• IN response to the report (Flea powder from pets killing wildlife on Hampstead Heath, study finds, October 3), assuming that dog flea powder is leaving toxic chemicals in Hampstead Heath dog ponds, I would like to contest this assumption on the origins of the chemicals.

People rarely use flea powder these days and it’s advised dogs do not bathe after treatment. People use spot-on treatment, after which dogs should also not bathe for a few days to allow it to seep along the dog’s skin to be effective. Or tablets are used which cannot affect an environment.

I am sure the findings of seasonal chemical traces are correct as many dogs are dying especially from blue-green pond algae in the summer. I feel there needs to be a deeper investigation to find the cause.

A ROWE, NW5