Key pesticides found in watercourses

Several different active ingredients have been found above the drinking water standard in watercourses across the country as well as the banned herbicide isoproturon.


Exceeding the 0.1ppb drinking water standard with approved pesticides didn’t mean growers had been acting illegally or carelessly, Patrick Goldsworthy, Voluntary Initiative manager, told Farmers Weekly. “It is up to water companies to ensure drinking water meets the standard.”

But the cost of removing some pesticides can be high in some, although not necessarily all, cases, and that is likely to mean products which do end up regularly exceeding the drinking water standard are likely to come under increased scrutiny from regulators.

Examples this autumn included major autumn oilseed rape herbicides and chlorotoluron, which many growers used in place of IPU.

The industry needed to show it was doing all it could to prevent products reaching water, the Voluntary Initiative Pilot Catchment manager Nick Humphrey said at last week’s VI, Catchment Sensitive Farming and ADAS workshop in Stowmarket, Suffolk.

The good news was that metaldehyde had been found at much reduced levels, partly due to a drier autumn but also the efforts of producers responding to the metaldehyde stewardship campaign, he noted.

The campaign promoted and encouraged the responsible use of slug pellets to minimise the environmental impact of their use and, in particular prevent, the active ingredient entering watercourses.

But levels had exceeded the legal limit in some places in October and November 2009, notably in the River Blythe in Staffordshire and Aberdeenshire’s River Ugie catchments, he reported. Peaks also exceeded the standard in Waveney and Yorkshire Ouse in November.

Removing metaldehyde was difficult, bordering on impossible to remove, even with an advanced pesticide removal plant, he noted, making blending with clean water, such as from boreholes, the only option to reduce levels, he said.

But metaldehyde had also been detected at low levels in some of these supplies.

“If they don’t have the ability to blend there is little they can do about levels over 0.1ppb.”

As a result there would be more pressure to prevent the problem occurring at source, he said.

The levels being found of key oilseed rape herbicides, propyzamide, carbetamide and metzachlor, could threaten their future too, Dr Humphrey warned.

“There is a threat under the Water Framework Directive that these products will be lost if levels don’t drop.

“The Environment Agency is looking at piloting water protection zones in eight catchments, one of which may the Cherwell where reducing pesticide levels will be a specific target.”

The peaks could be the result of general use, rather than irresponsible use, Mr Goldsworthy pointed out. “It is not always easy to pinpoint the exact cause of the peaks. Sometimes heavy rainfall after application can cause run-off losses, but very often growers will be following advice on how to get the best out of the product and this means in any area they may be applying the products at the same time, which could combine to form the peaks.”

Growers will need to review next year’s oilseed rape plans on a field-by-field basis with their agronomist, he believes.

“They will need to consider the risks to water, the precise nature of the weed problem and the control options. Where there is a high risk to water, growers need to follow all the stewardship advice and look at different control options and ways of spreading application dates that will give an acceptable level of weed control.”

Peak levels of IPU (ppb)

Catchment

2006/07

2007/08

2008/9

2009/10

Leam

>3

0.9

1.5

0.7

Waveney

1.25

1

0.6

0.1

Wensum

1.4

0.9

1.6

0.02


The most worrying aspect of the monitoring data was it pointed to illegal IPU use by growers since its withdrawal on 30 June 2009, said Dr Humphrey.

Surface water analyses from CSF and VI-monitored catchments suggested the traces were from applications made around the time the peaks were detected and not through the release of chemicals locked-up in the soil from previous seasons, he said.

However, the peaks were lower than the previous autumn, when the product was permitted for use.

While it was disappointing, it was not surprising the chemical had been detected, he added.

“People were obviously using up product they had left over, as it was expensive to dispose of.”

IPU was detected at seven times the drinking water standard of 0.1ppb in the River Leam, Warwickshire. The same pattern was also seen in a number of the other UK catchments, although levels in East Anglian catchments were generally low (see table).

Chlorotoluron levels had increased in some catchments showing growers were spraying larger quantities since the withdrawal of IPU.

Growers were wrong to use remaining stocks of IPU last autumn, said Paul Chambers, the NFU’s plant health adviser. But the Chemical Regulation Directorate’s decision to uphold the 30 June cut-off period did not help the situation, he said.

“The wet autumn in 2008 meant growers were unable to apply isoproturon product they had purchased and the 30 June cut-off didn’t give them sufficient time to use the product,” he said. “We asked CRD to extend the deadline, but it didn’t.”

He thought it was only a small number of farmers who decided apply the product beyond the deadline.

However, the findings did highlight the difficulty of policing regulatory controls, he said. “Using voluntary measures to get farmers onside is a much better solution.”

Growers needed to adhere to pesticide best guidelines to prevent pesticides being detected in watercourses, but stewardship measures needed to be practical. “They need to consider the efficacy of products as well as the environmental implications.”


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