Publication Summary

We measured concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and other polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) in suspended particulate matter (SPM) collected near the mouth of the Snake River during October 1996. The objective of this survey was to estimate the daily 2,3,7,8-TCDD load at the Snake River mouth under low-flow conditions and compare it to the target load for the Snake River watershed as described in EPA′s total maximum daily load (TMDL) for the Columbia River basin.

We measured concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and other polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) in suspended particulate matter (SPM) collected near the mouth of the Snake River during October 1996. The objective of this survey was to estimate the daily 2,3,7,8-TCDD load at the Snake River mouth under low-flow conditions and compare it to the target load for the Snake River watershed as described in EPA′s total maximum daily load (TMDL) for the Columbia River basin.

Two PCDDs and three PCDFs were detected in SPM; 2,3,7,8-TCDD was not found at a detection limit of 0.24 pg/g. The total maximum possible load of 2,3,7,8-TCDD at the Snake River mouth was 0.25 mg/day, about one-fifth of the target load for the Snake River watershed. The total maximum possible toxicity equivalent (TEQ) load was estimated to be 0.76 mg/day. We recommend additional monitoring to determine upstream loading of PCDDs/PCDFs and to assess the effects of high flows on the downstream transport of these compounds.