Manging contaminated sediments

Management of contaminated sediments, i.e. linking risk assessment and problem solutions, needs both quality criteria respecting recent findings on bioavailability of pollutants and in-depth knowledge on processes controlling their particular hydrological and biogeochemical dynamics. In thefirst part of our review, new insights into ‘diagenetic’ mechanisms on particles including ageing and their effects on biological interactions were presented. These findings clearly indicate the need to refine bioavailability models including equilibrium partitioning. A set of bioassays is a powerful supplement to assess sediment quality. In thesecond part, an interdisciplinary process approach relating to the release of DOC, nutrients and pollutants into the open water is described, which has been derived from the evaluation of the international state-of-the-technology with three major themes: ‘experimental techniques’, ‘processes and properties’ and ‘development and validation of models’. Special study targets are the formation of aggregates in turbulent water, flocs and biofilms from organic reactions, and formation of new surfaces for readsorption of dissolved pollutants. Of greatest importance is the degradation of organic matter, which affects both hydrodynamic processes and geochemical redox cycles, thus providing driving forces, e.g. for metal mobilization. Models for predicting pollutant transport in rivers are still dominated by hydromechanical parameters. A first step for extending these models could involve typical milieu factors such as competing ions, complexing agents, redox conditions and pH-values. The next steps would include binding constants and other factors describing solid/solution interactions of critical chemicals in a multicomponent system. In theforthcoming issues of JSS — J Soils and Sediments, two practical fields of application will be discussed: in-situ sediment treatment — natural attenuation approach (Part III) and subaquous storage/capping of dredged material (Part IV). The abstracts of both parts can be found in the appendix.     

Managing contaminated sediments

Remediation techniques on contaminated sediments are generally much more limited than for most other solid waste materials, except for mine wastes. The widely diverse contamination sources in larger catchment areas usually produce a complex mixture of contaminants that is more difficult to treat than an industrial waste. In the first two chapters, additional information will be presented onin- situ treatment methods, which were the central topic in the Spittelwasser Case Study (JSS - Journal of Soils and Sediments, Vol. 1, No. 3, pp. 181–187), and on the development of ecologically sound dredging and processing techniques, where practical applicability had to be demonstrated as part of an integrated remediation chain. In the latter respect, mechanical separation of less strongly contaminated fractions may be a useful step prior to the final storage of the residues (chapter 2, Treatment of Strongly Contaminated Dredged Materials) For most sediments from maintenance dredging, there are more arguments in favor of ‘disposal’ rather than ‘treatment’ (chapter 3, Subaqueous Storage and Capping). Consideration about the comparative assessment of the two basic management options ofin- situ capping and dredging followed by sub-aqueous disposal are discussed on a legislative, economic and technical-environmental basis. The concept of capping of contaminated sedimentsin- situ has been developed in the last two decades as an ecologically sound and economic alternative to more costly remediation techniques. The main characteristics are related to the passive character of this concept, which minimizes labor and process costs. Mechanisms of contaminant retention in sediment caps is discussed with special regard to the chemical isolation component. From this consideration, the development of the active barrier concept is derived that denotes the use of reactive additives in capping layers to chemically bind one or more contaminants specifically.     

