Vegetable food was, and is, the ultimate fundamental for human and animal life. It is, of course, complemented by foods of animal origin and in any consideration of chemicals in farming systems we must not lose sight of the contribution made by food producing animals to the total food supply.

Man, even in his most primitive stages, had to cultivate and store food and fight against his direct food-competitors; insects, fungi, bacteria, viruses, weeds and so on. These pests have accompanied mankind through the centuries, causing famines, poor health and a never-ending and seemingly futile struggle in the field. People prayed for protection of their crops, but they did not have sufficient tools to safeguard them.

We now do have the necessary tools and we need them badly because the world population is increasing far more rapidly than the world’s food production facilities. There is only limited perspective in extending world-areas for agriculture, horticulture and animal husbandry: in most developed countries these areas are tending to decrease whilst in developing countries the average increase in cultivated area is very slow, just as is the increase in crop yields per hectare.

Improvement in world food production therefore seems to lie in intensifying agriculture, horticulture and animal husbandry in a way that promises more and better crop and animal yields per hectare.

Agrochemicals and veterinary chemicals have played and continue to play an essential and indispensable part in modern and rational agriculture. Developments of the last 50 years have proved the enormous food production capacities of modern agricultural methods and the role of agrochemicals.

Throughout the world, but particularly in the industrialised countries, this role is being discussed for a variety of reasons. Uncertainty and anxiety about the possible hazards of agrochemicals are two underlying causes of this discussion. However, too great a gap between belief and facts may be a significant danger for the necessary development of even further improved agriculture and animal husbandry and greater food production.

Weeds, insects and fungus diseases reduce yield in the agriculturally developed countries by an average of 25%. In other regions, and in less favourable conditions, losses run at around 40%~ and in the case of rice, are actually estimated at 50% (Table 1), If suitable measures were taken to reduce these losses and at the same time to increase the yield per unit of land, it is conceivable that world food production could be trebled without adding to the land now under cultivation, for which there is in any case only limited scope.

Table 1. World crop losses of 5 major crops

	Rice	Maize	Wheat	Sugar	Cotton
Potential crop yield (,000 tons)	715,800	536,016	578,400	1,603,200	63,172
Actual crop 1978 (,000 tons)	378,645	362,582	437,236	737,483	41,757
Losses due to weeds(%)	10.6	13.0	9.8	15.1	5.8
Plant disease (.%)	9.0	9.6	9.5	19.4	12.4
Insects (%)	27.5	13.0	5.1	19.5	16.0
Total losses (%)	47.1	35.6	24.4	54.0	33.9
(.,000 tons)	337,155	200,434	141,164	865,717	21,415
Value (millions US$)	132,839	22,048	17,646	17,314	13,813
TOTAL(millions US$)	203,660

Source; FAO, 73.-77-78

Maximum productivity and efficiency in agriculture will depend on the development and wider use of improved practices, such as growing varieties with disease-and-insect resistance, application of proper kinds and amounts of fertiliser, efficient use of water on irrigated lands, and improved labour-saving machinery and equipment. But these advantages will be lost without the use of crop protecting chemicals.

There are pest problems today for which no satisfactory control methods exist to replace the use of chemicals and chemical pesticides will be the most dependable weapon of the applied biologist unless and until more acceptable techniques can be developed.

Historical

The use of toxic chemicals to combat pests is by no means new. Homer mentioned the fumigant value of burning sulphur, and Pliny (AD 79) advocated the insecticidal use of arsenic. By the 16th century, the Chinese were employing moderate amounts of arsenical compounds as insecticides, and at least three hundred years ago the first natural insecticide - the nicotine in extracts of tobacco was in use against the plum curculio and the lace bug. By 1828, another plant,. pyrethrum, was providing a second natural insecticide and in the middle of the 19th century, soap was added to the list of insecticides, for it was being used to kill aphids. Sulphur had been advocated as a fungicide on peach trees.

