Impact of disposal of dredged material on sediment quality in the Kaohsiung Ocean Dredged Material Disposal Site, Taiwan

A novel pollution index to assess the metal bioavailability and ecological risks in sediments

The chemical forms of metals in sediments of ports around Taiwan were investigated using sequential extraction. Based on the availability of different chemical forms, novel indices such as bioavailability, mobility, availability, and availability risk of metals in sediments were developed. The results showed that Co, Zn, Pb, Mn, and Cu were mainly present in available forms (49-84 %), and the proportion of oxidative or reductive fractionation was the highest. This suggests that the redox potential is a major factor for metal mobility in the sediments. The results from the proposed indexes showed that metals in sediments have low bioavailability but high to very high mobility and availability. Primarily, the proposed index is more appropriate, as the current index for assessing total metal content may overestimate the level of risk. The indexes established can comprehensively evaluate the bioavailability, mobility, availability, and ecological risk of metals in sediments.

Comparing the applicability of ecological risk indices of metals based on PCA-APCS-MLR receptor models for ports surface sediments

This study collected surface sediments from seven ports in Taiwan and analyzed their characteristics along with 10 metals. Enrichment factor (EF), relative EF (REF), potential ecological risk index (PERI), and mean effect range median quotient (m-ERM-q) were used to evaluate the levels of metal contamination and ecological risks in sediments. Principal component analysis (PCA) and the absolute principal component score-multiple linear regression (APCS-MLR) model were applied to quantify the main factors affecting the variations in sediment metals. The different normalization techniques that vary between indexes significantly affect the estimates of risk levels for sediment metals. APCS-MLR model confirmed the significant difference among the sediment quality indices in the degree of anthropogenic pollution, ranging in the order of REF (normalized with reference site and Fe, 97.0 %), PERI (normalized with reference site, 85.5 %), EF (normalized with crust and Fe, 79.4 %), and m-ERM-q (not normalized, 56.6 %).

Development of alternative disposals for waste rice husk and dredged harbor sediment by sintering as lightweight aggregates

This study developed the alternative disposals for dredged harbor sediments by co-sintering with waste rice husk into lightweight aggregates (LWA) to benefit resource sustainability and waste valorization. The effects of rice husk addition and sintering temperature on LWA performances such as water absorption, particle density, crushing strength, weight loss, volume shrinkage, and open porosity were investigated. The key parameters (e.g. C/Fe ratio in raw materials) controlling the LWA performances and engineering applications were determined. Results showed that dredged harbor sediments could be made into suitable LWA for engineering applications from the controlled rice husk addition and sintering temperature. The addition of rice husk led to lower LWA particle density, but raised water absorption and reduced crushing strength. The increase of sintering temperature reduced water absorption and improved crushing strength. The aggregates with 10-15% rice husk, sintered at 1150 °C had appropriate particle density (1.60-1.73 g/cm³), water absorption (11.8-16.6%), and crushing strength (6.0-10.6 MPa), which could be suitable for lightweight concrete applications. Low water-soluble chloride and heavy metals leachabilities aligned with Taiwan's regulatory standards for concrete aggregates. Co-treating waste rice husk and dredged harbor sediment into LWA can benefit the waste reduction and circular economy, and reduce the environmental impacts associated with their disposals.

Impact of Dredged Material Disposal on Heavy Metal Concentrations and Benthic Communities in Huangmao Island Marine Dumping Area near Pearl River Estuary

