Development of quality criteria based on a toxicological characterization of fertilizing residuals1

Toxicity tests were used to evaluate the environmental toxicity of municipal and industrial residuals compared to cow and hog manures. The goal was to evaluate the impact of chemicals that are either potentially present but not routinely analyzed, or unknown. Four toxicity tests were used: germination and growth of barley (Hordeum vulgare), mortality of Daphnia magna, light production inhibition of the bioluminescent bacteria Vibrio fischeri, and mortality of earthworms (Eisenia undrei). Twenty-five samples of residuals and 20 samples of manures were sampled and mixed into standardized soil samples. Part of the amended soil was used for barley tests whereas a water extract of the rest was used for toxicity tests with Daphnia and Vibrio. The worm tests were performed with fertilizing residuals and manures not mixed with soil. The toxicity varied according to the amount of manure or fertilizing residual added to the soil samples. At agronomic rates, toxicity of most of the residuals was low or even negative (stimulation of barley growth). A set of toxicological tests and criteria is proposed to assess if a given residual presents an elevated toxicity as compared to that of manures. Results of this study were used by the Ministère du Développement durable, de l'Environnement et des Parcs (MDDEP) to establish toxicity criteria in its guidelines for the valorization of fertilizing residuals. [PUBLICATION ABSTRACT]