Aluminium speciation in acidic natural waters: Testing of a model for al-humic complexation

Abstract Concentrations of organically-complexed monomeric Al, [Alm-org], in field samples are compared with those predicted from the equation where [HS] is the concentration of humic substances, curly brackets indicate activities, and α, β and γ are constants. Results for 114 field samples from 8 locations in N.W. Europe and N. America were considered with [Alm-org] in the range 0–10 μM. Using α, β and γ values derived from the results of laboratory experiments, a satisfactory agreement between measured and predicted values was obtained with a mean residual (measured —calculated value) of −0.2 μM Al, a root mean square (RMS) residual of 0.9 μM Al and r = 0.92. The 95% confidence limits for the estimation of [Alm-org] correspond to the calculated value ± 1.8 μM. For some sampling locations the RMS residual can be made smaller by using the measured values of [Alm-org] to rescale α.

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