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.
Risk versus Hazard
Pesticides are connected by one common characteristic namely to kill undesired organisms. This common characteristic is feared by the uninformed and used as a lobby tool against pesticides. Understanding the difference between hazard and risk is perhaps the most valuable tool to allay the public fears of pesticides, but also to instil a sense of responsibility into people who use pesticides.
The toxicity of a pesticide is mostly expressed as its hazard to human beings using oral and dermal acute toxicity. Taking a laboratory mouse into a controlled laboratory environment and exposing it to an acute dosage of a pesticide to monitor its response, is a hazard evaluation. Allowing mister mouse to range freely in an agricultural system where the same pesticide is sprayed at a highly diluted concentration over a very large area and monitoring the mouse’s response to the pesticide is a risk assessment. In the laboratory, the mouse is an obligate target of the pesticide because it is either fed the pesticide with its food, injected with the pesticide or exposed to an atmosphere filled with the pesticide’s vapours.
Such conditions only measure that hazard or the direct toxicity of the pesticide to the mouse. It is impossible to relate that to field conditions where the mouse will never eat food that is deliberately laced with the pesticide (unless it is a rodenticide), be injected with the pesticide or inhale air that is saturated with the pesticide. Although the pesticide may be hazardous, the risk for the mouse in field conditions is negligible. It is a great pity that some scientists do laboratory studies, force certain results to prove that certain compounds are hazardous, but deliberately fail to express the real-life risks to the environment and people.
That pesticides may pose a risk is indisputable, but it takes some extra logical thinking to unfathom the risk versus hazard. A benign compound like alpha-cypermethrin is a low hazard pesticide, but it is a high risk in the hands of the public who fail to use personal protective clothing and suffer severe dermal irritation because of skin contamination with the product. Technically speaking, the hazard is an inherent physical property of a compound and the risk is a man-made property. The most benign compounds of low hazard may pose a high risk to people if used irresponsibly, while high hazard compounds like dichlorvos can be low risk if used responsibly. Pyrethroids are typical low risk compounds for most mammals and birds, but extremely high risk for fish and amphibians due to extreme toxicity for such organisms.
A final word
A world without chemistry is unthinkable because human beings rely on chemicals for their well- being, food, fibre, homes, transport and medication. Take the man- made synthetic chemicals out of the picture and as a species, we head for extinction, maybe not too soon, but definitely in the long run. The medicines will be severely reduced, the household products will disappear, and the pesticide market will collapse.
What should we do? Abandon chemistry as one of the life support systems for humankind? No! Simply stop believing all the BS and Google rubbish and be responsible whenever using any chemical product. Do not use chemicals of whatever nature excessively. Do not use chemicals when not really required, like drenching a room in an aerosol mist because there is one mosquito. Read all the instructions of the chemical’s container and follow it, even if it is something like a laundry detergent. Store chemicals in a safe place out of reach of children and pets. A benign compound is a potentially high-risk weapon in the hands of the uninformed, irresponsible or careless person. There is no bad chemical in the Universe, it is people who turn chemicals into harmful compounds by being irresponsible.