Remediation of sediments contaminated by harmful heavy metals using aluminum sulfate: Sustainable approach for practical applications.

Chemical washing could be suitable for the remediation of marine sediments contaminated with harmful heavy metals. Considering green and sustainable remediation (GSR), the application of aluminum sulfate (AS) is intended to reduce the costs and environmental impacts. We extracted harmful heavy metals from manganese nodules using an ion exchange mechanism that occurs when AS dissociates in water. AS in the range from 2 % to 5 % was used. The remediation efficiencies using 5 % AS were found to be the highest, at 91.8 % for Ni and ≥ 100 % for other harmful heavy metals. The Pearson's coefficient evaluation showed that increasing elapsed time did not significantly affect the extraction of harmful heavy metals. Pollutants in post-processing products may not cause secondary pollutions if solidification/stabilization and additional treatments are used. Our results can serve as fundamental data for the actual remediation processes using AS not only for deep-sea mining tailings but also contaminated marine sediments.

Source identification and implications of heavy metals in urban roads for the coastal pollution in a beach town, Busan, Korea.

Heavy metals in the sediments of urban roads (RDS), storm drains (SDS), and marine areas (MS) were investigated to assess road pollution in a beach town adjacent to the coast in Busan and identify their relationships with the marine environment. RDS were considerably polluted with Zn, Cu, Cr, and Pb, with mean concentrations of 1090, 178, 171, and 199 mg/kg, respectively. MS were severely contaminated with Zn and Cu, exceeding the effects range median (ERM; Cu = 270, Zn = 410 mg/kg). PCA and HCA identified tire and brake wear in RDS as the major sources of Zn, Pb, Cu, and Cd, and that high levels of Zn, Cu, and Pb in RDS originating from traffic activities contaminated MS through the urban storm drain system. The results suggested that traffic-originated metals in RDS are potential pollutants in coastal environments, and further studies on their fate and management should be conducted.

Environmental assessment of contaminated marine sediments treated with solidification agents: Directions for improving environmental assessment guidelines.

Treatment of dredged materials is a critical issue, since management and disposal of these products requires considerable investment of monetary resources, time, and space. The high concentration of pollutants in dredged materials, along with high water content and many fine particles make recycling these materials particularly difficult. In order to solve this problem, solidification/stabilization has been considered as a potentially viable solution for recycling dredged marine sediments. However, there are currently no guidelines that address potential biological and environmental impacts. To evaluate the stability of treated materials and their biological impacts, dredged marine sediments, which were polluted with heavy metals, were treated by solidification/stabilization using two different solidifying agents. To assess potential impacts, toxicity characteristic leaching procedures (TCLP, USEPA) and a bioassay (with the rotifer, Brachionus sp.) were performed with treated materials. In a TCLP test, we found that treatment with a solidification agent decreased the leaching concentration of heavy metals from sediment compared to the control. The rotifer bioassay showed no change in the survival rate during 24 h of exposure to both agents. However, survival differed between the two agents after 48 h of exposure. Screening physiological status using gene expression, showed that oxidative stress genes were significantly altered. These results suggest that more studies are needed to provide guidelines for deciding the usability of treated materials created by the solidification or stabilization of dredged materials.

Chronic adverse effects of oil dispersed sediments on growth, hatching, and reproduction of benthic copepods: Indirect exposure for long-term tests.

Laboratory-scale sediment exposure was conducted as a preliminary study to assess the long-term effects of sediment contaminated with crude oil. For this purpose, indirect exposure using a glass filter crucible was tested and compared with direct exposure by observing several parameters (e.g., mortality, growth, reproduction, hatching, and uptake) in the benthic copepod Tigriopus japonicus. In direct exposure, short-term exposure caused significant damages to the eggs of ovigerous females, and there were difficulties in observing small oil droplets. However, indirect exposure did not induce any mortality during a 96-h exposure in adults. A 10-day exposure was also possible in an indirect exposure method and caused a decrease in reproduction and consequently a reduction in the hatching rate. In fact, the water phase collected from indirect exposure indicated significant polycyclic aromatic hydrocarbon (PAH) concentrations, although only a few components were present. The components of PAHs were similar to water-accommodated fractions (WAFs) of crude oil that are associated with the water-soluble part, but the relative portion of high-molecular-weight of PAHs was higher than WAF. In this approach, exposure tests caused reduction in the uptake rate in copepods even in the 24-h exposure. In conclusion, the biological effects of oil droplets from direct exposure were excluded by using a glass filter in indirect exposures, and several parameters could be derived in the long-term exposure. These results indicate that the indirect method could likely assess the chronic effects of oil-contaminated sediments on individual level parameters for deriving the ultimate effects on the population and community.

Magnetic characteristics of sediment grains concurrently contaminated with TBT and metals near a shipyard in Busan, Korea.

Bottom sediments near shipyards are often susceptible to receiving accidental spills of TBT and metals or their degradation products from hull scraping of antifouling system paints applied prior to 2008, when the AFS Convention 2001 was not in force. We investigated TBT and metal contamination of sediments near the shipyards of a small marina located in Busan, Korea and found that they were highly contaminated with TBT, Cu, and Zn. To better understand the environmental impacts and to make an optimal remediation plan, we characterized individual antifouling fragments in terms of metal and TBT contents, magnetic properties, and grain-size. Coarse-sized individual antifouling fragments exhibited simultaneously high levels of TBT, metals and high magnetic susceptibility, and appeared to be a major source of pollution in the sediment. Therefore, magnetic separation in combination with size-separation appears to be a cost-effective remediation method to remove the TBT and metals from contaminated shipyard sediments.

Change of monochloroacetic acid to biodegradable organic acids by hydrothermal reaction.

The feasibility of biodegradability improvement induced from the structural conversion of refractory pollutants by hydrothermal reaction was investigated. Monochloroacetic acid (MCAA) was selected as a preliminary material represented for linear hydrocarbon structured refractory pollutants. Under the tested conditions, MCAA was partially destructed and then converted to biodegradable reaction products by hydrolysis, dehydration and thermal decomposition. The identified products were glycolic acid, citric acid and formic acid. Total organic carbon (TOC) reduction during the structural conversion did not exceed 24%, except the results at the reaction conditions of 350 degrees C and 17 MPa. However, Produced biodegradable organic acids were reduced by thermal decomposition with increasing reaction temperature and time. At the reaction temperature of 250 and 300 degrees C, biodegradability (BOD/COD(Cr)) was reached at 0.51 in 6.9 min and 0.52 in 7.4 min despite the presence of dissociated chlorine ions. The detachment of recalcitrant chlorine ion from MCAA and the production of biodegradable organic acids by hydrothermal reaction were directly related to the biodegradability improvement of reaction products.