The effect of waste water treatment on river metal concentrations: removal or enrichment?

Netherlands Institute of Ecology (NIOO-KNAW), Centre for Estuarine and Marine Ecology, PO Box 140, 4400 AC Yerseke, The Netherlands
Journal of Soils and Sediments (Impact Factor: 1.97). 11(2):364-372. DOI: 10.1007/s11368-010-0321-4

ABSTRACT PurposeDischarge of untreated domestic and industrial waste in many European rivers resulted in low oxygen concentrations and contamination
with trace metals, often concentrated in sediments. Under these anoxic conditions, the formation of insoluble metal sulfides
is known to reduce metal availability. Nowadays, implementation of waste water treatment plants results in increasing surface
water oxygen concentrations. Under these conditions, sediments can be turned from a trace metal sink into a trace metal source.

Materials and methodsIn an ex situ experiment with metal contaminated sediment, we investigated the effect of surface water aeration on sediment
metal sulfide (acid volatile sulfides (AVS)) concentrations and sediment metal release to the surface water. These results
were compared with long-term field data, where surface water oxygen and metal concentrations, before and after the implementation
of a waste water treatment plant, were compared.

Results and discussionAeration of surface water in the experimental setup resulted in a decrease of sediment AVS concentrations due to sulfide oxidation.
Metals, known to precipitate with these sulfides, became more mobile and increasing dissolved metal (arsenic (As), cadmium
(Cd), copper (Cu)) concentrations in the surface water were observed. Contrary to As, Cd, or Cu, manganese (Mn) surface water
concentrations decreased in the aerated treatment. Mn ions will precipitate and accumulate in the sediment as Mn oxides under
the oxic conditions. Field data, however, demonstrated a decrease of all total metal surface water concentrations with increasing
oxygen concentrations following the implementation of the waste water treatment plant.

ConclusionsThe gradual decrease in surface water metal concentrations in the river before the treatment started and the removal of metals
in the waste water treatment process could not be countered by an increase in metal flux from the sediment as observed in
the experiment.

KeywordsAcid volatile sulfides (AVS)–Metal availability–Oxidation–Redox chemistry–Sediments–Simultaneously extracted metals (SEM)

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    ABSTRACT: PurposeThe development of Sediment Quality Guidelines (SQGs) is one of the remaining challenges for a better protection of aquatic biodiversity and in particular sediment dwelling organisms. So far, sediment quality assessment in Flanders was based on a comparison of chemical concentrations to the geometric mean of the concentrations at 12 reference sites. The study described in this paper addressed the need for more science-based guidelines. The developed guidelines are already incorporated into Flemish legislation. Materials and methodsBased on a large sediment monitoring database, containing physico-chemical properties, concentrations of chemicals, macrobenthic community assemblages and ecotoxicological data, Sediment Effect Concentrations (SECs) were calculated as basis for the SQGs. The derived SECs were based on ecological effects, namely Lowest and Severe Effect Levels (LEL/SEL), as well as ecotoxicological endpoints, namely Threshold and Probable Effect Levels (TEL/PEL). The average values of the ecological and ecotoxicological SECs were used to distinguish five sediment quality classes. Results and discussionThe ecological values were in general less stringent than the ecotoxicological values. However, the Lowest Effect Levels (95% of the benthic taxa can be present under this level) and Threshold Effect Levels (no toxic effect is expected under this level) did not differ significantly. Probable Effect Levels (concentrations above this level will certainly result in toxic effects) were generally lower than the Severe Effect Levels (above this level only 5% or less of the taxa are present). The SECs calculated in this study enabled us to correctly identify 87.9% of the sediments as toxic. The development of SQGs based on a combination of the LEL/SEL and TEL/PEL methods enabled us to underpin these SQGs based on field observations and will improve the assessment of sediment quality based on chemical parameters. Although sediments typically contain complex mixtures of contaminants, only a limited number of these contaminants will be measured. Additional application of bioassays for the overall sediment quality assessment is therefore recommended. ConclusionsThis study describes the development of SQGs in Flanders, which are based on ecological and ecotoxicological data derived from a TRIAD monitoring network. The combination of the LEL and PEL resulted in SQGs that were recently incorporated in Flemish legislation and for which the respective pore water concentrations were in the same order of magnitude as the Annual Average Environmental Quality Standards values for Water Framework Directive priority pollutants. KeywordsEQS–Macrobenthos–Priority substances–SEC–Sediment quality guidelines–SQG–TRIAD
    Journal of Soils and Sediments 11(3):504-517. · 1.97 Impact Factor
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    ABSTRACT: Ecosystem & Ecography "Man and man's earth are unexhausted and undiscovered. Wake and listen! Verily, the earth shall yet be a source of recovery. Remain faithful to the earth, with the power of your virtue. Let your gift-giving love and your knowledge serves the meaning of the earth." Friedrich Nietzche The presence of heavy metals in soils is an environmental hazard key and one of the most difficult contamination control problems to solve. There are two main causes: firstly, the chemical character of heavy metals (they are not subjected to biodegradation processes), favours accumulate in the environment and, secondly, the complexity of the geochemical soil matrix. Simplification of this matrix increase chances of recognition of basic soil processes [1]. Soil is a major reservoir for xenobiotic compounds as it possesses an ability to bind various chemicals [2]. The soil as an important ecological factor due to several characteristics: close correlation with the climate and region and its structure, configuration and nature; its own quality on which relies formation and protection of surface and underground matter resources; influence on humans nutrition and its role in social and economic development of mankind. The heavy metals have an important influence on plants, animals and humans development. The chemical compositions of these heavy metals don't exceed 0.01% in the analyzed systems and their physiologic role is essential for normal biological life cycle of organisms [3]. They are absolutely necessary for living organisms but their biological role is still difficult to establish. If taken alone they don't show deficiency symptom, only in combination with other mineral elements and don't seem to have a direct function in plants nutrition. Soil has the ability to immobilise introduced chemicals like heavy metal ions [4,5]. From the geological and chemical point of view the heavy metals can express lots of proprieties. The solid phase of soils and environmental factors play an important role in heavy metals solubility, dynamics and balance in the soil. Between solid, liquid and gaseous phases exists a dynamic equilibrium in the soil.
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    ABSTRACT: Inundation of formerly embanked areas in order to combine flood control and tidal marsh restoration will be applied increasingly. However, areas suitable for the implementation are often found to be contaminated. Re-inundation of metal contaminated soils can have consequences on total metal concentrations as well as metal mobility. In this study, metal mobility in a tidal marsh restoration project was evaluated based on the modified BCR sequential extraction method, concentrations of acid volatile sulfides (AVS) and simultaneously extracted metals (SEM) and metal concentrations in plants. The results obtained from the sequential extraction suggest an increase in metal mobility following inundation due to the reduction of Fe and Mn oxides and the subsequent release of associated metals. However, the differences in results between sequential extraction and [SEM-AVS] may indicate that redistribution of the metals to the mobile fraction can be caused by sample processing. High AVS concentrations in newly deposited sediments in the restored marsh may indicate that the formation of insoluble metal-sulfide complexes will reduce metal mobility on the longer term. Processes following inundation of metal contaminated land are complex and different conditions prevailing in other sites or estuaries can result in different behavior of the trace metals. More in situ research is needed to get a better insight in the risks involved.
    Science of The Total Environment 02/2013; 449C:174-183. · 3.26 Impact Factor

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