Repairing the FOCUS surface water risk assessments for pesticides

Since the late 1990’s, the FOCUS modelling work group has been busy trying to ensure that risk assessments for surface water strike the right balance. The balances are on two axes. The first is ‘empirical’ against ‘mechanistic’ and the second is ‘realistic’ against ‘protective’. Neither balance is easy to strike and the working group has made an excellent job of producing a system that allows regulation to be based on science. 

It is an excellent job, but it leaves room for improvement.  The biggest single flaw is that our assessments of risk to surface water are based on a single year of weather data, meaning that there is a big sensitivity in the risk related to the pesticide application and the weather just after it.  The FOCUS Repair working group has now attempted to resolve this problem and produced a proposal on multi-year simulations (as well as several other issues). At Enviresearch, we discussed the implications at a special meeting at the end of October 2018.  We submitted 14 comments to the working group about their proposals.

One of our comments relates to the timing of pesticide application.  In the current system, the application date is selected using the weather data, to ensure that the conditions are realistic for a farmer to get out and spray.  In the new proposal, the application date would be on the same date every year.  We anticipate that this will lead to unrealistic spray timings in several years out of the 20, increasing the uncertainty in the risk assessment.  Our view is that spray timing should always be linked to the weather.

The FOCUS repair working group has done an excellent job in preparing a suggested revision to the surface water assessments in a very short time.  At Enviresearch, we like the direction it is going, but would like to see some further work before it is finalised.