The Huangmao Island dumping area is adjacent to the Pearl River Estuary in the South China Sea. From its first dumping activity in 1986 to 2017, 6750 × 104 m3 dredged materials were dumped in this dumping area. Sediment pollution levels, ecological risk, and benthic communities in 2011–2017 were evaluated; the results showed that the concentrations of the heavy metals (HMs; except Hg) in surface sediments of the dumping area met the class I standard of marine sediment quality (GB 18668-2002). HMs in the surface sediments were relatively high in the northern and central areas but relatively low in the south of the dumping area. Speculation was that the spatial variation in HM concentrations might be caused by dumping activities. The Nemerow index implied that the contaminated area was mainly in the north of the dumping area (S1, S2, and S3), where the dumping amount was the largest. The potential ecological risk (Eir) indices of Zn, As, Cu, and Pb indicate that these metals posed a low risk to the ecosystem of the dumping area, whereas Cd and Hg posed a high risk at some stations. The geoaccumulation indices (Igeo) of Zn, As, Cu, and Pb specified no pollution or light pollution in the study area, whereas those of Cd and Hg in most years indicated mild contamination levels. Benthic organisms in the study area were arthropods, chordates, annelids, mollusks, echinoderms, nemertinean, coelenterate, and echiuran, among which arthropods were the most abundant. The abundance of taxa and density of benthic organisms had a little difference among the stations within the dumping area, but were significantly lower than those of the stations outside the dumping area. In addition, non-metric multidimensional scaling analysis confirmed that the observed patterns separated the stations within the dumping area from stations outside the dumping area. The evaluation results of the HMs revealed that the dumping area with a large dumping amount was more severely polluted. Dumping dredged materials seemed to have a negative impact on the benthic community in the dumping area.

Spatial distribution and ecological assessment of nickel in sediments of a typical small plateau lake from Yunnan Province, China

Nickel (Ni) in small plateau lake sediments plays an important role in influencing the quality of lake ecosystems with a high degree of endemism and toxicity. This paper focuses on the spatial distribution and ecological risks of nickel in the sediments of Jianhu Lake, a small plateau lake in China, and the influence of pH and total organic carbon (TOC) on nickel concentrations. The results showed that average total nickel concentrations were 138.99 ± 57.57 mg/kg (n = 38) and 184.31 ± 92.12 mg/kg (n = 60) in surface sediments (0-10 cm top layer) and sediment cores (0-75 cm depth), respectively, and that the residual fraction was the main form of nickel. Simultaneously, through a semivariogram model, strong spatial dependence among pH, TOC, and the oxidizable fraction was revealed, whereas total nickel, exchangeable and the weak acid soluble fraction, reducible fraction, and residual fraction showed moderate spatial dependence. The vertical distribution revealed that nickel accumulated mainly in the bottom 5 cm (70-75 cm) of the sediment layer and that the pH was higher there, whereas TOC was concentrated mainly in the top 5 cm of sediment. Using geoaccumulation and a potential ecological risk index, moderate nickel pollution and moderate risk levels were found in most surface sediments, but moderate nickel pollution and high risk levels were observed in most sediment cores. In addition, pH and TOC were found to have a strong effect on the distribution and concentration of nickel and its fractions in the small plateau lake. In summary, nickel posed a certain degree of pollution and ecological risk, which deserves attention in the sediments of small plateau lakes.

A novel systematic, risk based approach to support the designation of aquatic disposal sites

Humans rely fundamentally on the marine environment, which is at the same time subject to an increasingly broad range of anthropogenic pressures, leading to growing concerns and the need for effective management for marine protection. One activity is the dredging of ports and harbours which is necessary to maintain safe channels for commercial and recreational navigation. Regulatory authorities in developing countries have few resources to conduct full EIAs for determining dredged material disposal sites but are required to do so under international obligations. The Tool in this paper provides an effective, pragmatic, transparent, consistent, and robust approach to protect the environment whilst using limited technical and scientific resources through a risk based approach to defining need, characterising and designating disposal sites at sea for dredged material. Whilst this approach for dredged material disposal sites was developed for use in UK, this process is equally applicable to other waste types, worldwide.

