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Assessing the temporal and seasonal changes in the ecology of untreated mesocosms and natural water bodies - PS2339

Outdoor mesocosms are widely used in the pesticide regulations process to evaluate the effects of pesticides on aquatic communities at the ecosystem level. However, there is an ongoing debate as to whether these artificial systems are representative of natural water bodies and also whether the application timing used in mesocosm studies should reflect the actual application timing of the product. The majority of guidance documents recommend that mesocosm studies should be conducted during spring/summer when the communities are in their “growth” phases and the impact on test systems are perceived as “worst case”. However, a broad range of compounds, both herbicides (e.g. pendimethalin and sulfonylureas) and insecticides (e.g. cypermethrin), are applied in autumn and the derived ecological endpoints from mesocosms conducted in spring/summer may not be appropriate to assess the risks associated with autumn applications of the product. The uncertainty associated with the use of a mesocosm study conducted in spring to defend a notifiers wish to register a product for application in autumn is unknown and could lead to inappropriate assessment factors being used in aquatic risk assessments.

To date little research has been conducted on the temporal variations in the ecology of fresh water bodies. As such it is not possible to answer the following regulatory questions:

1. Are mesocosms sufficiently ecologically representative of natural water bodies in the agricultural landscape?
2. Do mesocosm studies with spring/summer applications of pesticides represent the “worst case” scenario (in relation to changes in the community composition during a season)?
3. Could differences in the ecology of fresh water bodies in autumn/winter when compared to spring/summer increase the uncertainty associated with the use of mesocosm endpoints derived from spring/summer studies of pesticides also applied in autumn/winter?

Research has been conducted that investigates the relevance of mesocosms to natural water bodies in the UK (Williams et al. 2002). The scope of the research conducted by Williams et al., 2002, was limited to aquatic macroinvertebrate and macrophyte communities in a range of natural ponds and four mesocosms at Jealotts Hill, Bracknell. The ecology of ditches and streams was not included in the study and no other variables or aquatic communities were investigated.

The purpose of this study is to deliver knowledge to PSD on the temporal variations of aquatic communities in edge-of-field water bodies in the UK and on the extent to which mesocosms realistically represent these systems. The overall aim is to assess the level of uncertainty associated with different pesticide application timings used in regulatory mesocosm studies and the relevance of derived ecological endpoints from such studies to aquatic risk assessments.
1a. Collect data on the composition of aquatic communities within mesocosm facilities in Europe and natural edge-of-field water bodies in the UK.

1b. Compare the species composition of natural edge-of-field water bodies with mesocosms to determine how ecologically representative of natural edge-of-field water bodies mesocosms are.

2. Determine temporal variations in the ecology of water bodies and assess the implications of the variability on the assigned seasonal sensitivity of such systems to impacts by pesticides.

3. Provide guidance to PSD on how appropriate assessment factors for mesocosm studies could be assigned.
Project Documents
• EVID4 - Final project report : evid4 ps2339   (3342k)
Time-Scale and Cost
From: 2007

To: 2011

Cost: £373,980
Contractor / Funded Organisations
Agriculture and Water Quality              
Biological Effects              
Environmental Effects              
Environmental Impacts              
Environmental monitoring              
Environmental Protection              
Monitoring and evaluation              
Nature conservation              
Pesticide use              
Water Quality              
Water quality monitoring              
Fields of Study
Pesticide Safety