Contaminated Marine Sediments Research Articles

Evaluating the environmental impact of contaminated sediment column stabilized by deep cement mixing

Deep cement mixing (DCM) method is a widely used geotechnical technique for increasing ground stabilization before construction works. However, the environmental influence of stabilized ground on the surrounding area remains a concern. A physical model experiment of DCM-treated sediment column was conducted to investigate both geotechnical and environmental effects on the surrounding sediment. The DCM column contained the cement-stabilized contaminated sediment and surrounded by uncontaminated sediment. The physical behaviour, including settlement, pore water pressure, and total pressure were measured under different loadings. Simultaneously, the migration of the major ions into seawater, and leaching of potentially toxic elements into the surrounding sediment were evaluated. The results revealed that the leaching of major ions from the DCM column followed the dissipation of excess pore water and migrated to the seawater above the sediment surface. Nevertheless, the leaching behaviour of potentially toxic elements into the surrounding sediment and variation of pH value after the DCM treatment were within an acceptable level. Therefore, the contaminated marine sediment could be effectively stabilized and solidified by in-situ remediation with minimal secondary pollution to the surrounding environment.

Hydrocarbon-Degrading Bacterial Strain Pseudomonas mendocina Newly Isolated from Marine Sediments and Seawater of Oran Harbor (Algerian Coast)

Contamination by petroleum hydrocarbons causes serious dangers to human health and the environment, whether by accidental or chronic contamination. Due to the large flow of ships, the commercial harbor of Oran is subject to pollution particularly by polycyclic aromatic hydrocarbons. For that, bioremediation by indigenous microorganisms is the most important method to eliminate or decrease this contamination. In the present paper, hydrocarbon-degrading bacterium strain SP57N has been studied, newly isolated from contaminated marine sediments and sea water from the harbor of Oran (Northwestern-Algeria), using of Bushnell-Hass salt medium (BHSM). The strain SP57N was Gram-negative, oxidase negative, catalase negative, motile, Rod-shaped bacteria, identified molecularly as Pseudomonas mendocina based on partial 16S rDNA gene sequence analysis, using the BLAST program on National Centre for Biotechnology Information (NCBI) and the EzBioCloud 16S rDNA databases. This isolate could growth on high concentrations of crude oil (up to 10 %, v/v). The effects of some culture conditions such as temperature, NaCl concentration and pH on growth rate of strain SP57N on crude oil as the sole carbon and energy source were studied. In addition, growth kinetic of this isolate on crude oil during 20 days of culture at 140 rpm, under optimal culture conditions was considered. The results showed maximum growth rate at temperature 25°C, 3% (w/v) of NaCl concentration and pH 7. Results of growth kinetic on crude oil as sole carbon and energy source showed that the stationary phase was attained at day 12. Thus, Pseudomonas mendocina SP57N had effectively hydrocarbon-degrading potential, and could be used as an efficacy degrader to initiate a biological eco-friendly method for the bioremediation of the hydrocarbon pollution on the port of Oran, and marine environment.

Temporal trends in aluminum smelter-derived polycyclic aromatic hydrocarbons in outmigrant juvenile Chinook salmon from Kitimat, British Columbia, Canada

Aluminum smelter-derived polycyclic aromatic hydrocarbons (PAHs) in outmigrant juvenile Chinook salmon were evaluated in Kitimat Arm, British Columbia, Canada from 2000 to 2004, and in 2015. Decades of continual smelter operations by Rio Tinto resulted in PAH contamination of marine sediments at levels associated with adverse effects in juvenile salmon. Recently, smelter operations have undergone process changes to reduce PAH input to the environment. The PAH concentrations in juvenile Chinook salmon observed in 2000 to 2004, at sites nearest the smelter were comparable to salmon in other urban areas where reduced disease resistance was observed; the levels were lower in 2015 than 2000–2004 suggesting that the recent process changes were effective. Further, these data establish a benchmark for assessing any future changes affecting PAH input and the potential risks to the receiving environment.

