Contaminants and Residues

Microbiological

Agricultural products and animals have a wide range of microbes on, or in, them at harvest/slaughter, whose type vary with commodity, geographic region, and production and harvesting/slaughtering methods. Some of these microbes (bacteria, yeasts, moulds) can grow on the food causing spoilage, which is a common cause of rejection at import. Other pose a hazard to man through illness, having the capacity to infect the consumer, or to intoxicate if they have multiplied in the food and produced a toxin (enterotoxin or exotoxin).

The levels of microbial contamination of food are influenced by harvesting / slaughtering technologies and by the processes applied during food manufacture. With current technologies it is impossible to guarantee the absence of pathogenic microorganisms on raw foods, both of plant and animal origin. Widespread and increasing incidence of foodborne diseases and the resultant social and economic impact on the human population have brought food safety to the forefront of public health concerns. Foodborne illness occurs in every country in ever increasing frequency. Many outbreaks are the consequence of a failed process, or inappropriate storage conditions (usually temperature abuse) during distribution, food service or by the consumer. There are also examples of sporadic outbreaks of illness attributed to raw products eaten unprocessed (e.g. lettuce, melons, raw fish). Foodborne illness has long been linked primarily to foods of animal origin, but in recent years many outbreaks of foodborne illness have been associated with fruits, vegetables and other foods.

There are also examples of imported foods causing human illness, exported from both developed and developing countries. Consequently there is widespread concern that food in international trade carries pathogenic microorganisms that could result in outbreaks of illness. Importing countries have sometimes responded to this concern with measures which are neither scientifically based nor statistically sound, and may be an impediment to fair trade.

The microbiological safety of food can never be achieved by end-product testing, which only detects that a failure has occurred and can only contribute indirectly to identification and control of the cause of the problem. No sampling plan can ensure the absence of pathogen in a food, and testing products at point-of-production, port-of-entry, or in the retail distribution chain cannot guarantee food safety. All too frequently, industry has become aware of microbiological problems in its products as the result of spoilage in the marketplace or from reports of illness. Control measures are then applied as a response to an existing problem. Furthermore, the isolation of a bacterial pathogen from a food does not mean that the food necessarily is dangerous, e.g. the food may be cooked before consumption. Hence preventive approaches are required, often as simple as control of storage time and temperature. Nevertheless, microbiological testing, used appropriately, is one of the measures that can be used to achieve microbiological safety.

Pesticides

Pesticides are important in modern farming and will remain indispensable for the foreseeable future. Without them it would be practically impossible to produce the required quantities of food to feed the world's growing population. However, there is growing concern about the safety and quality of food. Pesticides include many hazardous substances. They must be applied with utmost care in the most efficient manner to protect crops and farm animals, while leaving the lowest possible residues in food and the environment.

However, to be effective it is inevitable that some residues remains. As the use of pesticides has increased governments have introduced measures to restrict and regulate their use to protect the users of pesticides, consumers, domestic animals and the environment at large. The decision to register the use of a pesticide is based on the assessment of the results of very extensive research work on the toxicity and the fate of active ingredient, its metabolites and degradation products, together with data on the magnitude of residues obtained from supervised trials. The conditions of use specified in the registration document or use permit is called "Good Agricultural Practice" (GAP).

Veterinary Drugs

An increase in the use of veterinary drugs, including growth promoters, is a predictable consequence of expanded food animal production efforts. Unfortunately, many of the least developed countries suffer from a lack of effective regulatory control of their use. In the developed world, national legislation and international trade agreements dictate required withdrawal periods before slaughter and/or maximum permissible residue levels (MRLs) for the consumable parts (meat, milk, etc.) for an increasing number of veterinary drugs. The use of hormonal growth promoters and beta-agonists is either prohibited (European Union) or strongly regulated (e.g. USA, Canada and Australia). Producer compliance with these regulations is monitored by national testing laboratories according to nationally or internationally accepted sampling protocols and assay methods. Within the European Union a group of European Union Community Reference Laboratories have responsibility for the effectiveness of the analytical residue control programmes (methods, materials). This responsibility is directed towards both the EU Member States and countries trading with the EU. In order to ensure a safe and saleable food product for both local consumption and international trade, developing countries also require the capacity to operate quality assured testing programmes for detection of these regulated residues in food animals and their products. While assays for food contaminants (veterinary drug and pesticide residues, microbial pathogens, etc.) can be performed using a number of techniques at different stages of production, the ante-mortem or at-slaughter testing of livestock or livestock products (milk, meat, cheese, etc.) provides the most practical avenue for large-scale analysis both for home consumption or for export purposes.

