Food Science & Technology · Food Science Core · also Food Toxicology, Food Contaminants, Chemical Food Safety
The chemical side of food safety: how toxicity is measured and safe intakes set, the natural toxicants in foods, contaminants from the environment and from processing, residues of pesticides and veterinary drugs, and food allergens. Veterinary toxicology covers poisoning of animals; this subject covers the human consumer.
In the exams: ICAR AIEEA-PG Code 18 Unit I (contaminants and anti-nutritional factors); ICAR AICE 35.a Unit 8; FSSAI and state Food Safety Officer syllabi
Food toxicology is the study of harmful chemicals in food and of how safe levels of exposure are decided. It covers substances that occur naturally in foods, contaminants that enter from the environment or form during processing, residues of pesticides and veterinary drugs, chemicals that migrate from packaging, additives deliberately used, and food allergens, which act through the immune system rather than by ordinary toxicity. The question it answers is never simply whether a chemical is toxic, since almost everything is at some dose, but whether the amount people actually eat is safe.
The subject matters because chemical hazards are often invisible, chronic and spread across whole populations. A single microbial outbreak is obvious; a contaminant that slightly raises cancer risk or harms child development across millions of people is not, and can only be found and controlled through toxicological testing, exposure assessment and regulation. International limits are set through the Codex Alimentarius Commission on the advice of the Joint FAO/WHO Expert Committee on Food Additives (JECFA) for additives, contaminants and veterinary drug residues, and the Joint FAO/WHO Meeting on Pesticide Residues (JMPR) for pesticides, while regional and national authorities such as EFSA, the US FDA and FSSAI set the limits that apply in their markets.
The subject is examined in ICAR AIEEA-PG Code 18 Unit I, which names contaminants and anti-nutritional factors, in the ICAR AICE-JRF/SRF 35.a syllabus, and heavily in FSSAI and state Food Safety Officer and Food Analyst examinations. Examiners ask for definitions (NOAEL, ADI, TDI, MRL, margin of exposure), short calculations of safe intakes and exposure, the toxicant behind a named food or poisoning, sources and effects of heavy metals, process contaminants and their mitigation, and the major allergens and how intolerance differs from allergy. Mycotoxin-producing moulds are taught in food-microbiology and allergen management programmes in food-safety-management-systems; this subject covers their toxicology.
The principle that the dose makes the poison, attributed to Paracelsus in the sixteenth century, is the starting point of toxicology: water, salt and vitamin A are harmful in excess, and highly toxic substances are harmless at low enough doses. Toxicity is described by the relationship between dose and response. Dose in food toxicology is usually expressed per kilogram of body weight per day (mg/kg bw/day), so that animals and people of different sizes can be compared.
Acute toxicity follows a single or short exposure and is classically summarised by the LD50, the dose that kills half of a group of test animals; it is a crude measure now used less, and modern tests are designed to use fewer animals. Chronic toxicity follows long exposure at lower doses and is what matters for most food chemicals. For most toxic effects there is a threshold, a dose below which no adverse effect occurs, because the body can repair, detoxify or excrete low doses. For genotoxic carcinogens, which damage DNA directly, regulators generally assume there is no safe threshold, so any exposure carries some risk and the aim is to keep exposure as low as reasonably achievable.
The no-observed-adverse-effect level (NOAEL) is the highest dose in a study at which no adverse effect is seen; the lowest-observed-adverse-effect level (LOAEL) is the lowest dose at which an effect is seen. Both depend on the doses chosen in the study. The benchmark dose (BMD) approach fits a model to the whole dose-response curve and finds the dose giving a specified small effect, such as a 10 per cent increase in tumour incidence; its lower confidence limit, the BMDL10, is now preferred by EFSA and JECFA as the reference point because it uses all the data.
The acceptable daily intake (ADI) is the amount of a substance, deliberately added to food, such as an additive, or present as a residue of a pesticide or veterinary drug, that can be eaten daily over a lifetime without appreciable health risk. It is expressed in mg/kg bw/day and is normally derived by dividing the NOAEL, or BMDL, from the most sensitive relevant animal study by an uncertainty factor, by default 100: a factor of 10 for differences between animals and humans and 10 for differences between individuals. Larger factors are used when data are incomplete or effects severe. If the NOAEL for an additive is 10 mg/kg bw/day, the ADI is 10/100 = 0.1 mg/kg bw/day, and for a 60 kg adult that is 6 mg per day. Where toxicity is so low that no numerical limit is needed, JECFA assigns an ADI 'not specified'.
For contaminants, which are not deliberately added, the equivalent value is called tolerable rather than acceptable: the tolerable daily intake (TDI), or for substances that accumulate in the body, a provisional tolerable weekly intake (PTWI) or monthly intake (PTMI), which allows for day-to-day variation. JECFA's PTWI for methylmercury is 1.6 µg/kg bw, and its PTMI for cadmium is 25 µg/kg bw. Where JECFA concluded that no threshold could be identified, as for lead and inorganic arsenic in 2010, it withdrew the previous PTWI and expressed risk through margins of exposure instead.
