world cancer report - iarc
world cancer report - iarc
world cancer report - iarc
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FOOD CONTAMINANTS<br />
SUMMARY<br />
> Food may be contaminated by natural or<br />
man-made toxins, including substances<br />
shown to be carcinogenic in experimental<br />
animals and, in some cases, in<br />
humans.<br />
> Naturally-occurring carcinogens include<br />
mycotoxins, particularly aflatoxins,<br />
which contribute to causation of liver<br />
<strong>cancer</strong> in Africa and Asia.<br />
>Food can be contaminated by residual<br />
pesticides. Small quantities of heterocyclic<br />
amines, which are mutagenic and<br />
carcinogenic in experimental animals,<br />
can be generated during food processing<br />
and cooking.<br />
> Means to reduce and, in some cases,<br />
eliminate food contamination include<br />
storage hygiene, appropriately enforced<br />
by regulation.<br />
> The burden of <strong>cancer</strong> attributable to<br />
food contamination is difficult to quantify,<br />
except in some defined instances<br />
(e.g. aflatoxin B1).<br />
Differences between diets eaten by<br />
diverse communities, in terms of amount<br />
and relative proportion of the major food<br />
groupings (vegetable content, fat content<br />
etc) exert a major influence on the distribution<br />
of <strong>cancer</strong>s of the digestive tract and<br />
some other organs (Diet and nutrition,<br />
p62). By comparison, only a very minor<br />
part of the <strong>world</strong>wide burden of <strong>cancer</strong> is<br />
attributable to contamination of foodstuffs<br />
by toxins recognized to be chemical carcinogens.<br />
Despite this global perspective,<br />
the issue warrants close attention because<br />
it may be a serious concern for particular<br />
communities and, irrespective of demonstrated<br />
<strong>cancer</strong> causation, food contamination<br />
can be rectified. Removal of carcinogenic<br />
contaminants requires that such<br />
contaminants are identified, and that ways<br />
are found to avoid their inclusion, or generation,<br />
in food. Such public health aims<br />
are amenable to regulation. Contamination<br />
of water is not included in the present discussion,<br />
but is considered elsewhere<br />
(Environmental pollution, p39).<br />
Contamination of food may occur directly<br />
during its production, storage and preparation.<br />
For example, grains and cereals are<br />
subject to fungal growth and contamination<br />
by mycotoxins. Indirect contamination<br />
of food can occur when animals have been<br />
given contaminated feed or been otherwise<br />
treated with various products. The<br />
most contentious residues occurring in<br />
meat, milk and eggs are antibacterial<br />
drugs, hormonal growth promoters and<br />
certain pesticides, heavy metals and<br />
industrial chemicals. An additional category<br />
of contaminants comprises those generated<br />
in the course of food preparation.<br />
Naturally occurring contaminants<br />
Food may be contaminated by mycotoxins,<br />
the presence of one such agent being<br />
indicative of the possibility that others are<br />
also present. A single fungus can produce<br />
several mycotoxins and food or feed can<br />
be contaminated by several varieties of<br />
mycotoxin-producing fungi. Only a small<br />
number of mycotoxins have been categorized<br />
as carcinogenic hazards.<br />
Aflatoxins<br />
Aflatoxins are a family of related compounds<br />
(designated B 1, B 2, G 1, G 2 and M)<br />
which occur as food contaminants in hot,<br />
humid parts of the <strong>world</strong>, with particularly<br />
high levels in traditional diets based upon<br />
maize and groundnuts (peanuts) of sub-<br />
Saharan Africa, South-East Asia and South<br />
America. Aflatoxins are products of the<br />
Aspergillus fungi and particularly accumulate<br />
during storage of grains. In many<br />
countries, including Europe and North<br />
America, aflatoxin contamination is recognized<br />
as a hazard and aflatoxin levels in<br />
susceptible foods are subject to monitoring<br />
and associated regulatory control.<br />
The detection of aflatoxin adducts on<br />
serum albumin is indicative of human<br />
exposure and, in regions where aflatoxins<br />
are a common food contaminant, such<br />
adducts are detectable in up to 95% of<br />
the population. In these regions, chronic<br />
hepatitis virus infection (essentially<br />
involving hepatitis B virus, HBV) occurs in<br />
up to 20% of the population. Together,<br />
aflatoxin exposure and HBV infection are<br />
the main risk factors accounting for the<br />
high incidence of hepatocellular carcinoma<br />
in some regions of Africa, Asia and<br />
South America [1].<br />
Aflatoxin B 1 (the most common aflatoxin)<br />
causes liver <strong>cancer</strong> in experimental animals.<br />
In liver cells, aflatoxin B 1 is metabolized<br />
to form an epoxide which binds to<br />
the N7 position of specific guanines, leading<br />
to the formation of G to T transversions<br />
[2] (Carcinogen activation and DNA<br />
repair, p89). Mutations induced by aflatoxin<br />
B 1 are found in several genes<br />
involved in hepatocellular carcinogenesis.<br />
In particular, aflatoxin B 1 induces a typical<br />
Fig. 2.27 Groundnuts (peanuts) are particularly<br />
susceptible to contamination with aflatoxins in<br />
some regions, such as West Africa.<br />
Food contaminants 43