Recycling contaminated marine sediments as filling materials by pilot scale stabilization/solidification with lime, organoclay and activated carbon

Nowadays, stabilization/solidification (S/S) applied to the treatment of contaminated marine sediments (CMSs) represents a key technology for the production of new materials for civil engineering. Literature has shown the feasibility of CMSs recycling, although sediment needs pre-treatments for the removal of organic matter and to improve the mechanical properties of the product post S/S. In view of the full-scale applicability where it is essential to reduce any additional phase (i.e., pre-treatments), this study is aimed at demonstrating the technical feasibility of recycling CMSs as filling materials by S/S treatments with lime, organoclay and activated carbon. The original sediments are contaminated with heavy metals, PCBs, and PAHs, exceeding limits values prescribed by law. Different mixtures were tested on the STABSOL-P pilot scale plant. The absence of specific CMSs pre-treatments resulted in failure to comply with the 28-days leaching test only for copper; greater air curing with 56-days allowed it to be complied with for all the investigated metals. The organic contamination, while slowing down the process of chemical stabilization, allowed in any case to get a product environmentally compatible. The unconfined compression strength tests showed values (>28 kPa) that would allow potential CMSs recycling for environmental enhancement. The mass balance of the case study of the Mar Piccolo of Taranto (Southern Italy) showed potential recycling of marine sediments (the production of 974 kg filling materials per 1000 kg of dredged sediment) with a consequent missed disposal in landfills of 0.65 m3/1000 kg of sediment.

Microbial community evolution during the aerobic biodegradation of petroleum hydrocarbons in marine sediment microcosms: Effect of biostimulation and seasonal variations

Evolution of the microbial community structure in crude oil contaminated marine sediments was assessed under aerobic biodegradation during wet (18 °C) and dry (28 °C) seasons experiments, to account for seasonal variations in nutrients and temperature, under biostimulation and natural attenuation conditions. NMDS showed significant variation in the microbial communities between the wet and the dry season experiments, and between the biostimulation and the natural attenuation treatments in the dry season microcosms. No significant variation in the microbial community and oil biodegradation was observed during the wet season experiments due to high background nitrogen levels eliminating the effect of biostimulation. Larger variations were observed in the dry season experiments and were correlated to enhanced alkanes removal in the biostimulated microcosms, where Alphaproteobacteria dominated the total microbial community by the end of biodegradation (54%). Many hydrocarbonoclastic bacterial genera showed successive dominance during the operation affecting the ultimate performance of the microcosms.

In Situ Remediation of Lead Contaminated Marine Sediment using Bentonite, Kaolin and Sand as Capping Materials

There is a growing public concern over the issue of sediment contamination resulting from industrial and municipal waste discharge, mining activities, and improper use of chemical fertilizer, pesticides, and wastewater irrigation. However, there is a need to reduce the continuous contamination of the water column and biota by the pollutants in the sediment. The conventional approach of contaminated sediment treatment is dredging but is expensive and requires a large area of land for disposal. In situ capping of contaminated sediment is considered as a cheaper technique compared to dredging and efficient treatment technology to immobilize pollutants in sediments on site. A laboratory-scale capping experiment was conducted to evaluate the effectiveness of using bentonite (B), kaolin (K), a mixture of bentonite with kaolin (BK), and sand in immobilizing lead-contaminated sediment using in situ capping treatment technology. The results indicated that applying bentonite, kaolin, and sand as capping materials has the potential to effectively reduce the release of lead from the heavily spiked contaminated marine sediment (3000 ppm) to the overlying water. The adsorption kinetics results obtained showed that the experimental data for adsorption of Pb fitted well to the Elovich, Second-order and Two- constant rate kinetic models as judged by highest values of R2 and the lowest values of standard error of estimate (SE) such as R2 of 0.937, 0.735, 0.932 with SE values of 0.23, 2.62 and 0.26 for B, K and BK respectively in the Elovich, likewise R2 of 0.817, 0.935, 0.821 with SE values 0.33, 0.07 and 0.19 for B, K and BK in the Second-order and R2 of 0.938, 0.637, 0.925 with SE values of 0.000135, 0.0015 and 0.00024 for B, K and BK were obtained for Two-constant rate models, which implied that the process of adsorption was by chemisorption.

