Did you read the articles or any of the work referred to in those articles? If you did you would see that the main use of the stuff was sprayed on plants in areas of high arable farming activity and 80% of it was taken up by plants to kill insects on the plants. There was little evidence of significant retention in soils. They were banned because they were much more toxic against bees and were blamed for the drop in bee numbers. The only other possible source of neonicotinoids is from the flea treatments in pets, as since 2018 that is the only allowed use for them. Whether you think it is good science or not, the fact remains that neonicotinoids at toxic levels are still being found in many rivers 2 years after they were banned for agricultural use and have been traced back to sewage outlets from domestic sources.
The Great Ouse is one of the worst rivers, and as Grafham gets its water from there, if Anglian water authority do not monitor it, then it could mean the end of invertebrates in Grafham. Already AWA has to monitor for paraformaldehyde in the Ouse, from agricultural run offs from slug killers.
Also the long term toxicity of these agents in humans has not been sufficiently studied. There is some evidence of neurological toxicity in humans on chronic exposure. Before 2018, we were exposed to them in our food, now many of us will be exposed to it in our drinking water, as the water purification would probably not remove the neonicotinoids. If nothing else, it needs further investigation otherwise river fly fishing could end up only being viable in areas of low human population, upstream of any sewage outlets.
Yes, BWO eggs are killed by 'fine sediment and phosphate pollution washed off from arable farms and also result from untreated sewage' so maybe the key is to stop the illegal dumping of raw sewage into rivers, which combined with low flows due to water abstraction forms a fine sludge on the river bed that kills the eggs.
It is pointless getting into a debate over which is worse, phosphate, raw sewage or neonicotinoids. They are all potentially bad and need to be controlled. There are alternatives to neonicotinoids for controlling fleas in pets, we should be using them.