Managing contaminated sediments

While remediation and storage of contaminated dredged materials is a key issue at harbour sites, there is another type of sediment pollution problem, which mainly originates from large-scale dispersion of contaminants in flood-plains, dike foreshores and polder areas. In recent years, catastrophic cases of sediment contaminations have occurred in connection with the failure of tailing dams from mines. Unlike problems related to conventional polluted sites, the risks here are primarily connected with the transporting and depositing of contaminated solids in a catchment area, especially in downstream regions. A special example demonstrating the dispersion of highly contaminated sediments in a large catchment area will be shown from the so-called Chemistry Triangle of the upper Elbe River system, Germany. The Spittelwasser area, situated there, was chosen by the organisers of the international conference ConSoil 2000 for a case comparison and four expert teams from Denmark, Germany, the Netherlands and the UK were invited to participate in this Case Study. Evaluation of the plan was done by members of the networks of NICOLE (Network for Industrially Contaminated Land) and CLARINET (Contaminated Land Rehabilition Network). In the study of the German team, five major groups of technical measures have been identified by the environmental authorities to be discussed in relation to the Spittelwasser case or for similar problem solutions in contaminated flood-plain areas. The team came to the conclusion that none of these techniques would be applicable as an individual measure. Instead, a stepwise approach combining different monitoring techniques and remediation measures was proposed. These would include point excavations of critical material, promotion of plant growth as an element for stabilising the soil and flood sediments, as well as the installation of sediment traps. At the Spittelwasser site, investigations are planned on the effects of natural attenuation processes of organic and inorganic contaminants in flood-plain sediments and soils. In the practice of this concept, non-destructive, ‘intrinsic’ bonding mechanisms and their temporal development have thus far found much less recognition compared to destructive processes such as biological degradation. Yet these so-called ‘diagenetic’ effects, which apart from chemical processes involve an enhanced mechanical consolidation of soil and sediment components by compaction, loss of water, and mineral precipitations in the pore space, may induce a quite essential reduction of the reactivity of solid matrices [see Part I ‘Improving Chemical and Biological Criteria’ (JSS - Journal of Soils and Sediments, Vol 1, No 1, pp 30-36)]. Part IV ‘Subaqueous Storage/Capping of Dredged Material’ will be published in JSS No. 4 (December issue).     

Influence of environmental factors on the biological treatment of organic compounds in contaminated lagoon sediments

Background and Scope  Many technologies available to remediate soils are not cost-effective when applied to marine and lagoon sediments, due to the physico-chemical characteristics of these matrices (high percentages of small particle size material, high moisture and organic matter content, many different types of inorganic and organic contamination). For these types of waste, slurry phase bioreactors can provide versatile processes, with very high removal efficiencies of recalcitrant organic compounds. The biodegradation of these contaminants strictly depends on the specific structure of the molecules and on environmental factors, such as the dissolved oxygen concentration, salinity, pH, and macronutrient availability. This paper presents the results of lab-scale tests performed to investigate the effect of the above-mentioned factors on the removal efficiency of saturated hydrocarbons, polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls (PCBs) in slurry phase biological treatment of lagoon sediments. Methods  Sediments were contaminated by saturated hydrocarbons (958 mg/kg d.w.), polyaromatic hydrocarbons (PAHs) (29 mg/kg d.w.) and polychlorobiphenyls (PCBs) (236 μg/kg d.w.). Carbon to nitrogen to phosphorous ratios in the matrix were not properly balanced for biological treatment. High concentrations of metals were also present (Cu: 200 mg/kg d.w.; Zn: 1710 mg/kg d.w.; As: 33 mg/kg d.w.; Cd: 13 mg/kg d.w.; Pb: 244 mg/kg d.w.). Biodegradation studies were carried out at 21 ± 1°C, in completely mixed slurry phase aerobic, anaerobic and sequential anaerobic/aerobic batch systems (3.5 1), with a solid to liquid ratio of 10% w/w. Where required, anaerobic conditions occurred naturally within three days of not aerated treatment. The aerated reactors were also equipped with traps for the waste vapors. Twelve tests were performed, over a period between ten and twenty-two days, mixing water, sediments and different amounts of various additives (macronutrients to balance C:N:P to 100:10:1 w/w, sodium chloride from 0 to 20 g/1, pH buffer solution) in the reactors, depending on the test being performed. Results and Discussion  No significant differences among the removal efficiencies of saturated hydrocarbons in tests could be observed. Abatements between 63% and 93% were obtained. The dissolved oxygen concentration was the most critical factor affecting the treatment of PAHs. Removal efficiencies below 20% were obtained for two and three-ring PAHs in the non-aerated tests. Higher values, between 45% and 61%, were obtained for these compounds in the aerated treatments; however, large (16% to 21%) abiotic losses (volatilization) were observed in these cases. Four-ring PAH removal efficiency was below 5% in all the non-aerated treatments, except for test performed without additions (30%); in the aerobic processes, removal efficiencies between 40% and 50% were obtained, except for test performed with nutrient addition and 10 g NaCl/1 (16%). Abatements of five and six-ring PAHs were between 43% and 69% in the aerated tests, and between 17% and 51% in the non-aerated treatments. Concerning PCBs, tests evidenced that reductive dehalogenation mechanisms have occurred in the anaerobic reactors with the most stable pH values, resulting in an increase of 2,4,4′-CB and 2,2′,5,5′-CB concentrations; the aerobic treatments did not modify the PCB mixture. In both types of systems, no variation of the total PCB concentration could be observed. Conclusions  This study showed that saturated hydrocarbon removal efficiency was nearly insensitive to the environmental factors investigated. The molecule structure and the dissolved oxygen concentration were the most affecting factors the removal efficiency of PAHs. PCB degradation under anaerobic conditions could be related to the pH values measured during the tests. Evaluation of results suggested that the abatement of pollutants investigated was not limited by a high salinity. High concentrations of dissolved metals and macronutrient addition did not influence the removal efficiency. Recommendations and Outlook. The slurry phase biological treatment of contaminated sediments could be applied whenever moderate removal efficiencies were required for remediation from saturated hydrocarbons and PAHs within a few days; further studies should be performed to improve the PCB abatement. Aerobic conditions should be maintained for the biodegradation of polyaromatic compounds; seawater or lagoon water could be used in the system.     