Response of sediment microbial communities to crude oil contamination in marine sediment microbial fuel cells under ferric iron stimulation

In this study, response of the microbial communities associated with the bioremediation of crude oil contaminated marine sediments was addressed using sediment microbial fuel cells (SMFCs). Crude oil was spiked into marine sediments at 1 g/kg of dry sediment to simulate a heavily contaminated marine environment. Conventional SMFCs were used with carbon fiber brushes as the electrode components and were enhanced with ferric iron to stimulate electrochemically active bacteria. Controls were operated under open circuit with and without ferric iron stimulation, with the latter condition simulating natural attenuation. Crude oil removal in the Fe enhanced SMFCs reached 22.0 ± 5.5% and was comparable to the measured removal in the control treatments (19.2 ± 7.4% in natural attenuation SMFCs and 15.2 ± 2.7% in Fe stimulated open circuit SMFCs), indicating no major enhancement to biodegradation under the applied experimental conditions. The low removal efficiency could be due to limitations in the mass transfer of the electron donor to the microbes and the anodes. The microbial community structure showed similarity between the iron stimulated SMFCs operated under the open and closed circuit. Natural attenuation SMFCs showed a unique profile. All SMFCs showed high relative abundances of hydrocarbon degrading bacteria rather than anode reducers, such as Marinobacter and Arthrobacter in the case of the natural attenuation SMFCs, and Gordonia in the case of iron stimulated SMFCs. This indicated that the microbial structure during the bioremediation process was mainly determined by the presence of petroleum contamination and to a lesser extent the presence of the ferric iron, with no major involvement of the anode as a terminal electron acceptor. Under the adopted experimental conditions, the absence of electrochemically active microbes throughout the biodegradation process indicates that the use of SMFCs in crude oil bioremediation is not a successful approach. Further studies are required to optimize SMFCs systems for this aim.

Electrokinetic approach to assess the behaviour of a contaminated marine sediment

The present study focuses on the laboratory-scale application of an electrokinetic technique for the remediation of a contaminated marine sediment dredged from a harbour. The challenge of the study was the treatment of the silty sediment containing heavy metals and organic matter, as methods to remove heavy metals or organic matter separately do not usually yield satisfactory results for the mixture of both. The sediment was characterised in terms of elemental and mineralogical composition, heavy metals, total organic carbon, particle size distribution and zeta-potential. Five configurations of remediation tests have been explored. Four of these tests were employing electric field, two of which were carried out with carbon steel electrodes (CSE) and the other two with activated Ti electrodes (ATE). One test was conducted without electrical current, and it was used as a benchmark. In some tests, acetic acid was added to the catholyte to enhance heavy metal mobility. The pH, conductivity and composition of catholyte and anolyte were characterized as function of test duration. Electrophoretic measurements showed that the zeta-potential of raw, untreated sediment samples was negative across all the range of pH. In the tests with CSE, electroosmotic flow (EOF) towards the cathode was observed when acetic acid was added. In other tests, i.e. CSE without acetic acid and ATE with acetic acid, the flow initially directed towards the cathode but then reversed. In the case of ATE without acetic acid, the EOF aimed only at the anode. Without current, no heavy metals were removed. In the tests without acetic acid, the metals concentrated in the anolyte, most probably due to electroosmotic flow or migration of negatively charged aqueous metal complexes. Arsenic and a small amount of Cu and Zn were found in the catholyte. When acetic acid was added to the catholyte, and with ATE electrodes, all the metals were found in the catholyte, whilst Ni was not detected in the anolyte. The formation of an acidic front through the sediment and the control of the EOF appear to be the key factors for the successful remediation via electrokinetic technique. It has been demonstrated that electroremediation can be efficient for removal of all studied metals as all of them could be mobilised using Ti electrodes. The emission of metals such as Ni and Cr from dissolution of carbon steel anode must be taken into account in electrochemical remediation tests.

