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Agricultural compound residues in food

Agricultural compounds are chemicals (including veterinary medicines) used to improve the quantity and quality of produce and slow down the rate at which it spoils. They are used in the production of primary produce (farmed plants or animals). They are also used by home gardeners, and for the health of domestic animals such as cats and dogs.

The detailed information below is also available in a free printed booklet titled ‘Agricultural compound residues in food’. The ISBN for this publication is 0-478-29862-5. To be sent a printed copy call us on 0800 693 721 (0800 NZFSA1). Alternatively, you can download this page in PDF format.

PDF of this publication for downloading and printing [ 46K, 20 pages]

Introduction to agricultural compound residues in food

People have been competing with insects, animal pests, diseases and weeds for food throughout our history. Insects destroy crops, weeds compete for space and nutrients in fields, fungi and bacteria infect plants and animals and the stored food produced from them. Mice, rats and other animals create great loss and destruction. This battle for food has meant that populations have, for generations, had to wage war against pests and vermin to gain enough food for sustenance and trade.

As early as Greek and Roman times chemicals such as sulphur and bitumen were used as pesticides. By the 1700s, vinegar, slaked lime and mixtures of herbs were in use. As farming intensified and the understanding of chemical agents became more refined, the desire for more effective and human compatible products grew. Since the 1930s the use of sophisticated synthetic agricultural compounds has grown and with it public concern about residues and their effect on people and the environment. This concern has led to comprehensive testing and monitoring requirements, underpinned by policy and laws, to ease worries of possible ill effects.

This information has been developed to describe what agricultural compounds are; why they are used; how their residues come to remain in food; how maximum residue levels are set; and how we ensure these levels do not pose a public health or safety risk. It also explains where you can find more information on New Zealand’s residue monitoring programmes.

Note: Chemical residues from agricultural compounds are dealt with separately from additives. These are used in food production after the primary product is harvested or slaughtered, and include preservatives, colours etc.

Food additives – understanding and identifying food additives

What are agricultural compounds?

Agricultural compounds are chemicals (including veterinary medicines) used in the production of primary produce (farmed plants or animals). They are also used by home gardeners, and for the health of domestic animals such as cats and dogs.

Agricultural compounds can be natural or synthetic and include veterinary medicines, fertilisers and pesticides (fungicides, herbicides and insecticides). Farmers following either conventional or organic methods of production can use approved chemicals to control pests and weeds, treat their animals, and improve soil fertility (amongst other things).

There are at least 500,000 identified natural chemicals that are present in all foods, including natural pesticides that work to protect the plant or animal from attack or from loss of nutrients.

Why do growers and farmers use chemicals?

Agricultural compounds are used to improve the quantity and quality of produce and slow down the rate at which it spoils.

There is no point in producing food that is unsafe or will not last long enough to be eaten. Growers and farmers use agricultural compounds to protect the food supply and to maximise the quantity and quality of the food they grow.

Like medicines prescribed by doctors, they are used only if their benefits (in food production and storage) outweigh the risks to people and livestock from their residues. They allow countries to economically and efficiently feed their people and livestock and for others, like New Zealand, to maintain an economy based on trade in food. Food makes a significant contribution to our economy because we export about 80% of what we produce.

Because agricultural compounds are used worldwide, their safety must be checked both locally and internationally. They are only approved for use if they pose no greater risk to consumers than foods grown without their use.

No country wants to risk importing food that could carry pests and diseases that might cause harm to its people, animals, plants or environment. Equally, no country would wish its people to be at risk from residues of the chemicals used to control or eliminate these.

The use of agricultural compounds in food production is tightly controlled to meet the sometimes competing goals of least risk to human health, good plant and animal health, and supplies for consumption and trade.

Why do we allow residues in our food at all?

Using agricultural compounds at the time and in the strength needed to be effective can sometimes leave traces in the final food. The maximum level allowed has been carefully assessed to ensure that any possible health risk is so small that it is called ‘notional zero’.

Because farming is often an intensive form of production (many similar crops or animals raised in close proximity) the risk of disease, weeds, parasites and other pests spreading is high. Keeping animals and crops free from pests and diseases is important for their health and welfare. Using agricultural compounds and veterinary medicines helps achieve this.

