Environmental compartment cycling

This chapter also serves as an environmental road map, laying out the physical, physicochemical and chemical means by which lead is transported and mobilized in and out of environmental compartments that serve as lead contact points for human and ecological populations. Environmental compartment cycling of lead until recently was a largely unknown cluster of phenomena, and the multimedia impact of lead emissions on the larger biosphere was little understood and even misunderstood. This chapter is not intended to be encyclopedic, but it focuses on data eventually useful for human health risk assessment and regulatory initiatives. 

Exposure to a substance can potentially occur during each stage of the life cycle of the substance in the EU, from production to ultimate disposal or recovery (Table 19). At each of the stages of the lifecycle, the exposure to the various environmental compartments and human populations has to be assessed. 

Standards can be expressed in various units, such as a load (mass/unit area), a dose (mass/body mass), or a concentration (mass/volume mass contaminant/mass soil). The use of a unit depends on the environmental compartment under consideration. We might consider the amount of pollution in water (a concentration), the consequences of equilibrium uptake by (or exposure to) a human (a dose), or the acceptable uptake by an ecosystem under steady conditions (the loading). The choice of unit depends on the point in a cycle or pollutant linkage at which we set the standard, as illustrated in Figure 3.1. 

The transfer of an element between different environmental compartments, involving both chemical and biological processes, is termed biogeochemical cycling. The biogeochemical cycles of the elements lead and nitrogen will be discussed later in this chapter. 

Arsenic can exist in several oxidation states, as both inorganic and organometallic species, and in dissolved and gaseous phases (Table I). Dissolved arsenic species can adsorb to suspended solids and be carried down to the sediments in an aquatic system. Since gaseous arsenic compounds can form, arsenic can be removed from the sediments as dissolved gas or in gas bubbles (e.g. CH ). Thus, arsenic can cycle within aquatic ecosystems and this cyclic behavior has been reviewed by Ferguson and Gavis (1 ) and Woolson 2). In any given system, it is necessary to understand the behavior of a variety of different arsenic compounds as well as a variety of environmental compartments in order to totally characterize the cyclic behavior of this element. 

Arsenic moves between ditferent environmental compartments (rock-soil-water-air-biota) from the local to the global scale partly as a result of pH and redox changes. Being a minor component in the natural environment, arsenic responds to such changes rather than creating them. These changes are driven by the major (bio)geochemical cycles. 

The distribution and fate of a chemical substance discharged into an environmental compartment (air, water, soU) follows a specific biogeochemical cycle dependent not only on diffusion and transport patterns within the single compartment, but also on partition processes among the various compartments. Moreover, within each compartment the chemical is subject to transformation processes (degradation, chemical reactions). A scheme of the main mechanisms regulating distribution of a chemical in the environment is shown in Figure 4.2. 

Switching the manufacturing base (the origins of the carbon) from petro / fossil to biobased plant carbon feedstock offers an intrinsic zero material carbon footprint value proposition. This is readily apparent from reviewing nature s carbon cycle. Nature cycles carbon through various environmental compartments with specific rates and time scales, as shown in Figure 14.1. 

There are four main environmental sources of Hg (PNUMA 2005) (1) natural, (2) anthropogenic releases from mobilizing Hg impurities that exist in raw materials (e.g., fossil fuels and other ores), (3) anthropogenic releases from production processes, and (4) remobilization of Hg from soils, sediments, and water from past anthropogenic releases. Whatever the original source of Hg entry into the environment, the final receptors of such emissions are the atmosphere, aquatic ecosystems, soils, and biota. The biogeochemical cycle of Hg is complex in that several environmental compartments and processes are involved in the cycle. Estimates of Hg emissions to the atmosphere show that natural sources of Hg (median value... 

Life-cycle assessment when carried ont according to the ISO rules has shown its ability to deliver data for certain more global environmental compartments like the impact potential on saving of resonrces, global warming potential, acidification, ozone depletion, and the like. It nsnally does not cover local effects such as noise or smell and hazardons snbstances. Here risk assessment or other methodologies are needed. The evalnation of effects regarding human toxicity is hampered by a lack of sufficient data and by a still undecided question of data evaluation. Thns, life-cycle analysis is a nseful tool but not the only answer to all enviromnental aspects. 

Fig. 4.2 Diagram of the global iodine cycle at steady state, showing environmental compartments, compartment inventories in grams, tran ort pathways, and fluxes in g y" (from Kocher, 1982).

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