Search Results

Sorption of organic pollutants by soils and sediments is one of the main chemical processes that controls pollutant migration in the environment. Information about the molecular mechanisms by which an organic pollutant interacts with other solution-phase constituents and with solid-phase sorbents would be invaluable for more accurate prediction of pollutant fate and transport and for optimal design and application of remediation procedures. Many current models and remediation strategies are based upon the “partition theory” of organic compound sorption, which predicts sorption coefficients from properties such as water solubility or octanol-water partition coefficients. Partition theory is well suited for nonpolar hydrocarbons but may not be appropriate for pesticides with electrophilic or weakly acidic or basic substituents, which may interact with soils or organic matter through specific interactions such as hydrogen bonding or charge-transfer complexes. If a pesticide can form hydrogen bonds or a charge-transfer complex with a sorbent, sorption may be greater than in the absence of specific interactions. Nuclear magnetic resonance (NMR) spectroscopy is well suited for the study of pesticide-solution or pesticide-sorbent interactions because NMR is an element-specific method that is extremely sensitive to the electron density (shielding) near the nucleus of interest. Consequently, solution-state NMR can distinguish between closely related functional groups and can provide information about intermolecular interactions. All nuclei with nonzero nuclear spin quantum number can be studied by NMR spectroscopy. Of the more than 100 NMR-active nuclei, 1H and 19F are the easiest to study because both have natural abundances near 100% and greater NMR sensitivity than any other nuclei. In addition, both 1H and 19F have zero quadrupolar moments, which means that sharp, well resolved NMR peaks can be obtained, at least in homogeneous solutions. Proton NMR is well suited for elucidating molecular interactions in solution but cannot be used to study interactions between pesticides and heterogeneous sorbents such as soils, humic acid, or even cell extracts, since protons in the sorbent generally produce broad peaks that mask the NMR peaks from the solute or sorbate of interest. In contrast, 19F NMR can be used to study interactions between fluorine-containing molecules and heterogeneous sorbents because the fluorine concentration in most natural sorbents is negligible.

This chapter presents two examples to demonstrate that natural history is the necessary basis of any reliable understanding of the world. More than a half century ago, Rachel Carson revolutionized the public’s view of pesticides. The foundation of her success was the careful use of natural history data, collated from across North America. The examples she assembled left little doubt that DDT and other pesticides were causing a widespread decline in birds. More recently, the case for the impact of atrazine on wildlife was based on laboratory experiments, without the advantage of natural history observations. For atrazine, natural history observations now suggest that other chemical agents are more likely to be responsible for feminization of wildlife populations. Developing expectations for scientists to collect natural history information can help to avoid over-extrapolating lab results to wild populations, a tendency often seen when those lab results conform to preconceptions about chemicals in the environment.

Since World War II, the production of synthetic chemicals has increased more than 30-fold due to the post-war boom in petrochemical exploration, manufacture, and marketing. The modern chemical industry, now a global enterprise of $2 trillion annually, is central to the world economy, as it generates millions of jobs and consumes vast quantities of energy and raw materials. Today, more than 70,000 different industrial chemicals are synthesized and sold each year (Chandler 2005; McCoy et al. 2006). New technologies and methods for the detection of these synthetic chemicals have drawn increasing attention to the pervasive and persistent presence of hormone-disrupting chemicals in our lives. Hormones—the chemicals that deliver messages throughout the body in order to coordinate physical processes—are deeply sensitive to external interference, and the consequences of such interference are becoming ever more apparent. In July 2005, the Centers for Disease Control (2005) released its Third National Report on Human Exposure to Environmental Chemicals, revealing that industrial chemicals now permeate bodies and ecosystems. Many of these chemicals can interfere with the body’s hormonal signaling system (called the endocrine system), and many persistently resist the metabolic processes that bind and break down natural hormones. More than 358 industrial chemicals and pesticides have been detected in the cord blood of minority American infants (Environmental Working Group 2009). Accumulating data suggests that reproductive problems are also increasing across a broad range of animals, from Great Lakes fish to people. Many researchers suspect that the culprits are environmental exposures to synthetic chemicals that disrupt hormonal signals, particularly in the developing fetus. Endocrine-disrupting chemicals are not rare; they include the most common synthetic chemicals in production, such as many pesticides, plastics, and pharmaceutical drugs. Since World War II, synthetic endocrine-disrupting chemicals have permeated bodies and ecosystems throughout the globe, potentially with profound health and ecological effects (Krimsky 2000). Hormones are chemical signals that regulate communication among cells and organs, thus orchestrating a complex process of fetal development that relies on precise dosage and timing.