To be effective, agricultural compounds must stay in place long enough to do their job. One consequence of this is that some traces of the chemical may remain in meat, fruit or vegetables at the time they are slaughtered or harvested.

However, this must be balanced against the fact that without agricultural compounds, the price of everyday foods would be higher and there would be lower yields because of losses from pests. There would also be potential animal welfare and human health issues. It has been estimated¹ that globally even with modern agricultural chemicals, pests account for pre-harvest crop losses of more than 40 percent of the potential value of output, with 15 percent attributable to insects and 13 percent each to weeds and pathogens. An additional 10 percent of the potential value is lost post-harvest.

What has to happen before an agricultural compound can be used?

Before any agricultural compound is used in New Zealand it must meet the requirements of the Agricultural Compounds and Veterinary Medicines Act.

Before we register an agricultural compound for use it must undergo rigorous testing. The results from these tests determine – among other things – the least amount of a compound to use to give the maximum benefit. They also predict the amount of residue left in the food at harvest or slaughter. Based on this information, acceptable residue limits are recorded in New Zealand law, set in accordance with national and international procedures.

Instructions for safe and proper use are displayed on the product label. Users are legally required to follow the instructions, which include residue controls. Withholding periods (the minimum amount of time that has to pass between application of a chemical and harvest or slaughter) are one example of these controls.

We carry out random checks and monitoring programmes to ensure all instructions are being followed and the conditions around them are working.

What are ‘limits’ for agricultural compound residues in food?

There are two standards that relate to residues in our food. These are the MRL (Maximum Residue Limit) and the ADI (Acceptable Daily Intake) or, where set, the PDE (Potential Daily Exposure) for food².

Maximum Residue Limit (MRL)

Residues of an agricultural compound in food must be no higher than the MRL for that chemical. The MRL is the highest concentration of residue allowed in food crops or animal products at harvest or sale and is legally enforceable. A residue found at or below the MRL indicates that the farmer or grower has followed requirements and used the compound properly. This is sometimes referred to as following ‘good agricultural practice’.

MRLs are not safety limits, although they are set below levels which are known to have any adverse health effect (health implications are determined using the ADI calculation, see below). MRLs are set to ensure that, at harvest or slaughter, the chemical will have done its job and the resulting residue is as low as possible. An MRL also takes into account any other relevant breakdown or metabolism of chemicals in the plant or animal, as well as the residue of the agricultural compound itself.

Any health implications of consuming residues are considered by comparing how much of each food people are likely to eat (and assuming that all of that food will always have the maximum allowable residue – which is very unlikely) with the relevant ADI (or when set, the PDE). The ADI or PDE is set using internationally-agreed procedures which estimate the amount of a particular compound that can be safely consumed every day for your whole life without causing any harm. New Zealand often uses the ADI set by the World Health Organization (WHO).

Acceptable Daily Intake (ADI)

To determine the ADI for each agricultural compound, extensive tests (including animal studies) are done to find how much of the compound can be consumed without it having a toxic effect on the body. By using varying doses of the compound, researchers can determine the level at which the first or slightest signs of an observed toxic effect are indicated. They then take the dose just below this level, which is called the ‘no observed adverse effect level’ (NOAEL), and use it in calculations to set how much is safe to eat each day, over our lifetime.

The difference between animal and human studies, and between the most sensitive and least sensitive individual, is taken into account by dividing the NOAEL by a safety factor of at least 100. The final figure is the estimate for an acceptable daily intake for humans. Usually this is expressed as how many milligrams of chemical you can safely consume per kilogram of your body weight every day (or mg/kg bw/day) for your entire life.

For example, if the NOAEL occurs when you eat 100 mg and a safety factor of 100 is used, the ADI for that particular chemical would be 1 mg/kg bw/day. If there was some uncertainty around the toxic nature of the compound, a greater safety factor would be used, say 1000, and the ADI would be set at 0.1 mg/kg bw/day. You could eat at least 1 mg per kilogram of your weight (or 0.1 if there was some uncertainty) of this chemical per day, every day from birth to death, and still not be affected.

