DISTRIBUTION AND ELIMINATION OF HEDP IN AQUATIC TEST SYSTEMS

Basic reactions, including adsorption/desorption and photodegradation, which influence the behaviour and fate of chelating agents in sewage treatment processes and in aquatic ecosystems, were evaluated for HEDP (1-hydroxyethane-1,1-diphosphonic acid). Freundlich constants for the HEDP-sorption onto clay minerals, river sediments and sewage sludges are mostly in the range between 500 and 3000. A remarkable desorption occurs only in strong acidic or higher concentrated salt solutions. Photodegradation is initialized in the presence of heavy metal ions and/or by maintaining acid pH conditions. The possibility of HEDP photodegradation in river waters could be verified with a special equipment for the simulation of terrestric solar radiation. This investigation supports the assumption that discharged HEDP will be able to accumulate and persist in the aquatic environment, if adsorption processes restrict the efficiency of the phosphonate photolysis.