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 Disuccin ate ([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 metabolit es) biodegradation profile. Because its sorption to activated sludge solids is low ( Kp of 40 I/kg), removal of [S,S]EDDS during sewage treatment, whi ch is greater than 96% as determined by the Continuous Activated Sludge tes t, is mainly ascribed to biodegradation. At projected use volumes in deterg ent applications [S,S] - EDDS predicted steady-state concentration in river s leaving the mixing zone will be below 5 mu g/l due to rapid biodegradatio n. [S,S]-EDDS exhibits low toxicity to fish and Daphnia (both EC(50)s > 100 0 mg/l). By contrast, due to limitation of the algal test for chelators app arent toxicity was observed (EC50 = 0.290 mg/l, NOEC - No observable Effect Concentration = 0.125 mg/l). Schowanek et at. [1] demonstrated that this i s 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 extrapolate d to a field situation to perform realistic risk assessment. Metal speciati on calculations, using MINEQL+, show that at the predicted environmental co ncentrations of [S,S] - EDDS (1-5 mu g/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) progra m. EUSES is currently the EU recommended tool for conducting risk assessmen ts (TGD 1995). It was applied to estimate the river water and soil concentr ations from production, formulation and private use life stages. The estima ted PEC/PNEC ratio in all relevant environmental compartments is smaller th an 1, indicating "no immediate concern" at the anticipated usage level, (C) 1999 Elsevier Science Ltd. All rights reserved.