Nonionic and anionic surfactant-washing of polycyclic aromatic hydrocarbons in estuarine sediments around an industrial harbor in southern Taiwan

Various surfactants, such as nonionic Triton X-100 and Simple Green™ (SG), and anionic sodium dodecylsulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) were utilized to remove polycyclic aromatic hydrocarbons (PAHs) from heavily contaminated harbor sediments dredged from Kaohsiung Harbor in Taiwan. Desorption/re-sorption equilibrium, kinetics, and washability of PAHs using the selected surfactant were evaluated under different critical micelle concentrations (CMC). Experimental results revealed that the desorption rate of high molecular weight PAHs was greater than those of low molecular weight PAHs, and the anionic SDS was relatively effective in the removal of total PAHs (>50%) compared to the other surfactants. The correlation between the effectiveness of the surfactant washing processes and the physicochemical properties of individual PAH was statistically analyzed. The resulting data suggested that hydrophobic factors (K_ow, K_oc and S_w) affected PAH treatability more than the reactivity of PAH (electron affinity and ionization potential). Since the adsorption of anionic surfactant altered the hydrophobicity of organic matter in the sediment, PAHs preferred transferring from the sediment to the hydrophobic core of micelles in aqueous solution. Nevertheless, the nonionic surfactant enhanced the PAH partition in the aqueous phase, thus increasing the micellar solubilization of PAH.

Recycling dredged harbor sediment to construction materials by sintering with steel slag and waste glass: Characteristics, alkali-silica reactivity and metals stability

This work recovered the dredged sediment around Kaohsiung Harbor, Taiwan, for preparing lightweight aggregates (LWA), of which physicochemical properties as affected by the addition of basic-oxygen-furnace (BOF) slag and waste glass were investigated. LWA properties included water absorption, particle density, compressive strength, shrinkage, and microstructure of sintered pellets were evaluated to ensure feasibility of dredged harbor sediment reutilization technique. Results showed that adding appropriate amount of glass powders (~7%) to the mixtures of sediment and slag significantly reduced the water absorption (as low as 2.2%) of the sintered pellets and increase the compressive strength (as high as 23.1 MPa) of LWA, which were found to be controlled by open porosity and shrinkage. Excessive addition of glass (>10%) led to increase in internal pore sizes of the sintered pellets, and thus reduced the compressive strength. The alkali-silica reactivity (ASR) of the LWA was innocuous according to the ASTM C289 test. Sintering and glass addition improved the stability of heavy metal and environmental compatibility of the LWA. The recycling of waste sediment, slag, and glass for LWA production can provide an alternative for the disposal of dredge harbor sediment and has positive impact on waste reduction, which not only can reduce secondary contamination to the environment, but also can contribute to circular economy.

Assessment of the use of dredged marine materials in sanitary landfills: A case study from the Marmara sea

Worldwide production of large volumes of dredged materials (DMs) has become a pressing environmental problem. In Turkey, the government has yet to develop management strategies that successfully prevent or minimize dumping into the Marmara Sea. One potential solution is the utilization of the DMs as a source of material for earthworks, particularly in sanitary landfills in Istanbul and Kocaeli. The most economically developed cities in Turkey, they were evaluated in terms of potential environmental impacts and regulatory compliance. Five ports/harbors representing specific portions of the study area and different industrial activities were selected as pilot regions. Physical, chemical, mineralogical, toxicological, and leaching potential measurements of DMs dredged from the seabed revealed they qualify as non-hazardous waste. Index and engineering tests performed on raw and processed DMs were assessed to determine the geotechnical requirements for soil-based materials (SBM) used in sanitary landfills. The results showed that non-hazardous DMs could be utilized as a cover, base/cap liner, and/or fill material at various sections within the landfills. This method provides environmental advantages not seen with other management strategies for DMs such as dumping at sea or upland disposal.

