Testing of different plants to determine influence of physico-chemical properties and contaminants content on municipal sewage sludges phytotoxicity.

This study attempts to evaluate the Phytotoxkit as a tool for measuring the toxicity of municipal sewage sludges using 10 common plants: mustard, turnip, cress, red clover, cucumber, tomato, radish, sorrel, and spinach. The results were used to determine a germination index (GI) and a median effective concentration (EC) value for each plant. The trace metal and polycyclic aromatic hydrocarbon (PAH) contaminant content and the physical-chemical properties were examined. Most sewage sludges were characterized by an unfavorable electrical conductivity value of about 5.2 mS/cm(-1). The most abundant trace metals were zinc (Zn) at 871-1680 mg kg(-1), manganese (Mn) at 245-661 mg kg(-1), and copper (Cu) at 88.2-161.0 mg kg(-1). The lowest values were determined for cobalt (Co) at 2.9-3.8 mg kg(-1) and cadmium (Cd) at 0.7-3.7 mg kg(-1). The PAH sum was based on 10 individual compounds (USE EPA), and the PAH content ranged from 4.76 to 27.95 mg kg(-1), most of the sewage sludges showing a predomination by carcinogenic PAHs. The GI values, based on seed germination and root growth inhibition bioassays, showed increasing plant sensitivity to the tested sewage sludges in the following order: cress > turnip > mustard > sorrel > tomato > sorgo > red clover > radish > cucumber > spinach. The EC50 sewage sludge values lay in the range 31-404 g/kg of soil, and significant relationships were found for most of the plants between EC50 and the magnesium content (Mg(2+): alpha = 0.888-0.924, P = 0.05), calcium content (Ca(2+): alpha = 0.813-0.911, P < or = 0.05), and pH (alpha = -0.913-0.948, P = 0.05). In the case of sewage sludge pollutants, significant relationships were found for trace metals such as: strontium (Sr: alpha = 0.851-0.948, P < or = 0.05), chromium (Cr: alpha = 0.858, P < or = 0.05), and nickel (Ni: alpha = 0.955, P = 0.05), as well as pyrene (PAHs).