The acute reference dose (ARfD) is the amount that can be eaten in one meal or one day without appreciable risk, used for pesticides and some contaminants with acute effects. For chemicals with little toxicity data present at very low levels, the threshold of toxicological concern (TTC) approach uses structural classes, the Cramer classes, to set exposure levels below which risk is considered negligible.
Toxicity data come mainly from standardised animal and laboratory tests, increasingly supplemented by in vitro and computational methods. The OECD Test Guidelines are the internationally accepted protocols, so that data generated in one country are accepted in others. A typical data package for a new food additive or pesticide includes acute oral toxicity; repeated-dose studies of 28 days and 90 days in rodents, which identify target organs and give an early NOAEL; chronic toxicity and carcinogenicity studies lasting most of the animal's lifespan; reproductive and developmental toxicity studies, such as the extended one-generation reproductive toxicity study and prenatal developmental toxicity studies; and genotoxicity tests.
Genotoxicity testing uses a battery because no single test detects every mechanism. The bacterial reverse mutation test, or Ames test, detects gene mutations in strains of Salmonella Typhimurium and E. coli, with and without a liver enzyme preparation (S9) to mimic metabolic activation. The in vitro micronucleus test detects chromosome damage in mammalian cells, and positive results are followed up in vivo, for example by the rodent micronucleus test. Toxicokinetic studies describe absorption, distribution, metabolism and excretion, which explain species differences and the formation of reactive metabolites. Epidemiological studies in people, where available, are the most relevant evidence but are hard to interpret because of confounding and imprecise exposure measurement. Animal welfare law and the principles of replacement, reduction and refinement increasingly limit animal testing, especially in the European Union.
Risk depends on hazard and exposure together. Dietary exposure is estimated by combining the concentration of the chemical in each food with the amount of each food eaten, divided by body weight: exposure = Σ (concentration × consumption) / body weight. If rice contains 0.1 mg/kg of inorganic arsenic and an adult of 60 kg eats 0.3 kg of rice a day, exposure from rice is 0.1 × 0.3 / 60 = 0.0005 mg/kg bw/day, or 0.5 µg/kg bw/day. Consumption data come from national food consumption surveys or, more crudely, food balance sheets; concentration data from monitoring programmes, total diet studies, in which foods are prepared as eaten and analysed, or maximum permitted levels as a conservative assumption. Exposure is estimated for average and high consumers and for vulnerable groups such as infants, who eat more food per kilogram of body weight.
Risk characterisation compares exposure with the health-based guidance value. If exposure is below the ADI or TDI, risk is considered low; an occasional excursion above it does not mean harm, because these values include safety margins and refer to lifetime intake. For genotoxic carcinogens without a threshold, the margin of exposure (MOE) is used: MOE = reference point (usually BMDL10) / estimated exposure. EFSA considers an MOE of 10,000 or more, based on a BMDL10 from animal studies, to be of low concern for public health. If a BMDL10 is 0.17 mg/kg bw/day and exposure is 0.001 mg/kg bw/day, the MOE is 170, which indicates a health concern. Risk characterisation always states uncertainties, and its results feed risk management decisions such as setting maximum levels, the subject of food-risk-analysis.
Plants make many chemicals that defend them against insects, fungi and grazing animals, and some are toxic or anti-nutritional for people. Traditional processing, such as soaking, fermenting, cooking and discarding the cooking water, has developed over centuries to make such foods safe.
Cyanogenic glycosides release hydrogen cyanide when plant tissue is damaged and the glycoside meets a β-glucosidase enzyme. Linamarin in cassava, amygdalin in bitter almonds and the kernels of apricots and other stone fruits, and dhurrin in sorghum are standard examples; bamboo shoots and lima beans also contain them. Cyanide inhibits cytochrome oxidase and blocks cellular respiration. Bitter cassava eaten without adequate processing has caused acute poisoning and, with chronic exposure and low protein intake, konzo, a paralytic disease of the legs, in parts of Africa. Grating, soaking, fermenting and drying cassava allow the enzyme to act and the cyanide to escape. Codex sets a limit for total hydrocyanic acid in sweet cassava. Glucosinolates in brassicas such as cabbage, mustard and rapeseed break down to isothiocyanates and other products, some of which are goitrogenic, interfering with thyroid iodine uptake, particularly where iodine intake is low.
Glycoalkaloids in potatoes, mainly α-solanine and α-chaconine, rise when tubers are exposed to light (greening, though the green chlorophyll itself is harmless), damaged or sprouted, and cause gastrointestinal and neurological symptoms at high intake. They are not destroyed by normal cooking, so green or sprouted parts and peel of affected tubers should be removed. Pyrrolizidine alkaloids, from plants such as Senecio, Heliotropium and Crotalaria that contaminate grain, herbal teas, honey and herbal products, cause liver veno-occlusive disease, and some are genotoxic carcinogens. Tropane alkaloids such as atropine and scopolamine, from Datura seeds contaminating cereals and buckwheat, are anticholinergic.
Lectins are proteins that bind carbohydrates on cell surfaces. Phytohaemagglutinin in raw or undercooked red kidney beans damages the intestinal lining and causes severe vomiting and diarrhoea within a few hours of eating as few as a handful of soaked raw beans. It is destroyed by boiling: soaking followed by vigorous boiling, commonly advised for at least 10 minutes, makes the beans safe, while slow cooking at low temperatures can increase toxicity rather than reduce it. Protease inhibitors, such as the Kunitz and Bowman-Birk trypsin inhibitors of soybeans, reduce protein digestion and in rats cause pancreatic enlargement; they are largely inactivated by moist heat, which is why raw soy flour is toasted.
