Abstract
The distribution of the metallic trace elements (MTE) Zn, Pb and Cd in a sludge-amended soil and their partitioning in specific soil microystems are studied by comparing their contents in amended and control soils. This comparison is achieved at the metric scale of the bulk soil horizons and at the micrometric scale of the weathering microsites (weathering rock-forming minerals and their specific weathered products). The chemical analyses of the MTE in the bulk samples do not show any anthropic contamination of the amended soil with repeated sewage sludge spreading. The chemical analyses of the bulk
Highlights
As a result of the substantial increase in waste water treatment plants in Europe over the past thirty years, problems have emerged in disposing of sewage sludges in an environmentally sound manner
The two soils were sampled on the same dioritic parent-rock (Figures 1(b) and (c)): 1) the Amended Soil profile (AS) that received for ten years wet sewage sludges heavily loaded with Zn, Pb, and Cd, and 2) the Control Soil (CS) that is free of sludge spreading
The MTE concentrations in the bulk soil samples (Table 1) are always below the baseline values taken as the higher limits for non-contaminated soils in the new French regulations (NF French Standard U 44-041 modified by Ordinance 97-1133): Zinc concentrations are from 82.00 to 126.08 mg·kg−1 with 300 mg·kg−1 baseline, Pb values are from 14.84 to 39.08 mg·kg−1 with 100 mg·kg−1 baseline, and Cd ranges from values below analytical detection limit to 0.33 mg·kg−1 with 2.00 mg·kg−1 baseline
Summary
As a result of the substantial increase in waste water treatment plants in Europe over the past thirty years, problems have emerged in disposing of sewage sludges in an environmentally sound manner. Constructed and monitored landfillings are very expensive and will be forbidden in Europe in 2015 because they may generate point-source contaminations due to waste concentrations. Sludge incinerating is expensive due to the need for sludge dehydration prior to burning and the cost of incinerators preventing air pollution. These practices have decreased in the last decade in favor of sludge spreading on cropland, especially in France [1]. This spreading method is considered both a low cost disposal method as well as a source of nutrient-rich fertilizer.
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