The fate of EDTA and DTPA in aquatic environments receiving waste waters from two pulp and paper mills

Ethylenediaminetetraacetic acid (EDTA) and diaminepropanetetraacetic acid (PDTA) are two complexing agents that form strong complexes with divalent and trivalent metal ions. This property has been utilised technically in pulp bleaching processes to inhibit decomposition of the bleaching agent. The metal complexes and excess of complexing agents are discharged through the mill effluents. As EDTA and DTPA are not readily degraded by micro-organisms and not significantly interacting with sludge or sediment, they may be accumulated in receiving waters. Ferric complexes of EDTA and DTPA are known to be converted photolytically. In order to evaluate the fate of the complexing agents in receiving waters, two basic questions have to be addressed: (i) are EDTA and DTPA found in the aquatic environment after discharge into receiving waters and (ii) are they photolytically converted? Two mills, one pulp mill localised at a fresh water lake and one pulp and paper mill at a brackish water were investigated, both mills using bleaching technologies with EDTA and DTPA as complexing agents. Samples were collected at the discharge point and along a gradient in the receiving waters at two occasions: summer at solstice and winter with low light intensity. Samples were taken from surface water, an intermediate depth, and bottom water. A new analytical method was applied which made it possible to quantify the analytes at sub-µg/l level but could without any difficulty be extended to low ng/l level by using a greater sample. The method is robust and not sensitive to high ionic strength or dissolved organic matter. The complexing agents EDTA and DTPA and their first degradation products were detected in the effluent and the receiving waters in the vicinity of the mills. DTPA and the degradation products could only be detected a few kilometres from the effluent point while EDTA could be detected in more remote locations at fairly constant concentrations. The occurrence of EDTA in these samples was conclusively identified by means of GC-MS comparison of the sample with the authentic reference compound.