Other anti-nutritional factors reduce the availability of nutrients. Phytic acid in cereals and legumes binds iron, zinc and calcium; fermentation, germination and the enzyme phytase reduce it. Oxalates in spinach, rhubarb leaves and amaranth bind calcium and, at high intake, contribute to kidney stones. Tannins bind proteins and iron. Gossypol in cottonseed is toxic and binds lysine, so cottonseed products must be processed to remove it. β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP) in the grass pea Lathyrus sativus, known in India as khesari dal, causes neurolathyrism, a spastic paralysis of the legs, when the pulse forms a large part of the diet for months; low-toxin varieties have been bred. Vicine and convicine in fava beans cause favism, an acute haemolytic anaemia, in people with glucose-6-phosphate dehydrogenase deficiency. Erucic acid in traditional rapeseed oil caused heart lesions in animals, which led to breeding of low-erucic varieties. Hypoglycin A in unripe ackee fruit causes severe hypoglycaemia. Coumarin in cassia cinnamon, safrole in sassafras and myristicin in nutmeg are flavour constituents limited by regulation or good practice.
Marine biotoxins are produced by microalgae, mainly dinoflagellates and diatoms, and accumulate in filter-feeding shellfish or move up food chains into fish. They are heat-stable, so cooking does not make contaminated seafood safe, and they do not change the appearance or smell of the food. Control depends on monitoring of harvesting areas and closing them when toxins or toxic algae exceed set levels.
Paralytic shellfish poisoning is caused by saxitoxin and its analogues, produced by dinoflagellates such as Alexandrium; saxitoxins block voltage-gated sodium channels, causing tingling of the lips and mouth, numbness and, in severe cases, respiratory paralysis within hours. Diarrhetic shellfish poisoning is caused by okadaic acid and dinophysistoxins from Dinophysis and Prorocentrum; they inhibit protein phosphatases and cause diarrhoea, vomiting and cramps. Amnesic shellfish poisoning is caused by domoic acid from diatoms of the genus Pseudo-nitzschia, an excitatory amino acid that damages the hippocampus; it was identified after a 1987 outbreak from mussels in Prince Edward Island, Canada, in which several people died and survivors suffered permanent memory loss. Neurotoxic shellfish poisoning is caused by brevetoxins from Karenia brevis. Ciguatera fish poisoning is caused by ciguatoxins produced by Gambierdiscus on tropical reefs, which accumulate in large predatory reef fish; symptoms include gastrointestinal upset and characteristic neurological signs such as reversal of hot and cold sensation, which can last for months. Tetrodotoxin in puffer fish, produced by bacteria associated with the fish, is a potent sodium-channel blocker, and preparation of puffer fish is restricted to licensed cooks in Japan and banned in some countries.
Biogenic amines are formed in food by bacterial decarboxylation of amino acids: histamine from histidine, tyramine from tyrosine, putrescine from ornithine and cadaverine from lysine. They occur in fish, cheese, fermented meats, wine and fermented vegetables.
Histamine poisoning, also called scombroid poisoning, follows eating fish rich in free histidine, such as tuna, mackerel, sardines, anchovies and mahi-mahi, that have been held without adequate chilling after catch. Bacteria such as Morganella morganii and other Enterobacteriaceae decarboxylate the histidine. Symptoms resemble an allergic reaction: flushing, headache, peppery taste, rash, palpitations and gastrointestinal upset, usually within minutes to an hour, and respond to antihistamines. Histamine is heat-stable, so cooking, canning or smoking does not remove it once formed, and the fish may look and smell normal. Control is rapid chilling after catch and maintaining the cold chain. Limits differ: the EU sets a three-class plan for fishery products from species associated with high histidine, with n = 9, c = 2, m = 100 mg/kg and M = 200 mg/kg; US FDA guidance uses 50 ppm as a decomposition indicator and treats 500 ppm as the hazard level. Putrescine and cadaverine potentiate histamine toxicity by inhibiting the enzymes that detoxify it.
Tyramine is the cause of the 'cheese reaction': people taking monoamine oxidase inhibitor drugs cannot break down dietary tyramine, and aged cheese, cured meats, yeast extracts or some wines can then cause a dangerous rise in blood pressure.
The moulds that produce mycotoxins, the crops they affect and the conditions that favour them are described in food-microbiology. This chapter concerns how the toxins act and how their risks are judged.
Aflatoxin B1 is a pro-carcinogen: liver cytochrome P450 enzymes convert it to aflatoxin B1-8,9-epoxide, which binds to DNA, chiefly at guanine, forming adducts. In populations with high exposure, liver tumours often carry a characteristic mutation at codon 249 of the p53 tumour-suppressor gene. Chronic hepatitis B infection multiplies the risk of liver cancer from aflatoxin many-fold. Because aflatoxin B1 is a genotoxic carcinogen, no tolerable intake is set; intake is kept as low as reasonably achievable and risk is expressed by margin of exposure. Acute aflatoxicosis, with liver failure, has occurred in outbreaks in Kenya and India from heavily contaminated maize. Aflatoxin M1, the metabolite excreted in milk, is less potent but matters because milk is a major food for infants. Aflatoxins have also been linked to stunted growth in children in high-exposure regions.
