Environmentally relevant concentrations of aminopolycarboxylate chelating agents mobilize Cd from humic acid
Ashley E. North , Sophia Sarpong-Kumankomah , Andrew R. Bellavie , Wade M. White , Jürgen Gailer
DOI:10.1016/j.jes.2017.02.004
Received November 09, 2016,Revised February 07, 2017, Accepted February 07, 2017, Available online February 16, 2017
Volume 29,2017,Pages 249-257
Although Cd is a pollutant of public health relevance, many dietary sources from which it can be absorbed into human tissues remain unknown. While it is well established that the biogeochemical cycle of Cd involves its complexation with environment-derived ligands (e.g., humic acids, HAs) and anthropogenic ones (e.g., chelating agents, CAs), the interaction of Cd with both of these ligands is less well understood. To gain insight, a HA–Cd complex was injected on a size-exclusion chromatography (SEC) column coupled on-line with a flame atomic absorption spectrometer (FAAS)using10 mmol/LTrisbuffer(pH 8.0)asthemobilephase.Thisapproachallowedustoobserve the intact HA–Cd complex and the retention behavior of Cd as a function of 2–20 μmol/L
concentrations of ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) or methylglycinediacetic acid (MGDA) that were added to the mobile phase. An increase of theretentiontimeofCdwasindicativeofapartialorcompleteabstractionofCdfromHA.Ourresults revealed that all CAs abstracted Cd from the HA–Cd complex at concentrations of 5 μmol/L, while MGDA and DTPA were effective at 2 μmol/L. The bioavailability of some of the on-column formed CA–Cd complexes explains the previously reported increased accumulation of Cd in periphyton in the ecosystem downstream of wastewater treatment plants. In addition, our results imply that the use of effluents which contain CAs and Cd for the irrigation of food crops can introduce Cd into the food supply and compromise food safety.
