From the preliminary screening surveys [1,2] uranium was found to be the main radioactive element present, and has both a potential for a chemical toxicity and a radiological hazard. Current DWAF Water Quality Guidelines [7] give criteria for uranium-238 concentrations in drinking water. These criteria are based on the chemical toxicity of uranium to the kidney rather than its radiological toxicity.
From a radiological perspective, it is the total radiation dose from all radionuclides in the water that is important, and the Technical Committee has proposed interim guidelines in this regard, taking into account the following:
The World Health Organization (WHO) recommends a reference level for radiation dose, received from the continuous consumption of drinking water for a full year, of 0,1 mSv/a [8]. This value is only about 5% of the dose from the total natural background, and can therefore be regarded as an ideal situation. From section 3.3 it can be deduced that, on the conservative basis of the linear non-threshold theory, a radiation dose of 0,1 mSv/a represents a probability of attributable fatal cancer of 4 in 10 000 over a 70 year lifetime. By contrast, cancer from all causes is responsible for about 2 000 in 10 000 deaths, it thus being evident that, for the WHO reference level of 0,1 mSv/a, the increase in the probability of cancer induction, if it exists at all, is insignificantly small.
The dose limit to members of the public due to all anthropogenic sources is currently recommended internationally at 1 mSv/a [4,5], and this has been implemented in several countries. This value is based on acceptance of the linear non-threshold theory, and can therefore be regarded as conservative.
The dose limit for members of the public, recommended internationally, was previously 5 mSv/a, and many countries still adopt this limit. It is common practice in uranium mining remedial action programmes to design the programmes such that compliance with the 5 mSv/a limit is achieved in the short term, and with the 1 mSv/a limit in the longer term.
Dose limits to members of the public relate to the combined effect of all exposures from human activities. It is common practice to place a dose constraint on releases from individual facilities. Such a constraint is normally set at some fraction of the dose limit of 1mSv/a - commonly of the order of 0,25 mSv/a, i.e., allowing for the combined dose from up to four separate facilities on a single individual not exceeding the 1mSv/a limit. Although this approach is intended for new rather than existing operations, it may have some relevance to water systems in gold mining areas in that it embodies the concept of allowing for doses from other sources of exposure without causing the 1 mSv/a dose limit to be exceeded. The reference value of 0,25 mSv/a is the dose limit already imposed by the CNS on individual mines in the Mooi River catchment.
Table 2 gives information on the DWAF guidelines for uranium, while Table 3 embodies the proposed guidelines on radiation dose in drinking water. The DWAF guidelines have taken into consideration all the above limits for the protection of the public from anthropogenic sources of radiation.
The basis for the colour coded classification system was chosen to be in line with the approach used in the joint Assessment Guide, published by DWAF, the Department of Health, and the Water Research Commission [9]. The meaning of the colour classes for chemical constituents given in this DWAF/DOH/WRC guide are as follows:
Blue, class 0 = Ideal water quality. Suitable for lifetime use.
Green, class I = Good water quality. Suitable for use, rare instances of negative effects.
Yellow, class II = Marginal water quality. Conditionally acceptable. Negative effects may occur in some sensitive groups.
Red, class III = Poor water quality. Unsuitable for use without treatment. Chronic effects may occur.
Purple, class IV = Dangerous water quality. Totally unsuitable for use. Acute effects may occur.
The practical meaning intended for interpretation of the classes is that "blue" or "green" water is fit for lifetime use without any further questions. Yellow class or marginal water, is however, only fit for interim use, and should not be used for a lifetime if at all possible. Red and purple class water are seen as unfit for use.
| Uranium-238 (Bq/l ) | Uranium-238 (mg/l ) | Effects | Colour Class |
| Target water quality range 0 to 0,89 Bq/l | Target water quality range 0 to 0,070 mg/l | No significant effects. Annual cancer risk less than 1 in 4 000 000. | Blue, Ideal(<0,25 Bq/l ) and Green (0,25 to 0,89 Bq/l ) |
| 0,89 to 3,6 | 0,070 to 0,284* | Annual cancer risk less than 1 in 1 000 000. May potentially be a slight risk of renal toxicity in sensitive individuals where renal function is impaired, but unlikely to have demonstrable renal toxicity in healthy individuals. | Yellow |
| 3,6 to 18 | 0,284 to 1,42 | Annual cancer risk less than 1 in 200 000, but significant risk of chemical toxicity with renal damage. | Red |
| >18 | >1,42 | Increasing cancer risk in long term. Increasing risk of renal damage in short term. | Purple |
* If 0,284 mg/l is exceeded, human health may be at risk due to chemical toxicity.
| Radiation dose (mSv/a) | Suitability | Action required | Colour Class |
| £ 0,1 (WHO reference level) | Ideal, suitable for lifetime use | Water complies fully with radioactivity guideline. No further action necessary | Blue (ideal) |
| >0,1 and £ 0,25 | Water acceptable for lifetime use, subject to confirmation of dose. | Confirm dose level in respect of specific nuclide analysis | Green (acceptable for lifetime use). |
| >0,25 and £ 1 | Water acceptable for short term use. Use in longer term (lifetime) requires further investigation. | An environmental impact assessment may be necessitated | Yellow (acceptable for short term use) |
| >1 and £ 5 | Unacceptable for lifetime use | Remediation required over a reasonable time period. | Red (Unacceptable for lifetime use) |
| >5 | Unacceptable even for short term use | Immediate remediation required | Purple (Unacceptable even for short term use). |