Soil systems direct effects

Blum and Tingey found that ozone reduction in soybean root growth and nodulation was a function of foliar impact. They found no direct effect of ozone on the roots or soil systems surrounding the roots. 

Fungi clearly play significant direct and indirect roles in effecting and modulating transport of a wide range of elements in soil systems. The principal transport modes that they are implicated in can be summarized as dispersion, concentration, inter-organism and bulk transfer (Fig. 3.5). 

Cardiovascular Effects. In humans, oral exposure of intermediate duration to zinc has decreased serum HDL cholesterol levels (Chandra 1984 Hooper et al. 1980). Although this is not a direct effect on the cardiovascular system, the decrease in HDL levels may be associated with an increased risk of coronary artery disease. However, another study showed no effect on HDL levels and a decrease in LDL levels (Samman and Roberts 1988), which would be associated with a decreased risk of coronary artery disease. More information on this effect is presented later in this section under Other Systemic Effects. It is not known if exposure to zinc in air, water, or soil would result in cardiovascular effects in people living near hazardous waste sites. 

This conceptual approach has been developed in the framework of the concept of "chemical time bombs" (a waste deposit or contaminated hot-spot which initially appears to be relatively harmless, but which can eventually have disastrous environmental effects as toxic contaminants are released). The effects of these time bombs are non-linear and delayed, e.g. toxic metals can "break through" once the specific buffering capacity of a sediment or soil system has been surpassed. To make the scientific objectives clearer, it is useful to distinguish between two different mechanisms (Stigliani 1992) the first is direct saturation, by which the capacity of a soil or sediment for toxic chemicals becomes exhausted. The second way to "trigger" a time bomb is through a fundamental change in a chemical property of the substrate that reduces its capacity to adsorb (or keep adsorbed) toxic materials. 

Electro-osmosis has been defined in the literature in many indirect ways, but the simplest definition comes from the Oxford English Dictionary, which defines it as the effect of an external electric held on a system undergoing osmosis or reverse osmosis. Electro-osmosis is not a well-understood phenomenon, and this especially apphes to polar non-ionic solutions. Recent hterature and many standard text and reference books present a rather confused picture, and some imply directly or indirectly that it cannot take place in uniform electric fields [31-35]. This assumption is perhaps based on the fact that the interaction of an external electric held on a polar molecule can produce only a net torque, but no net force. This therefore appears to be an ideal problem for molecular simulation to address, and we will describe here how molecular simulation has helped to understand this phenomenon [26]. Electro-osmosis has many important applications in both the hfe and physical sciences, including processes as diverse as water desahnation, soil purification, and drug delivery. 

Pick-up of stray current (a.c. or d.c.) (Section 10.5). Decreased use of d.c. in many areas has led to less possibilities of pick-up of direct current from utilities, mines, etc. The importance of grounded a.c. systems has been discounted, but Waters has shown that alternating currents can accelerate corrosion. Furthermore the rectifying effects of oxide films, clay minerals and other soil factors are not understood. 

Current due to the anode effect The potential of the earth near the ground-bed of a cathodic-protection system becomes more positive as the groundbed is approached (see Fig. 10.7, p. 10 10). A structure buried near the ground-bed will pick up current due to this variation in the soil potential and current will flow in the structure in each direction away from a point close to the groundbed (Fig. 10.39). The upper curve AGA in Fig. 10.39 shows how the current in the unprotected structure changes owing to the anode effect. 

The amount of sand and other particles sucked from the soil must be viewed as a possible cause for bearing failure or for the generation of bearing noise (such effects can also be caused by the moisture). Noise can directly influence the occupant to shut down the SSD system. Sandblasting of the fan blades or plateout on the fan blades by particles sucked into the mitigation system could lead to degradation of fan performance over the long term. 

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