The ADI is considered to apply to children in the same way it does to adults. Despite their organs being less developed and more susceptible to damage, their repair mechanisms are usually superior. Experts from WHO and the United Nations Food and Agriculture Organisation (FAO) consider that the ADI protects children as well as adults because the large safety factor built into it accounts for individual sensitivity.

What if I eat a lot of foods, all with residues?

Providing your daily intake of each compound is below its ADI, and your diet contains a range of foods, it’s extremely unlikely that you could eat enough of a compound (even over a lifetime) to pose a risk to your health.

It is rare for us to regularly eat up to, or more than, the ADI of any particular agricultural compound. This is because the same chemical is not used on all of the same crop all of the time, and our diets are normally quite varied (so we are more likely to get little doses of residues from many different foods).

Whether you eat a lot of different foods containing the same compound or whether you eat a meal containing several different compounds, the health implication is the same – any effects would depend on the level of residue in the food and the amount you eat.

A substantial amount of research has been conducted into what some call the ‘cocktail effect’ and international experts agree that it is rare. Testing to date has shown that consuming a mix of chemicals at the levels found in foods is of no more concern than consuming each chemical individually.

It’s impossible to carry out tests on all combinations of the few hundred chemicals used in food production but, in the many, many tests that have been done, there is little evidence of the ‘cocktail effect’. Almost no agricultural compound interacts with another. This means you can consume residues of many different compounds without any health effect, providing the residues are below the respective ADIs.

Risk assessment of multiple residues of pesticides and veterinary medicines in food [UK Food Standards Agency]

If residues exceed the MRL, is the food still safe?

A residue level that is above the MRL means that the food may not have been produced according to best practice. But the large safety margins built into the MRL setting system mean the food is likely to be safe.

Very occasionally, agricultural compound residues are detected at levels above the MRL although it is extremely unlikely that they would ever pose an immediate health risk if the food was eaten.

When a residue above the MRL is found, we undertake an initial investigation to determine the significance of the breach. Depending on the outcome, actions may include recalls, public announcements, seizing products and suspending production. Education or legal action may follow.

Even in the unlikely event that you did buy food that was above the MRL, the normal processes of storage (reduction over time), washing and cooking the food will, in most cases, significantly reduce the levels of residues for the majority of compounds.

The extent of any health risk would depend on how much residue was found, how many foods it was found in, and how much of that food a person would be likely to eat.

For example, with kiwifruit, the New Zealand MRL for the fungicide iprodione is 5 mg/kg. The ADI for iprodione is 0.06 mg/kg bw/day. Even a highly sensitive 70 kg adult would need to eat almost one kilogram of kiwifruit a day (all containing iprodione at the MRL – itself very unlikely) every day of their life before they came close to consuming a dose that was near that found to exhibit a toxic effect.

The cocktail effect

There are three possible scenarios that apply to chemical mixtures when considering their combined effect. The compounds may be:

• synergistic (which means that the effect of the combination is more than expected from the simple sum of the effect of each, for example 1+1=3). This is very rare.

• antagonistic (which means that the combination is less than expected from the simple sum of the effect of each, for example 1+1=1). This is also uncommon.

• additive (the combined effect is the sum of the individual effects, so 1+1=2). This is almost always the case.

Does New Zealand food have more residues than, say, food in the USA or Europe?

New Zealand food has residue levels generally similar to, or lower than, overseas levels. The same applies to the number of residues found.

Making international comparisons can be difficult as many factors must be considered. These include climate, types and prevalence of pests, and agricultural production methods. In New Zealand, we have a temperate climate and many of our animals are grass-fed and live outdoors all year. We have a mixture of some pests from warmer and wetter climates and some from cooler and drier environments.

Seasons also vary, and this can have an effect on the types and numbers of pests in the environment (just as it does with non-pest insects and plants). This difference in pest types and numbers means the range and usage of agricultural compounds will also be different.

The important thing in any country is to ensure that agricultural compounds are used responsibly. This means following good agricultural practice and the requirements of use, such as withholding periods.

