Electronic authentic instruments (documents)

4.3.3.3. Total effective dose

For an igneous phosphate mining and beneficiation facility in South Africa, summing of the doses from external gamma exposure and inhalation of airborne dust gives total annual effective doses in the range 0.1–1 mSv (Table 12). The mean total annual effective dose received by workers in sedimentary phosphate mining and beneficiation facilities in Florida, USA, was calculated from measured exposure levels and found to be in the range 0.12–0.30 mSv [53]. In the mining area at this plant, 75% of the total dose arises from external exposure whereas in ore crushing, grinding and screening locations the reverse is the case, with the majority of the dose arising from internal exposure.

(c) Ingestion of foodstuffs affected by water and soil contamination through leaching and dust fallout;

(d) External gamma radiation from contaminated soil and bulk residues.

Exposure of members of the public, irrespective of the pathway involved, is likely to be very low because mining and beneficiation operations tend to be conducted at considerable distances from residential areas and involve materials with low activity concentrations. Most rock handling and processing operations are conducted under wet conditions. Under unfavourable wind conditions, it is possible for members of the public to be exposed to radionuclides in airborne dust generated by the crushing, milling and drying of rock. The migration of radionuclides from mining and residue management facilities into water bodies could result in the contamination of drinking water and food but, again, this exposure pathway is not expected to be significant, particularly because process water is usually recycled within the facility.

A study was conducted to determine if there was an elevated health risk due to ingestion of radionuclides (²²⁶Ra and ²¹⁰Pb) or toxic metals (cadmium, lead and mercury) in fish harvested from lakes on previously mined lands in the central Florida phosphate region [60]. The study examined ten lakes in total:

(a) Four unreclaimed lakes (pit lakes that are formed when strip mining cuts fill with water and the site is abandoned for nature to recover with no attempt to reclaim the land);

TABLE 13. EXPOSURE OF WORKERS INVOLVED IN THE TRANSPORT OF PHOSPHATE ROCK [58]

Exposure situation Dose rate (μSv/h) Annual dose (mSv)

Sea transport, loading 0.10 0.09

Inland ship:

Loading 0.26

Transport 0.10

Overall 0.18

Railway, loading and unloading 0.26 0.29

Truck:

Loading and unloading 0.26

Transport 0.16

Overall 0.33

(b) Two reclaimed lakes (lakes created as part of the mining process that are contoured, vegetated and stocked with fish to resemble and function like natural lakes);

(c) Three natural lakes (lakes in the study area that were formed by natural means and regarded as ‘control’ lakes unaffected by mining);

(d) One reservoir (an artificially constructed lake that was unrelated to phosphate mining).

Six species of fish were sampled, representing those most commonly consumed by humans. The radionuclide data indicated no significant health risk attributable to the former mining activities. Radium is known to concentrate in bones, but the bones of fish are not normally consumed in the study region and so the risk from bones was largely discounted. There was no difference in lead or cadmium levels among the different types of lake. However, it was noted that mercury levels in fish from natural lakes were higher than in those from the mining-impacted lakes and may be due to the fact that natural lakes tend to be TABLE 14. ESTIMATED INCREMENTAL DOSE RECEIVED BY A MEMBER OF THE PUBLIC LIVING NEXT TO AN IGNEOUS PHOSPHATE MINING AND BENEFICIATION FACILITY [61]

Source of dose Annual committed effective dose (rounded) (μSv)

Gamma radiation from soil 0.004

Inhalation:

Airborne dust 16

Radon 1

Ingestion:

Leafy vegetables 0.1

Root vegetables 0.3

Fruit 0.1

Meat 3

Milk 0.6

Cereals 0.1

Poultry 0.2

Eggs 0.07

Total 21

much older and have greater surface to volume ratios (more shallow areas), which provide more time and surface area to capture global fallout of mercury.

Another study in Florida, USA, surveyed radioactivity in food produced from a variety of land types, including mined lands (concentrating on lands which were reclaimed after phosphate mining) and unmined lands underlain with phosphate deposits [62]. More than 100 food samples were collected from 62 land parcels and analysed. This was followed by a study that investigated, more broadly, the presence of radioactivity in locally grown or caught foods, concentrating mainly on foods grown on reclaimed clay lands [63]. In extensive studies of foods grown on mined lands [62, 63], the doses were found to be trivial (less than 10 μSv/a).

Approximately 70 individual food samples were collected from five land parcels in the central Florida phosphate district and analysed for ²²⁶Ra, ²¹⁰Pb and

210Po. Corresponding soil samples were collected and analysed both for these radionuclides and for a variety of soil chemistry parameters. The results of the radioactivity and soil chemistry analyses of these samples were integrated into the database, which had been created from the initial study, and a variety of statistical analyses were conducted on this integrated data set [63]. The results of these analyses indicated that the concentrations of ²²⁶Ra and ²¹⁰Pb in edible crops grown on mined phosphate lands were statistically higher than those in crops grown on unmined phosphate lands. However, the ²¹⁰Po concentrations were extremely low, with many being below the lower limit of detection, and the dose from food consumption was only a small fraction of that received by an average individual from other environmental sources of radioactivity. An individual who sourced all the sampled food types from the reclaimed clay land areas and all remaining food types from the general food pool was estimated to receive a committed effective dose of 191 μSv in a year from food consumption. By comparison, the corresponding ingestion dose received by an individual obtaining all food from the general food pool was estimated to be 164 μSv. Thus, the incremental ingestion dose attributable to the former mining operation was only 27 μSv per year. Two beef samples were analysed, one from mined land and one from unmined land. Each sample was replicated three times, yielding a total of six beef observations. The geometric mean values of ²²⁶Ra activity concentration were 0.000147 and 0.000126 Bq/g for mined and unmined land, respectively. The difference between these results is statistically insignificant.

A dose assessment was conducted at an igneous phosphate mining and beneficiation facility in South Africa [61]. The assessment considered a member of the public residing on the perimeter of the facility, with all drinking water being obtained from an external source that was not influenced by the operation of the facility. The doses attributable to the operation of the facility were estimated from measurements of the concentrations of radionuclides in various

environmental media, including surface water, groundwater and food, using conservative assumptions. The results are given in Table 14.