Natural toxins are toxin compounds that are naturally produced by living organisms. These toxins are not harmful to the organisms themselves but may be toxic to other creatures, including humans, when eaten. This article explores naturally occurring toxins, focusing on microbial toxins, including algae and fungal toxins.
Microbial toxins are chemical substances produced naturally by microorganisms and are one of the primary concerns in the area of food safety. Microbial toxins are produced by algae, fungi, and bacteria.
Algal Toxins in Agricultural and Aquatic Systems
Algae can be unicellular (e.g., most phytoplanktons) or multicellular (e.g., seaweed) and are found in freshwater, marine, and terrestrial habitats. Some algae, such as dinoflagellates, produce algal toxins (phycotoxins) that can be harmful to humans.
Under certain conditions, the population of algae in an aquatic system can increase rapidly to become an algal bloom, commonly referred to as red tide or blue-green algae. Various species of algae are involved in algal blooms, and these species change over time, based on temperature, light, nutrients, and other factors.
Algal blooms are called Harmful Algal Blooms (HABs) when they pose environmental or health hazards. The blooms occur when water is contaminated by phosphates.
During HABs, or as a consequence of bioaccumulation through the marine food chain, the toxins produced by algae may accumulate in a variety of marine organisms, such as molluscs, crustaceans, and finfish, as well as in freshwater fish and shellfish.
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Types of Algal Toxins in Agriculture
Algal toxins are tasteless, odourless, and heat resistant. The most common algal toxins are saxitoxins, brevetoxins, dinophysistoxins, domoic acid, and ciguatoxins.
Shellfish and finfish contaminated with these toxins can be potentially harmful to human health, causing a variety of foodborne illnesses such as Paralytic Shellfish Poisoning (PSP), Neurotoxic Shellfish Poisoning (NSP), Diarrheic Shellfish Poisoning (DSP), Amnesic Shellfish Poisoning (ASP), and Ciguatera Fish Poisoning (CFP) (See Table 1).
Saxitoxins in Aquatic Food Production
Saxitoxins are natural toxins produced by microscopic marine algae found in coastal waters. Saxitoxins may accumulate in the neck (siphon) and the gills of butter clams; in the roe or gonads of scallops, and in the tomalley (also known as hepatopancreas soft green substance inside the body cavity) of crabs and lobsters.
It is recommended that people avoid eating these parts. The consumption of shellfish that contain high levels of saxitoxins can cause Paralytic Shellfish Poisoning in humans (See Table 1). Saxitoxins cannot be destroyed by cooking.
Brevetoxins in Marine Agriculture
Brevetoxins are natural toxins released by Karenia brevis, a marine dinoflagellate formerly known as Gymnodinium breve and Ptychodiscus brevis. These toxins, which are tasteless, odourless, and resistant to heat and acid, are toxic to fish, marine mammals, birds, and humans but not to shellfish such as oysters and mussels.
The consumption of raw or under-cooked shellfish that have accumulated high levels of brevetoxins can cause Neurotoxic Shellfish Poisoning in humans (see Table 1).
Dinophysistoxins in Shellfish Production
Dinophysistoxins are natural toxins produced by dinoflagellates belonging to the genus Dinophysis and the genus Prorocentrum. In humans, they can cause Diarrhetic Shellfish Poisoning, a gastrointestinal illness associated with the ingestion of contaminated bivalves, such as mussels, scallops, and oysters.
Domoic Acid in Agricultural Seafood Safety
Domoic acid, a naturally occurring toxin, is found in some marine algae of the genus Pseudo-nitzschia, particularly Pseudo-nitzschia pungens. Domoic acid is a neurotoxin that cannot be destroyed by cooking or freezing and that accumulates in filter-feeding, bivalve shellfish such as clams, mussels, oysters, and scallops. People may be at risk for Amnesic Shellfish Poisoning if they eat shellfish that contain high levels of domoic acid.