The aquatic sciences have their share of scientific controversies. In some cases the controversy is the classic situation of economic benefit versus environmental protection; in other cases it involves “genuine” scientific debate over uncertainties of the science or debate over what management option is optimal. This chapter discusses two pollution cases that pit scientists from universities or government agencies against those supported by the industry responsible for the pollution. Additional controversies that are also discussed are a disagreement over management options for shoreline protection, and a scientific disagreement over uncertainties in data on fish populations, which is usually the reason for controversies over fisheries. Controversies over effects of pollution often focus on how much (what concentration) of a chemical is needed to produce a certain harmful effect. Chemical companies tend to argue that levels of a chemical found in the environment are too low to cause problems, while environmentalists typically contend that lower levels can be harmful. One chemical about which there is sometimes controversy is oil. In the case of oil spills, debate commonly centers on how long the effects of pollution last. Oil degrades over time, resulting in less oil in the environment. The critical issue here is: When does this degradation reach a point where spilled oil is no longer harmful? Oil is a complex combination of various hydrocarbons that generally floats on water, although some lighter-weight components (the water-soluble fraction) dissolve. Weathering is a process that takes place in the air and water, in which the lightweight components evaporate, thus leaving the heavier components (e.g., tar), which have traditionally been viewed as less toxic. When oil comes into shallow water and marshes, it can coat and smother resident communities. It can sink below the surface of beaches and marshes and remain there for many years. Oil in marsh sediments undergoes some microbial breakdown but very slowly. Effects of a small oil spill (190,000 gallons of number 2 fuel oil) in Falmouth, Massachusetts, in the late 1960s lasted for over a decade, according to Sanders et al. (1980).

That scientists should countenance non-epistemic values in their scientific practices has become widely accepted, in part on the basis of arguments from inductive risk. But traditional arguments from inductive risk have focused narrowly on the risk of making mistakes about the truth of hypotheses. This chapter argues that there are inductive risks associated with characterizational choices in science even when there are no mistakes about the truth of hypotheses. Using research into the endocrine-disrupting properties of the herbicide, atrazine, as a case study, this chapter shows how choosing to characterize the effects of atrazine using gendered language poses the risk of reinforcing problematic societal gender norms, while choosing to eschew the use of that gendered language poses risks with respect to environmental protection. The argument that such risks are inductive risks is supported by an analysis of the concept of induction found in traditional arguments from inductive risk.

We discussed in Chapter 4 the movement of solute between small volumes of soil, and in Chapter 5 some properties of plant roots and associated hairs, particularly the relation between the rate of uptake at the root surface and the concentration of solute in the ambient solution. In the chapters to follow, we consider the plant root in contact with the soil, and deal with their association in increasingly complex situations; first, when the root acts merely as a sink and, second, when it modifies its relations with the surrounding soil by changing its pH, excreting ions, stimulating microorganisms, or developing mycorrhizas. In this chapter, we take the simplest situation that can be studied in detail, namely, a single intact root alone in a volume of soil so large that it can be considered infinite. The essential transport processes occurring near the root surface are illustrated in figure 6.1. We have examined in Chapter 3 the rapid dynamic equilibrium between solutes in the soil pore solution and those sorbed on the immediately adjacent solid surfaces. These sorbed solutes tend to buffer the soil solution against changes in concentration induced by root uptake. At the root surface, solutes are absorbed at a rate related to their concentration in the soil solution at the boundary (section 5.3.2); and the root demand coefficient, αa, is defined by the equation . . . I = 2παaCLa (6.1) . . . where I = inflow (rate of uptake per unit length), a = root radius, CLa = concentration in solution at the root surface. To calculate the inflow, we have to know CLa, and the main topic of this chapter is the relation between CLa, and the soil pore solution concentration CL. The root also absorbs water at its surface due to transpiration (Chapter 2) so that the soil solution flows through the soil pores, thus carrying solutes to the root surface by mass flow (convection). Barber et al. (1962) calculated whether the nutrients in maize could be acquired solely by this process, by multiplying the composition of the soil solution by the amount of water the maize had transpired.