Pristine site

The system was applied to the analysis of a series of water samples obtained from the Chesapeake Bay at both industrially polluted and relatively pristine sites. 

Phenol has been detected in surface waters, rainwater, sediments, drinking water, groundwater, industrial effluents, urban runoff, and at hazardous waste sites. Background levels of phenol from relatively pristine sites can be as high as 1 ppb for unpolluted groundwater and have been reported to range from 0.01 to 1 ppb in unpolluted rivers (Thurman 1985). Phenol has been detected in Lake Huron water at 3-24 ppb (Konasewich et al. 1978) and industrial rivers in the United States at 0-5 ppb (Sheldon and... 

The observation that imposex occurred primarily in marinas suggested causality with some contaminant originating from such facilities. Field experiments demonstrated that neogastropods transferred from pristine sites to marinas often developed imposex. Laboratory studies eventually implicated tributyltin, a biocide used in marine paints, as the cause of imposex. Tributyltin is toxic to most marine species evaluated in the... 

A distinction sometimes needs to be made between the natural background level of a substance, which arises purely as a result of natural processes, and the ambient background level, which is the concentration measurable in the environment at a pristine site (see Section 5.10). In practice, a pristine site is often considered to be one that does not receive any direct inputs from local sources, although it needs to be accepted that for many substances there may be an appreciable input from diffuse atmospheric sources. 

Although only 10% of atmospheric ozone resides in the troposphere (0-15 km altitude) it has a profound impact on tropospheric chemistry. Ozone concentrations in the troposphere vary from typically 20-40 ppb for a remote pristine site to 100-200 ppb in a highly polluted urban environment. Ozone is a reactive molecule, which readily adds to carbon-carbon double bonds [8]. Reaction with ozone provides an important removal mechanism for many unsaturated reactive organic compounds. 

Figure 7.2 The use of a biomarker index in temporal and spatial studies. In this survey, three sites were sampled over ten different time periods. In order to sort out natural variation in time, a control chart approach is used. The median value of the pristine site is plotted with the 10th, 25th, 75th and 90th centiles. Biomarker index values outside the 90th and 10th centiles are most likely to be outside natural variability and could be associated with pollution factors.

A detailed examination of the reaction products of 2MP on both USHY catalysts indicates the modes of reaction are 1) isomerization, monomolecular and dimerization-cracking on pristine sites and 2) biinolecular chain processes between an adsorbed product carbocations and a gas phase reactant molecule. Figure 1 presents the experimental average conversion and the corresponding predicted conversion, with respect to time on stream, along lines of constant catalyst to reactant ratio. The sigmoidal behaviour exhibited at low conversions and short times on stream is consistent with the presence of the second type of reaction, one mediated by chain processes. Such behaviour contrasts sharply with that previously reported for linear paraffins on USHY (9) where 1 was observed to increase monotonically with reaction time. A kinetic model has been proposed (10) which accounts for all the mechanisms active in this system. The model assumes that the surface reaction is rate controlling in all cases and is ... 

Figure 6 shows two force-distance plots for a PEO 200 kDa adsorbed silicon nitride surface. The initial curve recorded at the pristine site (Figure 6, plot A) shows... 

Figure 5. Two force-distance plots obtained when the PEO 900 kDa has been physically adsorbed to the silicon nitride surface in the presence of 0.1 N KNO3. A pristine site compression cycle is shown by the curves A. Occasionally, a compression cycle would yield a force-plot similar to the curves B. Here, a series of a esive "snap-offs" upon retraction is most likely due to the ripping of PEO chains off from one of two surfaces after they have bridged the two surfaces. The cantilever spring constant was 0.064 nN/nm and the frequency of oscillation was IHz.

Ferrier, R.C., Anderson, J.S., Miller, J.D. and N. Christophersen (1989). Changes in soil and stream hydrochemistry during periods of snowmelt at a pristine site in mid-Norway. Water, Air, and Soil Pollution 44, 321-337. 

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