Figure 34.  Selected frequency distributions for metal concentrations in sediments

The horizontal axes refer to concentrations in µg/g of copper (Cu), zinc (Zn), or lead (Pb). The vertical axes indicate the number of analyses within classes. The dashed vertical lines demarcate screening criteria for effects-based toxicity levels (Long and others, 1995) for bottom organisms. ERL and ERM values denote concentration levels of metals corresponding to the 10 and 50 percentile levels for toxic effects observed in a variety of test organisms (see Alert Range Table for more information). Bayou Trepagnier is an inlet formerly discharging to Lake Pontchartrain. It has been severely contaminated by effluent from a petroleum refining and petrochemical complex. (This figure does not include late-received data from the USEPA EMAP program or USGS piston core data. The additions would not significantly change the distributions.)

L.P. = Lake Pontchartrain;     B.T. = Bayou Trepagnier

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