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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!
Hi, this is Ngaio again.
Thanks to everyone for their comments and research. I think a few major issues are emerging here.
First and foremost, there is the issue of whether or not wildlife mortality and endangerment to human health have arrisen from legal (or labeled) useage or from illegal use. If it arises from legal use then FMC definitely has to take responsability for that. Now, strictly speaking, the company is not responsible for individuals using carbofuran illegally, but they are knowingly manufacturing a highly toxic compound that is being purchased to poison wildlife, not just for agricultural purposes. We are talking about numerous incidences that are decimating wildlife populations, not just one or two isolated cases. If FMC had andy sense of corporate responsability they could launch an education campaign and carry out a proper risk assessment relevant to Africa to establish various toxicity levels to the species likely to be exposed. But would an effective education campaign then result in a decrease in their sales? And might a risk assessment reveal the risks to wildlife?
Howard, you made a good point–I completely agree that we need to back up our claims with some good, hard science. We cannot afford to be emotional on this one, it’s too easy to tear down emotional arguments. It would be very useful to see what sort of hard data FMC has. I was interested to read Jophie’s post regarding the claim that a hippo would have to consume 300 to 500 kg of carbofuran at once to die. Is this on the basis of toxicity tests carried out on hippos or surrogate species who would respond similarly? What dose level would this correspond to? To make some headway, we will need to be able to clearly establish that a) the animal was exposed to carbofuran in x formulation, b) the exposure to the carbofuran was the predominant or only cause of death and c) the level of exposure was consistent with a legal / illegal application.
Another issue is the root cause of the poisoning: human-wildlife conflict. As Dipesh says, it’s going to take more than banning a compound (or suggesting a ‘safer’ alternative) to make the problem go away. Colleen, I thought your point about promoting more harmonious and equitable farming practices was very relevant. It’s certainly necessary to encourage people not to take matters into their own hands and go after a lion that has killed some of their livestock, for example, but it is also critical to take steps to minimise livestock losses in the first place. An audit of farming practices, crops and use of pesticides would likely reveal the occasions when pesticides are used, but not actually necessary. I’ll have a look through the list you sent and see about contacting some of the groups.
I guess the thing that strikes me the most, at the moment, is the argument that carbofuran does not pose an ‘unreasonable’ risk. This is a chillingly ambiguous term. Are we to believe that the wildlife and human health incidents noted up to now are ‘reasonable’ risks then? Who is setting this threshold?