Fluorescence properties of well-characterized sedimentary estuarine humic compounds and surrounding pore waters

Structural and spectroscopic properties of sedimentary estuarine humic comp ounds (HC) and surrounding pore waters were investigated. Elemental analysi s showed that sedimentary HC exhibit a molecular design compatible with a m ixed continental-marine environment. In some respects, they are well correl ated with the marine organic matter (e.g. low C/H ratio), while in others t hey are better associated to terrestrial material (e.g. high C/N ratio). Hi gh rates of microbiological activity, combined with a tide-dependent contri bution of an aliphatic marine-like source of organic matter, may account fo r such results. Chemical anomalies were not observed in samples from pollut ed sites, indicating that moderate anthropogenic disturbances will affect c hemical processes related to humic compounds rather than their chemical des ign. With respect to fluorescence properties, sedimentary humus exhibits a single and wide emission peak (lambda (ex) = 313 nm), with lambda (max) sim ilar to 431 nm for fulvic acid and lambda (max) similar to 446 nm for humic acids. For humic adds a shoulder at around 515 nm is also observed. HC cor rected excitation spectra (lambda (em) = 445 nm) are similar to those previ ously observed for HC from aquatic environments, presenting two peaks of va riable intensities, the first being more intense, located around 250 nm, an d the second located in the range 320-350 nm. pore waters extracted from th e same sediment samples as those of HC exhibited fluorescence properties co mparable to that of fulvic acids but exhibiting emission maxima around 424 nm. The significance of hydrophilic substances in relation to the fluoresce nce properties of natural waters is discussed.