Mercury desorption from contaminated sediments

The effects of pH and ionic strength on the release of Hg from contaminated coastal sediments to water were evaluated in a series of laboratory experiments. Data show that the higher the ionic strength and the pH the smaller is the amount of Hg desorbed into solutions. The effect of the ionic strength on the leaching of Hg from contaminated sediments is more evident for values lower than 0.4 mol dm⁻³, while the influence of pH becomes more pronounced for values lower than 7. Based on qualitative concepts from colloid chemistry an attempt is made to provide an explanation of the observed results.     

An assessment of the concentrations of PCDDs/Fs in contaminated bottom sediments and their sources and ecological risk

Purpose

The purpose of the study was to determine the levels of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD/F), two types of persistent organic pollutant (POP), in an urban retention reservoir located in an industrial zone within a coal-mining region. It also assesses the potential ecological risk of the PCDDs/Fs present in bottom sediments and the relationship between their content and the fraction of organic matter.

Materials and methods

The sediment samples were collected from Rybnik Reservoir, located in the centre of the Rybnik Coal Region, Silesia, one of Poland’s major industrial centres. Seventeen PCDD/F congeners in the surface of the sediments were analysed using high-resolution gas chromatography and high-resolution mass spectrometry (HRGC/HRMS).

Results and discussion

The toxic equivalency (TEQ) of the PCDDs/Fs in the sediments ranged from 1.65 to 32.68 pg TEQ g^?1. PCDDs constituted 59–78% of the total PCDDs/Fs, while the PCDFs accounted for 22–41%. The pattern of PCDD/F congeners in the sediments was dominated by OCDD. However, the second-most prevalent constituents were OCDF and ∑HpCDFs in the low TOC sediment (< 10 g TOC kg^?1), but HpCDD in the rich TOC samples (> 10 g TOC kg^?1). PCDD/F concentrations in the sediment samples were 2- to 38-fold higher than the sediment quality guidelines limit, indicating high ecological risk potential. Although a considerable proportion of PCDDs/Fs in the bottom sediments from the Rybnik Reservoir were derived from combustion processes, they were also obtained via transport, wastewater discharge, high-temperature processes and thermal electricity generation. The PCDD/F concentrations were significantly correlated with all fractions of organic matter; however, the strongest correlation coefficients were found between PCDDs/Fs and humic substances. Besides organic matter, the proportions of silt/clay fractions within sediments played an important role in the transport of PCDDs/Fs in bottom sediments.

