Environmental risk assessment for trisodium [S,S]-ethylene diamine disuccinate, a biodegradable chelator used in detergent applications.

Environmental safety data are presented for [S,S]-Ethylene Diamine Disuccinate ([S,S]-EDDS), a new, biodegradable, strong transition metal chelator. An environmental risk assessment for its use in detergent applications, which takes into account the chelating properties of [S,S]-EDDS, is proposed. A property of [S,S]-EDDS that distinguishes it from other strong transition metal chelators is its, "ready" and transparent (no recalcitrant metabolites) biodegradation profile. Because its sorption to activated sludge solids is low (Kp of 40 l/kg), removal of [S,S]-EDDS during sewage treatment, which is greater than 96% as determined by the Continuous Activated Sludge test, is mainly ascribed to biodegradation. At projected use volumes in detergent applications [S,S]-EDDS predicted steady-state concentration in rivers leaving the mixing zone will be below 5 micrograms/l due to rapid biodegradation. [S,S]-EDDS exhibits low toxicity to fish and Daphnia (both EC50S > 1000 mg/l). By contrast, due to limitation of the algal test for chelators apparent toxicity was observed (EC50 = 0.290 mg/l, NOEC--No observable Effect Concentration = 0.125 mg/l). Schowanek et al. [1] demonstrated that this is not toxicity sensu stricto but a chelation effect of trace metals in the test medium and of resulting essential nutrients limitation. This requires specific attention when the results of algal toxicity are to be extrapolated to a field situation to perform realistic risk assessment. Metal speciation calculations, using MINEQL+, show that at the predicted environmental concentrations of [S,S]-EDDS (1-5 micrograms/l), such a chelation effect would be insignificant. These calculations allow to estimate the NOEC for chelation effects in the field to be in the range of 0.250-0.500 mg/l, depending on the background water chemistry. These values are well above the laboratory NOEC. An environmental risk assessment was performed using the EUSES (1.0) program. EUSES is currently the EU recommended tool for conducting risk assessments (TGD 1995). It was applied to estimate the river water and soil concentrations from production, formulation and private use life stages. The estimated PEC/PNEC ratio in all relevant environmental compartments is smaller than 1, indicating "no immediate concern" at the anticipated usage level.