1968 EVALUATIONS OF SOME PESTICIDE RESIDUES IN FOOD
Issued jointly by FAO and WHO
The content of this document is the result of the deliberations of the
Joint Meeting of the FAO Working Party of Experts and the WHO Expert
Committee on Pesticide Residues, which met in Geneva, 9-16 December,
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
WORLD HEALTH ORGANIZATION
The definitions hereunder have been adopted by the joint meetings for
use in the reports and the associated monographs.
A pesticide residue is a residue in or on a food of any chemicals used
for the control of pests and the term includes derivatives of such
chemicals. The amounts are expressed in parts by weight of the
chemical and/or derivative per million parts by weight of the food
In interpreting this definition it is proposed to include the
consideration of any substance which may, at a given time, be known to
be derived from the product and which may be held to influence the
toxicology of the residue. Residues from unknown sources (i.e.
background residues) will be considered as well as those from known
uses of the chemical in question. The term pesticide will be held to
include any constituent of a pesticide used for the control of pests
during the production, transport, marketing or processing of food or
which may be administered to animals for the control of insects or
arachnids in or on their bodies; it will not apply to antibiotics or
other chemicals administered to animals for other purposes, such as to
stimulate their growth or to modify their reproductive behaviour, or
to fertilizers or, at least for the present, to other substances,
other than herbicides, used to influence the rate of growth of plants.
A negligible residue is an amount of a pesticide residue that is
regarded as toxicologically insignificant.
An unintentional residue is one which occurs in a food as a result of
circumstances not designed to protect the food against pest attack.
For this purpose the range of pesticide uses is as indicated under
'pesticide residue'. The food should be specified in each case and the
term includes products such as milk and meat from treated animals.
Furthermore, the residue may be acquired at any stage in the growing
harvesting, distribution, marketing or processing of the food. The
unintentional residue also includes a residue of a chemical which
occurs in nature as part of the environment but which cannot be
distinguished from residues due to the use of pesticides. Residues
sometimes described as 'incidental', 'accidental' or 'background'
residues are included within this term.
Practical residue limit
The practical residue limit is the maximum unintentional residue (see
definition) allowed in a specified food.
A practical residue limit is the level of pesticide residue above
which a regulatory action may be taken. it applies to a specific
commodity and pesticide for which no tolerance has been established.
Observation of a residue level above the "limit" may be presumptive
evidence of violation of good agricultural practice; values below the
'limit' are presumed to result from incidental effects, including
possibly isolated effects, from other approved use of the pesticide.
Acceptable daily intake
The acceptable daily intake of a chemical is the daily intake which,
during an entire lifetime, appears to be without appreciable risk on
the basis of all the known facts at the time. It is expressed in
milligrams of the chemical per kilogram of body weight (mg/kg).
For this purpose 'without appreciable risk' is taken to mean the
practical certainty that injury will not result even after a lifetime
of exposure. Furthermore, for a pesticide residue, the acceptable
daily intake is intended to give a guide to the maximum amount that
can be taken daily in the food 'without appreciable risk' to the
consumer. Accordingly, the figure is derived as far as possible from
feeding studies in animals and/or in man. The studies are usually
conducted with the pesticide chemical itself. However, if the residues
of a pesticide are known to consist of more than one chemical which
may influence the toxicology of the residue (see definition of
'pesticide residue'), information on the toxicology of the respective
residual chemicals and, where appropriate, their respective acceptable
daily intakes has to be taken into account when assessing the risks.
Acceptable daily intakes are always subject to revision at any time in
the light of new information.
Temporary acceptable daily intake
A temporary acceptable daily intake is one which is recommended for a
A specified period is provided to enable additional biochemical,
toxicological or other data to be obtained, as may be required for
establishing an ADI. (See 'Further Work Required'). In such cases any
recommendation will normally involve the application of a safety
factor, the size of which will be dependent upon the nature of the
toxicity of the compound, but which will be larger than that normally
used in estimating acceptable daily intakes. In all cases the position
will be reviewed not later than the first meeting following the
A tolerance is the maximum concentration of pesticide residue that is
permitted in or on food at a specified stage in the harvesting,
storage, transport, marketing or preparation of the food, up to the
final point of consumption, and the concentration is expressed in
parts by weight of the pesticide residue per million parts by weight
of the food (ppm).
A temporary tolerance is one that is valid for a limited time which is
specified in each case.
Such tolerance recommendations are made when they are derived from
Temporary Acceptable Daily Intakes or from figures for commodities at
some stage prior to the point of consumption as food and when, in the
absence of adequate information on losses of residue during storage,
handling or preparation, calculations based on such figures using
appropriate food consumption data reveal a theoretical possibility
that the acceptable daily intake could be exceeded. In cases of this
kind, to obtain assurance that acceptable daily intakes are not likely
to be exceeded in practice, and before proceeding to recommend
temporary tolerances, the meeting considers information on the actual
occurrence of residues in food as offered to the consumer. This
information includes the results from subjective sampling and/or from
objective sampling, including total diet studies, in various countries
and particularly in places where pesticides are most widely used. In
all cases the position will be reviewed not later than the first
meeting following the specified date.
