Agricultural Valorization of Urban Sewage Sludge: Short-Term Effects on Trace Elements Contamination in Cultivated Soil

Urban sewage sludge (USS) contains potentially hazardous Trace Elements (TEs), including Zn, Cu, Cr, Ni, Pb, and Cd, as well as Trace Organic Contaminants (TOCs), such as Aromatic Polycyclic Hydrocarbons (PAHs). The accumulation of TEs in agricultural soils increases their uptake by crops, thereby affecting food quality and human health. This study aimed to evaluate the short-term effects of different USS application rates on total TE (TTE) and soil metal pollution in cultivated soil in Boukhalfa, Tizi-Ouzou district, Algeria (4°0′52″E, 36°45′4″N), to prevent soil contamination and associated ecological and health risks. Based on legislative recommendations for their use in agriculture, TTEs and PAHs in the USS and TTEs in the soil samples were analyzed. A completely randomized block design was implemented with USS applied at rates of 15, 30, and 45t.ha-1 t USS, implemented in March 2017. One year later, composite soil samples were collected from the 0–20 cm surface layer of each elementary plot (EP). The results showed that the soil was suitable for USS application, with PAHs levels in the USS and TTE concentrations in the soil remaining below the regulatory limits. The increase in TTE concentrations in the amended soils (D3) was 32, 15, 18, 13, and 5% for Zn, Cu, Pb, Cr, and Ni, respectively. The maximum PI (0.32) was recorded on D3. However, all values remained below the regulatory limits. Overall, the short-term application of USS at 15, 30, and 45t. ha-¹ did not lead to soil contamination by multiple TEs. These findings support the safe use of USS as an organic amendment under controlled conditions with regulated application rates. However, long-term monitoring is essential to determine the potential cumulative effects on soil quality and crop uptake and to develop optimized management strategies for sustainable sludge reuse in agriculture.