Oenanthe crocata

The toxic principle in the plant is oenanthotoxin, a polyunsaturated fatty alcohol that works by blocking γ-aminobutyric acid (GABA) receptors. The plant is very poisonous to humans and livestock and can cause death if poisoning is left untreated after ingestion. Symptoms in livestock include increased salivation, dilated pupils, respiratory distress, and convulsions. Cattle poisoning from this plant occurs sporadically. For example, several cases were reported during the 1995 drought in the West Country, England. Due to the shortage of grass in the fields, the cattle were driven to graze by ditches where hemlock water-dropwort grew. Instances of poisoning in humans are rare, with only 13 cases reported in Britain between 1900 and 1978, mostly involving children. However, 9 of these 13 were fatal. Serious cases usually involved consumption of the roots, which were mistaken for parsnip. Symptoms include nausea, vomiting, seizures, hallucinations, ataxia, and haemorrhaging of the brain and lungs. Accidental splashing of some sap in the eye of a laboratory worker led to symptoms of poisoning that lasted 12 hours. The Scottish botanist John Lightfoot, in his 'Flora Scotica' (1777) related the experience of the illustrator Georg Ehret, who found that "the smell, or effluvia only, rendered him so giddy that he was several times obliged to quit the room" until he opened the door and windows so that he could finish his work. Being a polyyne, oenanthotoxin is quite unstable, and boiling the roots both lessens the severity of the symptoms and prolongs the delay before they appear.