By the middle of the 19th century the first scientific and systematic studies were appearing. The range of materials used for pest control widened somewhat, but the materials remained of simple chemical composition. Experimentation was new, arsenical compounds led, for example, to the introduction in 1867 of an impure copper arsenite called Paris Green in an attempt to check the serious spread of the Colorado beetle. Bordeaux mixture, comprising copper sulphate, lime and water, was introduced as a fungicide in 1885 and until comparatively recent times Bordeaux mixture has remained one of the most important fungicides.

The use of pesticides accelerated between 1920 and 1940 and the number and complexity of the materials employed increased simultaneously. Two advances of note occurred during the Second World War. One of these, the discovery of the insecticidal properties of DDT, was made in Switzerland and the second, the introduction of insecticidal organophosphorous compounds, was a German success. Although discovered in 1942, the great insecticidal potential of DDT was not fully appreciated until 1944, when it enabled a severe typhus epidemic in Italy to be brought under control, In 1942 BHC (benzene hexachloride) was discovered in the biological laboratories on Imperial Chemical Industries Limited in England.

Several organic substances had found rather restricted use as fungicides long before the success of the organochlorine and organophosphorous insecticides gave additional impetus to the search for new materials. Organomercury compounds had been marketed as seed dressings since 1912. In 1931 a patent was issued to an American firm covering the fungicidal uses of the dithiocarbamates, a group of fungicides which has proved to be one of the most valuable introduced so far,

Organic herbicides of a more or less selective nature such as petroleum oils and dinitro-ortho-cresol assumed an increasing importance in the late 1930’s but it was discovery of the effect of the phenoxyacetic acid group of compounds in 1945 which opened up the field of potent, selective and safe herbicides.

At present, developing countries are using relatively little in the way of chemicals to control pests in the majority of crops. In developed countries the use of crop protecting chemicals has played a major role in the increased and more efficient production of food (Table 2), Pesticides provide immediate effective control at practical costs.

Table 2. - Usage of Agrochemicals in Developed and Developing Countries

Countries	Herbicides	Insecticides	Fungicides	Total
		% of total
Developed	90	55	88	80
Developing	10	45	12	20
	100	100	100	100

The Agrochemical Industry Today

World sales of agrochemicals in 1980 were estimated at $USll,800 million to users split up between four main usage groups, namely; herbicides, insecticides, fungicides and growth regulators and others (Table 3).

Table 3. Agrochemical Usage Groups

Group	Sales 1980 US $ billion
Herbicides	4.7
Insecticides	3.9
Fungicides	2.5
Growth regulators and others	0.7
TOTAL	11.8

The major crops which accounted for over 75 per cent of global use are set out in Table 4.

Table 4. Usage of Agrochemicals by Crop - 1980

Crop	US $ billion
Maize	1.5
Cotton	1.3
Rice	1.2
Soya beans	1.0
Wheat	0.9
Sugar beet	0.4
Vines, fruit and vegetables	2.5

Table 5. Minimum requirements for registration

	1950	1960	1970
Toxicology	Acute 50-90 feeding	toxicity day rat	Acute toxicity 90 day rat feeding 90 day dog feeding 2 year rat feeding 1 year dog feeding	Acute toxicity 90 day rat feeding 90 day dog feeding 2 year rat feeding 2 year dog feeding Reproduction 3 rat generations Teratogenesis in rodents Toxicity to fish Toxicity to shellfish Toxicity to birds
Metabolism	None	Rat		Rat and dog Plant
Residues	Food crops l ppm	0.l ppm Meat0.1 ppm Milk0.1 ppm	Food crops	Food crops 0.01 ppm Meat 0.1 ppm Milk 0.005 ppm
Ecology	None	None		Environmental stability Environmental movement Environmental accumulation Effects on all non- targets species

Toxicity and Hazards

Many people, when considering chemicals, including pesticides, fail to distinguish between toxicity and hazard. Toxicity, on the one hand, refers to the ability of a chemical to cause poisoning when administered in adequate quantity through specified routes. Hazard on the other hand means the probability that a substance will cause harm in the circumstances of usage.

