Depleted Uranium

Proposal for a Research Programme on Depleted Uranium: Health, Safety And Environmental - Pathway

4.1 Pathway

4.1.1. This term describes DU movement in the environment. When DU munitions are tested or used in combat, varying amounts of dusts of mixed U oxides and metal fragments are produced in the vicinity of an impact. This dust may be inhaled or enter the food chain through the ingestion of DU dust on food or in surface waters and the various forms of DU may migrate to groundwater used as a drinking water source. Direct inhalation and ingestion are potential routes of intake from the instant the dust is released, but incorporation of DU into foodstuffs or groundwater via a range of mechanisms may occur over tens or hundreds of years.

4.1.2. Only a small amount of work has been done on the transport of DU, but a World Health Organisation (WHO) report (55) notes that there have been countless papers and reviews on the transport of U (e.g. see (56)). The report also notes that some aspects of U’s behaviour are still uncertain. U in typical ground and surface waters is generally dominated by carbonate species although sulphate and phosphate may be important in other circumstances. Carbonate species are highly mobile in most soils. In arid and semi-arid environments U may be particularly mobile but under weakly acidic conditions, typical of wetter climes, U may form stable complexes with soil organic matter resulting in retention and accumulation; although dissolution and mobilisation of soil bound U may be assisted when a significant proportion of the organic matter is in the dissolved form. U may be transported from soils and sediments into watercourses as, or sorbed onto, particulate matter during storms or other modes of physical erosion (55).

4.1.3. Most work on levels of uranic materials in the food chain has focussed on natural U rather than DU and there is relatively little data on the concentration of U in staple foods from contaminated environments (55). Studies at arid DU contaminated firing ranges indicate DU is relatively non-toxic to grasses (57), but studies on U contaminated land suggest it may have a detrimental effect on wheat productivity (58). The WHO note that these results are consistent with plants that form the basis of some U phyto-remediation methods (59) and observations made during studies of natural analogue sites, particularly in the Solway estuary where the translocation of U into fungal materials and plants has been studied (60). Data on the concentration of U or DU in exposed and unexposed farm animals is scarce (55). Deposition of relatively insoluble DU compounds on vegetation and soil and its subsequent uptake by grazing animals is probably of most importance. The research proposed in Section 4.3 on DU environmental transport mechanisms will address concentrations of DU in materials and organisms affecting the food chain. There is considerable literature on human ingestion of soils and dusts (55) and no further work is required in this area.

4.2.1 Most DU studies to date use very simple models to calculate airborne and surface DU levels that are translated into intakes or compared with health and safety or environmental standards (3,22,61,62). Worst-case scenarios have been studied because of the limited quality and quantity of the input (i.e. source) data and the approach has limitations with regard to long term mobilisation and distribution effects (55). More sophisticated approaches use models requiring knowledge of transfer parameters which describe DU movement in the environment (63-77). These approaches have been applied on a site-specific basis but the results cannot be used generically as DU behaviour is highly dependent on local geology and soil chemistry (55). Very detailed geochemical approaches have been used in a wide range of studies on U dispersal at natural analogue sites (56,60,78) in support of nuclear industry requirements, but such approaches have not yet been applied to or addressed in the context of studies of DU munitions, hence more DU specific research is needed.

4.2.2. There are a number of Government (21,79-82) and independent reviews (1,3,4,22,83,84) based on the use of the less-sophisticated environmental models. In all cases these reports are consistent with the experimental observation that most DU is initially contained within tens of metres of the point of impact and that this gradually dilutes and disperses. Practicable precautions should be taken in these areas, but no action is required in the surrounding essentially uncontaminated land and the overall risks are low. Some reviews are in peer reviewed journals (4,83,84) and the most authoritative independent work is by the UNEP (3,22) whose conclusions support MOD’s assessments (80,85,86) of DU munitions risks. A new assessment would simply duplicate previous work unless a radically different approach (e.g. based on systematic geochemical studies) or new experimental data was available. A review of existing modelling methodologies is proposed to compare and contrast the results of published findings. Work to assess the relevance of geochemical models of radioactive material transport will also be undertaken.

