Synthetic Chelating Agents in the Aquatic Environment: Effect on the Growth of Phytoplankton

Major commercial applications of chelators include the pulp and paper, textile, metal, photographic, cosmetic and detergent industry.The substitution of polyphosphates in P-free washing products with complexing agents such as nitrilotriacetic acid (NTA), sodium citrate, sodium carboxymethyltartonate (CMT) and recently co-polymeric carboxylic acids and inorganic builder Zeolite type A enabled the elimination of phosphates [6, 18]. However, domestic and industrial discharges brought about a dramatic increase of concentration of new organic compounds capable of metal chelation for instance (amino polycarboxylates as low-MW: NTA, EDTA or high-MW as copolymers acrylic acids, acrylic/maleic acids) in the environment, especially in the coastal waters where most of non-degradable matter is finally introduced. Industrial processes such as photography development, boiler descaling and water softening represent main sources of nitrilotriacetic acid [3]. At research laboratories, NTA as well as other synthetic agents chelating metals are specifically used to study the iron metabolism. For instance, in order to prevent precipitation of insoluble trace metals, especially iron, bacterial and algal growth media are commonly supplemented with either EDTA or NTA [1, 11, 12]. NTA has been shown to be a very strong chelating agent and has been implicated in promoting mobilisation of metals [6, 18]. Little is known, however, about the environmental impact of NTA.