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\bibitem{Roekens_etal1989} {\textquotedblleft}\textit{Sulphite and sulphate concentrations in weathering products of sandy limestone and in deposition samples}{\textquotedblright}. Roekens E, Bleyen C, Van Grieken R, Environmental pollution \textbf{57}, 289 (1989).   http://doi.org/10.1016/0269-7491(89)90084-5

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