Good agricultural practice
Good agricultural practice is the recommended usage of a pesticide
which is necessary and essential for the control of a pest under all
practical conditions bearing in mind any toxicological hazards
The 'recommended usage' complies with the procedures, including the
formulation, dosage rates, frequency of application and pre-harvest
intervals recommended by appropriately trained specialists; it is the
usage that has been registered, approved or otherwise accepted for the
purpose by the relevant official department and which is normally
included on the label. Such recommended methods of application should
be based on supervised trials and other experimental work and should
take into account such variations in climate, in crop husbandry and in
incidence of pests as may occur under practical conditions from time
to time in the various places in which the pesticide may be used. For
this purpose good agricultural practice shall be held to include
practice in the control of pests during the storage, transport,
marketing and processing of foods.
Total diet studies
A total diet study is one designed to show the pattern of pesticide
residue intake by a person consuming a typical diet.
To make total diet studies random samples of food usually are
purchased in representative population centres in the country, or
district, concerned and weighed out in the proportions in which they
are consumed in the total diet. The weighed portions are then washed,
cooked or otherwise prepared in the normal way for table presentation
and then mixed to give a number of predetermined food group samples
comprising, for example, cereals, green vegetables, root crops, fruits
and preserves, fats, meats and milk. These groups are chosen with the
intention of minimizing the subsequent analytical problems; they also
serve to identify the areas of the diet which contribute most to total
residue present. The foods are purchased and prepared under expert
supervision with the requirements of the studies in mind; but
otherwise they resemble as far as possible the normal character of the
total diet. Water and beverages are included.
Each food group sample, prepared as above, is analysed for various
residues. This may involve several different analyses for each group.
The exact analytical procedure may vary from group to group. In
addition, from experience, it may become possible to omit certain
analyses for some groups. Thus, the different groups will not
necessarily be subject to exactly the same analytical procedure.
Similar studies have also been described as 'market basket studies'.
A subjective sample is one taken after a known, or a suspected, use of
a pesticide on a crop.
Subjective samples include those taken during the early stages of the
introduction of a pesticide into practical application when it is
desirable to ascertain the residues occurring after known methods of
application in the field, as well as those taken in circumstances
where there are reasons to suspect that good agricultural practices
have not been properly followed. Such samples may relate to crops from
specific sites or from districts, or from countries where particular
pesticides are known, or suspected, to have been used. Subjective
sampling, rather than total diet studies, is sometimes used to assess
the actual dangers to consumers, particularly where the sampling and
analytical facilities are limited: it enables the facilities to be
concentrated on those categories of food intake considered to offer
the greatest risks. Subjective sampling also enables certain of the
analytical difficulties encountered in total diet studies to be
An objective sample is a random or impartial sample.
The samples taken during total diet intake studies fall into this
Regulatory method of analysis
A regulatory method is one used for the determination of residues in
the course of the administration of legislation relating to the
For this purpose, it is often necessary to identify the nature of the
residue as well as to determine its level. Subject to any expression
of requirements in the particular law, the accuracy, precision and
sensitivity of a regulatory method need be sufficient only to
demonstrate clearly whether a tolerance level has been exceeded.
Usually regulatory methods are not specified in pesticides legislation
and at any given time there may be a number of methods available for a
Referee method of analysis
A referee method is one that has been specified, or agreed upon, for
use in the event of a dispute.
Referee methods are mainly required to settle disputes concerning the
level of a residue but procedures for identification of a residue may
sometimes have to be included in such methods. Referee methods lay
special emphasis on accuracy and precision, even if this may involve
equipment and experience not normally available in laboratories
undertaking regulatory work. Nevertheless some regulatory methods are
suitable for use as referee methods, although their evaluation by
interlaboratory comparisons is desirable before they are adopted as
Further work required
Further work required is work which must be done and properly reported
before acceptable daily intakes and/or tolerances can be recommended
In certain instances although acceptable daily intakes have been
established, further work has been considered to be essential to
remove doubts about the toxicological significance of some
experimental observations, and it has therefore been "required".
Results of the further work required should be made available not
later than the specific date mentioned, after which the compound will
be re-evaluated. The re-evaluation may be done at an earlier meeting
should relevant information become available.
Further work desirable
Further work desirable is work which, when properly reported, would be
expected to provide additional assurance that recommended acceptable
daily intakes and/or tolerances are adequate for the protection of the
health of the consumer.
Definitions of the terms Food factor, Permissible level and
Acceptable consumer level have not been included because they are
regarded as obsolete.