Algal Toxins and Food Poisoning in Agriculture
Table 1 lists the most common types of food poisoning caused by shellfish and fish contaminated with algal toxins, as well as the preventive measures that can be followed in order to prevent such food poisoning.
A. Saxitoxin
i. ILLNESS: Paralytic Shellfish Poisoning – PSP
ii. Symptoms in humans (individuals experiencing any of these symptoms should seek medical attention immediately):
- In mild cases may experience: tingling sensation or numbness around the lips (which slowly spreads to the face and neck), prickly sensation in the fingertips and toes, headache, and dizziness
- In severe cases may experience: incoherent speech, prickly sensations in the arms and legs, stiffness and uncoordinated movement, weakness, rapid pulse, difficulty breathing, salivation, temporary blindness, nausea, and vomiting
- In extreme cases may experience: paralysis of respiratory muscles, which may lead to respiratory arrest and death within 2 to 12 hours after eating contaminated shellfish
iii. Reaction time: Usually within a few minutes (5 to 30) to 10 hours after ingestion
iv. Associated finfish and shellfish: Oysters, scallops (e.g., pink, spiny, and purple hinge rock scallops), clams (e.g., butter clams, razor clams, and little neck clams), mussels (e.g., blue mussels), cockles, whelks, and tomalley (hepatopancreas) of crustaceans such as crabs and lobsters
v. Preventive Measures:
- Do not harvest or eat shellfish from closed areas or areas prone to hazardous algal blooms
- Obtain shellfish from a reliable supplier
- Uncooked shellfish should be refrigerated or frozen until ready to be prepared
- Do not eat shellfish such as clams and scallops that do not open during cooking
- Because of the possibility of the accumulation of saxitoxin, Health Canada recommends that lobster tomalley (hepatopancreas) be eaten in small quantities: no more than the amount from one cooked lobster daily for adults and no consumption of lobster tomalley by children
B. Brevetoxins
i. ILLNESS: Neurotoxic Shellfish Poisoning – NSP
ii. Symptoms in humans (individuals experiencing any of these symptoms should seek medical attention immediately):
- Cardiovascular symptoms (hyper/hypotension)
- Neurological symptoms (sensation of tingling, prickling, numbness of lips, tongue, and throat, dizziness, and hot and cold sensations)
iii. Reaction time: Usually within a few hours after ingestion
Associated finfish and shellfish: Oysters, mussels
iv. Preventive Measures:
- Do not harvest or eat shellfish from closed areas or areas prone to Karenia brevis blooms
- Obtain shellfish from a reliable source
C. Dinophysistoxins
i. ILLNESS: Diarrheic Shellfish Poisoning – DSP
ii. Symptoms in humans (individuals experiencing any of these symptoms should seek medical attention immediately):
- May experience: diarrhea, nausea, vomiting, abdominal pain, chills, headache, and fever
iii. Reaction time: Usually within 30 minutes to a few hours (2-3) after ingestion
iv. Associated finfish and shellfish: Mussels, scallops, oysters, and clams
v. Preventive Measures:
- Do not harvest or eat shellfish from closed areas
- Obtain shellfish from a reliable source
- Refrigerate and use shellfish within 2-3 days or freeze until they are ready to be eaten
D. Domoic Acid
i. ILLNESS: Amnesic Shellfish Poisoning – ASP
ii. Symptoms in humans (individuals experiencing any of these symptoms should seek medical attention immediately):
- May experience: nausea, vomiting, diarrhea, muscle weakness, disorientation, and memory loss
- In severe cases (within 48 hours) may experience: headache, dizziness, confusion, disorientation, short-term memory loss, muscle weakness, seizures, profuse respiratory secretion, cardiac arrhythmias (irregular heartbeat), coma, and possibly death
iii. Reaction time: Usually within 30 minutes to 6 hours after ingestion
iv. Associated finfish and shellfish: Clams (e.g., foot/siphon/mantle of razor clams), mussels, oysters, scallops, and crabs (e.g., viscera of Dungeness crabs)
v. Preventive Measures:
- Do not harvest or eat shellfish from closed areas
- Cooking does not destroy domoic acid
- Clean crabs thoroughly by removing all viscera
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Fungal Toxins in Agricultural Crops
Some moulds and mushrooms have the ability to produce toxins, referred to as mycotoxins, which may cause illnesses (see Tables 2, 3, 4, 5, and 6).
