Title:

Completing a human health and ecological risk assessment for on-land disposal of dredged tributyltins

Abstract:

Historically, tributyltin (TBT) was extensively applied as an antifouling additive, principally for application to vessel hulls. This has made their presence common in sediments within working harbours or wharfs, which is concerning as they are highly toxic to aquatic life, and bioaccumulate and biomagnify strongly in aquatic food chains. While federal surface water guidelines exist for aquatic life, there is a lack of federal guidelines related to terrestrial-based exposures to people, plants and wildlife. This is of interest when sediments are dredged to increase navigational depth and must be placed on-land at a disposal site. The objective of this study was to assess the human health and ecological risks posed by TBT in sediment once placed in a containment cell using accepted Canadian Council of Ministers of the Environment (CCME) and Health Canada risk assessment methods. The risk assessment was completed for workers and terrestrial plants and wildlife that could potentially be exposed to TBT placed at the disposal site, as well as for members of the general public and aquatic life that could potentially be exposed from the migration of TBT downgradient of the disposal site. Both qualitative and quantitative risk assessment methods were applied following literature review of toxicological information related to TBT. Negligible health risks to humans, wildlife and aquatic life were predicted under normal operational conditions. Potential risks were identified for on-site terrestrial plants and soil invertebrates, and to off-site aquatic life if the volume of dredged sediment exceeded the operational limits. Ultimately, this study helped to determine the design elements required to mitigate the risks from TBT-contaminated sediments placed on-land within a containment cell. These design elements included a clean soil cap on top of the dredged material and the management of dewatering outputs.