New Zealand food must meet the levels of safety required by our laws, as well as by those countries importing our food. The same applies to food imported into New Zealand which must meet New Zealand’s standard. Our comprehensive testing programme provides us with confidence that our residue status is as good as any worldwide.

Why are some chemicals ‘banned’ overseas but not here?

Some agricultural compounds used in New Zealand may not be used in other countries. This is rarely because they are ‘banned’ due to concerns about their safety in food. There are many reasons they may not be used – for example, the crop they are used on might not be grown in that country, or the pest may not be present there.

When a restriction or ban is imposed on a compound overseas, the reasons are considered to see if they’re relevant to New Zealand. If they are, then the product would be restricted, additionally controlled or banned here.

Some examples:

• in Scandinavia, some products are simply not registered because the climate is such that they are not required

• antibiotics are said to be ‘banned’ in Scandinavian poultry industries because medicines such as ionophors and coccidiostats, although used, are not classed as antibiotics there, whereas they are classed as antibiotics in New Zealand

• Simazine is not allowed in some countries that have a high water table and sandy soils, such as the Netherlands, where the levels found in drinking water and available risk management options are different to New Zealand

• some countries do not have Endosulfan registered because their occupational safety and health systems are unsophisticated and proper handling requirements are often not followed, harming the growers who use it

• 1080 is particularly toxic to dogs so is not allowed in some countries where there are native dog species, such as coyotes in the USA.

Are naturally produced toxins safe to eat?

Comparatively little is known about safe levels of consumption of many of the natural toxins produced by plants, animals and micro-organisms.

All food contains, and indeed is made up of, chemicals. Some of these chemicals may be toxic at certain doses, and on some occasions may be present at levels that can cause harm.

Unlike registered chemicals, very few naturally-occurring toxins have been thoroughly researched or evaluated for their effects on people or animals. Those that have include solanine in potatoes, aflatoxins from a fungus that can grow on peanuts, lectins in raw kidney beans, and patulin from a fungus that is sometimes found in damaged or bruised apples. However, the rest are generally found at levels regarded as ‘safe’ for most people because the foods have been consumed for many years with the toxins at these levels without evidence of harmful effects.

The same comments about levels of chemicals, eating a balanced and varied diet, and the ‘cocktail effect’ apply to natural toxins just as they do to synthetic pesticides.

What are the laws that apply to use of agricultural compounds?

Agricultural compounds approved for use in New Zealand are subject to the provisions of the Agricultural Compounds and Veterinary Medicines Act 1997, the Food Act 1981, the Hazardous Substances and New Organisms Act 1996, the Animal Products Act 1999, and their relevant regulations and standards such as the Animal Products (Residue Specification Notice 2004) and the New Zealand (Maximum Residue Limits of Agricultural Compounds) Food Standards 2006. Each piece of legislation includes penalties that can be imposed for misuse.

Who tests the levels of residue in our food?

We monitor residues in food, and the exposure of the New Zealand population to them.

We have been running monitoring programmes since it was set up in July 2002, as part of our role as the New Zealand food regulator. Prior to that, both the Ministries of Health and Agriculture and Forestry conducted testing. New Zealand has a wealth of data that spans many years. These monitoring programmes cover an extensive range of primary products, both at the production and harvest stage and at the point of sale to consumers. Producers and retailers may also do their own independent testing.

At present we have five major monitoring programmes in place. Latest results of each programme are freely available on our website along with background information.

New Zealand total diet survey

National chemical residue programme

Dairy residue monitoring programme

Food residue surveillance programme

New Zealand Total Diet Survey (TDS)

The TDS is carried out every five or six years. It estimates New Zealanders’ dietary exposure to agricultural chemicals, contaminants (such as cadmium and mercury, pollutants, and natural and synthetic toxins) and selected nutrients. In 2003/04 it tested 121 representative foods and provided results for the average diet of different age and gender groups within New Zealand.

The foods tested represent 80% of the New Zealand diet and are sampled from various places around the country four times over a year to determine seasonal fluctuations and build a complete picture of exposure. The foods are tested ‘as consumed’. That means if a food, such as steak, is normally cooked before being eaten then the samples will also be cooked before being tested. This provides the best estimate of real human exposure and any potential risks from residues.