Conclusions

The silt/clay fraction of the bottom sediments plays a dominant role in the movement of PCDDs/Fs, while the organic matter fraction affects their sorption. The results indicate that the environmental behaviour of PCDDs/Fs is affected by the quantity and quality of organic matter and the texture of sediments.

     

Culture-based and culture-independent assessment of the impact of mixed and single plant treatments on rhizosphere microbial communities in hydrocarbon contaminated flare-pit soil

Phytoremediation is a novel treatment option for weathered, hydrocarbon contaminated, flare-pit soil in prairie ecosystems. The remediation potential of six different naturalized prairie plants was assessed by examining their impact on the degradation potential of indigenous bacterial communities. Culture-based and culture-independent microbiological methods were used to determine if mixed plant treatments stimulate different microbial communities and catabolic genotypes in comparison to individual plant species that comprise the mix. DGGE analysis of PCR-amplified 16S rRNA genes revealed that alfalfa (Medicago sativa) had a dominant effect on the structure of rhizosphere microbial communities in mixed plant treatments, stimulating relative increases in specific Bacteroidetes and Proteobacteria populations. Alfalfa and mixes containing alfalfa, while supporting 100 times more culturable PAH degraders than other treatments, exhibited only 10% TPH reduction, less than all planted treatments except perennial rye grass (Lolium perenne). Total petroleum hydrocarbon (TPH) reduction was greatest in single-species grass treatments, with creeping red fescue (Festuca rubra) reducing the TPH concentration by 50% after 4.5 months. Overall TPH reduction throughout the study was positively correlated (p<0.001) to culturable n-hexadecane degraders.     

Evaluation of biogeochemical reactivity of fresh and weathered contaminated dredged sediments

Journal of Soils and Sediments - Metal mobility in contaminated marine sediments is largely controlled by low-soluble sulfides. In dredged sediments exposed to air and water, geochemical and...     

Retention and toxicity of a coal liquid in artificially contaminated sediments

Water, Air, & Soil Pollution - Columbia River fine sediments were artificially spiked with coal liquids and removal rates and composition of retained phenolics were characterized following...     

Review of remediation technologies for sediments contaminated by heavy metals

Journal of Soils and Sediments - Contamination of sediments with heavy metals (HMs) is a worldwide environmental issue, due to the negative ecological effects of HMs. Sediments are an important...     

Stabilization of heavy metal contaminated marine sediments with red mud and apatite composite

Journal of Soils and Sediments - Chemical stabilization (or immobilization) is an in situ remediation method that uses amendments to reduce heavy metals availability in contaminated sediments. In...     

Bacterial community structure in lake sediments of microcosms contaminated with nonylphenol

The impact of nonylphenol, an estrogenic degradation product of alkylphenol polyethoxylates, on the bacterial community structure in contaminated sediments of aquatic microcosms was investigated over a period of 20 weeks using a 16S rDNA-based molecular phylogenetic approach. All microcosms showeda strong seasonal fluctuation of the dominant as well as the active bacterial microflora independent of their degree of contamination with nonylphenol. These changes were correlated with the dynamic of the total organic carbon content (TOC), ranging from 4–39 g/kg sediment dry weight and the redox potential in the sediment. Even at the highest observed nonylphenol concentration (3.4 mg/kg sediment dry weight) the bacterial community structure was mostly unchanged.     

