Environmental variables in a holistic evaluation of land contaminated by historic mine wastes: a study of multi-element mine wastes in West Devon, England using arsenic as an element of potential concern to human health.
Unusual and unexpected concentrations of a number of elements were identified in samples of house dust, that indicated the presence of mine wastes in an area where they were not expected. In pursuing this matter, several other very unusual observations and practices, involving highly contaminated mine wastes, were also identified. Here, using an available, but not a custom-made database, the matter is pursued. In England and Wales, the usual framework within which hazards are assessed, starts with an identification of those levels of exposure to elements which are considered to be safe and acceptable. At the other extreme, levels that are considered to be hazardous are identified together with procedures for dealing with them for different situations; for example, the manner in which contaminated land is to be used. The level at which an identification of sites and their use rests with the Local Authority, such as District Councils. Although new legislation is pending; at present for the non-occupationally exposed population there are no firm values to define which levels are acceptable and those that are not acceptable. One of the elements in the samples is arsenic and, because of its well-known toxicity, this element is selected to be of prime concern. However, simultaneous exposure to the general public is from a number of other elements, such as copper, lead, zinc, antimony, molybdenum, tin, selenium and mercury which are present in the mine wastes. The collective impairment to human health, if it should occur, is far too complex to evaluate, hence a need to focus attention upon arsenic which by any standard is present in some samples at very high concentrations, for example > 1000 mg/kg. Irrespective of any changes in permitted levels of exposure to the general public in the study area, together with those that are occupationally exposed, it is the past exposure that will give rise to the present patterns of morbidity and mortality. Because of a latent period between exposure and effects for the induction of cancers, of between 5 and 20 years, past exposures cannot be ignored. They need to be evaluated before changes are made in legislation. In England and Wales, concern to health is, in practice, invoked when there is clinical evidence of harm. With the exception of a few accidents in the study area of SW England, this is not identified, hence it is accepted, in practice, to conclude that no harm accrues following acute or chronic exposure to the mine wastes. There are reasons for questioning this, but if eventually supported, then the current very high costs for remediation of land may not be necessary and brown field sites can be used for a number of purposes. The primary concern is the lack of adequate scientific and clinical data, in relation to exposure to the wastes for the past 100 years or so. For many elements, compounds and substances, the general public is being made aware of potential risks to health but often the levels are extremely low. Using basic geochemical data for any area, it is possible to evaluate the expected background levels for elements. They should serve to identify levels that are acceptable, i.e. it is impractical or uneconomic to reduce them. Within the environment, simple tests are also available that can be used to rank risks to fauna and flora. There are also well-structured clinical evaluations of harm to humans available, which can also be ranked. All three need to be considered in the establishment of safe levels of exposure. It may not be practical to identify universal levels for exposure, rather each site, area or region needs to be considered separately in order to rank the potential risks. For the study area the exposures can be extremely high; compared with the general population, the number who are exposed is probably small. It is surprising that no effects upon human health have been noted.