Water from the River Arun in Sussex was found to have been contaminated with metaldehyde residues in two tests conducted last winter, it was revealed on Thursday (21st March). The pesticide, used to kill slugs and snails, was discovered in tests carried out by Southern Water in October and November, and revealed by the Brighton Argus newspaper on Thursday, the eve of World Water Day.  

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Extremely wet, dull and humid summer weather in the UK meant farmers faced the worst slug problems in living memory, which in many cases led to increased use of metaldehyde. Patterns of heavy rainfall and flooding also caused problems with run-off from fields in many areas. In the Northern, Central and Eastern regions of the UK, this sparked breaches of water quality regulations due to the presence of metaldehyde in surface waters.

Water UK, which represents water companies throughout the country, released a policy document on the issue in late October. In the briefing it said that, until 2012, there had been "a demonstrable downward trend in the number of occasions [on which] metaldehyde has been detected in raw and treated water."

However, the rise in contamination seen in autumn and winter last year is concerning for two reasons. Firstly, metaldehyde is extremely difficult to remove from water, and secondly Met Office data suggests that last year's extreme weather patterns (many areas of the country entered 2012 in a state of drought and suffered major flooding as the year wore on) could become more of a regular feature as climate change continues to take effect.

Although 'treated' water was found to be in breach of EU regulations, the levels of pesticides present in the Arun's water were far too low to cause harm, measuring 1.1 microgrammes per litre in October and 0.4 microgrammes per litre in November. Water UK pointed out in October that regulations are "not set on a health basis, but as a near-zero value reflecting European Union legislation that pesticides should not be present in drinking water."

Water company representatives and metaldehyde manufacturers in the Metaldehyde Stewardship Group were keen to point out this fact, with Southern Water's Sam Underwood stating that the EU's assumption that drinking water should not contain pesticide residues is, "a good rule of thumb but… not based on health grounds."

Mr Underwood added, "The Health Protection Agency says there is no reason to expect any adverse effect on human health from Metaldehyde at the miniscule levels being detected. The average-size person would have to drink more than 1,000 litres of water each and every day of their life" to surpass the 'acceptable daily intake'.

Stakeholders react to metaldehyde pollution

Water UK spokesperson Jim Marshall told Farming Online on Friday, UN World Water Day, that, "We do expect it to be a challenging year with drinking water standards likely to be breached," but said that there is currently no data available to give an accurate picture of contamination.

He added, "The situation is serious and water companies are closely considering their strategies to address the problem. The voluntary approach to controlling the use of pesticides at source at the point of application is central to this. Consideration should also be given to product substitution – finding less harmful but equally effective solutions."

Paul Fogg, of the Metaldehyde Stewardship Group, gave some context to the situation, and maintained that a voluntary approach to tackling pollution remains effective. He said, "Last autumn saw the highest ever slug pressure, and above average rainfall. In fact, winter 2012 was a perfect storm, with late drilled crops and severe weather preventing farmers from getting crops out of the ground."

Dr Fogg added that 2012 was "the worst case scenario" in terms of chemicals running off fields and entering surface waters, though he said "Stewardship is an evolutionary process. You learn lessons from year to year, and can look at whether you should give more robust or different advice next time around. If we are faced with a similar situation in 2013, hopefully we will be in a better position to deal with it."

In its policy document last year Water UK, which works with MSG, said, "The most sustainable solution is to control the pesticide at source to prevent metaldehyde getting into watercourses and rivers in the first instance. This is best achieved by changing the way metaldehyde is used in the catchment… If a voluntary approach does not generate sustainable reductions in levels in drinking water sources then it may be necessary for the introduction of tighter environmental restrictions… to protect essential water supplies."

MSG maintains that its 'Get Pelletwise' campaign has been successful in raising awareness of the issues around metaldehyde and encouraging farmers to follow best practice.

However, Pesticide Action Network spokesperson Nick Mole questioned the industry line. He said in response to incidents in November, "I find the situation quite alarming considering the attention given to metaldehyde. Not least because the cost of removing metaldehyde from water is passed on to the consumer, so we are paying for treatment resulting from overuse or improper use of pesticides.

"We have the potential for more unsettled weather; what we need to do is look at methods for dealing with pollution, not write it off as the result of freak conditions. If a voluntary approach is not working, then a legislative approach may be necessary. Otherwise, what’s going to happen when we have wet weather next year?"  

Celebrating World Water Day, the focus of which the UN announced will be 'Water Cooperation', EU farming group Copa-Cogeca called for more research and easier knowledge transfer between organisations, businesses and research institutes towards increasing the efficiency of water use in agriculture.

Meanwhile, the Barilla Centre for Food and Nutrition released a report calling for action to reduce waste and superfluous use of water in food production.