Effects of contaminated sediments and standard elutriates on primary production in Lake Ontario

A comparison of elutriate and sediments effects on phytoplankton photosynthesis was undertaken in view of the widespread use of sediment elutriates in bioassays. The logistic problem of measuring ¹⁴C in the presence of sediments was overcome by extracting ¹⁴C labelled photosynthate with DMSO. In Lake Ontario, sediments were more inhibitory than elutriates to photosynthesis, depressing Pmax, the light saturated photosynthesis by up to 50%. The less severe toxicity of elutriates is attributed mainly to binding and removal from solution of metals with phosphate, although phosphate rich elutriates may also allow algae to accumulate polyphosphate which binds, and thus detoxifies metals inside the cells. Also, any hydrophobic organic contaminants present in the sediments and toxic to algae are not likely to be extracted into elutriates. In P deficient phytoplankton populations, the high concentrations of phosphate in elutriates may lead to a temporary depression of photosynthesis.     

Control and assessment of the hydrocarbon contamination of Ukrainian soils

Regularities governing the self-purification of soils from oil hydrocarbons, as well as migration of hydrocarbons, and the effect on the water-physical properties and fertility of soils were revealed in a series of experiments. A system of ecological, economic, and reclamation standards was proposed for regulating economic activities in the case of soil contamination with hydrocarbons.     

Rapid assessment of orangutan density

In order to design effective conservation measures for the orangutan, accurate information on their distribution and densities are needed. Nest counts along line transects allow for fairly accurate assessment of orangutan density. However, large sample sizes are needed to obtain accurate estimations of the decay rate of nests, preventing a rapid estimate. Moreover, due to the structure of tropical forests, nest numbers above and near the trail are underestimated. In this study, a rapid assessment method for the estimation of orangutan density is developed, allowing for the estimation of density with a single survey. Procedures are provided for estimating a correction factor which adjusts for underestimating nest numbers near the transect trail. Furthermore, we provide a shortcut to rapidly assess nest decay rate without the need for consecutive surveys. Finally, recommendations are made for determining orangutan density using two different techniques. These techniques incorporate correction factors and a shortcut to accurately assess orangutan density with only one or two visits to an area.     

Emission of nitrous oxide from hydrocarbon contaminated soil amended with waste water sludge and earthworms

Soils in Mexico are often contaminated with hydrocarbons and addition of waste water sludge and earthworms accelerates their removal. However, little is known how contamination and subsequent bioremediation affects emissions of N₂O and CO₂. A laboratory study was done to investigate the effect of waste water sludge and the earthworm Eisenia fetida on emission of N₂O and CO₂ in a sandy loam soil contaminated with the polycyclic aromatic hydrocarbons (PAHs): phenanthrene, anthracene and benzo(a)pyrene. Emissions of N₂O and CO₂, and concentrations of inorganic N (ammonium (NH₄⁺), nitrite (NO₂^?) nitrate (NO₃^?)) were monitored after 0, 5, 24, 72 and 168 h. Adding E. fetida to the PAHs contaminated soil increased CO₂ production rate significantly 2.0 times independent of the addition of sludge. The N₂O emission rate from unamended soil expressed on a daily base was 5 μg N kg^?1 d^?1 for the first 2 h and increased to a maximum of 325 μg N kg^?1 d^?1 after 48 h and then decreased to 10 μg N kg^?1 d^?1 after 168 h. Addition of PAHs, E. fetida or PAHs + E. fetida had no significant effect on the N₂O emission rate. Adding sludge to the soil sharply increased the N₂O emission rate to >400 μg N kg^?1 d^?1 for the entire incubation with a maximum of 1134 μg N kg^?1 d^?1 after 48 h. Addition of E. fetida, PAHs or PAHs + E. fetida to the sludge-amended soil reduced the N₂O emission rate significantly compared to soil amended with sludge after 24 h. It was found that contaminating soil with PAHs and adding earthworms had no effect on emissions of N₂O. Emission of N₂O, however, increased in sludge-amended soil, but addition of earthworms to this soil and contamination reduced it.     

