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Assessment of multiple residues of pesticides in foods - Background information

A/2005, 09.11.2005

Background information for journalists

Headlines about pesticides in fruits and vegetables regularly cause a stir. Consumer protectionists, food control bodies as well as environmental organisations repeatedly present findings which are not necessarily comprehensible to consumers. Explanations of the findings do not always help either. One of the frequently discussed questions concerns multiple residues, the remains of several active substances in or on foods. Modern analytical methods and increasingly sensitive detection methods ensure that more and more substances can be identified and smaller and smaller amounts of substances can be detected. This has also attracted greater public interest in multiple residues.

It is unclear whether and, if so, what health risks are linked to multiple residues. Consumers are worried. If people are simultaneously exposed to several chemical substances, then health interactions are theoretically possible. EU Regulation 396/2005 on maximum residue levels in or on food and feed of plant and animal origin states in this context, "It is [also] important to carry out further work to develop a methodology to take into account cumulative and synergistic effects".

The BfR Consumer Protection Forum "Multiple residues of pesticides in foods" aims to promote the exchange of scientific experience between public agencies and interest groups from manufacturers over users down to consumer organisations. A glance beyond national horizons to approaches in other European countries and experience from the USA are to provide additional insight. The conference aims to improve the foundations for the development of suitable assessment models for multiple residues.

What are multiple residues?

When people talk about residues, they mostly mean the residues of sprays in or on foods. These sprays are applied to fruit and vegetables in order to control pests like insects, acarians, field weeds or fungi. If more than one substance can be detected in a food, then the term multiple residues is used.

According to an EU report, more than one residue was found in 2002 in around one third of the samples of foods of plant origin examined in Germany.

What leads to multiple residues?

The parallel occurrence of residues of several pesticides in or on a food may be caused by various things. Pesticides are used to specifically counteract certain harmful effects: herbicides are used to kill field weeds, fungicides to check mould, insecticides and acaricides to destroy insects and mites. Each individual pesticide may contain several active substances that supplement the action of the others (combination product). Multiple residues may result from the consecutive application of various agents during crop rotation (e.g. to prevent resistances) and from the use of combination products.

Besides these functional or application-related causes, mention has also been made of inappropriate use.

In which foods of plant origin have multiple residues been detected?

Residues of several active substances have currently been detected mainly in grapes, strawberries but also, for instance, in stone fruit like apples and pears, citrus fruits and in tomatoes, peppers and some types of lettuce.

One example of test results from food control in recent years: 90 percent of 133 grape samples had multiple residues. On average, the grapes contained residues of four to five active substances. Food control reported up to 17 different active substances in one sample. Similar results were obtained for strawberries. However, these figures do not permit any statements about health risks!

Pesticides are authorised according to which procedure?

All pesticides used in Germany must be officially authorised. To this end, the manufacturer submits an application to the Federal Agency for Consumer Protection and Food Safety (BVL). Authorisation from BVL is linked to a number of examinations by other federal agencies:

  • The Federal Biological Research Centre for Agriculture and Forestry (BBA) in Braunschweig examines the efficacy of the substance and lays down the application conditions for the product.
  • The Federal Environmental Agency (UBA) in Dessau examines the environmental compatibility of the product.
  • The Berlin Federal Institute for Risk Assessment (BfR) assesses its health safety in conjunction with appropriate use. To this end, the Institute examines the toxicological data submitted by the manufacturers as well as the residue data and analytical methods. On this basis, it assesses the health risks to consumers and users.

In principle, it can be said that the residues from pesticides may not impair the health of consumers. In order to guarantee this, maximum levels for residues are set within the framework of the authorisation procedure. They are primarily oriented towards three factors:

  • Good agricultural practice: Only so much of the product may be applied as is necessary for good agricultural practice in order to achieve the desired effect without promoting the emergence of resistances.
  • The ADI value: The ADI value (“Acceptable Daily Intake”) is used as the exposure limit value for long-term uptake of a pesticide residue from food. The World Health Organisation and the Food and Agriculture Organisation define this as the amount of a substance which can be ingested daily over a lifetime by a consumer without an appreciable health risk on the basis of all known facts. The ADI value is set for each pesticide and is expressed in milligrams per kilogram body weight (mg/kg body weight).
  • The ARfD value: The ADI is not ideally suited to the assessment of active substances in pesticides which have a high acute toxicity and can impact on health after one-off or short-term ingestion. As it is derived from longer-term studies, it may not sufficiently characterise the acute risk from residues in food. At the end of the 1990s another exposure value was introduced alongside the ADI value, the Acute Reference Dose. The World Health Organisation defines the ARfD as the amount of a substance that can be ingested from food during one day or one meal without an appreciable health risk to the consumer. Unlike the ADI, the ARfD value is not set for each pesticide but only for those active substances which are harmful to health even after one-off exposure.

