Affinity states of biocides determine bioavailability and release rates in marine paints

Abstract

A challenge for the next generation marine antifouling (AF) paints is to deliver minimum amounts of biocides to the environment. The candidate AF compound medetomidine is here shown to be released at very low concentrations, ie ng ml⁻¹ day⁻¹. Moreover, the release rate of medetomidine differs substantially depending on the formulation of the paint, while inhibition of barnacle settlement is independent of release to the ambient water, ie the paint with the lowest release rate was the most effective in impeding barnacle colonisation. This highlights the critical role of chemical interactions between biocide, paint carrier and the solid/aqueous interface for release rate and AF performance. The results are discussed in the light of differential affinity states of the biocide, predicting AF activity in terms of a high surface affinity and preserved bioavailability. This may offer a general framework for the design of low-release paint systems using biocides for protection against biofouling on marine surfaces.

Keywords:

• antifouling biocides
• release
• surface adsorption
• barnacle
• RP-HPLC
• ellipsometry

Acknowledgements

The authors thank Dr J. Salonen at Orion Pharmos Oy, Helsinki, Finland for advice on imidazole separation, Orion Pharmos Oy for generously providing medetomidine, Professor L. Bohlin at the Division of Pharmacognosy, Uppsala University for kindly letting them use research facilities at his laboratory, and L. Bohlin and E. Svangård for scientific advice.

Conflict of interest disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental material

The supplemental material for this paper is available online at http://dx.doi.org/10.1080/08927014.2015.1012639.

Additional information

Funding

This work was supported by the Carl Trygger Foundation, the Helge Ax:son Johnson Foundation, and the CF Lundström Foundation. Partial funding was received from Swedish MISTRA (www.mistra.org) through the Marine Paint project.