Mycotoxins in Food Safety
Mycotoxins are toxic secondary metabolites produced by fungi found in food (e.g., grains, nut crops, celery, grape juice, and apple juice). The consumption of foods contaminated with mycotoxins can cause mycotoxin poisoning, referred to as mycotoxicosis.
Mycotoxins released by fungi make food unsafe to eat. The production of mycotoxins depends on temperature and moisture, and can occur before or after harvest and during storage, transportation, and processing.
Because mouldy foods may contain any of the mycotoxins identified in Table 2, they should not be eaten, but should be discarded and destroyed properly.
Some mycotoxins, such as the aflatoxins (named from the fungus, Aspergillus flavus), are carcinogenic, while others may be responsible for kidney and liver damage (ochratoxin A), affect the reproductive function (zearalenone), and interfere with the body’s immune system (trichothecenes).
The most common types of mycotoxins are aflatoxin, ochratoxin, trichothecenes, patulin, fumonisin, zearalenone, and ergot alkaloids.
Aflatoxins in Grain and Dairy Production
Aflatoxins are produced by three species of Aspergillus and are usually associated with grains or toxins in some mushrooms or toadstool species. They can also be found in milk and milk products from animals that have consumed plants, plant products, or animal feed contaminated with the aflatoxin AFB1, which is transformed to AFM1, a less toxic metabolite. Long-term exposure to low levels of aflatoxin in the diet may pose certain health concerns for humans (see Table 2).
Ochratoxins in Agricultural Products
Ochratoxins are a group of toxic substances produced by the fungus, Penicillium verrucosum, and different species of Aspergillus. Ochratoxin can be found in beer and wine, some spices, and also in some foods such as cereals and fresh grapes.
Ochratoxins are also produced in grains that have not been properly dried during processing, or have not been properly stored and hence can be found in animal products that have been fed contaminated grains.
Trichothecenes in Cereal Crops
Trichothecenes are a large group of structurally related mycotoxins, with over 80 identified. Only a few are detected in cereals and grains such as T-2 toxin, deoxynivalenol, nivalenol, diacetoxyscirpenol, and satratoxins. Acute toxicity varies considerably and T-2 toxin is more toxic than deoxynivalenol.
Vomitoxin (deoxynivalenol) and HT-2 toxins, are non-volatile (do not evaporate at normal temperatures and pressures) and are heat-stable.
Patulin in Fruit-Based Products
Patulin is a toxic secondary metabolite produced by some species of mould, such as Penicillium and Aspergillus. Apple juice made from bruised or damaged apples is the main source of patulin intake for humans.
Patulin can be found mainly in mouldy fruits such as apples and apple products. To reduce exposure to patulin, wash food thoroughly and remove damaged portions before consumption or adding to other foods.
Fumonisins in Corn Production
Fumonisins are produced by fungi such as Fusarium proliferatum and Fusarium verticillioides. Fusarium moniliforme (Fusarium verticillioides) is a common pathogen of corn and is found wherever corn is grown. Kernels that are intact may contain the fungus and the toxin but show no visual signs of the fungal contamination.
Zearalenone in Cereal Crops
Zearalenone is a toxin excreted by fungi such as Fusarium culmorum and Fusarium equiseti. It targets the reproductive organs of animals. Zearalenone needs high humidity and low temperatures to survive, and is found in mouldy cereal crops, such as corn, barley, oats, wheat, rice, and sorghum.
Ergot Alkaloids in Grain Production
Ergot is a plant disease caused by the fungus Claviceps purpurea, which produces alkaloids and infects the developing grains of cereals and grasses.
