PubMed · 14923987
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1952. BATHING places; Engineering Section.. https://doi.org/10.2105/ajph.42.5_pt_2.99
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Hydrophobic organic groundwater contaminants, such as polynuclear aromatic hydrocarbons (PAHs), sorb strongly to soils and are difficult to remove. We report here on the synthesis of amphiphilic polyurethane (APU) nanoparticles for use in remediation of soil contaminated with PAHs. The particles are made of polyurethane acrylate anionomer (UAA) or poly(ethylene glycol)-modified urethane acrylate (PMUA) precursor chains that can be emulsified and cross-linked in water. The resulting particles are of colloidal size (17-97 nm as measured by dynamic light scattering). APU particles have the ability to enhance PAH desorption and transport in a manner comparable to that of surfactant micelles, but unlike the surface-active components of micelles, the individual cross-linked precursor chains in APU particles are not free to sorb to the soil surface. Thus, the APU particles are stable independent of their concentration in the aqueous phase. In this paper we show that APU particles can be engineered to achieve desired properties. Our experimental results show that the APU particles can be designed to have hydrophobic interior regions that confer a high affinity for phenanthrene (PHEN) and hydrophilic surfaces that promote particle mobility in soil. The affinity of APU particles for contaminants such as PHEN can be controlled by changing the size of the hydrophobic segment used in the chain synthesis. The mobility of colloidal APU suspensions in soil is controlled by the charge density or the size of the pendent water-soluble chains that reside on the particle surface. Exemplary results are provided illustrating the influence of alternative APU particle formulations with respect to their efficacy for contaminant removal. The ability to control particle properties offers the potential to produce different nanoparticles optimized for varying contaminant types and soil conditions.
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Our shared moral framework is negotiated as part of the social contract. Some elements of that framework are established (tell the truth under oath), but other elements lack an overlapping consensus (just when can an individual lie to protect his or her privacy?). The tidy bits of our accepted moral framework have been codified, becoming the subject of legal rather than ethical consideration. Those elements remaining in the realm of ethics seem fragmented and inconsistent. Yet, our engineering students will need to navigate the broken ground of this complex moral landscape. A minimalist approach would leave our students with formulated dogma--principles of right and wrong such as the National Society for Professional Engineers (NSPE) Code of Ethics for Engineers--but without any insight into the genesis of these principles. A slightly deeper, micro-ethics approach would teach our students to solve ethical problems by applying heuristics--giving our students a rational process to manipulate ethical dilemmas using the same principles simply referenced a priori by dogma. A macro-ethics approach--helping students to inductively construct a posteriori principles from case studies--goes beyond the simple statement or manipulation of principles, but falls short of linking personal moral principles to the larger, social context. Ultimately, it is this social context that requires both the application of ethical principles, and the negotiation of moral values--from an understanding of meta-ethics. The approaches to engineering ethics instruction (dogma, heuristics, case studies, and meta-ethics) can be associated with stages of moral development. If we leave our students with only a dogmatic reaction to ethical dilemmas, they will be dependent on the ethical decisions of others (a denial of their fundamental potential for moral autonomy). Heuristics offers a tool to deal independently with moral questions, but a tool that too frequently reduces to casuistry when rigidly applied to "simplified" dilemmas. Case studies, while providing a context for engineering ethics, can encourage the premature analysis of specific moral conduct rather than the development of broad moral principles--stifling our students' facility with meta-ethics. Clearly, if a moral sense is developmental, ethics instruction should lead our students from lower to higher stages of moral development.