Two distinct types of toxic effects (acute and chronic) can be observed from many poisons. Since, for any one poison, there may be little or no relation between either the mechanism of these two kinds of toxic action or the magnitude of the concentrations which evoke them, the two effects must be carefully distinguished. An acute toxic response is one which occurs shortly after application of a single dose of the poison. It is determined by the intrinsic toxicity of the substance to the organism and can often be traced to some specific disruptive effect at the biochemical level. A chronic effect, on the other hand, is one which sometimes occurs when an organism is exposed to repeated small and non-lethal doses of poison over a considerable period of time,

Most pesticides are not highly dangerous materials. Occupational pesticide poisoning is uncommon, most cases being due to accidental or intentional ingestion of large amounts. Safety problems are mainly confined to a few very highly poisonous substances which are so effective or so economical that at present they are unlikely to be supplanted. The hazard of a pesticide varies with its mode of formulation (e.g. solution, emulsion, powder, gas, granule, pellet, etc), and with its mode of application, which may be by dispersal as a spray, dust, smoke, gas, incorporation in soil, or by release from aircraft.

In a country in which primary industry is very important it is the responsibility of agricultural advisers and medical practitioners to be informed of the toxic manifestations of the major culprits in the wide range of agricultural poisons available today.

Many people may confuse accidents caused by direct exposure to chemicals with possible hazards presented by pesticide residues in air, water and food. There is no evidence that our drinking water supplies are contaminated to a level that would be injurious to man. Surveys carried out in the United States, Canada and the United Kingdom, where pesticides are used intensively, show that the food supply is both safe and nutritious. There is no evidence that anyone has been hurt by eating food that had residues of pesticides used in accordance with the label directions.

Analytical methods of determining chemical residues in foods and other materials are becoming fantastically sensitive and accurate. The level of pesticide residues found in food reflect the chemist’s ability to measure these “left-overs” but in no way suggest that the food is likely to cause harm to those eating it during a whole lifetime.

In situations where a significant proportion of users are illiterate, where methods of application depend largely upon manual labour and where transport and storage practices increase the risk of contamination of food, clothing and household commodities, the hazard involved in the use of many of the more toxic pesticides becomes high. A great deal of effort has to be expended in educating users in the precautions necessary to avoid unnecessary risks.

The safe, effective and economic use of pesticides requires not only a knowledge of the Pest and the crop but involves an appreciation of the chemical, biological, toxicological and metabolic features of each chemical under a variety of conditions.

Pesticides and the Environment

In recent years a tremendous amount has been said and written, particularly in North America and in parts of Europe, about the wholly bad effects of pesticides on the environment and their contribution to its pollution.

Whilst it cannot be denied that there has been indiscriminate and over-zealous use of highly potent pesticides in a number of localities, Australian experience has shown that when these same pesticides are used as tools for more efficient agriculture in an economy which does not provide for waste, no significant pollution of the environment occurs.

Not the least important factor contributing to the pollution of aquatic environments has been the discharge of pesticide chemicals in industrial effluents, domestic and municipal sewage and the dumping of unwanted pesticide chemicals.

The capacity of the soil to lock up and eventually destroy foreign substances is quite remarkable and there appears to be the minimum or accumulation of even the most persistent chemicals when these reach the soil as a result of application for crop protection, Obviously, however, it is the responsibility of each one of us to prevent the unnecessary pollution of the world in which we live and in which life must continue. There has been a significant change in attitude among manufacturers, research workers, administrators, users and the general public with the result that the handling and use of pesticides is now approached in a much more responsible manner. The most enlightened change is probably the recognition that difficulty with pesticides is part of a much larger difficulty -that of human adjustment to an intensifying technology. The difficulty of living with the modern waste products of technology has now been recognised as one problem with many facets. Environmental pollutants from whatever source - automobiles, sewers, industrial manufacture, agriculture - can and do produce ecological hazards. The ultimate risk of a degraded environment is the loss of biological productivity. No country can afford such loss.