Mycotoxins and Their Impact on Agriculture
Table 2 lists the organisms responsible for the production of these mycotoxins, the foods in which these toxins can be found, and the symptoms of exposure in humans.
| MYCOTOXINS | Moulds | Related foods | Symptoms in humans |
|---|---|---|---|
| Aflatoxins | Aspergillus flavus, A. parasiticus, A. nomius | Ground nuts, tree nuts, corn, wheat, bran, flour, peanuts, milk, and milk products | Chronic poisoning may cause: liver cancer, impaired immune function |
| Acute poisoning may cause: diminished appetite, malaise, low fever, vomiting, abdominal pain, hepatitis, liver failure (may also affect kidney, spleen, and pancreas), and possibly death | |||
| Ochratoxins | Penicillium verrucosum, A. carbonarius (grows at high temp. and can withstand heat and ultraviolet light), A. alliaceus, A. auricomus, A. niger, A. ochraceus | Corn, oats, rye, wheat, coffee beans, spices, wine, grapes, fruits (including vine fruits and dried vine products), and pork | There is insufficient evidence of health effects in humans; however, chronic exposure to Ochratoxin A from contaminated foods may cause: kidney tumours |
| Trichothecenes | Fusarium sporotrichioides, F. poae, F. equiseti, F. acuminatum | Corn, wheat, millet, barley, cereals, oats, sorghum, and rye | May experience: mouth and throat inflammation, inflammation of the mucous membrane of the stomach and intestines, vomiting, immunosuppression, skin hemorrhages and necrotic ulcers on the body, headaches, chills, severe nausea, vomiting, and visual disturbances |
| Patulin | Penicillium expansum, Byssochlamys spp., Aspergillus spp. | Mouldy fruits (especially apples and apple products made with bruised apples or unfermented apple juice), and vegetables | May cause: ulceration, congestion, and hemorrhagic lesions (especially in the gastrointestinal tract) |
| Fumonisins | Fusarium moniliforme, F. proliferatum, F. verticillioides | Corn, corn products (e.g., grits, germ, flour), wheat, and bran | May be linked to: oesophageal and liver cancer |
| Zearalenone | F. graminearum, F. culmorum, F. equiseti, F. crookwellense | Mouldy grains, corn, oats, wheat, and barley | There is inconclusive evidence of health effects in humans |
| Alkaloids | Claviceps purpurea fungus | Rye, wheat, and barley (to a lesser extent) | May cause: impaired blood circulation, causing alternating burning and freezing sensations, followed by gangrene of extremities (referred to as St. Anthony’s fire). Nervous convulsions may also occur leading to eventual death |
Mushroom Toxins in Agriculture
While there are many mushroom species that have been identified, few are able to cause poisoning in humans. Mushroom poisonings are not only caused by natural toxins; the conditions under which mushrooms are handled, packaged, stored, and transported can also facilitate bacterial growth.
The toxins released by poisonous mushrooms are produced naturally and cannot be destroyed by cooking, canning, or freezing. Mushroom poisoning can be caused by four types of toxins: protoplasmic toxins, neurotoxins, gastrointestinal irritants, and coprine or disulfiram-like toxins.
Protoplasmic Toxins in Mushroom Production
The consumption of mushrooms that contain protoplasmic toxins, such as amatoxin or orellanine, can cause protoplasmic poisoning. In humans, protoplasmic poisoning causes cell damage and organ failure (e.g., liver and kidney damage). Table 3 highlights the toxins responsible for protoplasmic poisoning, reaction times, and associated symptoms.
