Why is there a need for mesocosm studies?

As a farming community, we are all well aware of the on-going need for new agrochemicals, both to replace those removed from the market, and to combat emerging threats such as developing resistance in pest species.

Before any new agrochemical can be used in the field, or any existing product can be used for a new purpose, it is necessary to demonstrate to the appropriate authorities that it is safe for aquatic ecology.  Safety is demonstrated using a tiered approach, with lower tier assessments taking place in laboratories and higher tier assessments being made in semi-field mesocosm studies.

The combination of the aquatic laboratory facilities, offered by Fera Science Ltd, for lower tier studies and the E-Flows mesocosm, provided by CHAP, creates a complete platform for generating all the high quality data required for regulatory submission.  The aim is to  increase the range of solutions on the market and available to farmers.

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What is the E-Flows mesocosm?

The Edge of Field Waterbody Safety Assessment Facility (E-Flows) is a state of the art mesocosm providing a real-world test bed for regulatory risk assessment of agrochemicals and other products or ingredients that have the potential to reach the aquatic environment in everyday usage.

The E-Flows mesocosm is the first facility of this nature to provide fully flow through streams that can receive chemicals at the treatment rates predicted to occur in the environment, providing the ability to accurately reproduce the expected field exposure. 

Based at Sand Hutton in North Yorkshire, the E-Flows mesocosm is in close proximity to the excellent analytical facilities of Fera Science Ltd, and can also draw on the extensive expertise in agrochemical risk assessment and ecology provided by Fera, in tandem with the holistic agronomy expertise of CHAP.

In addition to this advantage, the E-flows mesocosm benefits from a continuous water supply via a borehole from the Grade A sandstone aquifer below it.  It is also ideally placed in the northern extent of the lowland growing region, providing the best estimate of realistic to worst case risk assessment.

How does it differ from existing mesocosms?

Semi-field regulatory risk assessments using a mesocosm approach have often been considered unsatisfactory as there is a tendency for results to be too variable to constitute scientific robustness.  The source of this problem is that the mesocosm units used are small volume static or recirculating chambers which tend to provide insufficient habitat for organisms and have limited capacity to buffer physico-chemical change.

Even with regular bailing, these mesocosms have a within-experiment effective volume of <5000 litres per experimental unit, and manual water changes can increase the stress to the organisms.  In contrast, the E-Flows mesocosm with flow-through capacity can provide a mean within-experiment effective volume of 75,000 litres per experimental unit, which brings a huge increase in buffering capacity against diurnal and weather-driven change, stabilising the habitat and reducing variation of results.

E-flows comprises of 60 experimental units (all flow-through streams), with the dimensions of each stream (or ditch) being 10 metres long, up 0.4 m deep and up to 2 metres wide at the surface, with a v-shaped cross-section, and with each unit ending in a capture pond approximately 1 metre deep and 1 metre in diameter.   Where the average experiment requires access to 20-30 units (according to EFSA Guidance) the E-flows facility has the capacity to support 2-3 independent concurrent experiments, reducing the waiting time for users.

The flow though and experimental unit size of E-flows can be varied to a great extent; the length of unit can be shortened and flow increased (giving a retention time of <0.1 days and an effective volume of 750,000 litres per unit) or otherwise independent units can be combined to increase the habitat area, and flow can be reduced to simulate slow ditches or static ponds.

Of course, all of this control means that application of chemicals and their residence in the system can also be closely controlled so that the E-Flows can mimic as accurately as possible the exposure predicted in the environment by models such as Focus.  In addition, all physico-chemical parameters including the analysis of the test chemical are performed under Fera Science GLP.

The increased size and realism of the experimental units provide the scope for the establishment of a wide diversity of macrophytes and invertebrates, allowing a greater range of available resources and refugia, consequently reducing the stress associated with an artificial environment.   This both increases the validity of the results for the Specific Protection Goal and reduces the chance of the design of the experiment adversely influencing the outcome of the risk assessment. By this means, the safety factors applied to the regulatory values can be reduced (as low as a factor of two).

How can it benefit farming industry?

Clearly, where more novel agro-chemicals can be demonstrated to be safe for the aquatic environment when applied as per the pack instructions, then there is more choice and scope of products for use by farmers in everyday practice.  The results provided by mesocosm studies commissioned by agro-chemical companies and assessed by regulatory authorities ultimately determines how much product is safe to use near water, and how and when it can be safely applied.

In short, E-Flows is an innovative step-change in mesocosm science; providing a flow-through aquatic habitat allowing increased diversity and reduced variability, leading to more applicable results for regulatory  submission.

 

For more information please contact
Dr Rachel Bensted  – Lead Scientist
Rachel.Benstead@fera.co.uk

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