MORE RESTRICTIONS on isoproturon use, if not an outright ban, could be around the corner as higher than hoped-for amounts of the popular cereal herbicide have appeared in watercourses this winter.
Precise details of IPU concentrations in two southern rivers, the Cherwell and Leam, where the impact of Voluntary Initiative anti-pollution measures are being closely monitored, are not yet available. But they are understood to be high enough to encourage Thames Water Utilities to arrange a meeting with the Pesticides Safety Directorate next Tuesday.
“We shall be taking our graphs with us,” says TWU”s Dinah Hillier. The water supplier has already called for IPU to be banned (News Nov 5).
Colleague Steve White points out that the level in the Cherwell peaked at 4.5ppb this season. The EU drinking water limit is 0.1ppb.
Other suppliers, such as Severn Trent, who saw lower levels after previous VI action, have also seen higher IPU levels this season, notes Dr White. “It makes you wonder whether the improvements were just a [seasonal] artefact. IPU is probably just too popular for its own good.”
VI water project manager Nick Humphrey admits the latest findings are unexpected and disappointing. “They are not what we want.”
They come despite widespread anti-pollution advice and regular text messaging warning potential IPU users when to avoid spraying because of unfavourable weather.
“Clearly some people have not been doing what we asked or we have simply been getting through to those who are already responsible.”
The wet harvest which left soils unusually sodden could also be partly to blame, Mr Humphrey believes. “It seems that when soils are extremely wet almost any amount of rain will cause a problem.”
Jonathan Staton of IPU supplier Nufarm UK agrees. “Soils became saturated very early this season. Clearly some people ignored that message.”
Colleague Tudor Dawkins says there is no evidence that, despite its cheapness, any more IPU was used than normal last autumn.
Although the maximum permitted IPU dose is 2500g/ha, most agronomists have tried to restrict its usage to 1500g in programmed treatments, adds Mr Staton. Mr Humphrey acknowledges that this season”s results reinforce TWU”s call for regulation on high dose, highly soluble residual herbicides.
“It”s not just about IPU. We have consistently been saying please ask your agronomist about alternatives to IPU, chlorotoluron and simazine.”
However, there is still much more to be understood about the way such materials get into watercourses, he says. “It”s not only due to the weather.
“The impression I get is that most people in the industry believe that if there is going to be regulation it should be complementary to the VI, rather than a straight ban.”