Plastics debris in the marine environment, including resin pellets, fragments and microscopic plastic fragments, contain organic contaminants, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons, petroleum hydrocarbons, organochlorine pesticides (2,2′-bis(p-chlorophenyl)-1,1,1-trichloroethane, hexachlorinated hexanes), polybrominated diphenylethers, alkylphenols and bisphenol A, at concentrations from sub ng g–1 to µg g–1. Some of these compounds are added during plastics manufacture, while others adsorb from the surrounding seawater. Concentrations of hydrophobic contaminants adsorbed on plastics showed distinct spatial variations reflecting global pollution patterns. Model calculations and experimental observations consistently show that polyethylene accumulates more organic contaminants than other plastics such as polypropylene and polyvinyl chloride. Both a mathematical model using equilibrium partitioning and experimental data have demonstrated the transfer of contaminants from plastic to organisms. A feeding experiment indicated that PCBs could transfer from contaminated plastics to streaked shearwater chicks. Plasticizers, other plastics additives and constitutional monomers also present potential threats in terrestrial environments because they can leach from waste disposal sites into groundwater and/or surface waters. Leaching and degradation of plasticizers and polymers are complex phenomena dependent on environmental conditions in the landfill and the chemical properties of each additive. Bisphenol A concentrations in leachates from municipal waste disposal sites in tropical Asia ranged from sub µg l–1 to mg l–1 and were correlated with the level of economic development.

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Transport and release of chemicals from plastics to the environment and to wildlife

The use of equilibrium expressions for sorption to natural particles in fate and transport models is often invalid due to slow kinetics. This paper reviews recent research into the causes of slow sorption and desorption rates at the intraparticle level and how this phenomenon relates to contaminant transport, bioavailability, and remediation. Sorption kinetics are complex and poorly predictable at present. Diffusion limitations appear to play a major role. Contending mechanisms include diffusion through natural organic matter matrices and diffusion through intraparticle nanopores. These mechanisms probably operate simultaneously, but the relative importance of each in a given system is indeterminate. Sorption shows anomalous behaviors that are presently not well explained by the simple diffusion models, including concentration dependence of the slow fraction, distributed rate constants, and kinetic hysteresis. Research is needed to determine whether adsorption/desorption bond energies may play a role alon...

Mechanisms of Slow Sorption of Organic Chemicals to Natural Particles

The unique and tunable properties of carbon-based nanomaterials enable new technologies for identifying and addressing environmental challenges. This review critically assesses the contributions of carbon-based nanomaterials to a broad range of environmental applications: sorbents, high-flux membranes, depth filters, antimicrobial agents, environmental sensors, renewable energy technologies, and pollution prevention strategies. In linking technological advance back to the physical, chemical, and electronic properties of carbonaceous nanomaterials, this article also outlines future opportunities for nanomaterial application in environmental systems.

Environmental applications of carbon-based nanomaterials.

Evidence is accumulating that sorption of organic chemicals to soils and sediments can be described by “dual-mode sorption”:  absorption in amorphous organic matter (AOM) and adsorption to carbonaceous materials such as black carbon (BC), coal, and kerogen, collectively termed “carbonaceous geosorbents” (CG). Median BC contents as a fraction of total organic carbon are 9% for sediments (number of sediments, n ≈ 300) and 4% for soils (n = 90). Adsorption of organic compounds to CG is nonlinear and generally exceeds absorption in AOM by a factor of 10−100. Sorption to CG is particularly extensive for organic compounds that can attain a more planar molecular configuration. The CG adsorption domain probably consists of surface sites and nanopores. In this review it is shown that nonlinear sorption to CG can completely dominate total sorption at low aqueous concentrations (<10-6 of maximum solid solubility). Therefore, the presence of CG can explain (i) sorption to soils and sediments being up to 2 orders of m...

Extensive sorption of organic compounds to black carbon, coal, and kerogen in sediments and soils: mechanisms and consequences for distribution, bioaccumulation, and biodegradation

Preface. 1. Introductory Remarks. 2. Fundamental Factors for Designing Adsorbent. 3. Sorbent Selection: Equilibrium Isotherms, Diffusion, Cyclic Processes, and Sorbent Selection Criteria. 4. Pore Size Distribution. 5. Activated Carbon. 6. Silica Gel, MCM, and Activated Alumina. 7. Zeolites and Molecular Sieves. 8. &pi -Complexation Sorbents and Applications. 9. Carbon Nanotubes, Pillared Clays, and Polymeric Resins. 10. Sorbents for Applications. Author Index. Subject Index.

