Synthetic chelating agents and compounds exhibiting complexing properties in the aquatic environment

Abstract Synthetic chelating agents are utilized in many industrial applications because of their capability of binding and masking metal ions. This review of 20 main compounds includes chelating agents and other compounds, such as the organophosphonates or polycarboxylates, which, by binding metal ions, also exhibit some complexing properties. It aimed to gather data about production, use, toxicity, entry into the aquatic environment, fate and environmental behavior. In spite of the low toxicity and metal mobilization values calculated for the measured or predicted environmentally observed concentrations, many of the investigated synthetic complexing agents, such as ethylene diamine tetra-acetic acid (EDTA), can be classified as environmentally relevant, since they are microbially poorly degradable and exhibit excellent water solubility. Thus they are not or only partially removed during drinking water treatment utilizing filtration and biodegradation steps. For other compounds that bind metal ions, such as the organophosphonates, adsorption is an important route of elimination from the water phase. The data available regarding concentrations of synthetic complexing agents in the aquatic environment has until now almost exclusively focused on the aminocarboxylates. The main examples are EDTA and nitrilo-tri-acetic acid (NTA), which are present in the low μg/L range in almost all anthropogenically influenced streams and rivers in industrialized countries, such as Germany. Concentration data regarding diethyl triamine penta-acetic acid (DTPA) and 1,3-propylenediamine tetra-acetic acid (PDTA) are quite scarce. Reported values of these compounds lie mostly in the detection-limit range 1–2 μg/L. DTPA concentrations found in sewage effluents of paper and pulp mills are in the mg/L range, while maximum concentrations reported for rivers are up to 72 μg/L. The predicted concentrations in surface waters for most of the investigated compounds are also in the lower μg/L range, e.g. for the organophosphonates between 0.25–2.5 μg/L. But until now, except for the aminocarboxylates, analytical methods do not exist for their quantification at these low concentrations. It is recommended that the entry of chelating and metal-binding agents into the water phase should be minimized by applying various measures. All industrial processes and productions dealing with poorly degradable chelating agents and compounds that bind metal ions should be used as little as possible, and their emission into the aquatic environment should be as low as possible. Wherever possible, substitution with compounds exhibiting better degradability should also be sought.