The impact of EFSA’s new Water Treatment guidance in the world of Environmental Fate 

Some things are not news.  Readers of this article will already know that pesticides and biocides can, under certain conditions, reach ground water or surface water bodies.  This has been discussed, debated and calculated for several decades.  But there is still room for something new to appear.  The something new, in this case, is what happens in a water-treatment facility. 

For PPP’s, those with longer memories will recall Annex VI of EU Directive 91/414.  At this point, the link between pesticides and water treatment was restricted to: 

a) Will water treatment be effective at removing pesticides from water? 

b) Will pesticide residues have an impact on the effectiveness of treatment processes? 

There was a big upgrade to the ambition with EU Regulation 1107/2009.  Article 4 includes a requirement that there should be no harmful effects on humans or other animals “taking into account substances resulting from water treatment”.  So we have moved from the effect on water treatment to the effect of water treatment. 

For some years, this corner of the legislation was not implemented with rigour.  Its introduction was an aspiration but methods had not been developed and there was no obvious way to evaluate the risks.  The assessments were variable and based on limited information.  In 2014 (well before Brexit), the UK HSE argued that it should remain this way: it suggested that this data requirement should be kept as a safeguard, to be invoked only in cases of concern.  However, ultimately the decision was taken that this requirement should be a standard assessment for all active substances. 

In the case of biocides, the ECHA guidance on disinfection by-products (BPR Volume V, 2017) sought to address the formation of transformation products, however only under limited circumstances and fell short of assessing what occurred in a water treatment facility.   

In 2019, a mandate from the European Commission was sent jointly to EFSA and ECHA to establish “a framework to assess the impact of water treatment processes on residues of active substances or their metabolites…”  This guidance was released in 2023 (https://efsa.onlinelibrary.wiley.com/doi/full/10.2903/j.efsa.2023.8194). 

The guidance is long (108 pages) and it is easy to get lost.  How best should it be understood?  To begin with, you need a long list of all the substances that might be caught in the net.  This includes the active ingredient along with metabolites formed in the environment.  For agricultural pesticides, the starting point is the output from the environmental fate assessments for surface water (modified with a dilution factor) and groundwater that are already required.  Any substances that are predicted in concentrations greater than 0.1 µg /L in groundwater will need to be evaluated, and this includes non-relevant metabolites. While substances with concentrations greater than 0.1 µg/L will also need to be evaluated in surface water, the guidance does recommend the use of the 4 day time-weighted average value, rather than the maximum value.  This may reduce the number of substances that need assessing, however as metabolites only found in surface water are often calculated using default endpoints, these may still trigger the need for an experimental assessment.     

The assessment is designed to cover a range of treatment processes, including filtration, chlorination, ozonation and UV treatment.  The tiered assessment starts with a desk-based study to check whether the substance will be transformed during the treatment process.  An experimental study is required for any substances that are not excluded by this method.  While it would be hoped that a desk-based literature review would avoid the need for further experimental work, the reality is that often the literature is not relevant.  

This experimental study is a rigorous set of studies, backed up by theory and literature, designed to define and quantify any transformation products formed by the typical water treatment procedures.  The general principle is that if transformation products are produced at concentrations greater than 0.075 µg /L, then a hazard assessment will be required to quantify the overall risk.  The tiers continue to a point where you are comparing exposure of a substance from all sources to a health-based guidance value or a toxic threshold of concern. 

Significant investment is required to comply with this new guidance.  Clearly the most efficient way to navigate through the risk assessment will be to have as few substances included as possible.  This may require a new approach to the calculation of predicted concentrations in groundwater and surface water.  Up to now, there has been no incentive to keep refining the calculations when the concentrations have met the relevant toxicity-based thresholds.  Therefore, many substances will now be required to be assessed under this new guidance, even though that is not the intention.  The demands on pesticide and biocide fate scientists have become even bigger.