Ochratoxin A is nephrotoxic and immunotoxic, has a long half-life in human blood because it binds to serum albumin, and is classed by IARC as possibly carcinogenic to humans. Fumonisins inhibit ceramide synthase, disrupting sphingolipid metabolism, which explains equine leukoencephalomalacia and porcine pulmonary oedema; in people, high maize intake contaminated with fumonisins has been associated with oesophageal cancer and neural tube defects. Deoxynivalenol binds to ribosomes and inhibits protein synthesis, causing vomiting and feed refusal at higher doses and reduced weight gain at lower ones; JECFA has set a group tolerable intake for it and its acetylated derivatives. Zearalenone binds oestrogen receptors. Patulin is toxic to the gastrointestinal tract at high doses and is controlled in apple products largely as an indicator of the use of rotten fruit. Ergot alkaloids from Claviceps purpurea in rye caused ergotism, a disease of gangrene and convulsions, in medieval Europe.
Mycotoxin limits vary widely between countries and between foods, reflecting both risk assessment and the practical ability of producers to meet them. Codex sets maximum levels for some combinations, for example total aflatoxins in several nuts and aflatoxin M1 in milk (0.5 µg/kg), while the European Union generally sets stricter limits for many products, with the strictest levels for foods for infants and young children. India sets limits through FSSAI's contaminants regulations. Exporters must meet the importing country's limits, and rejections of consignments at borders are common.
Exposure assessment for mycotoxins is difficult because contamination varies from year to year with weather and is distributed unevenly within lots. Biomarkers in urine or blood, such as aflatoxin-albumin adducts and urinary deoxynivalenol, measure actual human exposure better than food analysis in some studies. Mitigation follows the food chain, as described in food-microbiology: good agricultural practice, drying and storage, sorting and cleaning. Processing has variable effects: most mycotoxins are heat-stable and survive cooking and baking, but sorting and cleaning of grain and nuts remove much of the toxin, wet milling distributes it between fractions, nixtamalisation of maize with alkali reduces aflatoxin and fumonisin, and fermentation of apple juice destroys patulin. Decontamination of human food by chemical treatment is generally not permitted, though some binders and treatments are allowed for animal feed.
Heavy metals are persistent: they are not destroyed by cooking or processing, and several accumulate in the body. Their presence in food comes from soil and water, industrial pollution, and materials used in food production.
Lead harms the developing nervous system, and young children and the fetus are most vulnerable, because they absorb a larger fraction of ingested lead and their brains are developing; effects include lower intelligence scores and behavioural problems. In adults, lead raises blood pressure and harms the kidneys. No safe level of exposure has been identified, which is why JECFA withdrew its tolerable weekly intake in 2010. Sources in food include contaminated soil and dust, lead-glazed ceramics, lead solder formerly used in cans, old water pipes, and deliberate adulteration, such as lead chromate added to turmeric to brighten its colour. Leaded petrol was historically the largest source of environmental lead; its phase-out has lowered blood lead levels worldwide.
Cadmium accumulates in the kidney, where its biological half-life is in the order of decades, and chronic exposure causes kidney tubular damage and bone demineralisation. Itai-itai disease, with severe bone pain and fractures, occurred in Japan's Jinzu River basin after rice paddies were irrigated with water contaminated by mining waste. Main dietary sources are cereals, especially rice grown on contaminated soils, potatoes and vegetables, offal such as kidney and liver, shellfish and cocoa. Phosphate fertilisers and sewage sludge add cadmium to soil. Smoking is a major additional source. JECFA's provisional tolerable monthly intake is 25 µg/kg bw.
Mercury in food is mainly methylmercury, formed by microorganisms from inorganic mercury in water and sediment, which accumulates up aquatic food chains. Large, long-lived predatory fish such as shark, swordfish, king mackerel, marlin and some tuna contain the highest levels. Methylmercury crosses the placenta and harms the developing brain. The outbreak at Minamata, Japan, recognised in 1956, in which a chemical plant discharged mercury into the bay and people eating local fish and shellfish suffered severe neurological damage and congenital disease, is the classic example. Because fish is also nutritious, authorities advise pregnant women and young children to choose fish lower in mercury rather than avoid fish altogether. JECFA's PTWI for methylmercury is 1.6 µg/kg bw.
Arsenic exists in inorganic forms, which are carcinogenic and cause skin lesions, cardiovascular disease and other effects, and organic forms. Arsenobetaine, the main form in fish and seafood, is considered essentially non-toxic and is excreted unchanged, so total arsenic results for seafood overstate risk; speciation analysis that measures inorganic arsenic is needed. The major exposure is through drinking water from naturally contaminated groundwater, as in Bangladesh and West Bengal, where millions of people have been exposed, and through rice, which takes up arsenic from flooded paddy soils more than other cereals. Codex sets maximum levels for inorganic arsenic in rice. Tin is a further contaminant of canned foods, from unlacquered tinplate in contact with acidic foods; high levels cause acute gastrointestinal irritation, and Codex sets maximum levels for canned foods and beverages.
