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About UNEP
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United Nations Environment Programme
Division of Technology, Industry and Economics
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Newsletter and Technical Publications
Freshwater Management Series No. 5

Guidelines for the Integrated Management of the Watershed
- Phytotechnology and Ecohydrology -


B. Contamination of soil and water by organic and inorganic compounds

Limitations on natural resource use due to contamination and the possibly toxic, synergistic effects of different contaminating compounds, have been dramatically increasing. Contamination can be defined as the existence of substances at such concentrations above background levels - or which exceed of "normal" levels or established standards - as are likely to cause harm, directly or indirectly to humans and/or the environment. Contamination of soil and water has been occurring not only at old industrial areas, hazardous waste disposal sites or uncontrolled hazardous waste sites, but it also concerns the agricultural landscape as a result of increasing agro-chemical use (due to high levels of fertilisation and pesticide use). Thus, in part, the emphasis is on the actual presence of such potentially harmful contaminants rather on the past use.

That are many substances giving rise to concern due to human activity as:

  • certain heavy metals and their compounds, including Pb, As, Cd, Cu, Hg, etc.,
  • organic chemicals,
  • oils and tars,
  • toxic, explosive and asphyxiate gases,
  • combustible materials,
  • radioactive materials,
  • biologically active materials,
  • asbestos and other hazardous materials.

The catchment-scale assessment and localisation of pollution sources allow decision-makers to elaborate specific water and soil protection plans to minimise the transport of these hazardous contaminants through the landscape. Such approach is needed to limit the harmful effects in catchment as a whole, and to decrease transport and translocation of the contaminants into the food chain.

There are three main steps for implementing mitigation measures to minimise the contamination of soils and water:

  • Identification of the contaminants;
  • Assessment of the hazard;
  • Reclamation/remediation measures,

The first phase - identification of contaminants

An initial step in managing contamination is to conduct a screening assessment at the catchment scale to identify areas of potential contamination. This screening should be done for three time scales: past (based on paleolimnological studies), present, and future (based on plans for proposed development). Utilising these three time scales not only eliminates threats and risks of future problems, but simultaneously increases opportunities for appropriate and sustainable development according to ecohydrological principles.

The identification of threats can be done by elaboration of appropriate land use and contaminant concentration layers within a GIS system. Industrial development, urbanisation, and other human activities in the catchment likely to generate (or have generated) contamination can be mapped and potential directions of flow (both surface and subsurface) can be identified. The presence of following activities, inter alia, within a catchment would suggest an high probability of soil and water contamination:

  • mining and other extractive industries, especially those relating to minerals and coal,
  • smelting and refining plants, steel works, etc.,
  • scrap yards,
  • gas works,
  • waste disposal sites, especially those that pre-date sanitary landfill operations,
  • wood preservation plants,
  • tanning industries and associated trades,
  • asbestos mining and manufacturing industries,
  • pesticide manufacturing industries, areas where an high level of pesticide usage is likely, and pesticide stockpile areas,
  • fertiliser manufacturing industries, areas where an high level of fertiliser usage is likely, and fertiliser stockpile areas,
  • railway yards,
  • chemical and allied product factories and refineries,
  • explosives and munitions plants,
  • metal treatment and finishing industries,
  • paints and varnish manufacturing and distribution facilities,
  • sewage works and farms,
  • oil storage depots,
  • oil production facilities,
  • docklands and aerodromes,
  • acid/alkaline plants,
  • pharmaceutical industries and perfumes/cosmetics/toiletries manufacturers.

Second phase - assessment of hazards

The level of contamination in soil or water is dependent upon the types of human activity and the local situation. Depending upon the watershed characteristics, concentrations of some elements may increase from headwaters to main stream as a result of natural processes, underlying geology, and related factors. Other increases may be human-mediated. Such increases are usually significantly higher than those that occur naturally. Natural concentrations of lead (Pb) in soil range from 8 part per million to 57 ppm. In Poland, the average lead concentration in soils is 18 ppm dry mass of Pb. In the United States, in non-ferrous metal mining areas, lead concentrations can range from 15 to 13,000 ppm, and, in Germany, lead concentrations exceed 300 ppm dry mass of Pb in soils. Very high concentrations of lead also have been noted near highways in these countries: in Poland, concentrations range from 165 ppm to 2400 ppm; and, in the United States, from 220 ppm to 7000 ppm dry mass of Pb. Lead is an example of anthropogenic effects on soil and water contamination. Similar results have been reported for other heavy metals. Thus, it is important to know not only the level of contamination, but also the source of the contaminant, and its metabolic products and behaviour in the environment.

An optimal strategy for the remediation of environmental pollution requires information on (Shaw and Chadwick 1998):

  • the level of contamination in relation to natural background concentrations,
  • the local conditions at and upstream of the point of contamination, with special emphasis on the likelihood of pollutant transport not only in the media (i.e., the soil and water) but also within the food chain,
  • the characteristics and condition of the site (stable or unstable),
  • an assessment of environmental toxicity,
  • an assessment of human risk,
  • the transport or movement of the contaminant within the environment (based upon model outputs),
  • an assessment of the potential indirect and cumulative effects of the contaminant.

Third phase - reclamation/remediation measures

Currently, reclamation and remedial measures focus primarily on physical measures. Removal of contaminated soil from a site and encapsulation of the pollutant within a secure landfill is the most common remedial measure employed. However, this option is costly, especially if considered for use on a large scale. In addition, the potential exists for further environmental degradation if the disposal site is not constructed in such a way as to minimise surface runoff and groundwater movements (leaching) through the site. Alternative measures, such as the use of phytotechnologies are being developed and are being applied in a number of situations where contaminants are required to be stabilised. Examples include the use of vegetation to stabilise wind drift and runoff from mine dumps in southern Africa. Other plants can be used to preferentially take up specific contaminants, such as heavy metals, and limit their biological availability within a drainage system. Both terrestrial and aquatic plants exhibit specific characteristics that would permit bioremediation of disturbed sites.

 

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