The Organisation for Economic Co-operation and Development (OECD) Emission Scenario Document (ESD) for Wood Preservatives provides methods to quantify the release of active substances from treated wood for various scenarios including sheet pilings in a flowing waterway (OECD 2013). The ESD is used for environmental risk assessment of wood preservatives according to the Biocidal Products Regulation (BPR) in Europe. In this research, ESD equations for copper release from treated sheet pilings were reviewed and compared to classical mass balance equations used in surface water quality modelling to better understand their theoretical basis. ESD equations and a screening-level numerical surface water quality model, TICKET-2D, were used to calculate water column and sediment predicted environmental concentrations (PECs) using typical long-term copper emission rates. TICKET-2D is different from the ESD approach in that it models copper in the water column as well as a discrete sediment compartment and calculates equilibrium copper speciation. A comparison of calculated PECs to threshold levels indicated that: (1) at lower emission rates, water column and sediment PECs are below threshold levels; (2) sediment PECs below threshold values are more difficult to attain compared to water column PECs. TICKET-2D provides additional insight into copper behavior in sediment since it simulates binding of copper to iron sulfides (i.e. AVS) which has been shown to reduce the toxicity of copper.

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