Contaminated marine sediment stabilization/solidification treatment with cement/lime: leaching behaviour investigation.

Among ex situ remediation technologies, stabilization/solidification (S/S) provides for the addition of a binder to dredged materials in order to chemically immobilise the contaminants and improve mechanical behaviour of sediments. The simplest form of treatment is obtained by the addition of Portland cement or lime (calcium oxide), although other additives such as adsorbents may be added. Nevertheless, the success of the S/S treatment may be affected by the contaminants present or by the salt content in the water. In this study, experimental laboratory investigation was carried out on sediments carefully collected from the Mar Piccolo of Taranto in Southern Italy, contaminated by heavy metals, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs); the goal was to explore the effectiveness of S/S treatment by using Portland cement/lime as binders, monitoring over time (28days) the leaching of the different mixtures of treated sediment. It is noted that the Mar Piccolo of Taranto is one of the sites of national interest subject to remediation by the Italian government. Once taken within the first meter under the sea floor by a team of experienced divers, the samples were stored at a controlled temperature, characterised in terms of grain size and physical-chemical characteristics and treated by S/S laboratory tests. The results indicate that the addition of binders increased the pH of the mixtures with a consequent leachability of different metals. The mobility of the metals appeared to be governed also by the curing time. The performance of the mixtures in terms of immobilised metals was influenced by the presence of organic contaminants (e.g. organic matter, PAHs and PCBs). As a lesson, high organic matter and fine-grained particles can negatively affect the effectiveness of the S/S treatment in terms of metal immobilisation.

Heavy metals and persistent organic pollutants contamination in river, estuary, and marine sediments from Atlantic Coast of Democratic Republic of the Congo.

The pollution assessment and the evaluation of potential risks in the Atlantic Coastal Region of the Democratic Republic of the Congo are still very limited. Consequently, the present study investigates for the first time the concentrations of heavy metals and persistent organic pollutants (organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and polycyclic aromatic hydrocarbons (PAHs)) in river, estuary, and marine sediments from this area. The results highlighted high concentrations of Cr, Zn, As, and Pb exceeding the probable effect level (PEL) on aquatic life. Zn was the most dominant element detected at a range of 180-480mgkg-1 in marine sediment, 132-382mgkg-1 in estuary sediment, and 121-687mgkg-1 in river sediment. Total PCBs (∑7 × 4.3) ranged from 1995 to 20,156μgkg-1, 2013-12,058μgkg-1, and 1861-36,417μgkg-1 in marine, estuary, and river sediments, respectively. Total PCBs (∑7 × 4.3) were above PEL for all sediments, suggesting potential adverse effects on benthic organisms. The OCP, PBDE, and PAH levels were low to moderate for all sediments. Taking into consideration, the concentrations of Zn, Pb, PCBs, and DDTs, probable environmental risks, are present.

Status of contaminated marine sediments in four Nordic countries: assessments, regulations, and remediation approaches

PurposeSince the 1960s, pollution of the marine environment has been observed around the world, and a general awareness of the potential environmental hazards from contaminants arose. This general awareness was followed by implementation of environmental regulations at the national and international levels regarding industrial discharges, and forcing the development of management programs to improve the environmental quality. This overview focuses on the status of assessments, regulations, and remediation actions of contaminated marine sediments in four North European countries: Sweden, Norway, Finland, and Denmark.Results and discussionWe found that the extent of assessment surveys and the implementation of sediment remediation actions vary between the countries, with Norway the most advanced. Norway has initiated national pilot remediation tests, followed by full-scale site remediation by dredging and in situ capping in several projects along the coast. Sweden is following Norway’s example, although with fewer completed projects. In Finland, the tradition of maintenance dredging is still very strong although the main purpose has not been cleanup actions. Accordingly, in Denmark, dredging is primarily used to maintain sailing depths. All four countries have implemented the Water Framework Directive in addition to national regulations that provide the authority for imposing and implementing sediment remediation measures. However, only Norway has implemented a national strategy on remediation of contaminated sediments.ConclusionsThis overview highlights the need for enhanced communication and exchange of experiences between the four Nordic countries of concern with regard to sediment remediation strategy and management.

