Mississippi River copper

Total copper and cadmium concentrations increased from Sites 1-4, ranging from 1.2 to 6.8 /xg/L for copper, and 0.2 to 1.0 /xg/L for cadmium. Copper transported in the dissolved phase ranged from 56% at Site 4 to 68% at Sites 1 and 3, and 80% at Site 2. Dissolved cadmium accounted for more than 50% of the total concentrations at all sites. Thus, copper and cadmium transport in the Mississippi River was dominated by apparent solution-phase transport. Total mean lead concentrations ranged from 2.3 to 5.7 /xg/L at Sites 1-4, with dissolved metal accounting for 16 to 38% of the total. The unexpectedly large contribution of dissolved lead indicates the potential role played by organic matter in maintaining lead in solution. 

Total metal concentrations in the Mississippi River are elevated somewhat over average river waters (Table IV), except for polluted areas. The elevated concentrations of copper, cadmium, and lead at Site 4 compared to Site 3 are in part attributable to the discharge of treated sewage effluent and urban runoff. The Minnesota River may be important for all metals studied with the exception of cadmium. Under low flow conditions, 10 to 50% of the trace metal load to the Mississippi... 

Figures 4 and 5 show the seasonal variation in dissolved, particulate, and total iron, manganese, copper, and cadmium concentrations for Sites 3 and 4 in the upper Mississippi River. Maximum concentrations of iron and aluminum at Site 4 during maximum flows were three to five times...

Figure 9. Measurement of copper complexation capacity in upper Mississippi River water—Site 4, 1978 current (fx amps) vs. copper added...

Figure 12. Copper transport phases in the upper Mississippi River,...

The general trend for spring is that the majority of metals are found in the lower molecular weight fractions and therefore can be considered to be soluble. Calcium was found for the most part in the lowest molecular weight fraction, whereas the major trace metals were found predominately in the 1-lOK fraction. ASV measurements for copper, cadmium, and lead showed no detectable free or labile metal. These results, combined with the molecular size distribution of metals in proportion to organics, indicate that metal speciation in the upper Mississippi and Minnesota Rivers is dominated by organometallic interactions. 

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