A Study of Short-term Toxicity, Catalytic Oxidative Degradation and Concentrations in Industrial Waste Waters

Background Complexing agents are widely used in various industrial processes and household products throughout the world. Amongst the well-known complexing agents, not only EDTA but also DTPA and NTA are widely used. Possible legislative restrictions of the use of biologically recalcitrant complexing agents brings about studies of novel and alternative products and at the same time more sophisticated degradation methods are being searched. Materials and Methods This work studies the short-term toxicity of commonly used complexing agents. The assays used were Daphnia magna, Photobacterium phosphoreum (Microtox), and Raphidocelis subcapitata. Also catalytic oxidative degradation of commonly used and novel complexing agents was studied. Both biomimetic metallophthalocyanines and Fenton’s catalyst were used. Also the concentrations of complexing agents in Finnish electrolytic and chemical surface treatment plant waste waters were studied. The analytical methods used are: UV-vis spectrophotometry, HPLC, GC-FID, and GC-MS for complexing agents; TOC for organic load; ICPAES for metal concentrations. Results Free complexing agents proved to be rather non-toxic. They also proved to be effective in reducing heavy metal toxicity. In degradation experiments both adapted methods are effective with varying degradation rate for different complexing agents. In electrolytic and chemical surface treatment plant waste waters, complexing agents, namely EDTA, DTPA, and NTA were found to be present mostly in trace amounts, but some of the selected waste water samples also had relatively high concentrations. Concentrations were lower than PNECaqua value for EDTA, which is 2.2 mg/l. However, highest concentrations were not significantly lower in comparison to PNECaqua. Conclusions Complexing agents are rather non-toxic compounds in terms of short-term toxicity. Their environmental fate is yet still under discussion. Traditional complexing agents can be effectively degraded: up to ninety percent of EDTA was degraded with Fenton’s catalyst in spiked pulp and paper mill waste water. In Finnish electrolytic and chemical surface treatment industry, NTA seems to be a common compound in degreasing baths, while DTPA is in treatment baths. On the other hand, new chemically even more stable compounds are under constant research to improve the bath stability. The concern over the environmental impacts of complexing agents seems therefore to be too tightly focused on EDTA only. Universal Decimal Classification: 502.175, 544.142.3, 544.47, 628.312, 628.345, 66.096.4 National Library of Medicine Classification: QV 290, WA 785, WA 788 CAB Thesaurus: chelating agents; EDTA; nitrilotriacetic acid; toxicity; degradation; concentration; catalytic activity; industrial wastes; waste water; heavy metals