The basis for the authorisation of pesticides in all EU Member States is Directive 91/414/EEC. This regulates both the requirements to be met by data and also the principles for the decisions. Annex l to this Directive lists those active substances which may be contained in pesticides. As a decision has not yet been taken about the inclusion of many active substances in this Annex, it is incomplete. The individual Member State decides on whether or not to issue authorisation. Products, not active substances, are given this authorisation.

An authorisation is normally issued for 10 years. An application can be made for renewed authorisation which is linked to a new test. The authorisation stipulates the crops to which the product may be applied as well as the frequency and level. The waiting times between the last treatment and harvest are laid down in the authorisation as are other environmental and application requirements. At present, around 250 active substances are authorised in just under 660 different commercial products in the Federal Republic of Germany. Throughout the EU around 500 active substances are probably used at present.

Where’s the problem?

Like all chemical residues (multiple) residues of pesticides in foods are not desirable. However, in technical terms it is difficult to avoid them. As already outlined above, they may only be contained in an amount which definitely does not constitute a risk to health. Not every exceeding of the maximum level automatically leads to a health risk. Nevertheless, a food with residues over the maximum level may no longer be sold on the market.

There is growing awareness amongst the public at large about pesticide residues: they are seen per se as a risk. Differentiated consideration involving for instance the amounts actually detected and the average intake of the food is, therefore, something of an exception. This applies even more so to multiple residues.

Even today there is no scientific clarity about whether multiple residues do, in fact, constitute a health risk.  In principle, harmful interactions are possible when the organism is exposed at the same time to several chemical substances. However, the impact of a mixture of various active substances on man has only been clarified for a few active substance groups. Detailed examination is difficult because the multiple residues identified have very different compositions as a consequence of the many active substances used. Furthermore, a large number of controversial animal tests would be needed to undertake a more in-depth analysis of the effects.

A special concept is needed to assess the health impact of multiple residues. So far, no comprehensive scientific proposal has been drawn up that takes into account the fundamental questions of risk assessment which, at the same time, would enjoy wide public acceptance. The following fundamental approaches are recommended by international experts from the USA, the United Kingdom and the Netherlands:

  • Substances with different mechanisms of action have an effect independently of one another and should be assessed as individual substances.
  • Substances with the same toxicological mechanism of action have an additive effect and should be assessed together. The following assumption applies: all substances in the mixture have the same mechanism of action. They only differ in terms of potency and thus in terms of the dose-response relationship. This means it is possible to determine the overall effect by adding up the relative residue amounts taking into account the different potency of the individual substances (relative potency factor, RPF).

According to BfR the results and conclusions of the American, British and Dutch scientists, which are presented at the Forum, can be transposed to the German situation.

What are the publicly discussed positions?

In the public debate the users stress that the targeted application of pesticides is necessary in order to safeguard the yield and quality of foods. Application in line with the rules of Good Agricultural Practice (GAP) aims to guarantee the necessary protection of consumers and the environment.

According to non-governmental organisations, the aspect of possible combined effects of multiple residues is not sufficiently taken into account in risk assessment. They believe it is necessary and possible to assess substance mixtures. They are of the opinion that "both the additive and independent effects of several substances are stronger than those of individual substances".

In its risk assessment BfR currently adopts various approaches:

  • For some groups of active substances with the same mechanism of action, aggregate maximum levels are used to estimate multiple residues. This is possible, for instance, for fungicides like dithiocarbamates, the substances in the benomyl group or captan/folpet.
  • Most of the active substances are still assessed individually. The setting of maximum residue levels for the individual active substance is done - as already outlined above - on the basis of two principles: It must be safe and may not be higher than the amount which is unavoidable in conjunction with proper use of the substance as an active substance residue in the harvested crop (agricultural product). The benchmarks for safety are the ADI (Acceptable Daily Intake) and ARfD (Acute Reference Dose) derived from toxicity tests using high safety factors.

BfR intends to develop a concept for the health assessment of multiple residues which builds on international findings and experience. What are primarily needed here are comprehensive exposure data (data on the scale on which consumers come into contact with a substance). Furthermore, there is a need for studies on mechanisms of action and possible interactions between the substances. Based on these data groups of active substances can be identified with the same mechanism of action and equivalency factors can be derived.

In the public debate the subject of multiple residues is frequently linked to the suspicion of incorrect use and careless handling of pesticides. What’s more, there is regular criticism in the same breath of pesticide residues in imports that “are not authorised in Germany”. These agents are not authorised in this country because, for instance, the harmful organisms do not occur here for climatic reasons. There is not, therefore, any need to use them and hence no application has been made for authorisation. It is not that they have been refused authorisation because they constitute a risk to consumers. For these pesticides a maximum level of 0.01 milligram per kilogram applies almost automatically. This value corresponds roughly to the analytical detection limit; it does not initially say anything about the safety or harmfulness of a substance. Very few consumers know that. They assume that they are being sold a harmful product and are concerned.

What is the goal of the Forum?

BfR is staging this second Consumer Protection Forum on this important subject in order to encourage the exchange of scientific experience. The goal of the Forum is to provide the basis for the development of suitable scientific assessment models for multiple residues and to also take into account the experience of the Forum guests in these further considerations.