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Analysis and assessment of pesticide residues

B/2008, 02.06.2008

Background information for journalists

German consumers see pesticide residues as the number one risk associated with food. This is one of the survey results of the Eurobarometer which was published by the European Commission in 2006. According to this survey, 69% of Germans are concerned about pesticide residues on fruit and vegetables. Active substances in pesticides may reach the consumer as residues on foods of plant origin. However, the amount of these residues must be so low that they do not harm consumer health. Statutory maximum levels must be complied with. The official food control bodies of the federal states monitor compliance. For this they need efficient detection methods which BfR tests.

Pesticides must be approved. They contain one or more active substances. Active substances are chemical elements and compounds or microorganisms that target harmful organisms like insects and mould on plants, parts of plants or plant products. Most of the pesticides approved in Germany only contain one or two active substances. Some pesticides may contain up to four active substances. The active substances are not separately approved but are always approved as components of a pesticide and for the use for which they are envisaged.

Pesticides must be approved

The approval body for pesticides in Germany is the Federal Office of Consumer Protection and Food Safety (BVL). Other public authorities are involved in the approval procedure. The Federal Institute for Risk Assessment (BfR) assesses the health risks from pesticides for humans, the Federal Environmental Agency (UBA) assesses the impact of pesticides on the environment and the Federal Research Centre for Cultivated Plants (Julius Kühn Institute, JKI) their impact on plants. BVL publishes a list of pesticides approved in Germany on its website. According to this list, in May 2008 there were 626 different approved pesticides in Germany with 1,060 commercial names. These products contained a total of 253 different active substances.

Residues may not harm health

Residues of active substances and their degradation products, pesticide residues, can remain on food treated with pesticides. The degradation products of active substances can be formed in the plant metabolism or for example when exposed to sunlight. Residues on harvest products cannot be completely avoided even when the principles of good agricultural practice are upheld and pesticides are used properly. Pesticides are used at various times during the vegetation period. The degradation speed of their active substances varies. Particularly when pesticides are used just before harvesting or when their active substances are persistent, residues are likely at the time of harvest. They must, however, be so low that they do not harm the health of consumers. Residues of pesticides can be found above all on food of plant origin. However, food of animal origin can also have residues of this kind when the animals have been given feed of plant origin.

The ALARA principle applies

In order to ensure that pesticide residues do not constitute a health hazard for consumers, a number of factors are examined prior to approval of a pesticide for instance whether and, if so, how toxic the active substances are, what substances are formed when the residues degrade and how quickly they degrade. In principle, the residues should be as low as possible. According to the ALARA principle (As Low As Reasonably Achievable), maximum residue levels should only be as high as is necessary to meet the requirements of good agricultural practice and never higher than toxicologically defensible. Comprehensive field studies, therefore, determine what amount and what application frequency are needed to achieve the intended effect. A maximum residue which occurs under these circumstances is only accepted as a maximum residue level for an agricultural product if it is guaranteed that the concentration does not have any harmful effects on human health according to the latest scientific findings available.

In order to make a statement of this kind, various unfavourable assumptions are taken as the basis for estimating both the chronic and the acute consumer risk, for instance the amounts consumed and eating habits. The assessment principles for this estimation are specified on the European and international levels (FAO/WHO). The maximum permissible concentration is laid down in law after careful examination in order to protect consumers from health risks. If these maximum residue levels are complied with, then the products are "safe" within the meaning of consumer health protection. Foods may also only then be sold when the valid maximum residue levels are complied with.

Toxicological limit values in risk assessment: ADI and ARfD

The risk from pesticide residues is evaluated on the basis of two toxicological limit values: the ADI and the ARfD.

ADI stands for "Acceptable Daily Intake“. It indicates the amount of a substance which can be ingested daily over a lifetime by consumers without any appreciable health risk. The ADI is used to assess the chronic risk and the Acute Reference Dose (ARfD) to assess the acute risk. The ARfD is a comparatively new risk assessment tool. It is defined as the amount of a substance which a consumer can ingest from one meal or several meals spread over the day without any appreciable health risk. A one-off exceeding of the ADI value is not relevant as this value takes into account the lifelong daily intake of a substance. Even a short-term exceeding of the ADI value does not constitute a risk for consumers. By contrast, a possible health impairment of the consumer cannot be ruled out from the very outset in conjunction with a one-off or short-term exceeding of the ARfD. It must be examined in each individual case whether damage to health is, in fact, possible.

In principle the following applies. If the maximum permissible level for pesticides is complied with, then the Acute Reference Dose will not be exceeded. There are two possible constellations which could lead to a temporary deviation from this rule:

  1. A maximum residue level was derived when the assessment of risks from the short-term intake of a substance was not yet used as the basis for assessment. If the maximum level proves to be too high in conjunction with later consideration of the ARfD, then the maximum level will have to be adjusted to bring it into line with existing statutory provisions and ordinances.

  2. New scientific findings are available which require a review of the existing toxicological limit values and may justify a raising or lowering of the ARfD. In this case, too, it may be necessary to adjust the maximum levels.

