Static and dynamic sorption of phenanthrene in mangrove sediment slurry
Introduction
The efficiency and effectiveness of bioremediation always vary among contaminated sites, due to the heterogeneity of soil/sediment and their effects on the sorption and desorption patterns of the organic contaminant especially the hydrophobic one such as polycyclic aromatic hydrocarbons (PAHs). PAHs, because of their strong hydrophobicity, are generally associated with the non-aqueous phase in soil/sediment. Luthy et al. [1] reported that the organic compartments in soil determined the sorption behavior of the highly hydrophobic compounds. In saturated soil, partitioning to total organic matter (TOM) or organic carbon was often the main interaction; however, the sorption of hydrophobic contaminants to clay minerals was dominant in dry soil [2], [3], [4]. Hwang and Cutright [5] found that clay in soil was a dominant factor affecting the sorption behavior of PAHs in sediment slurry. Because of the strong association of PAHs with organic fraction and/or clay minerals in soil/sediment, the amount of PAHs available in the aqueous phase is relatively small and depends on the sorption–desorption equilibrium between aqueous and non-aqueous phases.
The static sorption behavior of PAHs onto soil/sediment has been described by three models. They are the linear model [6], [7], the Freundlich model [8], [9] and the Langmuir model [10], [11]; and these models were evaluated under different situations [12], [13]. Salinity was found to be one of the significant factors affecting the biodegradation of PAHs [14], [15], [16], [17]. The physico-chemical properties of soil/sediment, in particular, the amount and nature of organic matter and clay minerals are also important factors leading to different sorption behavior. Mangrove sediment, subject to tidal flushing is often under alternate wet and dry cycles, is known to be rich in organic matter and clay minerals, thus it is unique and different from other soil types [18]. The mangrove sediment properties are also heterogeneous, vary from sites to sites even in a small city like Hong Kong with an area around 1000 km2 [18]. However, the research on sorption–desorption of PAHs in mangrove sediment is rare although many studies reported the biodegradation of PAHs in mangrove sediment [19], [20], [21].
The sorption behavior of PAHs is never static because the PAHs in the aqueous phase will be continuously degraded by the microorganisms in soil/sediment, and the adsorbed compound will be gradually transferred to the aqueous phase [22], [23], [24], [25]. The sorption behavior during biodegradation is therefore dynamic and the three models for static sorption may not be applicable. The present study aims to (i) investigate the static sorption behavior of phenanthrene (Phe), a model 3-ring PAH, in different types of mangrove sediment slurries with and without the inoculation of Sphingomonas sp., a PAH-degrading bacterial isolate; (ii) study the effect of salinity on the static sorption of Phe in silty sediment slurry and (iii) explore the dynamic sorption behavior of Phe during biodegradation by indigenous microorganisms with the inoculation of Sphingomonas sp.
Section snippets
Chemicals and PAH-degrading isolate
Standards of Phe (96%) were purchased from Sigma Chemicals, USA. The stock solution of each PAH compound was prepared by dissolving an appropriate amount of the standard in acetone, with a final concentration of 5000 mg L−1. All solutions were kept in a brown bottle at 4 °C and wrapped with aluminum folds to avoid any light exposure prior to use. Ethyl acetate (A.R.) was bought from Lab Scan Asia Co. Ltd. (Thailand) and was distilled before use. Calcium chloride (CaCl2) and sodium azide (NaN3)
General properties of mangrove sediment
The sediment collected from MP was muddy with 62% clay and a very large surface area of 42.6 m2 g−1, the sediment also had the highest organic matter and nutrient content (Table 1). Conversely, KLH sediment was sandy, with 89% sand and a small surface area of 8.9 m2 g−1. The organic matter content of KLH sediment was also the lowest. Among three sediment types, the properties of HC sediment were somewhat in the middle, it was silty with 24% silt, 21% clay and a surface area of 16.7 m2 g−1.
Static sorption
In all
Discussion
The sorption behavior of PAHs was dependent on the amount and nature of clay minerals and organic matter in sediment/soil [1], [30]. Silt and clay provide larger surface areas and higher cation exchange capacity for the organic pollutant to adsorb onto their surface than sand or bulk soil [2], [31]. The hydrophobic organic pollutant also has a tendency to adsorb onto organic matter. The relative importance of clay and organic matter on the sorption behavior varies from sediment to sediment, and
Conclusions
- •
The Freundlich adsorption isotherm was the best model to describe the static sorption behavior of Phe in mangrove sediment slurry while for the dynamic sorption behavior during the process of biodegradation, linear regression was the most suitable model to describe the sorption of Phe onto mangrove sediment.
- •
The sorption capacity (kf) and sorption intensity (n) of Freundlich adsorption isotherm were significantly lower in sandy than in muddy and silty sediment slurries and were reduced with the
Acknowledgement
The work described in this paper was supported by a grant from the Research Grants Council of the Hong Kong SAR, China (Project No. CityU 1406/06M).
References (45)
- et al.
Sorption of hydrophobic pollutants on natural sediments
Water Res.
(1979) - et al.
Biodegradability of aged pyrene and phenanthrene in a natural soil
Chemosphere
(2002) - et al.