Pesticides - A Risk/Benefit Analysis

The development and use of chemical pesticides has produced immeasurable benefits for mankind in general and western society in particular. Continued and expanded pest control will be necessary, and will require integration of all the methods which scientists can devise.

The food supply of Australia is the envy of the world, and the critical assurance that these abundant crops can be prof it- ably grown, harvested, and stored is due to pest control, at present largely with chemical pesticides. Fertilisers, hybrid seeds, and modern machinery set the limits of crop yields, but pest control helps assure that the bounty is not lost to the competitive forces of insects, weeds, and plant disease.

Pesticides have made possible a greater abundance and variety of agricultural products at far less cost to the consumer than would otherwise be the case. Their use has also resulted in foodstuffs of the highest quality; the housewife is now thoroughly accustomed to unmarred and blemish-free foods. Moreover, pesticides have saved millions of lives through eradication of disease-carrying insects. Except in certain areas of the world, malaria, typhus, and yellow fever have been eradicated or severely limited. Additionally, pesticides have had many less essential benefits such as the control of nuisance insects in the home and desirable recreational areas.

The use of pesticides has been accompanied by several ironies. They have been a major contributor to the upsurge in agricultural productivity over the past three decades. But from this productivity came the great surpluses, and the farmers’ temporary gains from increased efficiency have often been erased by lower prices. In another vein, the use of pesticides to eradicate disease-carrying insects throughout the world has sharply reduced the death rate and thus has been a substantial factor in the population explosion.

The concern is with the irony that pesticides also constitute a potential hazard to our health and are capable of contaminating our environment. Chemical pesticides kill pests because they are toxic, and because they are toxic some are also capable, in excessive dosages, of causing illness, even death in people and wildlife.

Man aspires to continually improve his lot and from his creative genius has come a parade of innovations, and civilisation has advanced. But virtually each beneficial innovation has its attendant risks; modern drugs save millions of lives but some people have died because of them; the automobile kills and maims but it has changed our lives generally for the better. Thus, society is continually faced with the task of balancing benefits against risks.

The concept of the benefit-risk equation has a compelling logic which all accept in principle. But going from principle to practice always is attended with disagreement and conflict. This occurs because a diverse society generates a diverse range of material and aesthetic interests and values. Conflict occurs even though all concur with the ultimate goal of the promotion of the public good.

Although all of us are consumers and all have a stake in an expanding and prosperous economy, our attitudes on pesticides and their regulation differ; the wildlife conservationist and the chemical manufacturer approach the subject from different perspectives, the housewife buying processed foods at the supermarket has different concerns than the farmer who grows the food.

In the introduction of technological innovations such as chemical pesticides, there is not sufficient information available which can measure with complete precision all the factors of the benefit-risk equation. Differing interests generate disagreements but the sharpness of these disagreements often varies inversely with the quality of available empirical data needed to evaluate alternative approaches and the general awareness of that information.

The public debate over pesticides is but one facet of a wider debate which reflects a greater sensitivity to the fundamental questions raised by the continuing and accelerating pace of man s modification of his total environment. Pesticides are but one factor and we are increasingly aware that our environment is being altered, perhaps even more dramatically, by air and water pollution, atomic fallout, and the population explosion.

These are manifestations of the great issues of our time -man s relationship to the world around him. As we come to appreciate more keenly the significance of this vast, accelerating, irreversible alteration of our environment, we recognise the need for stocktaking and the necessity of endeavouring to take into account all the multitude of complex relationships between man and his natural and artificial surroundings.

Reduced to its fundamentals, a risk/benefit analysis is a simple thing. Whether or not we are consciously aware of it, each and everyone of us is making risk/benefit judgements many times a day. You make such a judgement every time you drive a car, every time you cross a busy street, In fact, an assessment of risk versus benefit determines the way in which we lead our lives.

Three quotations from the literature on this subject may help to put the risk/benefit situation into its proper perspective.

