Water & Wastewater Treatment

WWT July 2018

Water & Wastewater Treatment Magazine

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Page 21 of 47

22 | JULY 2018 | WWT | www.wwtonline.co.uk • PESTICIDES AND THE DWD • The European Drinking Water Directive (DWD) places a limit of 0.1μg/l (microgrammes per litre) for each individual pesticide in drinking water – a concentration of one part in 10 billion, equivalent to a single grain of wheat in 390 tonnes – and 0.5μg/l for total pesticides • For water companies, that leaves little margin for error, particularly when having to contend with hard- to-treat pesticides like clopyralid or metaldehyde • The DWD was never designed to be a health-based standard – it was set by the European Commission in 1980 to reflect the limit of analytical methodology at the time while also serving to limit pesticides generally for environmental reasons, adopting the precautionary principle • The World Health Organization (WHO)'s guideline values for pesticides of health significance in drinking water is a useful reference point for the health effects of pesticides. Most of the recommended levels are far less stringent than the 0.1μg/l stipulated by the European Commission, and clopyralid (or 3,6-dichloro- 2-pyridinecarboxylic acid) is not included on the list • During the 2016 REFIT evaluation of the DWD, agricultural interests and some water experts argued that the permitted pesticide levels should be relaxed in favour of a more risk-based approach to drinking water regulation • However, the European Commission rejected this in favour of keeping the strict DWD limits, saying that any contamination could be potentially adverse to human health and that pesticide- free drinking water ought to be the aim. It has pointed out that stopping pesticide contamination at source costs a fraction of the cost of treatment solutions and should be the preferred solution The Works: catchment management • THE CHALLENGE L incolnshire is a richly agricultural area, where pesticides are used extensively as they are a key part of arable farm management. The European Drinking Water Directive (see box) places a limit of 0.1μg/l (microgrammes per litre) for each individual pesticide in drinking water, and 0.5μg/l for total pesticides. So there is little margin for error for water utilities, especially with the substances that are hardest to treat. Up to 70 per cent of pesticide losses found in rivers can be attributed to pesticide handling areas in farm yards. According to investigations a…er the incident, the clopyralid pollution that caused Winterton to fail DWI standards was likely to have come from no more than a single capful spilt in a yard. "The drinking water standard is there and needs to be met, which means just one drip or a spill of pesticide can cause catastrophic results," Kelly Hewson- Fisher, catchment manager for the Winterton project, says. In 2015, a…er the completion of an external investigation, Anglian Water sought and received DWI approval for a catchment management approach to tackle the Winterton pesticide problem at source. 70% of pesticides found in rivers can be traced back to handling areas in farmyards

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