Transport of suspended-sediment-bound toxaphene in the Mississippi River.

Suspended sediment samples from approximately 30 locations along the Mississippi River and six of its major tributaries were collected during July and August 2002 and March 2003 to investigate the distribution and transport of toxaphene in the Mississippi River. The concentration of toxaphene was measured, and the load of toxaphene carried by the river at each site was calculated using water discharge and suspended sediment concentrations. Results indicate that toxaphene is widespread throughout the Mississippi River Basin with the highest concentrations and loads observed for samples collected in the Lower Mississippi River. Among the tributaries, the Yazoo River carried the largest load, amounting to approximately 21% of the estimated load carried by the Mississippi River just below Vicksburg, MS. The majority of the contamination is most likely from nonpoint source runoff from agricultural lands. We also found evidence of a localized toxaphene source in the vicinity of Memphis, perhaps coming from the Wolf River. From our data we estimate that between 200 and 1000 kg of toxaphene were released into the Gulf of Mexico in 2002 from the main stem of the Mississippi River.