THE CONTRIBUTION OF AMMONIA AND ALKALINITY TO LANDFILL LEACHATE TOXICITY TO DUCKWEED

Twenty-five landfill leachates were tested using duckweed and the contribution of ammonia and alkalinity to their acute toxicity was studied by means of the following experiments: bioassays with ammonium sulphate ((NH4)(2)SO4) and sodium bicarbonate (NaHCO3) and tests on one sample following ammonia stripping. The results show that un-ionized ammonia is the toxic form of ammonia. Furthermore, this compound appears to be the major toxicant for most leachates from landfills receiving household refuse. Alkalinity is not directly toxic to duckweed, but enhances ammonia toxicity by controlling the pH of the samples. These results are discussed regarding the regulations in France of landfill leachate monitoring.