Metals are analysed by atomic absorption spectrometry and, increasingly, by inductively coupled plasma mass spectrometry (ICP-MS), which measures many elements at very low concentrations; speciation of arsenic and mercury uses chromatography coupled to ICP-MS.
Pesticides include insecticides, herbicides, fungicides, rodenticides and plant growth regulators. Residues are the pesticide and its relevant metabolites remaining in food after use. Organophosphates, such as chlorpyrifos and malathion, and carbamates inhibit acetylcholinesterase, so acetylcholine accumulates at nerve endings, causing salivation, sweating, muscle twitching and, in severe poisoning, respiratory failure; organophosphate inhibition is largely irreversible, while carbamate inhibition reverses. Organochlorines such as DDT, aldrin and endosulfan are persistent and fat-soluble, accumulate in food chains and body fat, and have been banned or severely restricted in most countries, though residues persist in the environment. Pyrethroids are synthetic analogues of natural pyrethrins with lower mammalian toxicity. Neonicotinoids act on insect nicotinic receptors. Herbicides such as glyphosate and fungicides such as the dithiocarbamates have their own toxicological profiles.
Acute pesticide poisoning in people is mostly occupational or deliberate rather than dietary, and is a major problem in parts of Asia. Dietary residues raise questions of chronic exposure, of acute exposure from a single highly contaminated item, and of combined exposure to several pesticides with the same mode of action, which regulators increasingly assess as cumulative risk.
A maximum residue limit (MRL) is the highest concentration of a pesticide residue legally permitted in or on a food or feed, expressed in mg/kg. An MRL is first a trading and enforcement standard based on good agricultural practice: supervised field trials, using the pesticide at the highest approved rate with the shortest interval before harvest, show the residues that result, and the MRL is set to cover them. It is then checked against health-based values to make sure that dietary exposure at the MRL would be safe. A residue above the MRL shows that the pesticide was misused or used without approval; it does not by itself mean the food is unsafe, which depends on the ADI and ARfD.
Internationally, JMPR evaluates toxicology and residue data and recommends ADIs, ARfDs and MRLs, and the Codex Committee on Pesticide Residues proposes Codex MRLs for adoption. National systems differ. The European Union sets MRLs under Regulation (EC) No 396/2005, with a default MRL of 0.01 mg/kg for pesticides with no specific MRL, close to the limit of quantification. In India, pesticides are registered by the Central Insecticides Board and Registration Committee under the Insecticides Act, 1968, and MRLs are set by FSSAI. Because MRLs differ between countries, a residue legal in one market can cause rejection of an export consignment in another.
Exposure is estimated as the theoretical maximum daily intake, the sum of each MRL multiplied by daily consumption of the food, or more realistically using median residues from supervised trials and processing factors. Washing, peeling and cooking reduce many residues; drying and concentration can increase them per kilogram. Residues are analysed by multi-residue methods, typically using the QuEChERS extraction (quick, easy, cheap, effective, rugged and safe) followed by gas or liquid chromatography with tandem mass spectrometry.
Veterinary drugs, including antimicrobials, antiparasitic drugs, anti-inflammatories and hormones, leave residues in meat, milk, eggs, fish and honey if animals are slaughtered or their products used too soon after treatment. Residues matter because some cause allergic reactions, as penicillin can in sensitised people; some are toxic or carcinogenic; antimicrobial residues in milk inhibit the starter cultures used for yoghurt and cheese; and the use of antimicrobials in animals contributes to antimicrobial resistance, which is covered in other subjects.
Maximum residue limits for veterinary drugs are set in the same way as for pesticides: JECFA evaluates the toxicology and sets an ADI, which may include microbiological endpoints for antimicrobials, such as effects on human gut flora, and recommends MRLs for each target tissue; the Codex Committee on Residues of Veterinary Drugs in Foods proposes them. In the European Union, Regulation (EU) No 37/2010 lists substances with their MRLs and a table of prohibited substances for which no MRL can be set because no safe level exists, including chloramphenicol, nitrofurans, nitroimidazoles and malachite green. For such prohibited substances, the EU uses reference points for action, set at levels that laboratories can reliably detect, to decide when a consignment must be rejected. The Codex and EU MRL for benzylpenicillin in milk is 4 µg/kg.
The withdrawal period is the time that must elapse between the last dose and slaughter or use of milk or eggs, so that residues fall below the MRL. It is set for each product, species and route, and printed on the label; it is not a property of the drug alone. Residues above the MRL usually result from ignoring the withdrawal period, using a drug off-label, dosing errors, or failure to identify treated animals.
Growth-promoting hormones are a classic example of regulatory difference. The United States, Canada and several other countries permit some natural and synthetic hormones as implants in beef cattle under conditions of use, while the European Union has banned their use for growth promotion since the 1980s and bans imports of meat from treated animals, a policy that led to the EC — Hormones dispute at the World Trade Organization. β-Agonists such as clenbuterol increase lean meat but have caused outbreaks of acute poisoning, with tremor and palpitations, in people who ate liver or meat from treated animals; clenbuterol is banned for food animals in the European Union, China and many other countries. Ractopamine is permitted in some countries and banned in others.
