Publication Summary

We analyzed polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) concentrations in suspended particulate matter (SPM) collected from the Columbia River at Northport during 1990, 1992, 1993, and 1994 autumn low-flow conditions. The primary objective was to document the effects of pollution abatement efforts by the Celgar pulp mill in Castlegar, British Columbia, 46 river miles upstream of Northport. We also estimated PCDD/PCDF loads in the river and compared the 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) loads to the target for the watershed north of the international boundary as detailed in EPA′s total maximum daily load (TMDL) for the Columbia River basin.

We analyzed polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) concentrations in suspended particulate matter (SPM) collected from the Columbia River at Northport during 1990, 1992, 1993, and 1994 autumn low-flow conditions. The primary objective was to document the effects of pollution abatement efforts by the Celgar pulp mill in Castlegar, British Columbia, 46 river miles upstream of Northport. We also estimated PCDD/PCDF loads in the river and compared the 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) loads to the target for the watershed north of the international boundary as detailed in EPA′s total maximum daily load (TMDL) for the Columbia River basin.

Concentrations of 2,3,7,8-tetrachlorodibenzofuran (2,3,7,8-TCDF), the major congener detected, decreased by two orders of magnitude; and the daily 2,3,7,8-TCDF load in Columbia River SPM decreased 300-fold from 1990 to 1994. The decline in 2,3,7,8-TCDF concentrations agreed well with improvements and discharge reductions reported by Celgar. 2,3,7,8-TCDD, the most toxic congener, was not detected in any samples at quantitation limits ranging from 0.4 to 1.8 pg/g. Maximum possible 2,3,7,8-TCDD loads in SPM were 0.5 mg/day or less, much lower than the watershed target specified in the TMDL (2.3 mg/day). By estimating dissolved 2,3,7,8-TCDD concentrations, we calculated the total maximum possible 2,3,7,8-TCDD loads were about one-half the watershed target in 1990 and 1994, and slightly above the target load in 1992 and 1993.

Toxicity equivalent (TEQ) concentrations, the PCDD/PCDF-associated toxicity expressed as equivalent concentrations of 2,3,7,8-TCDD, decreased seven-fold and the daily TEQ load decreased sixteen-fold from 1990 to 1994. These declines were due mainly to lower 2,3,7,8-TCDF concentrations. Congener profiles changed from year to year, yet aside from 2,3,7,8-TCDF, there was no clear trend in concentrations of SPM-bound PCDDs/PCDFs. We do not have an explanation for the shifting congener patterns but there is little evidence that it was directly related to Celgar discharges.

We recommend additional rounds of SPM collection to verify the findings of this study, check for the presence of 2,3,7,8-TCDD, and determine if sediment resuspension during high-flows contributes significant PCDD/PCDF loads to the Columbia River. Further monitoring should also include analysis for dissolved PCDDs/PCDFs.

Link to EIM data for User Study ID DSER0001