Hurricane Katrina's impact on New Orleans soils treated with low Lead Mississippi River alluvium.

Before Hurricane Katrina flooded 80% of New Orleans, 25 heavily Pb contaminated properties were treated with 15 cm of low Pb Mississippi River alluvium from the Bonnet Carré Spillway (BCS). Four phases of soil collection on the properties included pretreatment (phase 1) median surface soil Pb was 1051 mg/kg (range 5-19 627); after BCS cover (phase 2) the median soil Pb decreased to 6.3 mg/ kg (range 3-18); just before Katrina, a soil collection was partially completed (phase 3); and finally, a post-Katrina collection (phase 4) on all 25 properties. Twenty-three properties were flooded. The objective was to compare Pb changes of phases 2 and 3 pre-Katrina with the post-Katrina (phase 4) soil collection. The post-Katrina soil Pb (phase 4) (median of 16.3, range 5.5-1,155) increased significantly (P-value = 3.7 x 10(-10)) from the clean soil, phase 2 results. Matched soil samples collected in phase 3 before flooding and phase 4 after flooding showed that on initially vacant lots the amounts of Pb were not significantly different (P-value = 0.97); but, on properties with homes, the changes were significant (P-value = 0.03). After catastrophic flooding, the clean soil remained relatively undisturbed; the soil Pb changes were small with increases of median Pb of 12 and 6 mg/kg for vacant lots and properties with homes, respectively. Processes accounting for Pb increases include Pb-based paint abatement on one property, home construction on the vacant lots, and resuspension and deposition of Pb dust. As part of the post-Katrina recovery, the combined benefits of Pb-safe paint abatement or renovation and clean soil cover should outweigh the estimated annual cost of Pb poisoning of children returning to New Orleans.