Residue monitoring programmes sample animals and products according to a national plan, often risk-based, and analyse them for authorised and prohibited substances. Screening methods include microbial inhibition tests for antimicrobials in milk and meat, receptor-based and immunological tests, and rapid strip tests at milk collection centres; positive screens are confirmed by liquid chromatography with tandem mass spectrometry, which identifies and quantifies the residue. In India, residue monitoring is part of FSSAI's work and of export certification for honey, shrimp and other products, where rejections for residues of banned antimicrobials have occurred. Prevention depends on prescription control, correct dosing, records of treatment, identification of treated animals and respect for withdrawal periods.
Process contaminants are harmful substances formed in food during processing or cooking rather than present in raw materials. They are a reminder that the processes that make food safe and palatable can also create hazards.
Acrylamide forms in the Maillard reaction between the amino acid asparagine and reducing sugars such as glucose and fructose, at temperatures above about 120 °C in low-moisture conditions. Its presence in common foods was reported by Swedish researchers in 2002. The main sources are fried potato products such as chips and crisps, bread and bakery products, breakfast cereals, biscuits and coffee. Acrylamide is classed by IARC as probably carcinogenic to humans (Group 2A), and is neurotoxic at high exposure. Mitigation includes choosing potato varieties and storage conditions that keep reducing sugars low (cold storage raises them), blanching potato pieces, lowering frying temperatures and times and cooking to a golden rather than brown colour, using the enzyme asparaginase in doughs, and replacing ammonium bicarbonate in biscuits. The European Union requires food businesses to apply mitigation measures and sets benchmark levels under Regulation (EU) 2017/2158.
Polycyclic aromatic hydrocarbons (PAHs) form during incomplete combustion of organic matter and enter food through smoking, grilling over open flames, direct drying with combustion gases, and from environmental contamination of oils and seafood. Benzo[a]pyrene is a genotoxic carcinogen (IARC Group 1) and has been used as a marker; the EU now also regulates the sum of four PAHs. Control includes indirect smoking, liquid smoke, avoiding contact of food with flames and fat dripping onto them, and refining of contaminated oils. Heterocyclic aromatic amines form in meat and fish cooked at high temperatures, from creatine, amino acids and sugars.
3-Monochloropropane-1,2-diol (3-MCPD) was first identified in acid-hydrolysed vegetable protein and soy sauces made by hydrochloric acid hydrolysis. Its fatty acid esters, together with glycidyl esters, form during high-temperature deodorisation of refined vegetable oils, especially palm oil, and are found in refined oils and in foods made from them, including infant formula. 3-MCPD is a kidney and testicular toxicant with a tolerable daily intake set by EFSA, while glycidol, released from glycidyl esters, is a genotoxic carcinogen. Mitigation includes better selection of crude oil, washing, lower deodorisation temperatures and post-refining treatments.
Furan forms during heat treatment of foods in closed containers, such as canned and jarred foods and coffee, from carbohydrates, ascorbic acid and polyunsaturated fatty acids; it is volatile, so heating jarred food in an open pan reduces it. It is carcinogenic in rodents. Nitrosamines, such as N-nitrosodimethylamine, form from nitrite or nitrogen oxides reacting with secondary amines; cured meats fried at high temperatures, such as bacon, smoked and dried fish, and beer made from malt dried by direct firing were historical sources. Adding ascorbate or erythorbate to cured meats inhibits nitrosation, and indirect malt kilning reduced levels in beer. Ethyl carbamate forms from urea and other precursors in fermented foods and beverages, and especially in stone-fruit spirits from cyanogenic glycosides in the stones. Benzene can form in soft drinks containing both benzoate and ascorbic acid, especially when exposed to heat and light. Trans fatty acids, formed by partial hydrogenation of oils, are a further processing hazard, now restricted by limits in many countries, including India, which limits industrial trans fat to 2 per cent of total fat in oils and fats.
Food contact materials, such as plastics, paper and board, metals, glass, ceramics, coatings, inks and adhesives, can transfer substances into food, a process called migration. Migration depends on the nature of the migrant (its molecular size and solubility), the type of food (fatty foods extract fat-soluble substances far more than aqueous foods), the temperature and time of contact, and the ratio of contact surface area to food volume. Hot filling, microwave heating, long storage and high fat content all increase migration.
The European Union's framework Regulation (EC) No 1935/2004 requires that materials do not transfer constituents to food in quantities that could endanger health, change the composition unacceptably or deteriorate its taste or odour, and requires traceability and a declaration of compliance. Good manufacturing practice for these materials is set by Regulation (EC) No 2023/2006. For plastics, Regulation (EU) No 10/2011 lists authorised substances and sets an overall migration limit of 10 mg per dm² of contact surface, or 60 mg per kg of food for some cases, and specific migration limits for individual substances based on toxicology. Migration testing uses food simulants: 10 per cent ethanol (simulant A) for aqueous foods, 3 per cent acetic acid (B) for acidic foods, 20 and 50 per cent ethanol (C and D1) for alcoholic and some fatty foods, vegetable oil (D2) for fatty foods, and modified polyphenylene oxide (E) for dry foods, under conditions of time and temperature that represent the worst foreseeable use. In the United States, substances used in food contact materials are regulated as indirect food additives or through food contact notifications to FDA. In India, FSSAI's packaging regulations of 2018 set general and specific requirements and refer to Indian Standards for materials.
