TP4 Toxicity of Complex Mixtures
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1:20 PM - 4:40 PM, Tuesday

() Investigating the cause of effects of final treated pulp mill effluent on fathead minnow reproduction.

Rickwood, C1, 2, Dube, M2, MacLatchy, D3, Hewitt, L4, Parrott, J4, 1 University of Saskatchewan, Saskatoon, SK, Canada2 National Water Research Institute, Saskatoon, SK, Canada3 University of New Brunswick, Saint John, NB, Canada4 National Water Research Institute, Burlington, ON, Canada

ABSTRACT- Reproductive effects (e.g., reduced gonad size, altered hormone levels and secondary sex characteristics) have been recorded in wild fish in waters receiving pulp mill effluent (PME) since the mid to late 1980s. Although, treatment of final effluent has made significant improvements in effluent toxicity, reproductive responses in wild fish continue to be documented. There is a pressing need to identify the source or cause of these responses so process/treatment changes or other mitigation options can be explored. The objective of this study was to determine if the effects observed in pair-breeding fathead minnows (Pimephales promelas) with final effluent exposure (see Rickwood et al., poster submission) could be traced to a particular process stream/s in the mill using an investigation of cause approach. The reproductive output of P. promelas was initially assessed using a mobile bioassay trailer on-site over a three week period to obtain baseline data of cumulative egg production, fecundity, spawning events, hatching success and occurrence of deformed larvae. At the end of the pre-exposure period, breeding pairs were exposed to final PME for 21 d to determine the activity of the final effluent at maximum (100% v/v) and environmentally relevant (1% v/v) concentrations, results from this comparison are discussed in Rickwood et al. poster submission. Breeding pairs were also exposed for 21 d to 4 selected process effluents (including primary treated, stripped condensates, acid and alkaline streams) at various concentrations using a flow proportion approach based on acute toxicity studies. Examination of responses to various in-mill process streams identified the alkaline stream from the bleach plant of the softwood mill as a possible principle source of compound/s that were causing the reproductive effects observed in final PME. Further investigations are underway to confirm responses to the alkaline process stream and to conduct a Toxicity Identification and Evaluation.

Key words: pulp mill, Fathead minnow, process stream, reproduction

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