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

▪ Abstract Among several viable explanations for the ubiquitous SES-health gradient is differential exposure to environmental risk. We document evidence of inverse relations between income and other indices of SES with environmental risk factors including hazardous wastes and other toxins, ambient and indoor air pollutants, water quality, ambient noise, residential crowding, housing quality, educational facilities, work environments, and neighborhood conditions. We then briefly overview evidence that such exposures are inimical to health and well-being. We conclude with a discussion of the research and policy implications of environmental justice, arguing that a particularly salient feature of poverty for health consequences is exposure to multiple environmental risk factors.

Socioeconomic Status and Health: The Potential Role of Environmental Risk Exposure

The American Academy of Pediatrics places emphasis on increasing breastfeeding in the United States. A common reason for the cessation of breastfeeding is the use of medication by the nursing mother and advice by her physician to stop nursing. Such advice may not be warranted. This statement is intended to supply the pediatrician, obstetrician, and family physician with data, if known, concerning the excretion of drugs into human milk. Most drugs likely to be prescribed to the nursing mother should have no effect on milk supply or on infant well-being. This information is important not only to protect nursing infants from untoward effects of maternal medication but also to allow effective pharmacologic treatment of breastfeeding mothers. Nicotine, psychotropic drugs, and silicone implants are 3 important topics reviewed in this statement.

Transfer of drugs and other chemicals into human milk

Overview of flotation as a wastewater treatment technique

Remediation technologies for heavy metal contaminated groundwater.

Foam Flotation: Theory and Applications

Utility of placental tissue as an indicator of trace element exposure to adult and fetus

Data on the solubilization of p-dichlorobenzene (DCB), naphthalene, and biphenyl in aqueous solutions of sodium dodecylsulfate (SDS) (0-100 mM concentration) indicate increases in effective solubilities of these hydrophobic compounds by factors of roughly 20 to 100. DCB is effectively removed from spiked clay-sand mixtures by leaching with SDS solutions in laboratory columns. Surfactant solutions loaded with DCB are satisfactorily treated by gentle extraction with hexane, and the recovered surfactant solution satisfactorily solubilizes biphenyl. A simple model for predicting the solubilization behavior of surfactants is developed and tested experimentally.

Soil Clean Up by in-situ Surfactant Flushing. III. Laboratory Results

As contamination moves through a fractured rock aquifer, it tends to diffuse from the flowing fracture water into the rock's essentially stagnant pore water. This process tends both to retard a contamination plume's advance through a fractured rock aquifer and to substantially increase the difficulty of purging contamination from the aquifer. A mathematical model has been developed to evaluate the potential impact of this phenomenon upon water quality restoration in fractured rock aquifers. The numerical modeling reveals that cleanup of fractured rock aquifers will, in many cases, require many decades, even centuries, to achieve, particularly where substantial improvements in water quality are sought. The parameters which most strongly govern the degree to which matrix diffusion prolongs the aquifer restoration process are the rock's matrix porosity, fracture spacing, and matrix diffusivity, the chemical identity of the contaminant(s), and the length of time the aquifer has been contaminated.

Cleanup of fractured rock aquifers: Implications of matrix diffusion.

Mathematical models are developed suitable for use in evaluating the feasibility of in-situ vapor stripping approaches for selected chemicals and site-specific environments. These models simulate the operation of both laboratory soil stripping columns and field-scale vacuum extraction wells (vent pipes). The effect of an anisotropic Darcy's constant is examined and the compressibility of the extracting gas is taken into account. The models incorporate the assumption of local equilibrium for the volatile compounds between the condensed and vapor phases. These models may use Henry's law or more complex isotherms for this equilibrium. A method is developed for calculating Henry's constant from field analytical data, and it is noted that use of Henry's constants calculated from laboratory data on solutions of volatile solutes in pure water can lead to very serious errors. It is shown that evacuation wells should be screened only down near the impermeable layer beneath the zone of stripping (unsaturat...

David J. Wilson

Papers

Foam Flotation: Theory and Applications

Utility of placental tissue as an indicator of trace element exposure to adult and fetus

Soil Clean Up by in-situ Surfactant Flushing. III. Laboratory Results

Cleanup of fractured rock aquifers: Implications of matrix diffusion.

Soil Clean Up by in-situ Aeration. I. Mathematical Modeling