The first quotation comes from Dr Clayton Yeutter, former Administrator of the Consumer and Marketing Service of USDA, who made the following remarks about eleven years ago:- “As with most issues, extreme positions may well be appealing, but they will be simplistic, and neither sensible nor practical. At the one extreme is no surveillance and no protection. This nation departed from that extreme many years ago and will never return.

But at the other extreme is condemnation of our entire food supply., far-fetched as that may seem. Obviously a middle ground, represented by all the protection that can be afforded in a reasonable manner, is in order. It is that which we seek, but which will require the work of many capable and dedicated people, both in and out of Government.

The second comes from Dr Robert Miki, former Director of the Office of Environmental Economics in the US Department of Commerce and is as follows:- “Environmental protection and economic growth are frequently conflicting goals and the conflict must be reconciled. It is imperative that technological achievability, economic feasibility, and environmental protectability be weighed together.”

The final quotation is taken from the well-known address “So reason might rule” by Earl Butz, formerly US Secretary of Agriculture:- “Clearly, man cannot have all he wants to consume and at the sane time maintain a super pure environment and a completely risk-free society.

If we are to continue to reap the benefits of technology in a time when the limits of our resources become more clear each day, we must first come to grips with just how we shall proceed to deal with our environmental idealism and our attitude toward risk.”

Obviously what we have to do is to define the border-line between acceptable and unacceptable risk so that, as Earl Butz said “Reason might rule in the use of technology in agriculture.”

Now let’s have a look at the two sides of the equation. The benefit can usually be measured with some accuracy. The use of a pesticide gives tangible results in the form of control over a pest problem or a disease problem in animals or crops. This can be expressed in terms of dollars and cents. It is, however, more difficult to put a value on the control of human disease.

The risk side of the equation, on the other hand, is by no means so easily defined. Most of the untoward events against which we are on guard have never occurred. Our inability to assess the true significance of this intangible risk is the limiting factor in the use of risk/benefit analysis.

We have made considerable headway in the definition of risk.

Safe threshold levels have been established for many intentional and unintentional additives in food.

These are embodied for instance in the acceptable daily intakes which serve as a basis for establishing tolerances, or maximum residue limits as we prefer to call them nowadays.

The recognised procedures for establishing safe threshold levels work well enough in most cases but we run into all sorts of problems when we come to deal with substances that are proven or suspected carcinogens.

The sort of information we really need could only come from a lifetime study in a large human population but this is hardly possible. What we have to do then, is fall back on animal feeding studies and extrapolate from these as best we can.

If you have never given this question very much thought you might say why not have a zero tolerance for these substances. Let me hasten to explain that this is not the answer.

In this context, zero is not a constant or a precise value and the administration of a zero tolerance is fraught with difficulties.

This is best explained in a passage from the Cummings Memorial Lecture given in 1975 by Dr William Deichmann:- “During the immediate past years, a zero tolerance meant certain parts per million. Today it means certain parts per billion, and what it may mean tomorrow we can only speculate.

For men who place high value on scientific facts it is time to abandon 'zero' and define what we truly mean, namely a value or values that can be expressed in quantitative terms.

Whether we like it or not, because of improved sensitivity of our analytical methods, we are going to have to establish a tolerance for everything, even for carcinogens.

It should also be pointed out that the zero tolerance philosophy means that, any risk, no matter how small, dictates complete abandonment of benefits, no matter how great.

Having introduced the subject, let’s consider two well documented examples. I will endeavour to describe the risks and benefits and I will ask you to be the judge of what compromise should be made.

The first example that I have chosen is DDT and I think that you are all aware that DDT has been banned in many countries and is being phased out in others.

One of the significant milestones in the history of DDT occurred in 1972 when the administrator of the Environmental Protection Agency, William D. Ruckleshaus, ordered the remaining uses of DDT to be banned and declared DDT a “potential human carcinogen”.

It is interesting to note that in 1970, the same man, then Assistant Attorney-General, had filed a brief in the US Court of Appeals on behalf of the Department of Agriculture. The brief included the following statement:- “DDT is not endangering the public health and has an amazing and exemplary record of safe use.”

