Estuarine sediment quality assessment by Fourier-transform infrared spectroscopy

Partial least squares Fourier-transform infrared (PLS-FTIR) models were developed for the quality assessment of estuarine sediments through the evaluation of several physico-chemical parameters. Models were based on the chemometric treatment of attenuated total reflection (ATR) spectra directly obtained from samples previously lyophilized and sieved through a lower than 63 μm grid. Spectra were scanned from 3997 to 523 cm−1, averaging 36 scans per spectrum with a nominal resolution of 8 cm−1. Models were built using reference data obtained for sediment samples collected from Ria de Arousa estuary. Hierarchical cluster classification of sediment ATR spectra was employed for the establishment of the independent calibration and validation sample sets. Several parameters, like trace element content (Sn, Pb, Cd, As, Sb and total Cr and also acid soluble, reducible and oxidizable Cr fractions), elemental composition (carbon (C), nitrogen (N) and hydrogen (H) content), pH, redox potential (Eh), together with the amount of fulvic and humic acids, were evaluated. Residual predictive deviation (RPD) values ranging from 1.79 to 2.28 were obtained for all trace elements with the exception of Pb, which exhibited a RPD value of 1.5, similar to those obtained for the different extractable fractions of Cr. Regarding the elemental analysis, excellent RPD values were also obtained for C and N, but for H only adequate values for screening purposes were achieved. Prediction errors for pH and Eh were 0.13 units and 30 mV, respectively, thus indicating the good prediction capabilities of the method. For humic substances, excellent results were obtained for humic acids when compared with fulvic ones. In short, direct ART-FTIR measurements on solid sediments allow a rapid screening of many components of sediments and quantitative data of the main physico-chemical parameters.