Alkylphenol ethoxylate metabolites in coastal sediments off southwestern Taiwan: Spatiotemporal variations, possible sources, and ecological risk

Alkylphenol ethoxylates (APEOs) are one of the most widely used classes of surfactants, but they are also ubiquitous environmental pollutants and known endocrin-disrupting chemicals. This study is the first to investigate the spatiotemporal variations and possible sources of APEOs and their metabolites, including nonylphenol ethoxylates (NPEOs) and octylphenol ethoxylates (OPEOs), in coastal sediments off southwestern Taiwan. The highest APEO concentration in the dry season was observed for the Kaohsiung coastal area, whereas the highest alkylphenol (AP) concentration in the wet season was found offshore at the Tainan Canal exit. No continuous accumulation of alkylphenol metabolites was evident in the area. One possible reason is that seasonal current and wind waves disperse the coastal pollutants. Application of multivariate statistical tools (hierarchical cluster analysis and principal component analysis) confirmed the role of rivers and the Tainan Canal in transporting contaminants to coastal environments, suggesting influences of industrial and human activities on APEO distribution. A further comparison with the predicted no-effect concentrations (PNECs) proposed by the European Union indicates that nonylphenol (NP) and octylphenol (OP) might pose potential ecological risks to the aquatic environment in the studied area. These findings provide useful information for environmental policy implementation and ecological assessments of different types of endocrine-disrupting chemicals and raise warnings about surfactant applications.

Spatial distribution and ecological risk assessment of sediment metals in a highly industrialized coastal zone southwestern Taiwan

Spatial variations of Cr, Cu, Hg, Ni, Pb, and Zn in the surface sediments from 34 stations of the Kaohsiung coastal zone southwestern Taiwan were studied to address the current pollution status, sediment quality, and potential ecological risk. The study revealed that the concentrations of sediment metals in Kaohsiung Harbor were alarmingly high compared to the other region of Kaohsiung coast. The concentrations of Cr, Cu, Hg, Ni, Pb, and Zn in the harbor sediments were as high as 351, 247, 1.93, 61.8, 60.9, and 940 mg kg^-1, respectively. The current situation of metal pollution was assessed by different pollution indices and results showed moderate to severe enrichment of Cu, Hg, and Zn in the harbor sediments. According to the degree of contamination, pollution load index, and contamination severity index, the sediments from the inner Kaohsiung Harbor show high degree and high severity of metal contamination, while the rest of Kaohsiung coastal areas show uncontaminated or low-level pollution. Results of mean ERM quotient and potential ecological risk index also indicated that the harbor sediments posed a 49% probability of biological toxicity and very high ecological risk. The toxic units indicated that the negative biological effects of the six metals in the harbor sediments were Zn > Cu > Cr > Ni > Hg > Pb. In contrast to Kaohsiung Harbor as a trap where considerable amount of anthropogenic metal loadings accumulated in sediments, low metal concentrations were observed in most Kaohsiung coastal sediments. It probably resulted from the limited fine-grained sediment deposition. In the wave-dominated Kaohsiung coastal zone, fine-grained sediments associated with polluted metals tend to be easily resuspended and transported offshore via waves and wave-induced currents. The results of this study can provide valuable information for river and coastal zone management.

Quantitative Assessment of the Environmental Impacts of Dredging and Dumping Activities at Sea

The dumping of dredge materials often raises concerns about the release of pollutants to the marine environment. Wind data from the Global Forecast System (GFS) model was used to simulate the wind-wave propagation from offshore in a two-dimensional (2D) model during September and October 2016. The calibration and validation of the 2D model showed a high conformity in both the phases and amplitude between the observed and simulated data. The 2D mud transport simulation results of three scenarios showed that the concentration of suspended material in the third scenario tested (scenario 3) was greater than 0.004 kg/m3 in the low tide, spreading to a 9 km2 area, and in the high tide, the concentration was 0.004 kg/m3 in a 6 km2 area. Finally, the results of 2D particle tracking (PT) showed changes in the seabed due to the concentration of dredged material, and its dump (approximately 180 days) increased from 0.08 m to 0.16 m in 2.85 ha. In scenario 3, the element block moved quite far—approximately 2.9 km—from the dredge position. Therefore, the simulation results were qualified, as the dredging position situated far from the sea is significantly affected by the direction and velocity of wave-wind in the dredging position.