Multiple residues

For the approval of pesticides and the setting of maximum residue levels, a dose is determined in experiments for all active substances in pesticides below which a toxic effect can no longer be determined. It is, therefore, possible to estimate the dose range in which these substances have no harmful effect even when several substances could be present at the same time as residues on food (multiple residues). As a rule there are two or three digit safety margins between the dose with a biological effect determined in animal experiments and the toxicological limit value derived from it. Maximum residue levels are only set as high as is required by good agricultural practice. In principle, however, they are not higher than the toxicologically based limit values, ADI and ARfD, permit. Hence, it can be practically ruled out that the additive or synergistic effects of several pesticide residues in a food could lead to health impairments of consumers as long as the maximum permissible levels for the individual active substances are not exceeded. Work is currently underway to develop a uniform concept for the assessment of the cumulative risk of residues from the use of pesticides on the European level, with the participation of BfR. There are plans for a publication of the European Food Safety Authority (EFSA) in the near future.

Control is the responsibility of the federal state authorities

Manufacturers and retail distributors of foods are responsible for the compliance of their foods with the valid maximum levels. The official control authorities of the federal states monitor whether they fulfil this obligation.

Confusion has been caused amongst consumers by articles in the press stating that pesticides, which are not approved in Germany, have been found in imported fruit and vegetables. These products do not necessarily pose a threat to health. Some pesticides have been approved in other EU Member States and assessed toxicologically which have not been approved in Germany or vice versa. There are several possible reasons: the most common is that agriculture and horticulture conditions vary in the various Member States of the European Union. This applies to plant species, types of production and also harmful organisms. For instance in one region in Europe a harmful organism must be controlled which does not occur in another. In the latter case farmers see no need and distributors have no economic interest in submitting an application for the approval of this pesticide which is effective against this harmful organism. A product containing an active substance from a pesticide approved in the country of production below the maximum residue levels valid there may indeed be on the market in Germany when an application has been made for corresponding permission and an assessment has been undertaken by the German authorities.

Uniform EU provisions from September 2008

The introduction of uniform EU provisions on 1 September 2008 will remedy this situation which is not easily comprehensible for the consumer and an obstacle to the free movement of goods. In future, the permissible residue levels must take into account more than just the national uses. It is to be expected that, with the entry into force of the EU Regulation on maximum residue levels of pesticides in or on food and feed of plant and animal origin (396/2005), various maximum levels will be raised compared with the German Ordinance on maximum residue levels for pesticides. Nevertheless, BfR does not assume that the level of health protection will be lowered since it is ensured that the health-based limit values – ADI and ARfD – will be complied with. Since the entry into force of the harmonisation of testing of pesticide active substances in the European Union in 1991 (Directive 91/414 EEC), the number of active substances in products approved in the EU has fallen from slightly more than 700 in 1994 to approximately 400 today. Many harmful substances have been withdrawn from the market.

Analysis of pesticide residues - the challenge

In order to be able to set a maximum level, not only do the health risks have to be assessed but the residues must also be determinable analytically. Suitable analytical methods for the detection of pesticide residues in food and drinking water but also methods for pesticide detection in all environmental compartments (water, soil and air) must be provided by the applicant (as a rule the producer of an agent) within the framework of the pesticide approval procedure. The Federal Institute for Risk Assessment assesses the suitability of these methods using specific guidelines and by means of its own experimental work in the laboratory. BfR passes on its analytical experience to the control laboratories in the individual Federal States.

Depending on the statutory maximum levels, pesticide residues in and on food must be determined in the range of a few milligrams per kilogram down to three micrograms per kilogram. As, normally, only 10 up to 100 grams of a sample are examined, the material sometimes only contains three nanograms (0.003 millionth gram) of an active substance. Complicated test methods are needed in order to detect this small amount. They always start with the extraction of the sample and lead to a solution which contains the pesticide residues in addition to many other soluble substances from the sample. Frequently, these extracts undergo further chemical purification. The low residue amounts must not be lost during this process. The final step is the quantitative assay which again involves complicated analytical systems.

Multiple methods permit a high density of control

Efficient analysis is possible when very many active substances from pesticides can be detected in one step. A high density of control can only be achieved with multi-analyte methods. If, however, the control of a substance has to be done separately using methods (individual methods) tailored to the individual active substance, then the control density will be lower. Individual methods are, therefore, normally only used in justified cases of suspicion. One well-known example was the use of illegal growth regulators in apples and pears from Belgium, the Netherlands and Germany which was exposed in 2000/2001 and led to numerous call-back actions. Sometimes the high degree of instability of active substances from pesticides can cause problems for analysis. For instance there are substances which already decay during normal extraction and then form small, not easily detectable molecules.

Sights trained on legal and illegal substances

Besides pesticide residues a food sample extract also contains several thousand different natural ingredients. It does not make sense to clarify the identity of all these substances. Hence analytical devices are oriented towards only finding the substances regulated by law. This does, however, mean that substances previously unknown in Europe, substances which have been banned for a long time or substances produced illegally could be missed. That is why analysts focus today on developing strategies in order to detect these substances too.

The test strategy for food control should be designed to identify as many violations as possible of valid provisions. It is not possible to always look for all pesticide active substances in all foods. All the same, by means of a suitable choice of substances, food control can discover a high number of non-marketable products. In this context the test spectrum is adapted as far as possible to the constantly changing markets.