Polycyclic aromatic compounds and microtox® acute toxicity in contaminated sediments in Sweden

Limnic and brackish aquatic sediments from contaminated locations in Sweden were analysed for polycyclic aromatic compounds (PACs) and tested for acute aquatic toxicity. The organic compounds were analysed in solvent-extractable and alkaline-treated fractions to complete the analysis of a set of priority pollutants according to the Swedish EPA. Additionally, the acute toxicity was measured by the solid phase Microtox test. The measured effects were correlated with sedimentological and chemical parameters. Analysis revealed no indication of a contribution of PACs to the acute sediment toxicity in highly contaminated sediments, with concentrations in the range of 11.3-307 μg SPAC_37/39/g dry matter. Despite a high ranking of 3 to 5 within the Swedish EPA list for coastal sediments, the acute toxicity results indicate a very low bioavailability of the analysed PACs from the creosote and combustion-contaminated sediments. A correlation of acute toxicity to elemental sulfur was indicated.     

Heavy metal and chlorinated hydrocarbon contamination of selected aquatic sediments from the Berlin area

Sediments from the Berlin area were analysed for heavy metals and chlorinated hydrocarbons. the sedimentological and hydrogeological aspects of the Holocene sediments are discussed and an adapted sampling device for muds with a high water content is described. the contamination of surface sediments and dated cores is shown back in the 19th century; the hydrological influences on the degree of contamination and potential threats to groundwater and, via remobilisation, to surface waters are considered. It is concluded that the sediments of the Berlin area are highly contaminated.     

Evaluation of two bacterial delivery systems for in-situ remediation of PAH contaminated sediments

Intention, Goal and Background  Contaminated sediments represent a significant, worldwide environmental problem since they contain a mixture of different xenobiotics and heavy metals. The presence of mixed contamination presents a unique set of obstacles for remediation efforts. Often sediment remediation occurs as an ex-situ application (i.e., after dredging) in an attempt to minimize some of the problems. However, dredging poses it’s own issues. It does not address contaminated water and often material is not completely removed thereby leaving a long-term residual contamination source in the waterway. Objective  The potential of bio remediation to treat sediments contaminated with polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, and heavy metals was addressed. The primary objective was to assess two delivery mechanisms for microbial inoculation to facilitate in-situ remediation of PAH contaminated sediments. Methods  Simulated river beds were constructed to mimic the Mahoning River. Contaminated sediment from the river was added to each reactor at a uniform depth, followed by the addition of river water. Fifteen inoculation points were used in each simulated river bed to ensure adequate microbial populations. One tank was inoculated with an acclimated bacteria solution as a free suspension. The other tank was inoculated with an attached growth biofilm system. Sediment samples were taken throughout the experiment and the percent PAH degradation determined. Water characteristics (DO, pH, bacterial activity, etc.) were also tracked as corroborating evidence. Results and Discussion  The monitoring sites indicated that an attached growth system was more effective, and achieved a 99% PAH degradation efficiency at some of the sampling sites. Tracking individual PAH compounds also indicated a higher overall microbial activity with the attached growth system. This activity was evident by the formation and subsequent biodegradation of lower molecular weight degradation byproducts. However, more of the sediment area was treated by the free suspension inoculum due to the ease of microbial migration. Conclusions  The applicability of using an aerobic microbial consortium composed ofMycobacterium sp., Pseudomonas aeruginosa, andPseudomonas flourescens to treat contaminated sediment was demonstrated. In addition, it was found that introducing the consortium as an attached growth was more effective than when delivered as a free suspension. Recommendation and Outlook  The results demonstrated that the consortium was effective at treating the PAHs present in the contaminated soil. An additional study to evaluate the consortium’s effectiveness at remediating the PCB present in the sediment is warranted. Optimization of the consortium-nutrient combination could enable a treatment approach to effective for all the organic contaminants present. Although this would not address the heavy metals present in the sediment, it would afford a great opportunity at remediating a severely contaminated sediment system.