Use of ecotoxicity assessment for determining reusability of treated marine sediment on terrestrial land

Contaminated marine sediment can be treated to satisfy the concentration-based chemical criteria, but the treated sediment could still not be appropriate for reuse. This study used ecotoxicity tests to determine the reusability of treated marine sediment on terrestrial land. Changes in the toxicity of sediment contaminated with a mixture of total petroleum hydrocarbons (TPH) and heavy metals after treatment were investigated using both terrestrial (earthworm and wheat) and aquatic organisms (Daphnia magna, Allivibrio fischeri). The contaminant concentrations were reduced to meet the remedial goal of this study. As a result, the toxic effects on the tested organisms were reduced. The toxic effects of the reference sediment sample (RSS) that represents the background sediment toxicity were greater on wheat and earthworms than the treated sediment samples (TSSs). This was attributed to factors such as salinity and sediment texture. By comparing the toxicities of the sediment samples with that of the RSS, it was found that not only the contaminant concentrations, but also the sediment physicochemical properties such as pH, salinity, particle size distribution, and nutrient contents need to be considered from the step when the treatment processes are selected. In conclusion, different aspects of the treated marine sediment quality, apart from the level of contaminants regulated, could be tested using ecotoxicity tests to determine the reusability of the treated marine sediment on land.

A Remediation Study of Contaminated Marine Sediment through Application of Naturally Developed Oxygen Releasing Compound

Blocking the influx of nutrients from contaminated sediment and reducing terrigenous loads are essential to control eutrophication in coastal water areas. In this study, the use of an oyster-shell-based ORC (oxygen-releasing compound) was investigated with respect to nutrients such as nitrogen, phosphorous, and sulfur compounds in the sediment environment. The ORC, which was produced by pyrolyzing oyster shell powder, was found to be overoxidized and consisted of calcium peroxide. A series of experiments simulating a typical overlying water-sediment system were carried out in open-lid cylindrical columns over the fifteen-day experimental period. The elution and distribution of crucial contaminating species within that system are discussed. T-N, NH4 +-N, T-P, and Pi propagated with time toward the overlying water from the sediment through diffusive migration, showing a constrained increase over distance at the sediment-water interface. The nitrate levels decreased with time, possibly due to local denitrification. Partial oxidation in a homogenized mixture of sediment and oxidized oyster shell powder resulted in an increased DO level within the experimental time frame, which in turn caused T-N, NH4 +-N, T-P, and Pi to propagate at a lower rate than sediment without any ORC. Analyses for sulfates and sulfides in the sediment mixed with ORC confirmed that the chemical environment changed into a more oxidized state in fifteen days. Diffusive migration, along with chemical reactions and/or adsorption, successfully explained the propagation and distribution of the concerned nutrient species resulting from the use of oyster shell powders.

Assessment of metal contamination in coastal marine sediments of Makadi Bay on the Red Sea, Egypt

To assess the heavy metal contamination in the sediments of Makadi Bay (Hurghada, Egypt), surface samples were collected from 32 locations. Six heavy metals (Fe, Mn, Zn, Cu, Pb and Cd) were analysed using atomic absorption spectrophotometry. The order of trace metal concentration in the samples was Mn>Zn>Pb>Cu>Cd. The analytical results were subjected to univariate statistical analyses to evaluate the distribution and abundance of the metals in the area. The degree of pollution of the sediments by these metals was evaluated by calculating enrichment factors and the geoaccumulation, pollution load and soil pollution indices. The results indicated that all marine sediment locations are practically unpolluted by metals. The high metal concentrations of Pb and Cd due to anthropogenic sources (mean 38.76 and 2.43μgg–1 respectively) recorded in most samples are essentially attributable to the anomalous concentrations of Pb and Cd in these samples. Both natural and anthropogenic sources of Pb and Cd contamination around Makadi Bay are possible. Generally, the levels of heavy metals in the study area do not constitute any serious environmental risk, except in the case of Pb and Cd.