Let us now look at some of the benefits from DDT:- Some of these are summed up in a statement issued by WHO in 1969:-

“DDT has been the main agent in eradicating malaria in countries where populations total 550 million people, of having saved about 5 million lives, and prevented 100 million illnesses in the first 8 years of its use, of having recently reduced the annual malaria death rate in India from 750,000 down to 1,500, and of having served at least 2 billion people in the world without causing the loss of a single life by poisoning from DDT alone,”

The statement goes on to say:- “It is so safe that no symptoms have been observed among the spraymen or among the inhabitants of the spray areas which numbered 130,000 and 535 million (respectively) at the peak of the campaign.”

A further statement issued in 1971 said:- “The only confirmed cases of injury have been the result of massive accidental or suicidal ingestion."

These are substantial benefits in anyone’s language.

On the agricultural scene, DDT has played an important part in pest control for about 30 years. When it first became available for agricultural use, about 1946, it provided efficient control of a variety of insect pests for the first time. Effective substitutes for some of these uses have yet to be found.

In Australia, as elsewhere, DDT is being phased out. Its use on livestock was discontinued in Australia about 1962. At the present time its use is mainly confined to tobacco and vegetables. The extensive use on cotton in Queensland and New South Wales was phased out as of 1 July 1981.

Now let us have a look at some of the risks with DDT.

DDT was already on the way out because of its persistence and its possible adverse environmental effects, but its doom was sealed when, rightly or wrongly, it was branded as a potential carcinogen.

The case for carcinogenesis in humans rests on the extrapolation of data from studies with mice. These mice studies have received their share of criticism.

The critics have questioned the virtue of using strains of mice in which spontaneous cancer is common. They also query the use of unrealistically high dose rates. In addition, they claim that the liver lesions produced are not true malignant tumors. Moreover, the mice lesions, they say, are quite unlike any tumors ever recorded or described in humans.

They conclude that the results of studies in mice do not have good predictive value for other rodents - let alone for man.

A former Director of the International Agency for Research on Cancer questions the significance of the mouse studies -and concludes that there is no evidence that DDT is in any way carcinogenic for man and received considerable support in this belief from a variety of sources₁ including the American Medical Association and a former Surgeon General of the US Public Health Service.

During the past 30 odd years, people have been exposed to DDT in just about every conceivable way. A great deal of information has accumulated and it is reassuring to note that there is no suggestion of carcinogenesis, or for that matter any other significant adverse effect on human health.

On the environmental side DDT has been blamed for the decline in the numbers of certain species of birds. There is no doubt that considerable biomagnification occurs in certain carnivorous birds, especially those at or near the top of the food chain.

These birds may be at risk - but even this is not certain. The very encroachment of man on the habitat of these birds causes their numbers to decline. The record shows that eagles were declining in numbers in USA as far back as 1921.

Another environmental effect attributed to DDT is egg shell thinning. The theory is that it reduces the chances of reproductive success. There is little doubt that egg shell thinning has in fact occurred, but the evidence incriminating DDT is largely circumstantial.

In most of these investigations DDT was the only chemical looked for. In addition, it was not until 1967 that analytical chemists learned to distinguish polychlorinated biphenyls from DDT in residue analysis.

We know more about the behaviour of DDT than we know about any other pesticide, and more than we know about most other chemicals. We still don’t know that it is completely harmless in the long term - and we never will. Nor do we have this reassuring information for other chemicals.

It is logically impossible to prove that an event will never occur. This is one of the risks that we have to accept.

Dieldrin may be selected as our next example.

Dieldrin is a very persistent chemical and this is an advantage in the treatment of soil and timber for protection against termites. Dieldrin has been very useful in agriculture, especially as a soil insecticide where some degree of persistence is advantageous. It is relatively easy to apply and is quite cheap by comparison with some of the more sophisticated insecticides now becoming popular. When dieldrin is used as a soil insecticide at sowing or planting it does not give rise to any residue problems.