Several migrants have been prominent. Bisphenol A (BPA), used in polycarbonate and in epoxy can coatings, has oestrogenic activity; after EFSA lowered its tolerable daily intake sharply in 2023, the European Union decided to ban its use in food contact materials, with transition periods. Phthalates, used as plasticisers in PVC, including in jar lid gaskets, migrate readily into fatty foods and have reproductive toxicity, so several are restricted. Primary aromatic amines can migrate from polyurethane adhesives and from some kitchen utensils. Styrene can migrate from polystyrene. Mineral oil hydrocarbons, saturated (MOSH) and aromatic (MOAH), migrate from recycled paperboard containing newspaper inks and from printing inks, especially into dry foods such as rice and cereals; MOAH may include genotoxic carcinogens, and functional barriers or virgin fibre are used to prevent migration. Per- and polyfluoroalkyl substances (PFAS) used for grease resistance in paper are persistent and increasingly restricted. Tin and lead can migrate from cans and ceramics, as described in chapter 6.
Non-intentionally added substances (NIAS), such as impurities, reaction and breakdown products and contaminants from recycling, form a growing concern because they are not on any list and may be unknown; manufacturers must assess them using analysis and risk assessment. Recycled plastics for food contact require processes that remove contaminants to safe levels, which is why authorities authorise specific recycling processes, particularly for polyethylene terephthalate.
A food allergy is an adverse reaction caused by an immune response to a food, usually a protein. The commonest form is immunoglobulin E (IgE)-mediated allergy. On first exposure, a sensitised person makes IgE antibodies against the protein, which bind to mast cells and basophils. On later exposure, the protein cross-links the IgE on these cells, which release histamine and other mediators within minutes, causing hives, swelling, vomiting, wheeze and, in the most severe cases, anaphylaxis, a rapid, generalised and potentially fatal reaction. Tiny amounts, in the order of milligrams of protein, can provoke reactions in highly sensitive people. Non-IgE-mediated allergies, such as food protein-induced enterocolitis syndrome in infants, are delayed. Coeliac disease is an immune-mediated enteropathy triggered by gluten proteins in wheat, barley and rye in genetically susceptible people carrying HLA-DQ2 or DQ8; it is autoimmune rather than allergic, and the only treatment is lifelong avoidance of gluten. Codex defines gluten-free foods as containing no more than 20 mg/kg of gluten.
A small number of foods cause most allergic reactions, and regulations list them. The EU list in Regulation (EU) No 1169/2011 has fourteen: cereals containing gluten, crustaceans, eggs, fish, peanuts, soybeans, milk, tree nuts, celery, mustard, sesame, sulphur dioxide and sulphites above 10 mg/kg or 10 mg/L expressed as SO2, lupin and molluscs. The United States has nine major allergens: milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans and, since 2023, sesame. Codex and India have their own lists. Sulphites are listed because they cause reactions in some asthmatics, although these are not IgE-mediated.
Allergenic proteins differ in stability. Peanut proteins such as Ara h 2, the caseins of milk and ovomucoid of egg resist heat and digestion, which helps explain their potency; many fruit and vegetable allergens are labile. People sensitised to birch pollen often react to raw apple, cherry or hazelnut because of similar proteins, the pollen-food or oral allergy syndrome, usually with mild mouth symptoms and tolerance of the cooked fruit. Tropomyosin causes cross-reactivity between crustaceans, molluscs and dust mites. Allergens in foods are detected by ELISA, which measures protein, by PCR, which detects DNA of the allergenic food, and increasingly by mass spectrometry of marker peptides; managing them in factories is covered in food-safety-management-systems.
A food intolerance is an adverse reaction to food that does not involve the immune system. It is usually dose-dependent, so small amounts are tolerated, unlike allergy, where traces can be dangerous. Lactose intolerance results from low intestinal lactase: most of the world's adults lose lactase activity after weaning, a trait called lactase non-persistence, while lactase persistence is common in populations with a long history of dairying, such as those of northern Europe and some pastoral groups in Africa and India. Undigested lactose is fermented in the colon, causing bloating, gas and diarrhoea; most people with lactose intolerance tolerate small amounts of milk, yoghurt and hard cheese, and lactose-free milk is made with added lactase. Lactose intolerance must not be confused with cow's milk allergy, an immune reaction to milk proteins.
Other intolerances include fructose malabsorption and sensitivity to fermentable carbohydrates (FODMAPs) in irritable bowel syndrome; histamine intolerance, thought to involve low activity of the enzyme diamine oxidase; and reactions to sulphites in asthmatics. Inborn errors of metabolism are rarer but severe: phenylketonuria, in which phenylalanine cannot be metabolised, requires a low-phenylalanine diet, which is why foods containing the sweetener aspartame must state that they contain a source of phenylalanine; hereditary fructose intolerance, due to aldolase B deficiency, makes fructose and sucrose dangerous; and favism, described in chapter 3, affects people with G6PD deficiency. The 'monosodium glutamate symptom complex' reported after Chinese restaurant meals has not been consistently reproduced in controlled studies, and JECFA has given glutamate an ADI 'not specified'.
