Poisons, relationship between

Marsh, DO, Clarkson TW, Cox C, Amin-Zaki L, Al-Tikriti S. Fetal methyl mercury poisoning Relationship between concentration in single strands of maternal hair and child effects. Arch Neurol 1987 44 1017-22. 

Assessment of whether a chemical has the potential to cause adverse effects in humans arises usually from direct observation of an effect in animals or humans, such as the acute poisoning episodes that have occurred when potatoes contain high levels of glycoalkaloids. Epidemiological studies have also been used to infer a possible relationship between intake of a particular type of food, or constituent of that food, and the potential to cause an adverse effect. Such observations led to the characterisation of the aflatoxins as human carcinogens. However, natural toxic substances that occur in plant foods have often been identified through observations in animals, particularly farm animals. It was observations of adverse effects in farm animals that led to the further characterisation of the phytoestrogens and the mycotoxins. In other instances, the concern arises from the chemical similarity to other known toxins. 

An alternative nomenclature (Type I and Type II) has been proposed for subgroups of pyrethroids based not only on the syndromes of intoxication produced in mammals but also on their chemical structures, their signs of poisoning in insects, and their actions on insect nerve preparations [2, 14, 18]. The Type I/II nomenclature has been used in parallel with the T/CS nomenclature, so that Type I and Type II pyrethroids are generally considered to induce T- or CS syndrome, respectively [4]. However, the relationship between the two syndromes and types are neither necessarily confirmed in all pyrethroids nor absolute from the recent available data. 

Symptoms of poisoning may affect all or only few individuals in a particular population. Symptoms may be divided into early, late, and delayed early symptoms occur a few hours after toxin ingestion, late symptoms up to several days after, and delayed symptoms affect patients after some weeks, or even months. The most dangerous situation involves delayed, subacute symptoms that do not affect all individuals in an analyzed population. In such a cases, a relationship between consumed food and disease symptoms is practically impossible to confirm and may lead to a misdiagnosis. 

The basic principle of toxicology, as first noted by the Swiss physician Paracelsus, is that the dose makes the poison. While this principle is easy to understand, the processes used to understand the relationships between dose and biological response, and ultimately to determine what dose of a chemical poses a reasonable certainty of no harm , are much more complicated. 

One of the most carefully worked out dose-response relationships is that for carbon monoxide poisoning. Based on controlled studies of exposure in humans at low levels and on observations in humans who have suffered high level exposures because of their occupation or because of accidents or suicide attempts, the relationship between blood levels of carboxyhemoglobin (COHb) and toxicity is understood as follows ... 

Ichthyootoxic Fishes. Those fish that produce a poison which is generally restricted to the gonads of the fish. The musculature and other parts of the fish are usually edible. There is a definite relationship between gonadal activity and toxin production. Fishes in this group are mainly freshwater species, but a few marine species have been incriminated. 

---