Elizabeth A. Casman

BioWar: scalable agent-based model of bioattacks

While structured by social and institutional networks, disease outbreaks are modulated by physical, economical, technological, communication, health, and governmental infrastructures. To systematically reason about the nature of outbreaks, the potential outcomes of media, prophylaxis, and vaccination campaigns, and the relative value of various early warning devices, social context, and infrastructure, must be considered. Numerical models provide a cost-effective ethical system for reasoning about such events. BioWar, a scalable citywide multiagent network numerical model, is described in this paper. BioWar simulates individuals as agents who are embedded in social, health, and professional networks and tracks the incidence of background and maliciously introduced diseases. In addition to epidemiology, BioWar simulates health-care-seeking behaviors, absenteeism patterns, and pharmaceutical purchases, information useful for syndromic and behavioral surveillance algorithms.

Modeling nanomaterial environmental fate in aquatic systems.

Mathematical models improve our fundamental understanding of the environmental behavior, fate, and transport of engineered nanomaterials (NMs, chemical substances or materials roughly 1-100 nm in size) and facilitate risk assessment and management activities. Although todays large-scale environmental fate models for NMs are a considerable improvement over early efforts, a gap still remains between the experimental research performed to date on the environmental fate of NMs and its incorporation into models. This article provides an introduction to the current state of the science in modeling the fate and behavior of NMs in aquatic environments. We address the strengths and weaknesses of existing fate models, identify the challenges facing researchers in developing and validating these models, and offer a perspective on how these challenges can be addressed through the combined efforts of modelers and experimentalists.

Modeling nanomaterial fate in wastewater treatment: Monte Carlo simulation of silver nanoparticles (nano-Ag).

Wastewater effluent and sewage sludge are predicted to be important release pathways for nanomaterials used in many consumer products. The uncertainty and variability of potential nanomaterial inputs, nanomaterial properties, and the operation of the wastewater treatment plant contribute to the difficulty of predicting sludge and effluent nanomaterial concentration. With a model parsimony approach, we developed a mass-balance representation of engineered nanomaterial (ENM) behavior based on a minimal number of input variables to describe release quantities to the environment. Our simulations show that significant differences in the removal of silver nanoparticles (nano-Ag) can be expected based on the type of engineered coatings used to stabilize these materials in suspension. At current production estimates, 95% of the estimated effluent concentrations of the nano-Ag considered to be least well-removed by the average wastewater treatment plant are calculated to fall below 0.12 μg/L, while 95% of the estimated sludge concentrations of nano-Ag with coatings that increase their likelihood of being present in biosolids, fall below 0.35 μg/L.

Meditations on the Ubiquity and Mutability of Nano-Sized Materials in the Environment

A wide variety of nanomaterials can be found naturally occurring in the environment, although finding and characterizing these materials remains a challenge due to their size. Recent studies in the field have shown that natural nanomaterials are common in many geochemical systems. In this issue of ACS Nano, Hutchison and co-workers make us realize that manmade nanomaterials can often be practically identical to those that spontaneously form in the environment. This Perspective discusses the prevalence of nanomaterials in nature, including anthropogenic and naturally occurring nanomaterials, and the dynamic behavior of these materials in the environment.

Modeling Nanosilver Transformations in Freshwater Sediments

Silver nanoparticles (AgNPs), an effective antibacterial agent, are a significant and fast-growing application of nanotechnology in consumer goods. The toxicity of AgNPs released to surface waters during the use or disposal of AgNP-containing products will depend on the chemical transformations the nanoparticles undergo in the environment. We present a simple one-dimensional diagenetic model for predicting AgNP distribution and silver speciation in freshwater sediments. The model is calibrated to data collected from AgNP-dosed large-scale freshwater wetland mesocosms. The model predicts that AgNP sulfidation will retard nanoparticle oxidation and ion release. The resultant Ag2S-coated AgNPs are expected to persist and accumulate in sediment downstream from sources of AgNPs. Silver speciation and persistence in the sediment depend on the seasonally variable availability of organic carbon and dissolved oxygen. The half-life of typical sulfidized (85% Ag2S) AgNPs may vary from less than 10 years to over a century depending on redox conditions. No significant difference in silver speciation and distribution is observed between ≥50% Ag2S and 100% Ag2S AgNPs. Formation and efflux of toxic silver ion is reduced in eutrophic systems and maximized in oligotrophic systems.

The Economic Impact of Bt Corn Resulting from Mycotoxin Reduction

The insecticidal proteins in genetically modified hybrid Bt corn (Zea mays spp.) reduce insect damage, which in turn can reduce infection of the grain by mycotoxigenic fungi. Lower levels of Fusarium mycotoxins, fumonisin, and deoxynivalenol in Bt corn could have significant market and health impacts, both in the United States and around the world. These impacts are foregone losses through market rejection, human health losses, and animal health losses. We estimate that at current planting levels, Bt corn saves farmers in the United States about

An Integrated Risk Model of a Drinking-Water-Borne Cryptosporidiosis Outbreak

17 million annually through reduced fumonisin and deoxynivalenol damage alone. Though not extensively grown in developing countries, the benefits there in mycotoxin reduction could be even more significant, particularly in regions where corn is a staple in the human diet.

Economic incentives and regulatory framework for shale gas well site reclamation in Pennsylvania.

A dynamic risk model is developed to track the occurrence and evolution of a drinking-water-borne cryptosporidiosis outbreak. The model characterizes and integrates the various environmental, medical, institutional, and behavioral factors that determine outbreak development and outcome. These include contaminant delivery and detection, water treatment efficiency, the timing of interventions, and the choices that people make when confronted with a known or suspected risk. The model is used to evaluate the efficacy of alternative strategies for improving risk management during an outbreak, and to identify priorities for improvements in the public health system. Modeling results indicate that the greatest opportunity for curtailing a large outbreak is realized by minimizing delays in identifying and correcting a drinking-water problem. If these delays cannot be reduced, then the effectiveness of risk communication in preemptively reaching and persuading target populations to avoid exposure becomes important.

Incorporating individual health-protective decisions into disease transmission models: a mathematical framework

Improperly abandoned gas wells threaten human health and safety as well as pollute the air and water. In the next 20 years, tens of thousands of new gas wells will be drilled into the Marcellus, Utica, and Upper Devonian shale formations of Pennsylvania. Pennsylvania currently requires production companies to post a bond to ensure environmental reclamation of abandoned well sites, but the size of the bond covers only a small fraction of the site reclamation costs. The economics of shale gas development favor transfer of assets from large entities to smaller ones. With the assets go the liabilities, and without a mechanism to prevent the new owners from assuming reclamation liabilities beyond their means, the economics favor default on well-plugging and site restoration obligations. Policy options and alternatives to bonding are discussed and evaluated.

A Meta‐Analysis of Carbon Nanotube Pulmonary Toxicity Studies—How Physical Dimensions and Impurities Affect the Toxicity of Carbon Nanotubes

It is anticipated that the next generation of computational epidemic models will simulate both infectious disease transmission and dynamic human behaviour change. Individual agents within a simulation will not only infect one another, but will also have situational awareness and a decision algorithm that enables them to modify their behaviour. This paper develops such a model of behavioural response, presenting a mathematical interpretation of a well-known psychological model of individual decision making, the health belief model, suitable for incorporation within an agent-based disease-transmission model. We formalize the health belief model and demonstrate its application in modelling the prevalence of facemask use observed over the course of the 2003 Hong Kong SARS epidemic, a well-documented example of behaviour change in response to a disease outbreak.