Researching Water-Friendly Slug Pellets

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UK drinking water sources are intermittently contaminated with metaldehyde released from slug pellets. There is no effective technique for its removal from drinking water so to avoid contamination of water supplies the water is often run to waste.

Lipodisqs®, developed and patented by Malvern Cosmoceutics Ltd (MCL), comprise a biodegradable nano-sized (20 nm) cylinder of polymer within which a lipid can be placed. Lipodisqs® are currently used to topically deliver poorly soluble cosmetic preparations, which can be dissolved in the lipid. With funding from Innovate_UK I commissioned MCL to investigate whether using Lipodisqs might offer a viable solution to these pollution problems.

Lipodisqs® might also be able to deliver hydrophobic pesticides in the same way as cosmetics. It seems reasonable to expect that dissolution of metaldehyde, for example, in the lipid could reduce or slow its release into the environment. In the presence of a fatty nutrient, the pesticide may even be more amenable to breakdown by soil bacteria. This novel idea, if adopted, therefore promises considerable potential for improvement of drinking water supply from agricultural catchments.

Innovate_UK (formerly the Technology Strategy Board) offered Stephen Buss Environmental Consulting Ltd a £5000 innovation voucher to investigate this idea. MCL was engaged to confirm some of the assumptions made; namely that metaldehyde could be deployed within Lipodisq® formulations. In initial discussions, MCL suggested that the polymer alone might be configured to take up metaldehyde and release it at a certain pH. In this way the pesticide could remain inside an environmentally inert polymer capsule until released by slug stomach acids. It also seemed feasible that the Lipodisq® technology could be used as a chelating agent to strip the pesticide out of contaminated water in a water treatment works.

MCL carried out a program of compatibility screening and control experiments: a range of Lipodisq® formulations were prepared with varying concentrations of metaldehyde, across a range of pH conditions, to identify a viable formulation. Conventional Lipodisq® formulations were modified and reformulated in an attempt to improve their metaldehyde carrying potential. These formulations were evaluated for their ability to solubilise a viable concentration of metaldehyde and to remain stable in an aqueous phase.

Disappointingly no Lipodisq® formulation was found to take up metaldehyde: either with or without the lipid. This finding robustly disproves the feasibility of the idea when applied to metaldehyde.

Stephen Buss Environmental Consulting and Malvern Cosmoceutics continue, together, to explore the environmental benefits offered by Lipodisq® technology for water treatment. The Technology Strategy Board is gratefully acknowledged for promoting this initial collaboration.