Concentrations of Chlorinated Organic Compounds in Various Receiving Environment Compartments Following Implementation of Technological Changes at a Pulp Mill

Concentrations of chlorinated organics in the Wapiti/Smoky River system downstream of the Grande Prairie, Alberta kraft pulp mill have declined in all measured compartments. Since 1992, the mill has converted the bleaching process to chlorine dioxide delignification (100% ClO₂ substitution), implemented condensate stripping, upgraded the aerated stabilization basins, and improved effluent monitoring and management. Since these changes, monthly average final mill effluent parameters have been 0.5 kg ADMT⁻¹ AOX and <0.1 μg L⁻¹ of tri-, tetra- and pentachlorinated phenol compounds. Concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF) are now below detection limits of 1.0–5.0 pg L⁻¹. Environmental concentrations have shown a concomitant decrease, which has been rapid in water and sediments. TCDD/TCDF is not detectable in water and is at or near the detection limit in suspended sediments (at both near and far-field sites). Concentrations of TCDD/TCDF have also declined in fish, although at a slower pace which indicates a biological half-life of over 6 months for mountain whitefish (Prosopium williamsoni) fillets and >1 yr for burbot (Lota lota) livers. Chlorinated phenolic concentrations have paralleled the trends seen for dioxins and furans, with a rapid decrease to non-detectable concentrations in water and concentrations in the very low μg L⁻¹ range (for up to 4 compounds only) in suspended sediments. These compounds were rarely detectable in fish fillets even before the mill changes. Extractable organic chlorine (EOCl) was not detectable in water and was generally in the <0.5–2 mg L⁻¹ range on suspended sediments. EOCl in fish fillets has declined from 13 to 43 mg L⁻¹ before the mill changes to 1–2 mg L⁻¹ in September 1993. EOCl in fish bile was not detectable in the current survey.