Neonicotinoid pesticides have been used worldwide since the early 1990’s. Despite their high target efficacy, and their low mammalian toxicity their use has been severely restricted across EU member countries and the UK. The use of neonicotinoid insecticides has been linked, on numerous occasions, to various deleterious effects in non-target populations, including reductions in honeybee queen production, increases in songbird mortalities, and decreases in earthworm activity. Despite neonicotinoid seed coatings leaving up to 90 % of the applied treatments in the soil, the effects of neonicotinoids on soil communities, functions and processes are vastly underrepresented in the literature. Even with the shift away from the use of seed dressings, systemic pesticides are still readily incorporated into the soil system.
The primary objective of this thesis was to assess the impact of the neonicotinoid acetamiprid on soil systems and soil ecology, accounting for realistic practices and agriculturally relevant management where possible. This thesis starts by presenting a review of our state of knowledge around neonicotinoids in the soil system, highlighting possible research areas and unanswered questions. It then leads into an analysis of the physicochemical behaviour and persistence of a selection of commercial formulations under different soil organic matter treatments (Chapter 2). Our findings demonstrated that both the different chemical formulation and organic matter treatment had significant influence on some of these behaviours within soil. Building upon these results we assess the biological influence of an agricultural formulation under true field conditions (Chapter 3), in this case finding that seasonal variation was a much larger driver in regulating soil-dwelling communities.
The studies presented in Chapter 4 & 5 continue to explore the biological responses to acetamiprid exposure, this time on a single target species (Lumbricus terrestris) under a mesocosm set-up. We employed a selection of commercial pesticide formulations whilst also including isolated active ingredients to allow for different chemical interactions to be disentangled. Across these experiments we once again found differences in response across the chemical treatment, as well as an overall significant response to acetamiprid exposure. When combined, these findings begin to reveal the true consequences of neonicotinoid use, as well as highlighting the need to employ realistic and relevant conditions, chemicals, and test species.