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APPENDIX VI (continued)
(1) Restriction of Choice of Pesticide
That consideration should be given to a policy of reducing the number of potentially toxic
residues by limiting the choice of remedies for any particular crop to, say, two or three products
which shall have been recommended by an independent authority, e.g., one of the agricultural
or horticultural research stations acting in conjunction with the General Medical Council, as
having the lowest toxicity to human beings whilst affording adequate control of the pests to
which the crop is subject.
It is recognised that such a policy would involve drastic re-organisation among the manufacturers
concerned. But it is felt that the interference and disadvantages to the chemical trade
would be more than balanced by the following advantages :
(a) the advantage to the farmer or market gardener in having the best and safest known remedies
or prophylactices for his purposes ;
(b) the reduction in manufacturing costs that should result from the larger quantities of fewer
products required ;
(c) the safeguarding of public health by avoiding as far as possible the more toxic products;
(d) the simplifying of such analytical control as might still be necessary;
(e) permitting the thorough toxicity trials necessary for a basis of official limits by reducing the
immense number of pesticides now in use to a manageable few.
It is not, of course, suggested that the search for better and safer pesticides should be suspended,
but merely that use should be restricted to the two or three most suitable compounds at
any given time.
(2) Addition of Tracers
Secondly, that consideration should be given to a policy of requiring by Government Order the
incorporation of an easily detectable substance with any toxic pesticide before sale to a user.
The use of a different tell-tale, or tracer, for each pesticide would enable an analyst, perhaps any
other interested person, to discover by a simple examination or test what compound, or at least
what class of compounds, was likely to have been used. The appropriate method of analysis
could then be carried out, without loss of time; and the absence of the respective tracers
would save laborious, time-consuming and unnecessary analyses for compounds which had not
been used.
Precedents for the addition of tracers to aid analysis exist in the addition of cornflour to
margarine during the War (to distinguish between "Standard" and "Special" grades), and in the
addition of diphenylamine and a red dye to "Commercial" petrol.
To be suitable for the purpose the tracers selected would have to satisfy the following
requirements, viz. to be —
(1) non-toxic;
(2) stable, and at least as resistant to weathering as the pesticide;
(3) readily available and inexpensive;
(4) capable of identification in microgram quantities;
(5) uncommon substances and not normally associated with the crops on which they might be
used;
(6) non-reactive with either the crop or the pesticide, including its solvent or emulsifier, spreader,
sticker, or water.
It is suggested that a selection might be made from the following groups of substances:—
(a) Pigments. Two pigments (carbon black and ultramarine) and 30 coal tar dyes are regarded as
non-toxic and permitted in foods. The solubility of the dyes can be reduced by the formation of
the calcium or aluminium lakes (also permitted), or, alternatively, by absorbing the dyes on
suitable powdered resins, as in the manufacture of printing inks.
(b) Starches. A wide choice of starchy powders that are easily recognisable under a microscope,
such as potato, maize, rice, sago, bean, ginger, etc., is available. Turmeric powder falls under
both headings. Such starches can readily be coloured, with permitted dyes. Thus the nature of a
selected starch could be used to denote a particular group of pesticides, and the dye to denote
the specific member of the group. This system might permit the marking of well over a hundred
different pesticides; and, since the number of starch grains per microgram ranges from 70 in the
case of potato to 10,000 in rice, there should be little difficulty in recognising sub-microgram
quantities on the surface of fruit or vegetables.
(c) Chemicals. Substances that are capable of detection by a simple chemical test, and unlikely
to be toxic, in microgram quantities are known. The following might be considered:— Aluminium
powder (which can be produced in many colours); zinc dust; manganese dioxide; indicators,
soluble, insoluble and fluorescent; calamine and many other powdered minerals.