A food additive is a substance not normally eaten as a food in itself, added intentionally for a technological purpose such as preservation, colour, texture or sweetness. Additives are the most thoroughly tested chemicals in food because they are deliberately added and approved before use. Internationally, JECFA evaluates each additive's toxicology, sets an ADI or an ADI 'not specified' for substances of very low toxicity, and specifies purity; the Codex General Standard for Food Additives (CXS 192-1995) lists permitted additives, the foods in which they may be used and maximum use levels. Additives are identified by International Numbering System (INS) numbers, and in the European Union by E numbers. National lists differ: in India, permitted additives and limits are set in FSSAI's food products standards and food additives regulations, in the EU in Regulation (EC) No 1333/2008, and in the United States through food additive approvals and substances generally recognised as safe.
Approval requires that the additive is safe at the proposed use, that there is a technological need that cannot be met otherwise, and that its use does not mislead the consumer. Maximum use levels are set so that estimated intake, for average and high consumers, stays below the ADI; if intake estimates exceed it, use levels or permitted foods are reduced. Additives are re-evaluated when new data appear: the EU has run a systematic re-evaluation of all additives approved before 2009. A worked check: if an additive's ADI is 5 mg/kg bw/day, a 20 kg child may take in 100 mg a day; a drink containing 150 mg/L consumed at 1 litre a day would exceed it.
Several additives are taught because of their toxicological history. Nitrite, used in curing meat for colour, flavour and protection against Clostridium botulinum, can cause methaemoglobinaemia at high doses and contributes to nitrosamine formation, so maximum levels balance its preservative benefit against its risks. Sulphites, used as preservatives and antioxidants in wine, dried fruit and some processed foods, can trigger reactions in some people with asthma and destroy thiamine, so they must be declared above 10 mg/kg. Benzoic acid and benzoates are effective in acidic foods; with ascorbic acid they can form benzene under heat and light. Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are antioxidants whose use is limited by their ADIs.
Colours have attracted the most public concern. A study published in 2007 by researchers at the University of Southampton found that mixtures of certain synthetic colours with sodium benzoate increased hyperactive behaviour in some children; the EU then required foods containing six of these colours, including tartrazine and sunset yellow, to carry a warning that they may have an adverse effect on activity and attention in children. Titanium dioxide (E171), used as a white colour, was judged by EFSA in 2021 to be no longer considered safe as a food additive, because concerns about genotoxicity could not be ruled out, and it was withdrawn in the EU in 2022; other jurisdictions reached different conclusions. Aspartame was classified by IARC in 2023 as possibly carcinogenic to humans (Group 2B), while JECFA in the same year reaffirmed its ADI of 40 mg/kg bw, a contrast that illustrates the difference between hazard identification, which asks whether a substance can cause harm, and risk assessment, which asks whether it does at actual intakes. Monosodium glutamate has an ADI 'not specified'.
A student uses this subject to master definitions that every exam asks (NOAEL, ADI, TDI, PTWI, ARfD, MRL, MOE) and the arithmetic that links them: ADI from NOAEL and uncertainty factor, intake in mg per day for a given body weight, dietary exposure from concentration and consumption, and margin of exposure. Pairing each toxicant with its food and effect, such as linamarin with cassava, β-ODAP with khesari dal, phytohaemagglutinin with raw kidney beans and cadmium with itai-itai disease, answers most recall questions.
Five years into a quality, regulatory or laboratory role, a technologist checks that raw materials meet contaminant and residue limits for each destination market, commissions and interprets residue and metal analyses, applies acrylamide mitigation in a frying or baking line, assesses packaging suppliers' declarations of compliance and migration tests, keeps the allergen list for every product accurate, and answers customer questions about additives. When a consignment is rejected at a border for a residue, the same person traces the cause back to the farm or supplier.
A senior regulatory affairs or technical leader with twenty-five years' experience sets company positions on emerging contaminants such as MOAH, PFAS or new process contaminants, represents the company or country in standard-setting bodies, decides how to respond when IARC or EFSA publishes a new evaluation, manages supplier programmes for mycotoxins and residues across sourcing regions, and communicates risk to customers, consumers and the media in a way that neither dismisses nor exaggerates it.
A researcher at this level works on the open problems: replacing animal tests with new approach methods, assessing mixtures and cumulative exposure, identifying and evaluating non-intentionally added substances, using biomarkers to measure real exposure, understanding thresholds for food allergens to set reference doses for precautionary labelling, and designing processing interventions that reduce contaminants without creating new ones. Such work requires both laboratory toxicology and exposure science, and an honest statement of uncertainty.
This manual does not reproduce national maximum levels, MRLs or migration limits in tables, which differ between Codex, the EU, the US and India and change often; values quoted are examples from named sources and must be checked in current law. Quantitative dose-response modelling, cumulative risk assessment of pesticide mixtures, radionuclides in food, dioxins and PCBs, and the detailed regulation of novel foods are not covered or only mentioned. Allergen reference doses for precautionary labelling are not given because international recommendations are still being adopted. Mould ecology is in food-microbiology, allergen management in food-safety-management-systems and the risk-analysis framework in food-risk-analysis.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
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