Neonicotinoids in the Environment- Fate and Impact

Over the last half century, society’s dependence on insect-assisted pollination of crops has risen by over 300% globally, while recent findings have estimated a 76% decline in flying insect biomass over the last 27 years. These losses in invertebrate numbers are thought to be due to a possible combination of various factors including parasites and diseases, agricultural intensification, climate change and possible chemical exposure including pesticides such as neonicotinoids.

Neonicotinoids are one of the most widely used insecticides on the global market. Their systemic mechanisms allow for ease of application and relatively successful outcomes in controlling biting and sucking invertebrates, however neonicotinoids have been strongly associated with recent declines in non-target organisms. Many neonicotinoids come directly in contact with the soil, either through application as a seed coating or soil drench, or through spray drift and drip from foliar applications. Relatively little research has focussed on the movement, fate and interactions of these chemicals in UK soils under general field management strategies, although evidence suggests that the addition of soil bio-amendments, such as fertilisers, can influence the mechanisms behind pesticide mobility.

My study aims to quantify the effects of Acetamiprid-based pesticide mixtures on below-ground soil functions, through the analysis of their movement and behaviour in soils of contrasting organic matter contents. A secondary aim is to assess the impact of neonicotinoids on select non-target organisms.

We used ¹⁴C labelled Acetamiprid to track the behaviour of the mixtures compared to the pure active ingredient. Previous research has only used the pure active ingredient, however this isn’t representative of true field scenarios. These spiked pesticides were added to soils of contrasting organic matter content collected from a long-term experiment at Woburn Experimental Farm, Rothamsted Research. We assessed the behaviour of these mixtures across a range of leaching, sorption and mineralisation experiments.

The mineralisation of all mixtures was found to be comparatively slow, with <23% of any given chemical/SOM combination being mineralised over the 60 day experimental period. The highest mineralisation rates were in samples with the highest SOM levels. The preliminary leaching data found that >80% of each chemical was recovered from the soil during the experiment. This, combined with low sorption and mineralisation rates, suggests that neonicotinoids are highly persistent within the environment.

Ongoing work is being conducted to investigate the knock-on impacts and biological implications of acetamiprid use under true field conditions.