In Situ Capping Remediation of Contaminated Marine Sediment using Bentonite, Kaolin and Sand to Interrupt the Release of Trace Metals

In Situ Capping Remediation of Contaminated Marine Sediment using Bentonite, Kaolin and Sand to Interrupt the Release of Trace Metals

Morphological and molecular responses of the sea urchin Paracentrotus lividus to highly contaminated marine sediments: The case study of Bagnoli-Coroglio brownfield (Mediterranean Sea)

Marine sediments store complex mixtures of compounds, including heavy metals, organotins and a large array of other contaminants. Sediment quality monitoring, characterization and management are priorities, due to potential impacts of the above compounds on coastal waters and their biota, especially in cases of pollutants released during dredging activities. Harbours and marinas, as well as estuaries and bays, where limited exchanges of water occurr, the accumulation of toxic compounds poses major concerns for human and environmental health.Here we report the effects of highly contaminated sediments from the site of national interest Bagnoli-Coroglio (Tyrrhenian Sea, Western Mediterranean) on the sea urchin Paracentrotus lividus, considered a good model for ecotoxicological studies. Adult sea urchins were reared one month in aquaria in the presence of contaminated sediment that was experimentally subject to different patterns of re-suspension events (mimicking the effect of natural storms occurring in the field), crossed with O2 enrichment versus natural gas exchanges in the water. The development of embryos deriving from adult urchins exposed to such experimental conditions was followed until the pluteus stage, checking the power of contaminated sediment to induce morphological malformations and its eventual buffering by high oxygenation. Real-Time qPCR analysis revealed that the expression of several genes (among the fifty analyzed, involved in different functional processes) was targeted by contaminated sediments more than those exposed in oxygen-enriched condition. Our findings have biological and ecological relevance in terms of assessing the actual impact on local organisms of chronic environmental contamination by heavy metals and polycyclic aromatic hydrocarbons affecting the Bagnoli-Coroglio area, and of exploring enhanced sediment and water oxygenation as a promising tool to mitigate the effects of contamination in future environmental restoration actions.

From waste to resource: mycoremediation of contaminated marine sediments in the SEDITERRA Project

Port-dredging activities produce large volumes of contaminated sediments. Dredged sediments are considered a waste by national laws, but recently the desire to consider them a resource has become widespread and remedies for their contamination are being searched to allow their reuse. In this work, we studied, developed, and tested a method for remediate marine-dredged sediments contaminated by heavy metals using native fungi and a microporous membrane, in order to achieve the sediment quality and allow their reuse. Activity was carried out on port sediments from Genoa, Leghorn, Pisa, and Cagliari (Italy). Autochthonous fungi were isolated from each sediment and employed in mycoremediation tests. Two plastic boxes were prepared (for each Port) with 5 kg of sediment in each box, employed for metal bioaccumulation using a sterile polyester membrane inoculated with fungi. Membranes were analyzed at 15, 30, and 60 days after inoculums, and sediments were analyzed after 60 days at the end of the experiment to verify metal contamination degree. Recovery efficiency (RE%) and difference recovery efficiency (DRE%) were calculated for each experiment: the first shows the absorption capability of the membrane-fungi consortium; the second evidences only the fungal contribution to the metal absorption. To assess sediment contamination before and after the mycoremediation treatment, we considered chemical levels of reference L1 (the lowest chemical level of reference) and L2 (the highest chemical level of reference), and the evaluation of chemical hazard (HQ) for the chemical contaminants defined by the Italian Ministerial Decree 173/2016. Fungi from Genoa sediments increase the membrane absorption of Cu and Zn. Regarding Leghorn results, RE (%) increases and reaches the maximum value after 60 days of treatment for each considered metal. Cr tot, Ni, and Mn appear to be hyper-bioaccumulated. DRE values of Pisa sediments show that Mn is excluded by fungi and it does not bioaccumulate, while other metals and in particular Cd, Cr tot, Zn, and Sb are bioaccumulated. Cagliari DREs show that fungi are not able to bioaccumulate Cr tot, Ni, and Mn and their accumulation is due to the membrane, while As and Cd are bioaccumulated. Our work evidenced that selected fungi are able to grow on a microporous support and actively reduce metal concentrations in the sediments, achieving their quality. This biomembrane system may represent an important instrument for the remediation of the residual metal contamination of port sediments.