Dieldrin, like DDT, is being phased out in Australia. It is however, still permitted for a number of agricultural uses.

It was once used quite extensively on livestock - especially for the control of fly strike in sheep. All livestock uses in Australia however, were discontinued about 1962.

The regulatory authorities have dieldrin under continuous review with the object of minimising its use as far as possible.

In the US, all agricultural uses have been banned since late 1974. Now what about the risks with dieldrin:- Dieldrin, like DDT has been banned in the US because it was

suspected of carcinogenicity on the basis of some controversial experiments in mice. These experiments are subject to the same criticisms that were mentioned in relation to DDT.

In addition, it has been pointed out that the same liver lesions in mice can be produced by the administration of phenobarbitone. It is of some interest to note that a study of the long term effects of phenobarbitone in humans has been carried out in a series of 10,000 epileptics in Denmark. Many of the epileptics studied had received total doses of phenobarbitone ranging from 1 kg to 4.5 kg over a period of years, but there was no evidence to show that the incidence of neoplasms had been affected one way or the other.

As in the case of DDT, there is a great deal of evidence from people who have been occupationally exposed to dieldrin. There are detailed records of workers in dieldrin manufacturing and formulating plants, dating back to 1952.

Some of these workers have had quite severe exposure, including a number of acute episodes which resulted in clinical intoxication, and have had extensive biochemical and other tests performed regularly for 18 years. There were 19 cases in which convulsions occurred. Despite this extreme exposure there were no demonstrable signs of liver injury which might have been predicted from the mouse data.

It is claimed that these human data show a clear no effect level at 17.5 mcg per kg body weight per day. This is about 600 times the average US intake!

DDT and dieldrin and other organochlorine pesticides have a long history of safe use under a variety of conditions.

They are comparatively easy to manufacture. They are cheap. Their acute toxicity is generally low. They have a broad spectrum of activity. Their residual activity is often an advantage.

We are not replacing them with pesticides about which we have more knowledge. For the main part we are merely substituting materials which are less persistent and which do not biomagnify.

Conclusion

Do we need to be reminded that Australia’s national economy still depends quite heavily on the overseas sale of agricultural commodities?

It is not generally known that without the aid of pesticides, without the technology of the agricultural chemical industry, we would not have a large exportable surplus. We would in fact, be barely able to feed our present population - and certainly not in the manner to which it has become accustomed.

It appears that we passed the point of no return, so far as the use of pesticides is concerned, many years ago.

All pesticides, and many other chemicals indispensable to modern life, may at times have unintended and undesirable side-effects. Very often these are unpredictable. It is obvious that these risks, and their unpredictability, are very much greater in the case of toxicants which persist in the environment than with those which are inactivated in a matter of hours or days. The amenity value of wildlife is very high even in purely financial terms. We in the industrialised countries must be constantly aware of our obligation to hand on to future generations what little remains of these assets, the source of so much health and happiness.

Pollution is assuming alarming proportions all over the world, and looks like becoming one of the major problems of our time. Pesticides are only a small part of that problem, but an important one. All reasonable efforts must be made to reduce these dangers as far as possible. It is fair to add that investigations to date have not shown any significant damage to wildlife in Australia for which pesticides can clearly be held responsible.

This paper has attempted to outline some of the pros and cons relevant to the role of chemicals in food production and to provide a background against which decisions can be made.

In making these decisions it is necessary to bear in mind that we live in a world of probabilities where few human decisions can be made with certainty. There is no mathematical formula which can be used to derive the one and only possible answer. Therefore, in identifying a particular chemical as either “Friend” or “Foe”, what we have to use is judgement.

We can probably do no better than to conclude with the words of Dr Alexander Schmidt, formerly Commissioner of Food and Drugs in the United States:- “At some point, the amount of risk a society is willing

to assume in order to achieve a certain benefit becomes a matter for the public at large to decide. It thus is imperative for scientists to educate the public in these matters and to serve as expert witnesses for our social institutions.”