The purity of seeds intended for processing for human consumption or animal feed is an essential element from a technological and consumer safety standpoint. Some impurities can be easily separated during the cleaning operations, while others are more difficult to remove, thereby altering the organoleptic and technological qualities of the end products. Certain impurities contain toxic substances, while others act as a source of microbial contamination for the final product, leading to mycotoxicological contamination. Depending on the ease of removing impurities, they can be classified as black impurities (mineral impurities, damaged grains, organic impurities, completely compromised grains due to insects, weed seeds, etc.), white impurities (cracked, crushed, stained, or dry grains of the main crop), and hard-to-separate impurities that have similar shape and size to the seeds of the main crop.

Among the hard-to-separate weed seeds, the most commonly encountered ones are Lolium temulentum (darnel), Melampyrum sp. (cow wheat), Bromus secalinus (Chess’ or ‘Cheat, rye brome), Avena fatua and Avena ludoviciana (wild oats), Raphanus raphanistrum (wild radish), Echinocloa crus-galli, oryzicola and macrocarpa (barnyard grass).

The most commonly encountered toxic weed seeds are:

Agrostemma githago (corncockle): It is more frequently found in autumn cereals but can also occur in spring cereals, often reaching over 3% of the total mass of grains. Corncockle contains a potent alkaloid called agrostemine and an extremely toxic saponin toxin called githagin, which exhibits strong hemolytic properties. High temperatures can reduce its toxicity, although not completely, as is the case with bread baking. Given the increasing prevalence of raw cereal diets (oats, rye, barley, etc.) combined with milk, yogurt, creams, etc., without undergoing thermal processing, greater attention must be paid to removing corncockle. Symptoms of acute intoxication include nausea, vomiting, diarrhea, and excessive salivation. Severe cases can involve seizures, respiratory disorders, asthenia, and hypothermia. In such situations, emergency medical assistance should be sought.

The optimal removal efficiency of corncockle during the grain cleaning process should ensure that it does not exceed 0.1% in the final product. Flour obtained from wheat with inadequate corncockle removal has a darker color, with particles of black color, and the crumb of bread made from such flour has a greenish-blue tint and a pungent taste. Waste resulting from cereal cleaning operations with a high corncockle content is not recommended for animal feed.

Melampyrum arvense (field cow wheat), also known as „black wheat” has seeds that closely resemble wheat but with a much tougher husk. When milled, it has the property of coloring the bran. Bread made from flour with a high content of Melampyrum arvense has a dirty violet color, and an unpleasant taste, and is considered unhealthy.

Lolium temulentum (darnel) is also known as „false wheat” and is found primarily in cereals grown in dry regions. Homeopathy enthusiasts may be familiar with a case described by one of the pioneers of this alternative form of medicine, Dr. Dessaix. A relative of his suddenly developed symptoms similar to intoxication caused by Darnel. Farmers and peasants in the area where he lived recommended that he eat their bread made from wheat flour with a high content of darnel seeds, based on a logic that incorporated one of the principles of homeopathy: „bread produces the same symptoms as those you suffer from, and therefore, this bread should heal you.”

The toxicity is generated by lolines (saturated 1-amino pyrrolizidine alkaloids) with insecticidal action produced as a result of symbiosis between a species of endophytic fungi (Neotyphodium coenophialum) and plants of the Lolium and Festuca genera.

Intoxication symptoms manifest in the nervous system (brain and spinal cord), characterized by headaches, dizziness, visual disturbances, ringing in the ears, and fatigue.

The presence of darnel flour in wheat flour can be detected by preparing dough from alcohol and flour. If the resulting dough turns greenish and smells unpleasant, then the wheat from which the flour was obtained had a high content of darnel seeds.

Bromus secalinus (meadow brome) results in obtaining unusable grayish flour. The bread produced from such flour is hard to digest and causes gastric disorders and dizziness.

Sinapis arvensis (wild mustard) produces seeds that are quite easily separated during the cereal cleaning process. However, if the removal of mustard seeds is incomplete, the resulting flour has a bitter taste and is toxic, causing irritation and gastric disorders.

Raphanus raphanistrum (wild radish) produces flours with a pungent and sharp taste, consumption of which can cause intoxication and intestinal damage. The seeds are enclosed within pods that end up in the cereal mass. This plant is also popularly known as „field rape” or „wild radish.”

Delphinium consolida (field larkspur), despite being used as a medicinal plant, contains toxins that can cause serious disorders in all parts of the plant.

Other weed seeds with potentially toxic properties encountered in cereal masses include Avena fatua (wild oat), Galium aparine (cleavers), Setaria sp. (foxtail), Thlapsi arvense (penny grass), and Ranunculus arvensis (corn buttercup).