Secondary poisoning refers to when a consumer gets intoxicated by eating another organism that has the poison in its system.
Secondary poisoning is known in a number of other chemical pesticides for instance organophosphates. In carbofuran, a carbamate, it is argued whether or not secondary poisoning actually does occur.
It is a known fact that carbofuran is a sleek killer especially in birds. It is also true that organisms with bigger body mass die after a longer time compared to animals with smaller body mass which die faster. I have witnessed small seed-eating birds succumb to carbofuran within 5 minutes while bigger Storks may take up to half an hour or more. In simple explanation,the chemical must get incorporated in the consumer’s tissues and if this consumer dies and is predated upon by another which in the process also gets intoxicated, then secondary poisoning is said to have occured.
There have been reported cases of possible secondary poisoning in Kenya: lions getting intoxicated after feeding on poisoned hippopotamus, vultures after feeding on poisoned carnivore. Today I talked to a senior scientist in a prominent organization who pointed out that after working it out with the chief vet of their wildlife conservation organization, the Lethal Dose (LD) required to kill a hippo is actually much lower compared to the hippo’s body mass. So, some some granules of carbofuran sprinkled on the grass will intoxicate the hippo (and any other herbivore) and even though the lethal dose required to kill the hippo is not attained, the dose may well be enough to kill a wild dog. Nonetheless, my reasoning in the lions getting intoxicated by the alleged carbofuran poisoning of the hippos is that the hippo may have taken much more of the carbofuran and while this may have paralysed the hippos nervous system, not all of it was ‘used’. Therefore, the ‘excess’ carbofuran that circulated in the hippo while still alive and was not ‘used’ in paralysing the nervous system of the hippo got to its tissues and the amount being equal or more than the lion’s lethal dose (the lion’s whose mass may just be about a quarter of the hippos) got the lions got intoxicated.
If that is so and if it is man who had eaten the hippo(as he has been known to in some places), then may be he would have probably succumbed to the poisoning much faster than the lions. Still on man, as earlier said, I have seen Storks take over 30 minutes before dying after eating Carbofuran-laced snails. Man eats these guys regularly. Since the similar organophosphates’ poisoning results to chronic/persistent effects in wildlife and people, there might be chronic effects due to carbamates as well and cumulatively, these could be catastrophic. I cannot avoid worrying that in the long run, most of our wildlife and man are actually already intoxicated and continue to be by carbofuran.
Just a thought for the day!