Mushrooms and Protoplasmic Toxins
| TOXINS | Mushrooms | Reaction time | Symptoms in humans |
|---|---|---|---|
| Amatoxins | Amanita phalloides, A. virosa, A. verna (The green death cap, destroying angel, and fool’s mushroom), Galerina autumnales (Autumn skullcap), G. marginata, Lepiota helveola, L. brunneoincarnata, L. josserandii | Usually between 8 (or as early as 6) to 12 hours after ingestion | In mild cases may experience: vomiting, diarrhea, abdominal pain, and nausea. |
| In severe cases may experience: liver failure, coagulation disorders, brain damage, acute renal failure, and death | |||
| Hydrazines | Gyromitra esculenta, G. gigas | Usually within 6 to 10 hours after ingestion | May experience: abdominal pain, severe headache, vomiting, diarrhea, liver damage, and damage to the central nervous system and blood cells |
| Orellanine | Cortinarius speciocissimus, C. orellanus (Sorrel webcap) | Usually within 3 to 14 days after ingestion | May experience: burning thirst, excessive urination, nausea, headache, muscular pain, chills, spasms, and loss of consciousness. |
| In severe cases may experience: kidney and liver damage, renal failure, and death |
Neurotoxins in Mushroom Safety
Some mushroom species contain neurotoxins (see Table 4), poisons that attack the nervous system and affect, damage, or destroy nerve cells. The most common mushroom neurotoxins are muscarine, ibotenic acid/muscimol, and psilocybin.
Mushrooms and Neurotoxins
| Toxins | Mushrooms | Reaction time | Symptoms in humans |
|---|---|---|---|
| Muscarine | Inocybe geophylla, I. patouillardii, I. fastigiata, I. geophylla, C. dealbata, A. muscaria, Boletus, Lactarius | Usually within 15 to 30 minutes after ingestion | In mild cases may experience: increased salivation, perspiration/sweating, and watery eyes/tearing (lacrimation). |
| In severe cases may experience: abdominal pain, severe nausea, diarrhea, blurred vision, laboured breathing, and ingestion of large doses may cause cardiac/respiratory failure | |||
| Ibotenic Acid and Muscimol | A. muscaria (Fly Agaric), A. pantherina (Panthercap), A. gemmata | Usually within 1 to 2 hours after ingestion | May experience: nausea, vomiting, diarrhea, colour hallucinations, slow pulse, hypotension, irritability, lack of coordination, anxiety, hysteria, convulsions, fever and seizures (in children), abdominal discomfort, drowsiness, dizziness, hyperactivity, excitability, and coma |
| Psilocybin and Psilocin | P. cubensis (Golden tops), P. mexicana, P. cyanescens, P. semilanceata (Liberty cap), C. cyanopus | Usually within 20 minutes after ingestion | May experience: anxiety, tension, visual effects (e.g., blurring), euphoria, increased colour perception (with eyes closed), headache, and fatigue |
Gastrointestinal Irritants in Mushroom Production
Some mushrooms (such as Jack O’Lantern and Naked Brimcap) contain toxins that can irritate the gastrointestinal tract (see Table 5).
Mushrooms and Gastrointestinal Irritants
| Toxins | Mushrooms | Symptoms in humans |
|---|---|---|
| Gastrointestinal Irritants | Chlorophyllum molybditis (Green Gill), Entoloma lividum (Gray Pink gill), Tricholoma pardinum (Tigertop), Omphalotus illudens (Jack O’Lantern), Paxillus involutus (Naked Brimcap), Russula emetica (Sickener), Verpa bohemica (Early False Morel) confused with Morchella esculenta (True Morel), Agaricus arvensis, A. xanthodermus (Horse Mushroom), and Boletus piperatus, B. calopus, B. santanas (Pepper Bolete) | May experience: nausea, vomiting, diarrhea, and abdominal pain |
Coprine or Disulfiram-like Toxins in Mushrooms
Coprine is an amino acid produced by some mushroom species such as Coprinus atramentarius (Inky-cap mushroom) and Clitocybe clavipes (Fat-footed Clitocybe). Coprine is converted in the body to cyclopropanone hydrate, which interferes with the breakdown of alcohol during the consumption of alcoholic beverages.
It is important to note that no illness (see Table 6) will occur if no alcohol is consumed within 72 hours of eating mushrooms that contain coprine or disulfiram-like toxins.
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