Increasingly the approach is to use screening assays (radio-immunoassay, ELISA, thin layer chromatography) followed by confirmatory methods such as high pressure liquid chromatography HPLC/MS (MS) on suspected positive samples.

Mycotoxins

Mycotoxins are toxic metabolites produced by different genera of fungi (Aspergillus, Fusarium, Penicillium, Claviceps, etc.) that can contaminate a wide range of foods and feeds. These fungi are ubiquitous and wide-spread at all levels of the food chain. They are present in food produced at all latitudes save the polar regions. They are natural contaminants and yet some of the most poisonous toxins known to man. Their presence is considered unavoidable and it is not possible to predict or prevent entirely their occurrence during cultivation, harvest, storage, and processing operations by current good agronomic and good manufacturing practices.

Under favourable conditions of temperature and humidity, these fungi grow on certain foods (grains, cereals, oilseeds, edible nuts, dried fruits) resulting in the production of toxins. Mycotoxins can also be metabolized by animals fed contaminated grains and pass into milk, eggs and other organs entering the food chain once again.

Mycotoxins in our staple foods and their medical consequences have been known since historical records exist. Ergotism, a vaso-constricting disease with severe neurological alterations, caused by ergot alkaloids produced by the fungal genus Claviceps, has been extensively described since the Middle Ages. There have been over three hundred mycotoxins identified, produced by some 350 fungal species, but the most agriculturally important ones are: aflatoxins, deoxynivalenol, nivalenol, T-2 toxin, zearalenone,ochratoxin, fumonisins, and patulin.

There is a continuous need to protect the health of humans and susceptible animals by limiting their exposure to mycotoxins because of their toxicological manifestations which include acute and chronic ones such as cancer, immunosuppression, mutagenicity and estrogenic gastrointestinal, urogenital, vascular, kidney and nervous disorders. Many countries regulate for or suggest permitted levels of mycotoxins in foods and feed because of the public health significance and commercial consequences. In developing countries mycotoxins also have profound economic implications. Losses in grain and animal production are also increased by losses of markets by non-tariff barriers due to mycotoxin level restrictions. According to FAO estimates, world losses of foodstuffs due to mycotoxins are in the range of 1000 million tonnes per year.

For governments to routinely monitor their domestic and imported products to ensure that the mycotoxin levels are below the required limits their laboratories need sensitive, accurate and precise methods of analysis and sampling.

Radionuclides

Foods and feed can become contaminated by various causes and processes. Contamination generally has a negative impact on the quality of the food or feed and may imply a risk to human or animal health or a barrier to trade. Contamination levels in foods shall be as low as reasonably achievable.

Actions to prevent or to reduce contamination of foods and feeds in an emergency may be found under Emergency Preparedness & Response. Compliance of food and feed contaminant levels to internationally accepted maximum levels for particular uses has to be demonstrated by monitoring and survey programmes, following measurement principles and procedures that will be subjected themselves to international acceptance. Moreover, the correct application of those principles and procedures in practical situations will have to be demonstrated by an appropriate quality assurance system, involving the use of validated analytical procedures, adequate reference materials for equipment calibration and the participation to inter-comparison exercises for independent capability assessment.

In contrast to the routine monitoring programmes, contamination occurring as the consequence of an accidental release of radionuclides into the environment, will generate pressure on the laboratories to provide a rapid survey of the situation in order to provide the data for matching the emergency response and the corrective actions to the risk represented by the event. Because the contaminant levels will then generally be different from the levels routinely measured and the response time will be shorter, rapid methods dedicated to and developed for accidental situations should be available and should be maintained operative by regular exercises and practice.