DDT all over again

In 1939, Paul Müller discovered that DDT (dichlorodiphenyltrichloroethane) was a very effective insecticide. It became widely used to kill mosquitoes and reduce the incidence of malaria and other insect-spread diseases. In 1948, Müller received the Nobel Prize in Medicine for his work on the effects of DDT and how it aided the fight against disease. Yet by 1962, with the publication of Rachel Carson’s book Silent Spring, the public became aware of the significant negative environmental impact of the use of DDT. Today, DDT is banned except in some minimal situations sanctioned by the World Health Organization, and we continue to develop other methods to fight malaria.

Battling rats

A similar challenge arises from our interactions with rats. Rats destroy crops, spread disease and cause harm to our infrastructure. As long as we have shared our environment with them, we have tried to kill or reduce the population of rats and other rodents.

As a researcher, I worked with rats. But the rats I used in experiments were cute, white, docile creatures, bred for generations to be gentle for lab work. They are far removed from the rats that populate our world almost everywhere humans live. I can affirm, however, that rats are intelligent, and I understand why it is hard work to trap them and eradicate their colonies.

For example, rats eat new food cautiously and only in small amounts to ensure it is not poisonous. If the food is found to be safe, they return and eat more. Thus, the most effective way to poison a rat is with a slow-acting toxin. The most common rodenticides are drugs that prevent blood clotting and kill rats over several days. One of the first of these drugs was warfarin. It worked but required the rat to consume the poisoned bait more than once, which made it less effective.

Poison downstream

We have now developed what are called second-generation anticoagulant rodenticides. These drugs are much more powerful and can kill with a small dose consumed in a single meal. However, these drugs do not degrade over a reasonable time window (warfarin, by contrast, decays relatively rapidly). This has downstream environmental consequences. Animals that eat rats are happy to prey on a rat that is ill or has recently died. In doing so, they also ingest the fatal rat toxin, which is toxic to all animals. Predatory birds and larger mammals that feed on rodents are dying. Also, the bait that contains these second-generation drugs is, of course, available to other animals to consume directly. Rat poisons have been found in different places in the food web, in shellfish, cod and mussels as well as in many insects like ants and beetles. Given the interconnection of the food web, rodenticides are also likely to end up in our food chain

Just like with mosquitoes and malaria, we need effective ways to kill rodents because of the harm they do. However, as in the case of DDT, the secondary effects of these potent poisons must be weighed against the benefits. Many of our regulatory agencies are dealing with this complexity.

Pray that they make decisions that are in the best interest of our world and its rich God-given environment.