Assessing Heavy Metal Contamination in Marine Sediments Around the Coastal Waters of Mimika Regency, Papua Province, Indonesia

Assessing Heavy Metal Contamination in Marine Sediments Around the Coastal Waters of Mimika Regency, Papua Province, Indonesia

Experimental investigations and numerical modelling of in-situ reactive caps for PAH contaminated marine sediments

The present study compared numerical modelling and experimental investigations to evaluate the effectiveness of in-situ reactive capping for marine sediments contaminated by polycyclic aromatic hydrocarbons (PAHs). As a case study, sediment samples from Mar Piccolo (Italy) were analyzed and experiments were undertaken using batch columns. Two types of capping amendments were tested: AquaGate® + 5 % of powdered activated carbon (AG PAC) and Organoclay Reactive Core Mat (OC RCM). The column tests were carried out for 20 days, obtaining a short-term PAH distribution for three cases analysed, which compared the application of the two caps with no intervention. In parallel, in order to evaluate the intervention long term efficacy, an ad-hoc multilayered model predicting PAH concentrations into the sediments and the overlying water column was developed and validated with the experimental results. Both capping systems considerably reduced PAH concentrations in the overlying water, with the highest performance seen in AG PAC for benzo[a]pyrene (99 %) and anthracene (72 %); results also confirmed in the model predictions. In addition, the numerical simulations indicated a good efficiency of both caps over time, obtaining PAH values below the threshold limit in the long term. Although further experiments need to be developed accounting for multiple contamination competitiveness.

Conflicting outcomes of an integrated approach to sediment quality assessment in a Sardinian coastal area subjected to mining activities

Multidisciplinary research was carried out to verify the best approach for a reliable assessment of sediment quality in marine areas affected by strong metal enrichment. The study was carried out on Sulcis-Iglesiente marine coastal areas (Sardinia, Italy), where a long-lasting past mining operation strongly contaminated marine sediments with heavy metals (Cd, Pb and Zn). Surface sediments were analysed for grain size and mineralogical content, total organic carbon, total metal concentrations and sequential extractions. Additionally, ecotoxicological bioassays were performed using Vibrio fischeri (Microtox®) on the solid phase and elutriate, Dunaliella tertiolecta on elutriate and Brachionus plicatilis on elutriate. Analysed sediments were nearly exclusively sand (98.5–100%) with a very low TOC content; their texture and mineralogy indicated a N-S drift affecting the dispersion of mining contributions. The total concentrations of Cd, Pb and Zn, which are positively correlated, exceeded background and Environmental Quality Standards (EQS) values by up to two orders of magnitude, while sequential extractions revealed their high mobility because Cd and Pb were mainly extracted in the first phase (up to 77 and 82%, respectively) and Zn in the second phase (up to 99%). In spite of this, bioassays recorded the absence of toxicity in all the samples. These apparently conflicting results suggest that ecotoxicological tests cannot replace chemical analyses in sediment quality assessments because they could fail to provide reliable information on the bioavailability of contaminants over time.