In this 4-part series, renowned toxicologist and organic chemist dr. Gerhard Verdoorn takes us on a journey to illustrate some of the fundamentals of chemistry. In doing so, the widely misunderstood subject of what makes a product toxic as well as organic versus synthetic chemistry will be explored and explained with the help of practical examples and within the context of the particular environment.
Part 3 – Pesticides are poisonous: Yes, but what about the other chemicals?
It is very important for people to distinguish between peer reviewed science and sensational garbage. The father of toxicology, namely Philippus Aureolus Theophrastus Bombastus von Hohenheim, generally known as Paracelsus, cast the founding principle of toxicology in stone: “All substances are poisons, there is none that is not a poison. The right dose differentiates a poison from a remedy”. Without even knowing it, Paracelsus also founded the principles of hazard versus risk with this statement, which we will explore in the last part of this series. Being mindful of Paracelsus’s founding principle, let us evaluate human medicines.
Paracetamol must be one of the most used pain killers in South Africa and is sold over the counter in pharmacies, retail outlets and even the forecourts of fuel stations. Its acute mammal oral toxicity is on par with that of the pyrethroid cyphenothrin, which is used in many household insecticides. The tetracycline anti-microbial doxycycline that is very effective to cure patients who contracted tick bite fever, is of the same level of mammal oral toxicity as the organophosphate fenthion. Codeine hydrochloride is quite a poisonous substance and is also known as a potential habit-forming drug (developing dependence) but is sold over the counter for self-medication.
The list of substances that are toxic is endless but what does it mean for the layman who is not a toxicologist? Go back to Paracelsus’s statement and do not eat the entire tube of toothpaste because what is supposed to be a remedy, becomes a poison!
Take 1,000 mg of paracetamol tablets and not half the container because the medicine becomes a poison at such a dosage, and yes, many patients overdose on paracetamol and end up in hospital with paracetamol poisoning. The concept of toxicology is far wider than acute or chronic oral (intake) or dermal (touch) toxicity.
Some chemicals are carcinogens (cancer causing agents), other teratogens (cause birth defects), some mutagens (cause mutations of genetic coding in DNA), others clastogens (accelerates existing cancer in a patients), some ototoxins (affects hearing) while some effects on vision, organ function and the endocrine system must also be considered in the discipline of toxicology.
The drug that shook the world in the 1960s and 1970s was thalidomide that has virtually no acute oral toxicity but is a terrible teratogen that caused birth defects in thousands of babies. Considering the massive amount of chemicals in the environment and what is consumed daily via food, water and beverages, one wonders how we remain alive and healthy? The answer lies in the science of toxicology.
It is all about the dosage, not about the substance
The caffeine in energy drinks is in a very high dosage and gulping down two cans of it is bound to trigger a near toxic response in the person who does so. Meanwhile, caffeine is a stimulant taken in billions of cups of coffee every day all over the world without any adverse effects on people apart from offering serious enjoyment to the coffee drinkers. Paracelsus was very clear: it is all about the dosage.
Botulinum toxin is toxic at a level of 0.0001 mg per kg body mass, but does it kill a person with food poisoning? Not always, because the person may not have ingested enough to perish from the toxin. Two dogs, one a Jack Russell and the other a Rottweiler, may lick a methomyl-based fly bait. The Rottweiler is unaffected, but the Jack Russell becomes violently ill with shivering, nausea, vomiting, pupil constriction and rapid breathing. Both dogs ingested the same quantity, but the dose was too little to affect the 70 kg Rottweiler, but near fatal for the Jack Russell. It is all about the dosage.
Why do you think a medical doctor gives a prescription for a scheduled medicine? Not only to cure the patient but also to ensure that the patient takes a therapeutic instead of toxic dosage. In toxicology there are certain safety parameters for all substances, most important of which is the ADI or allowed daily intake. Toxicologists do meticulous calculations of the substance’s toxicology, the food basket (meaning looking at the average food consumption of a person) and the MRLs or maximum residue limits of the substance and then produce an allowed daily intake of the substance for human beings. That figure is universally accepted as the daily dosage of a substance that a person may ingest without it having any health effects on the person.
Glyphosate is regularly in the news, so let’s consider glyphosate. The ADI for glyphosate is between 1 and 2 mg/kg body mass per day meaning an 80 kg adult can safely consume 80 mg to 160 mg glyphosate per day without any adverse effects. It is alleged that bread in South Africa contains 2 to 4 mg glyphosate per loaf, so go ahead and eat 20 to 40 loaves of bread if you can. This assessment of the allowed daily intake is not only based on acute oral toxicity, it also considers all other toxicological effects. Some substances may not have a significant oral toxicity but may damage organs over prolonged period of times. Aspirin developed a reputation as a nephrotoxin (kidney toxin) simply because people overdosed on aspirin by continuously using excessive dosages of this wonderful medicine.
To add some flavour here: the same principles are applied to man-made synthetic pesticides, natural pesticides and so-called “organic” pesticides. Every pesticide must have an ADI, whether nature made it, or man made it.
In the final part of this series we will explore pesticides and toxicity within the hazard versus risk framework.