National Residues Programme (NRP)

The NRP tests animal products (meat from animals, birds and salmon, as well as honey) for registered veterinary medicines and agricultural compounds, deregistered agricultural chemicals that are persistent environmental contaminants, banned or restricted substances and toxic agents (eg, poisons used to control possums). Some tissues and fluids (eg, bile) of an animal may show the highest levels of residue concentration. These are referred to as the ‘marker tissue’. These marker tissues are tested for residues, even though they’re very rarely eaten. This means that levels of residue reported in the marker tissue are usually far higher than those likely to be found in the meat. If the marker tissue residues exceed food standards, the carcass is subjected to further testing to ensure the levels of chemicals in the edible tissues comply.

Dairy Residue Monitoring Programme

The Dairy Residue Monitoring programme is also known as the National Chemical Contaminants Programme (NCCP). It tests raw (unpasteurised) milk at the farm and before it’s transferred to the tanker or dairy factory. It follows on from the National Residue Monitoring Programme for Raw Milk that was established in 1997 by the then New Zealand Dairy Board on behalf of the export dairy industry. As with the NRP, it tests for a wide range of agricultural compounds and contaminants.

Food Residue Surveillance Programme (FRSP)

This complements the other programmes by providing an opportunity for detailed investigation of specified foods. Food and residue combinations for investigation are prioritised annually, with the FRSP focusing mainly on plant products and imported foods. Any results from the New Zealand Total Diet Survey warranting further investigation can also be followed up through the FRSP.

Targeted surveys

These may be done as part of our annual work plan and be commissioned from specialist independent experts, or could be undertaken in response to an event. Targeted surveys can be used to investigate current levels of compounds, new concerns arising overseas that need to be assessed here, determine public interest, produce new scientific evidence, or evaluate the effects of changes in agricultural practice.

These surveys and monitoring programmes show that New Zealand has a food residue status to rival any in the world.

Can I do anything to lower my intake of residues?

The many studies carried out on the New Zealand diet show our exposure to residues and other synthetic chemicals in food is well below safety levels. If you are still concerned about residues you can reduce any exposure even further. The following suggestions are good practice and have the added benefit of reducing the number of pathogens (micro-organisms such as bacteria and viruses that cause illness) on produce.

• wash all produce thoroughly, separating the leaves from the base of upright growing vegetables (eg, celery, silverbeet) especially if eaten raw. (This will also help wash off any dirt or pathogens that may have contaminated the produce)

• around the home and garden, always follow manufacturers’ instructions for mixing chemicals and waiting for the entire withholding periods

• use compost from reputable firms and make sure it is well composted and mixed into the soil (incidentally this may help reduce your exposure to soil-borne pathogens such as E. coli O157:H7 which can be taken up into the tissue of the plants)

• to minimise exposure to natural toxins, eat undamaged produce that looks fresh. Healthy plants and animals are likely to have produced fewer natural toxins or produced them at lower levels

• prepare and eat the food in the commonly accepted manner and, if it is to be cooked, make sure it is properly cooked.

Where can I find out more?

Further information on anything you have read here is available from:

New Zealand Food Safety Authority

86 Jervois Quay,

PO Box 2835,

Wellington,

New Zealand

Consumer Helpline: 0800 693 721

Email: info@nzfsa.govt.nz

Website: www.nzfsa.govt.nz

FOOD SAFETY CONCERNS 0800 NZFSA1 (0800 693 721)

IMPORTANT DISCLAIMER: Every effort has been made to ensure the information in this guide is accurate. NZFSA does not accept any responsibility or liability whatsoever for any error of fact, omission, interpretation or opinion that may be present, however it may have occurred.

July 2007

¹ Orke, E. C., H. W. Dehne, F. Schonbeck, and A. Weber. 1994. Crop production and crop protection: Estimated losses in major food and cash crops. Amsterdam: Elsevier.

² The Environmental Risk Management Authority is responsible for setting Potential Daily Exposures for various routes of exposure in New Zealand.