Quantities and associations of lead, zinc, cadmium, manganese, chromium, nickel, vanadium, and copper in fresh Mississippi delta alluvium and New Orleans alluvial soils

The topic of this study is the effect of anthropogenic metals on the geoche mical quality of urban soils. This is accomplished by comparing the metal c ontents and associations between two alluvial soils of the lower Mississipp i River Delta, freshly deposited alluvial parent materials and alluvial soi ls collected from a nearby urban environment. Fresh alluvium samples (n = 9 7) were collected from the Bonnet Carre Spillway. The urban alluvial soil s amples (n = 4026) were collected from New Orleans and stratified by census tracts (n = 286). The Spillway samples tend to have less Pb and Zn than gen erally noted for the baseline of natural soils. Except for Mn and V, Spillw ay alluvium contains significantly less metal than urban soils. For Spillwa y samples, the median metal content (in mu g g(-1)) is 4.7 Pb, 11.1 Zn, 0.7 Cd, 164 Mn, 0.8 Cr, 3.9 Ni, 3.2 V, and 3.9 Cu. For urban soils, the median metal content (in mu g g(-1)) is 120 Pb, 130 Zn, 3.2 Cd, 138 Mn, 2.1 Cr, 9 .8 Ni, 3.8 V, and 12.7 Cu. Metal associations also differ between Spillway alluvium and urban alluvial soils. Fresh alluvium correlation coefficients between individual metals vary from 0.87 to 0.99 (P < 10(-13)) except for C r which ranges from 0.57 to 0.68 (P < 10(-7)). The urban soil correlation c oefficients for metals and the index value are 0.40-0.98. In urban soils, P b, Zn, Cr, and Cu are dominant metals and highly associated, with a correla tion coefficient ranging from 0.83 to 0.98 (P < 10(-25)). Their strong asso ciation justifies the use of GIS to map the integrated soil metal index (su m of the medians of metals by census tract) of New Orleans. Although also p ositively correlated (0.40-0.68, P < 10(-10)), Cd, Mn, Ni and V differ in t heir distribution in the city compared to Pb, Zn, Cr and Cu. Overall, signi ficantly higher metal values occur in the inner city and lower values occur in outlying areas. The human health impact of the mixture of metals is not well understood. This study provides empirical data about the mixture and distribution of metals in New Orleans alluvial soils. Given common technica l development, especially of traffic hows in cities, similar patterns of so il metals are expected for all US cities and probably international cities as well. Primary prevention of urban metal accumulations is necessary to en hance and sustain the development of urban culture. (C) 2000 Elsevier Scien ce B.V. AU rights reserved.