not this
link could have been foreseen.
In 1987, it was reported that long-term intakes of total mercury and
methyl-mercury in the Faeroes were close to the critical level decreed by the
WHO at which negative health effects might be expected. Dietary guidelines for
total mercury and cadmium were also exceeded.
Not surprisingly, the researchers involved recommended that the population of
the Faeroes should significantly restrict consumption of pilot whale tissues.
Whale kidney and liver, the main sources of the metal contaminants, are
apparently no longer eaten in the Faeroes.
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In 1994, in The Science of the Total Environment (vol 149, p 97), I
and some colleagues presented data on other contaminants in pilot whale blubber.
Using these and reported dietary intake levels, we calculated that the islanders
would be likely to be exceeding the US Food and Drug Administration’s tolerable
daily intake level for PCBs.
In the US, 2 parts per million (ppm) of PCBs is the official limit in food,
compared with the mean PCB level we found in pilot whale blubber of 20.6 ppm.
Similarly, we found that dieldrin levels were likely to exceed FAO/WHO
acceptable daily intakes.
Recommended dietary limits are generally calculated for an individual
chemical or a closely related group of chemicals. This does not seem to be an
adequate approach where a variety of contaminants with potential synergistic
effects are present in food.
However, on a simple quantitative basis, we felt that the PCBs probably
represented the greatest threat to the consumers. Indeed, dietary levels of PCBs
for the Faeroese were comparable to those of people who eat sports fish from the
Great Lakes, where developmental abnormalities had been associated with
consumption of contaminated fish in the 1980s.
Whilst the effects seen so far in the Faeroes are associated with exposure to
mercury rather than organochlorines, they are perhaps just the tip of the
iceberg of possible consequences. Surely, the time has come to stop taking an
unnecessary risk by eating such highly contaminated food.
