Chronic Toxicity of NTA (Nitrilotriacetate) and Metal-NTA Complexes to Daphnia magna

Abstract

The chronic toxicity of NTA (nitrilotriacetate) tested as the trisodium salt, to Daphnia magna in eight natural waters varied tenfold. A strong negative correlation (r = 0.95) between water hardness and NTA toxicity was found; NTA was most toxic in water with a total hardness of 22 mg/liter and was least toxic in water with a total hardness of 438 mg/liter. The 21-day LC50 in all cases closely approximated the calculated molar equivalence point of total hardness and NTA. Bioassay experiments of NTA, with copper and zinc added, confirmed earlier reports that chelates of copper and zinc with NTA are relatively nontoxic. The solutions were toxic only when the metals or NTA were present in excess. The toxicity of iron (III) was not appreciably changed by NTA chelation.