Due to the destruction of a wasp nest at the beginning of August 2013, Permethrin ended up in my pond (14000 l). All fish were dead after a few days. I have changed 10000 l but still (20/10/13) beetles die after several weeks. How long does it take for that Permethrin to break down? Thank you.
Answer
Hi Peter,
Permethrin is quite easily biodegradable in the environment, in a pond half of the substance can disappear after 40 days. The amount that remains will then be halved again after another 40 days, and so on. The main factor for the disappearance of permethrin from the environment is the breakdown by bacteria in the soil. Scientists have already found many different types of bacteria that are able to break down permethrin. They were usually found in places where the substance is frequently used, such as in livestock farming. If there are bacteria in your pond that can break down permethrin, the problem will resolve itself over time.
On the other hand, permethrin is not easily soluble in water and, moreover, it sticks well to soil particles, organic matter and materials such as plastic. I suspect that the water change did not remove much of the dust because a very large part of the permethrin has stuck to the bottom plastic of the pond.
Finally, permethrin is indeed very toxic to aquatic organisms, which means that there can be effects even at very low concentrations.
Conclusion: changing the pond water probably does not make much sense. I would rather give nature some time until next spring. If you see that there is still no improvement, then I would consider replacing the tarpaulin of the pond as well.
Good luck and I hope I was able to help you!
Pieter
Answered by
ir. Pieter Vandermeeren
Environmental microbiology, agricultural pesticides and our environment
Old Market 13 3000 Leuven
https://www.kuleuven.be/
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