Analytical Methods:Pollution Monitoring

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Degradation processes linked to soil pollution
There are a number of different aspects to soil pollution, including the source of the pollution and the nature of the pollution:
 * Point sources - These are direct inputs to the soil from a source of limited area.
 * Diffuse sources - These are often indirect inputs to the soil from diffuse sources such as the atmosphere or groundwater. Diffuse sources of pollution may have a regional, national or even global extent.


 * Phosphate - The association of phosphate with cess, dung and ash makes it a good indicator of former human activity (Crowther, 1997). These signals, however, can be swamped by modern applications of organic and inorganic fertilisers.
 * Metals and other inorganic pollutants – Soil concentrations of metals and ither inorganic materials have been used variously in archaeology as markers of historical and prehistoric pollution (Rawlins et al, 2006) and to aid interpretation of space use in and around archaeological sites (e.g. Entwistle et al., 2000). In particular Pb, Cu, Zn and As are typically enhanced by human activity (Wilson et al., 2005; Davidson et al., 2007) These signals are effectively the legacy of past pollution event. Both past and modern pollution may come from either a point or aerial source. As well as the concentration of pollutants, their effect will depend on the drainage, pH, cation exchange capacity, and redox potential, which will affect their transport laterally and vertically through the soil.
 * Organics – The study of biomolecules in soil (Bull et al., 1999) and as residues on artefacts (e.g. Oudemans et al., 2007) is relatively new in archaeology, but these organic molecules are an important potential source of cultural information. Potentially they are susceptible to changes in oxidation state, biological and microbial activity and down profile percolation of organic residues. However, very little is known about the persistence of biomolecules in soil.
 * Fertilisers and pesticides - Recent studies of metal detectorists finds have indicated a potential problem arising from fertiliser and pesticide application (Dobinson and Denison, 1995). This could be a potentially important factor in cultural heritage preservation judging by the reported increase in the degree of degradation over a period of only a decade or two. A subsequent pilot study into the effects of agrichemicals on buried iron and copper artefacts (Pollard et al., 2004), suggests that agrochemicals can accelerate the rate of corrosion, but more research is needed to establish critical loads.

Approaches to monitoring soil pollution
The best approach to monitoring soil pollution is heavily dependant on the nature and source of pollution.

In-situ field measurements are possible using field XRF (X-ray flourescence) for example, however, they will only measure surface concentrations and don't provide information on the dispersal of pollutants vertically through the soil. Loadings of fertilisers and pesticides can be monitored using a questionnaire type approach of landowners. However, interpretation of actual damage can be difficult becuase too little is known about critical loads (the concentrations required to do significant damage) or the residency times of some of these substances in the soil. Where atmospheric inputs of pollutants are of specific interest, these can be monitored directly from using moss bags or other traps.

In general, however, soil sampling and laboratory analysis is required for pollution monitoring.

Sampling strategies
The sampling strategy should be heavily dependant on the nature of the pollutants and the questions being asked. Diffuse sources of pollutions are perhaps best monitored over regional scales, whilst point sources of pollution may be site-specific. It is important that the time frame, likely effects and spatial extent of the pollution event being monitored is carefully considered prior to monitoring.

Related techniques

 * Element concentration analysis
 * Multi-element concentration analysis

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