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Adsorbents: Fundamentals and Applications

Contaminant sorption by soils and sediments is characterized as a multiple reaction phenomenon. The approach is predicated on the observation that most natural soils and sediments are intrinsically heterogeneous even at the microscopic scale; that is, variable in composition and structure at both interparticle and intraparticle scales. Heterogeneity is demonstrated for a number of soils which, on the basis of conventional macroscopic properties, would be considered homogeneous. That such heterogeneities are reflected in sorption reactions which differ between soils and between different fractions of soil is also demonstrated. A composite model, the distributed reactivity model (DRM), is introduced to characterize intrinsic heterogeneities in the properties and behaviors of soils and sediments and to capture the resulting nonlinearities of sorption isotherms. Finally, the significance of particle-scale heterogeneity and distributed reactivity is illustrated by using measured parameters and DRM calculations to characterize differences in the relative sorption behavior of soils comprising different mass fractions of differently reactive components. 31 refs., 9 figs., 2 tabs.

A distributed reactivity model for sorption by soils and sediments. 1. Conceptual basis and equilibrium assessments

Sorption phenomena in subsurface systems: Concepts, models and effects on contaminant fate and transport

The solubilization of dodecane by polyoxyethylene (20) sorbitan monooleate, a nonionic surfactant, was investigated as a potential means of recovering nonaqueous-phase liquids from contaminated aquifers. Residual saturations of dodecane were established by injecting [sup 14]C-labeled dodecane into water-saturated soil columns and displacing the free product with water. Flushing with a 43 g/L surfactant solution increased the concentration of dodecane in the column effluent by 5 orders of magnitude. However, effluent dodecane concentrations were considerably less than the equilibrium value of 3500 mg/L measured in batch studies. Subsequent column experiments conducted at several flow velocities and with periods of flow interruption confirmed the existence of rate-limited, rather than instantaneous, solubilization of residual dodecane. The results of this study demonstrate the sizable capacity of surfactant solutions to enhance the recovery of residual dodecane, even under conditions of rate-limited solubilization. 67 refs., 6 figs., 1 tab.

Surfactant-enhanced solubilization of residual dodecane in soil columns. 1. Experimental investigation

Overview. Process Characterization and Analysis. Macrotransport Processes. Microtransport Processes. Energy Relationships: Concepts and Applications to Homogeneous Systems. Energy Relationships: Applications to Heterogeneous Systems. Rate Relationships: Concepts and Applications to Homogeneous Systems. Rate Relationships: Applications to Homogeneous Systems. Rate Relationships: Applications to Heterogeneous Systems. Reactor Engineering: Steady-State Homogeneous Systems. Reactor Engineering: Steady-State Heterogeneous Systems. Reactor Engineering: Unsteady-State Systems. Retrospections and Perspectives. Appendices. Index.

Process Dynamics in Environmental Systems

A methodology relating changes in the isotherm parameters for sorption of one solute by a heterogeneous sorbent to changes in the site energy distributions of that sorbent caused by prior irreversible sorption (preloading) of other solutes is proposed. Approximate site energy distributions underlying three isotherm models commonly used to describe sorption of organic solutes from aqueous solutions are developed using the theory of heterogeneous surfaces. It is demonstrated that, regardless of the type of initial site energy distribution assumed, preloading by a non-desorbable solute results in a loss of surface heterogeneity. The loss occurs preferentially across sites having the highest energies, with the number of sites in the lowest energy ranges actually increasing in some cases. Activated carbon is used to demonstrate the methodology, but the approach is generally applicable to other heterogeneous adsorbents in both natural and engineered systems.

Walter J. Weber

Papers

A distributed reactivity model for sorption by soils and sediments. 1. Conceptual basis and equilibrium assessments

Sorption phenomena in subsurface systems: Concepts, models and effects on contaminant fate and transport

Surfactant-enhanced solubilization of residual dodecane in soil columns. 1. Experimental investigation

Process Dynamics in Environmental Systems

Site energy distribution analysis of preloaded adsorbents.