A nonlinear parametric model for phenanthrene sorption
J. Colloid Interface Sci.
(2006) - et al.
Evaluation of matrices for the sorption and biodegradation of phenanthrene
Water Res.
(2006) - et al.
Release of bacteria into soil: cell numbers and distribution
J. Microbiol. Methods
(1994) - et al.
Preliminary study on biodegradation of phenanthrene by bacteria isolated from mangrove sediments in Hong Kong
Mar. Pollut. Bull.
(2002) - et al.
Multi-factors on biodegradation kinetics of polycyclic aromatic hydrocarbons (PAHs) by Sphingomonas sp. a bacterial strain isolated from mangrove sediment
Mar. Pollut. Bull.
(2008) - et al.
Isolation of PAH-degrading bacteria from mangrove sediments and their biodegradation potential
Mar. Pollut. Bull.
(2005) - et al.
Degradation of polycyclic aromatic hydrocarbons (PAHs) by a bacterial consortium enriched from mangrove sediments
Environ. Int.
(2005) - et al.
Different bacterial groups for biodegradation of three- and four-ring PAHs isolated from a Hong Kong mangrove sediment
J. Hazard. Mater.
(2008)
Nonlinear sorption of naphthalene and phenanthrene during saturated transport in natural porous media
Phys. Chem. Earth Pt. B
Solubility of medium molecular-weight aromatic-hydrocarbons and effects of hydrocarbon co-solutes and salinity
Geochim. Cosmochim. Ac.
The effects of temperature and salinity on the aqueous solubility of polynuclear aromatic-hydrocarbons
Mar. Chem.
Adsorption studies of caesium on zirconium molybdoarsenate (ZrMAs)
Waste Manag.
Sequestration of hydrophobic organic contaminants by geosorbents
Environ. Sci. Technol.
Partition equilibria of nonorganic compounds between soil organic matter and water
Environ. Sci. Technol.
Influence of mineral-bound humic substances on the sorption of hydrophobic organic compounds
Environ. Sci. Technol.
Impact of clay minerals and DOM on the competitive sorption/desorption of PAHs
Soil Sediment Contam.
Evaluation of the interaction between biodegradation and sorption of phenanthrene in soil–slurry systems
Biotechnol. Bioeng.
Adsorption of polycyclic aromatic hydrocarbons in aged harbor sediments
J. Environ. Eng. ASCE
Phenanthrene adsorption by soils treated with humic substances under different pH and temperature conditions
Environ. Geochem. Health
Decontamination of polyaromatic hydrocarbons from soil by steam stripping: mathematical modeling of the mass transfer and energy requirement
Environ. Sci. Technol.
Cited by (19)
Polycyclic aromatic hydrocarbons (PAHs) in mangrove ecosystems: A review
2022, Environmental PollutionCitation Excerpt :Smaller particles tend to have higher concentrations of contaminants because smaller particles imply greater surface area per volume of sorption and lower density particles (Zhao et al., 2010). In addition, clays have good fixing capacities and tend to form aggregates (Chen et al., 2009; Liu et al., 2011). Mangrove soil texture is variable between regions and depend on multiple parameters.
Occurrence, bioavailability and toxic effects of trace metals and organic contaminants in mangrove ecosystems: A review
2012, Environment InternationalCitation Excerpt :However, studies on the sorption behavior using mangrove sediments are relatively scarce, and focused mainly on PAHs (Bei et al., 2011; Chen et al., 2009). More sorption studies are needed to investigate if, in mangroves, clays may play an important role on bioavailability, especially when POC is low, as sometimes suggested (Chen et al., 2009). Marchand et al. (2011) noted that, in mangrove sediments, “redox conditions are dependent on the quantity and reactivity of organic matter, sediment grain size, bioturbation activity, like in marine sediments, but also on forest age, physiological activities of the root system, extent of water logging and crabs burrowing”.
Modeling sorption and biodegradation of phenanthrene in mangrove sediment slurry
2011, Journal of Hazardous MaterialsCitation Excerpt :With the discovery of a wide variety of microorganisms which have the ability to degrade PAHs [2], bioremediation, a technology that utilizes microorganisms to reduce environmental contaminants, has become a popular and effective remediation technique [3,4]. However, the heterogeneity of soil/sediment has been known to exert a significant influence on the efficiency and effectiveness of bioremediation in various sites [5], probably due to its effects on the sorption and desorption patterns associated with hydrophobic organic contaminants [6]. The organic compartments and the clay content in the sediment were proved to be the two dominant factors which would affect the sorption behavior of PAHs in the sediment/soil–water system [7,8].
In situ simultaneous determination the photolysis of multi-component PAHs adsorbed on the leaf surfaces of living Kandelia candel seedlings
2010, TalantaCitation Excerpt :Thus, it is very necessary to establish an in situ method to discuss the environmental behaviors of PAHs adsorbed on plant leaves. The mangrove ecosystem, a predominantly intertidal estuarine wetland, nowadays, is exposed to anthropogenic contamination which bring many pollutants, such as, heavy metals, organochlorine pesticides, polychlorinated biphenyls, PAHs and so on [10,14–18]. Mangrove forest is important to humans for a variety of reasons, including aquaculture, agriculture, forestry and protection against shoreline erosion.