Insects and Insecticides

Further written evidence submitted by Bayer CropScience

On 30 November, the Environmental Audit Committee forwarded this question to Dr Julian Little of Bayer CropScience:

I wonder whether you can comment on the attached EFSA document. The attached PDF, which I obtained on behalf of the Committee from the European Food Safety Agency, is taken from the Public Draft Assessment Report by the Rapporteur Member State (Germany) for Imidacloprid as part of the review programme referred to in Article 8(2) of the Council Directive 91/414/EEC. The document is dated February 2006. The passage is taken from Volume 3, Annex B, B.8 on Environmental Fate and Behaviour. At page 637, there are details of a study conducted by Bayer on Imidacloprid in relation to winter barley in Bury St Edmunds and Wellesbourne in the 1990s. Tables B.8.1-60 and B.8.1-61 on pages 639 and 640 appear to show a build-up of neonicotinoid residues in soil over time, but the report concludes that "the compound has no potential for accumulation in soil", which appears anomalous. Were you aware of this EFSA document? Is there a simple explanation that I’m missing why the residues build-up over time rather than dissipating, as you suggested in Committee at Q187? Do you agree with the conclusions drawn by the EFSA that those trials show that "the compound has no potential for accumulation in soil" and that the trial showed a "plateau level"? [All quotes pages 639/640] To the untrained eye, the results of the Bayer field trials appear rather striking, which is why I have brought it to your attention and would be grateful if you could comment on it at the first available opportunity.

Dr Little replied on 11 December 2012:

As promised, our view on your ‘question 2’ on the soil persistence of imidacloprid. This is an extremely complicated area of the regulatory process but hopefully, I can shed some light upon it.

In the DAR there have been a number of studies carried out on the accumulation of imidacloprid, including three in Germany and two in the UK. The main difference between the UK and the German studies was the study designs used to estimate the half-life of the product in the soil. These studies are notoriously difficult to do, especially in terms of understanding the dose rate applied to the soil, sampling and the frequent issue of hot-spots – normally where treated seed arises in the core samples taken, which tend to skew the results. Hence why there is extensive use of modelling using field derived data.

The UK study used relatively high levels of treatment and involved six successive years of barley growing; something that is not by any means considered ‘normal’ in the UK. Indeed, data derived would be expected to be right at the extreme end of the spectrum of possibilities of what would be seen in normal agronomic practice. Also worth noting that in the UK study, attempts were made to estimate half-lives in soil using a single data point, again something that makes the validity of any conclusions difficult to assess.

The German study essentially removed some of these issues, including that of hot spots and more data points would have been collected, although the variability remains high. Although the German studies suggested a DT50 of 182 days, overall, the results suggest that in ‘worse-case scenarios’, the half-life of imidacloprid in normal soils would be variable but around 288 days, and would be expected to plateau upon repeated doses after three years.

Just a quick comment on the word ‘persistence’ which seems to have gained a negative connotation when associated with pesticides. Prior to the arrival of modern insecticides such as the neonicotinoids, insecticides tended to have very low half-lives, sometimes in hours, but as a result, were applied at very high dose rates, normally in kilograms per hectare. The move to lower dose products, frequently in the range of ten’s of grams per hectare, which have been so welcomed by everyone involved in agriculture, has been facilitated by having slightly longer persistency levels.

11 December 2012

Prepared 21st December 2012