4.2.3. The major MOD work is the publicly available environmental impact assessment of DU test firing published by W S Atkins in 1995 (87-89). The UK is probably the major source for information relating to U and DU in the marine environment but there is a need for further studies to be undertaken specifically where DU has been fired into the sea. Further work is required to fully understand the fate of DU in seawater and the consequences for marine life. This work links in with the proposed work on fired and unfired DU rounds described at para. 3.7.2. and will be supported by controlled laboratory studies on DU corrosion and dissolution rates. More success is being achieved in a continuing study to understand the fate of DU in the terrestrial environment at the Eskmeals and Kirkcudbright ranges. These studies are being conducted using unfired DU.

4.3.1. MOD consider that there is a considerable body of knowledge on the behaviour of natural U in the environment from the study of radioactive waste and the mining and processing of natural ore deposits. An important task is to determine to what extent this information can be applied to DU. This is particularly important for assessing the longer-term environmental risks and is consistent with the WHO view on DU (55,90) that research priorities should focus on investigating leaching and subsequent environmental cycling of specific forms of U derived from industrial and military sources. Understanding the transport mechanisms and processes associated with "point sources" (i.e. localised events) is essential to assessing the short and long term environmental impact of DU use and we are proposing to ask the Natural Environment Research Council (NERC) to advise on and manage a research programme in this area. One particular issue is the heterogeneous nature of DU contamination on both firing ranges and battlefields. This heterogeneity emphasises the importance of understanding site specific, rather than generic, exposure. Whilst generic non-site specific information is available for U, there is a lack of information relating to the potential bioavailability of DU specifically derived from munitions. Information from such detailed studies will provide a firm foundation for subsequent evaluations of long-term human and environmental effects and indicate to what extent the existing knowledge base can be used in the context of the military use of DU.

4.4.1. Little monitoring has been carried out in areas where DU munitions have been used in combat and what has been done is focussed on current military bases rather than battlefields (91,92). Locating suitable sites is difficult, as battle-damaged vehicles have been removed. UNEP did not manage to identify any areas of DU contamination in Kosovo in 1999 (22) but, following the provision by the US of grid references of locations where DU munitions were used, they found some contaminated points, where penetrators were recovered, during a further survey in November 2000. A report of their findings has been published (3). The report stated that 'the analyses of the samples collected showed only low levels of radioactivity'. Furthermore, the results suggested that there is no immediate cause for concern regarding toxicity. However, major scientific uncertainties persist over the long-term environmental impacts of DU, especially regarding groundwater. The research proposed in Section 4.3 will provide useful input to this latter point. Further information on conditions in areas where DU munitions have been used in armed conflicts is arising from the enhanced environmental surveillance being carried out (93) or planned (94) by military missions and international organisations in the Balkans and there is a need to collect and review the emerging data.

4.5.1. A great deal of monitoring has been carried out around the UK (95-104) and US ranges (63-77, 105) where DU munitions are tested. These surveys have reported that DU testing has had a negligible impact on the environment, other than in some localised areas within ranges where remediation should be carried out before unrestricted access is allowed. Monitoring of the working conditions at firing ranges has also been carried out, but such information has not been collated. A review of all the available information is required to identify where advances in best practice could be used to enhance the understanding of the impact of DU in these areas of comparatively heavy use. Work should be undertaken to collate the information and publish it.

4.6.1. Many reference quantities can be compared with DU deposits on battlefields. These include: the average range of activity concentration of U in the earth's crust (63), the U content of ambient air and certain common rocks and ores (63), typical activity concentrations of U in freshwater, groundwater and seawater (106,107), the mean daily intake from drinking water (63,106), the average intake of U in food (63,104) and guidelines for the levels of U in drinking water laid down by the WHO (108). Thus there is no need for further work in this area.

Last Updated: 14 Mar 02