D.J. Smallman

Catchment source contributions to the sediment-bound organic matter degrading salmonid spawning gravels in a lowland river, southern England.

The ingress of particulate material into freshwater spawning substrates is thought to be contributing to the declining success of salmonids reported over recent years for many rivers. Accordingly, the need for reliable information on the key sources of the sediment problem has progressed up the management agenda. Whilst previous work has focussed on apportioning the sources of minerogenic fine sediment degrading spawning habitats, there remains a need to develop procedures for generating corresponding information for the potentially harmful sediment-bound organic matter that represents an overlooked component of interstitial sediment. A source tracing procedure based on composite signatures combining bulk stable (13)C and (15)N isotope values with organic molecular structures detected using near infrared (NIR) reflectance spectroscopy was therefore used to assess the primary sources of sediment-bound organic matter sampled from artificial spawning redds. Composite signatures were selected using a combination of the Kruskal-Wallis H-test, principal component analysis and GA-driven discriminant function analysis. Interstitial sediment samples were collected using time-integrating basket traps which were inserted at the start of the salmonid spawning season and extracted in conjunction with critical phases of fish development (eyeing, hatch, emergence, late spawning). Over the duration of these four basket extractions, the overall relative frequency-weighted average median (±95% confidence limits) source contributions to the interstitial sediment-bound organic matter were estimated to be in the order: instream decaying vegetation (39±<1%; full range 0-77%); damaged road verges (28±<1%; full range 0-77%); septic tanks (22±<1%; full range 0-50%), and; farm yard manures/slurries (11±<1%; full range 0-61%). The reported procedure provides a promising basis for understanding the key sources of interstitial sediment-bound organic matter and can be applied alongside apportionment for the minerogenic component of fine-grained sediment ingressing the benthos. The findings suggest that human septic waste contributes to the interstitial fines ingressing salmonid spawning habitat in the study area.

Sorption of Mecoprop by two clay landfill liner materials: Oxford Clay and Mercia Mudstone

Abstract As part of a programme of research into natural attenuation of contaminants in landfill liners, the sorption and desorption of Mecoprop (MCPP) by mineral liner materials was investigated. Mercia Mudstone and Oxford Clay have the potential to attenuate MCPP by sorption processes, which were observed to be rapid in both materials. Sorption to iron hydroxides was thought to be the main mechanism operating in Mercia Mudstone and may be responsible for some of the sorption occurring in Oxford Clay. Additional sorption to Oxford Clay may be related to its kerogen content, as this type of organic matter has been shown to be highly sorbent for hydrophobic organic compounds, but further research is needed to assess whether kerogen has a high affinity for polar compounds such as MCPP. Desorption tests demonstrated that desorption was rapid and that sorption was potentially reversible. There was some evidence that tannic acid in the synthetic leachate did not affect MCPP sorption, but the high ionic strength leachate reduced sorption of MCPP in Oxford Clay. For regulatory risk assessments, this result emphasizes the importance of conducting sorption tests in a matrix similar to that of the environment under investigation to obtain realistic results for sorption coefficients.

Influence of iron valency on the magnetic susceptibility of a microbially produced iron sulphide.

Microbial iron sulphide is well known as an adsorbent for the treatment of metallic ion polluted wastewater. Under certain culture conditions a highly magnetic iron sulphide can be produced which would enable a low cost biomagnetic separation process to be developed. This paper illustrates that by raising the ferrous content of a ferrous - ferric sulphate rich medium the magnetic susceptibility of the iron sulphide produced is increased.

Sorption of organic contaminants by Oxford Clay and Mercia Mudstone landfill liners

Abstract This study provides an evaluation of the sorption capacity of two contrasting mineral liners or barriers widely used in the UK for a range of organic contaminants of varying hydrophobicity commonly found in landfill leachate. Batch tests (involving toluene, trichlorobenzene, trichloroethene and naphthalene) showed that the sorption capacity of Oxford Clay was not only significantly greater than that of Mercia Mudstone, but was also greater than the sorption capacity of many soils or clays reported in the literature. The organic carbon normalized sorption coefficients (Koc) for Mercia Mudstone were comparable with both published and empirically derived Koc values, but the Koc for Oxford Clay was underestimated by literature values by several orders of magnitude. Retardation of these contaminants by Oxford Clay was also under-predicted by estimates based solely on organic carbon content. Amorphous organic matter (the main component of the organic matter in the Oxford Clay as characterized using ‘coal petrography’ methods) was believed to be responsible for the elevated sorption capacity of the Oxford Clay liner. Sorption coefficients were reduced in the presence of dissolved organic carbon in leachate, suggesting that published Koc values derived in synthetic groundwater may overestimate the sorption capacity in landfill scenarios. Sorption coefficients and Koc–Kow correlations determined in this study can be used for modelling organic contaminant sorption in Oxford Clay and Mercia Mudstone liners as part of landfill risk assessments in the absence of site-specific data, in particular for Oxford Clay, for which published correlations were shown to be too conservative. For other types of clay liner material, the cautious approach would be to determine site-specific sorption coefficients following characterization of the organic carbon. Further research is needed into the effects of leachate dissolved organic carbon and the composition of clay liner organic carbon on sorption of hydrophobic organic compounds.