Natural radionuclides (NORM) in a Moroccan river affected by former conventional metal mining activities

HOSTED BY Contents lists available at ScienceDirect Journal of Sustainable Mining journal homepage: www.elsevier.com/locate/jsm Research paper Natural radionuclides (NORM) in a Moroccan river affected by former conventional metal mining activities Guillermo Manjón a , Juan Mantero a , Ignacio Vioque a,∗ , Inmaculada Díaz-Francés a , José Antonio Galván a , Said Chakiri b , Abdelmajid Choukri c , Rafael García-Tenorio a,d a Applied Nuclear Physics Group, Applied Physics II Department, ETSA, Universidad de Sevilla, Av Reina Mercedes 2, 41012, Seville, Spain b Geosciences of Natural Resources Laboratory, IbnTofail University, Faculty of Sciences, BP 133, 14000, Kénitra, Morocco c Laboratory of Polymers, Radiations and Environment, IbnTofail University, Faculty of Sciences, BP 133, 14000, Kénitra, Morocco d Spanish National Accelerator Center (CNA), Universidad de Sevilla-Junta de Andalucía-CSIC, Seville, Spain ARTICLE INFO Keywords: NORM (Naturally occurring radioactive material) Abandoned mines Moulouya river Morocco ABSTRACT The main aim of this work was to determine the levels of multiple natural radionuclides in an aquatic system (Moulouya river, Morocco) impacted by multiple abandoned Zinc and Lead mines. 238 U, 234 U, 232 Th, 230 Th and 210 Po were determined by alpha-particle spectrometry in water and sediment samples collected along the river and in samples from three pit lakes of abandoned mines, located in the Upper Moulouya catchment area. The results enabled the analysis of the different levels of impact of former mining activities, depending on the natural radionuclides. While the activity concentration of U-isotopes in Moulouya river water was slightly elevated in the vicinity of abandoned mine wastes, other natural radionuclides (Th-isotopes and 210 Po) levels were typical of a natural environment. This fact is clearly reflected in the magnitude and range observed in the distribution coefficients for the different radionuclides analyzed. 1. Introduction Natural radioactivity is omnipresent in the Earth's environment. All living beings are exposed to ionizing radiation and it is well-known that human activities such as the mining and processing of some raw materials can increase both the aforementioned exposure and the concentration of natural radionuclides in the environment. While it is true that occupational risks due to these elevated concentrations have been deeply studied and even regulated, their environmental role has not been given much consideration. The importance of measuring the radioactive environmental consequences of non-nuclear industry and mining, not related to nuclear-fuel cycle, was recently highlighted by the International Commission of Radiation Protection (ICRP) (Michalik, Brown, & Krajewski, 2013). Generate waste material from mining activities can be potentially hazardous to the environment. For this reason, mining corporations need to prioritize their management in order to prevent the contamination of ground water, rivers and lakes (Kossoffet al., 2014). The waste formed can be, in some specific cases, a source of natural radionuclides to the environment and the analysis of their behavior is imperative in order to minimize its impact. Although there are many cases of studies on rivers affected by uranium mines (Carvalho, Oliveira, Lopes, & Batista, 2007), the NORM environmental effects of non-uranium mines on aquatic systems are rarely mentioned in the literature, with a few exceptions (Barbero et al., 2014;Huang et al., 2015). Natural radioactivity in different ecosystems, which are potentially affected by non-uranium mining, are often excluded from radiological control due to the moderate levels of radioactivity, but radionuclides can play a role as tracers of metal and other anthropogenic contaminations. Some recent articles describe aquatic systems where both natural radionuclides and heavy metal concentrations have been used as tracers (González-Labajo, Bolívar, & García- Tenorio, 2001;Saç, Ortabuk, Kumru, Içhedef, & Sert, 2012). In this paper, the objective is to evaluate the possible NORM impact generated by the legacies remaining from former Lead and Zinc mining activities in the catchment area of the Moulouya river (Morocco) and to study the different behavior of the natural radionuclides analyzed once they have been incorporated in to the aquatic system. 2. Materials and methods The Upper Moulouya Lead district, Fig. 1, is crossed by the Moulouya river (Oued Moulouya), which is the most important river in Morocco. The geological and geographical description of the area is https://doi.org/10.1016/j.jsm.2019.02.003 Received 26 December 2018; Received in revised form 18 January 2019; Accepted 12 February 2019 ∗ Corresponding author.Departamento de Física Aplicada II, Universidad de Sevilla, E-41012, Sevilla, Spain. E-mail address: [email protected] (I. Vioque). Journal of Sustainable Mining 18 (2019) 45–51 Available online 15 February 2019 2300-3960/ © 2019 Central Mining Institute. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/). T presented by Iavazzo, Adamo, Boni, Hillier, and Zampella (2012). In the Upper Moulouya Lead district there are three main lead deposits: Zaida, Mibladen and Aouli (Fig. 1) that were exploited from 1972 to 1985, 1936 to 1985 and 1926 to 1985, respectively (Iavazzo et al., 2012). Mining activities have created abandoned mine sites comprised of: waste deposits, pit lakes, processing plants and waste tailings. Leaching and erosion are processes, among others, that can introduce metals and natural radionuclides into the Moulouya River and its tributaries where heavy metals and natural radionuclides could increase. The heavy metal contamination of the Moulouya river from the abandoned mines of Aouli, Mibladen and Zaida was studied by Makhoukh, Sbaa, Berrahou, and Vanclooster (2011), who observed high concentrations of metals in the vicinity of abandoned mines and facilities. However, no similar studies concerning NORM have been performed in this ecosystem. A sampling campaign was performed in 2010. Water was collected directly from the Moulouya river, some tributaries and three pit lakes. These waters were transferred into 25 L plastic bottles and 10 ml of HNO 3 were added to avoid adsorption by plastic walls. Sediment samples were collected directly at the same points as the water and stored in plastic bags. The sampling stations are shown in Fig. 1 and some physico-che- mical parameters of the waters are compiled in Table 1. The pH of the water samples shows slight alkalinity due to the presence of carbonates (Makhoukh et al., 2011). Higher pH values (around pH = 9) were also measured in the pit lake waters where the mineral is also carbonated (Makhoukh et al., 2011;Iavazzo et al., 2012) and where the nature of sediments would also be affected by mining. The high pH values are in agreement with the alkalinity of the pit lake sediments and the river substrates. The high percentage of CaO (36.77%) in the sediments of this river has been shown to be is related to its limestone nature (Bounakhla et al., 2012). The conductivity in the Upper Moulouya river is in the range of 3.3–3.7 mS/cm for the river water samples and 3.4–3.6 mS/cm for the pit lake waters. These high values can be explained by the high mineralization of the waters (Makhoukh et al., 2011). Conductivity is higher in samples collected from the Middle Moulouya river (4.8–5.5 mS/cm), because these waters could be affected by a dam Fig. 1. Map of study area showing the Moulouya river and the sampling points of this work. Table 1 Values of pH, conductivity and TDS in waters. Sample pH Conductivity (mS/cm) TDS g/l Notes Upper Moulouya HM01 8.14 3.5 1.9 Not contaminated HM02 7.56 3.6 1.9 Urban wastes AN1 8.28 3.7 2 Tributary HM03 8.07 3.6 1.9 Zaida HM06 8.09 3.6 1.9 Zaida HM13 7.86 3.3 1.8 Aouli HM20 8.58 3.3 1.8 Aouli Middle Moulouya MM01 7.86 4.8 2.6 MM02 8.24 4.5 2.4 MM03 8.15 5.1 2.7 MM04 8.21 5.1 2.7 MM05 8.06 5.5 2.9 Pit lakes HM04 9.15 3.5 1.9 Pit lake HM05 9.57 3.6 1.9 Pit lake HM07 9.23 3.4 1.8 Pit lake G. Manjón, et al. Journal of Sustainable Mining 18 (2019) 45–51 46 located upstream (between HM20 and MM01) and by urban waste. For radionuclide determination in the waters, an aliquot of 1 L which was previously acidified was taken and initially an accurate activity of 232 U, 229 Th and 209 Po was added for radiochemical yield determination. Afterwards the actinides and polonium were co-pre- cipitated from the waters with Fe(OH) 3 (Holm & Fukai, 1977) and the precipitate was separated from the aqueous solution by centrifugation. After drying, the precipitate was dissolved with 10 ml of 8 M HNO 3 . The sediments were dried, powdered and sieved after their collection and representative aliquots were traced with an accurate activity of 232 U, 229 Th and 209 Po and dissolved with acid (Lee & Lee, 2001) for radionuclide determination. The dissolution was performed using first aqua regia with H 2 O 2 and afterwards nitric acid 60%, being the obtained solution evaporated until it is dry and then dissolved with 8 M HNO 3 . From this solution, actinides were co-precipitated with Fe 3+ , and the precipitate was separated from the solution by centrifugation, dried and finally dissolved in 10 ml of 8 M HNO 3 . From the obtained 10 ml 8 M HNO 3 solutions (in both waters and sediments) the sequential isolation of the Uranium-isotopes, the Thorium-isotopes, and 210 Po was performed by using UTEVA (Uranium and TEtraValents Actinides, Eichrom trade mark) chromatographic resins. The radiochemical procedure, based on the use of UTEVA chromatographic resin as described by Casacuberta et al. (2012), provides three aqueous solutions containing, in an isolated form, the U-isotopes, the Th-isotopes and Po-210. The Uranium and Thorium sources for alpha-particle spectrometric measurements were prepared by the electrodeposition of the elements onto stainless steel planchets following the method of Hallstadius (1984). With this purpose the aqueous solutions containing Uranium or Thorium after application of the selected radiochemical procedure are evaporated until they are near to being completely dry and conditioned as described by Mantero, Lehritane, Hurtado, and García-Tenorio (2010). The electrodeposition arrangement depends on the radionuclide of interest, using the electrical intensity 1.2 A in the case of Uranium and 1.5 A for Thorium. On the other hand, a well-established method (Flynn, 1968) based on the self-deposition of Polonium on a silver or copper disc is used for obtaining radioactive sources of 210 Po from the aqueous solutions containing this radionuclide. The adaptation of the Flynn method to our laboratory conditions is described in detail by Díaz-Francés, Mantero, Manjón, Díaz, and García-Tenorio (2013). Uranium-isotopes ( 238 U, 235 U, 234 U), Thorium-isotopes ( 230 Th, 232 Th) and 210 Po activity determinations were performed by applying the alpha-particle spectrometric technique using an Alpha-Analyst, spectrometer manufactured by Canberra Co. The system is formed by eight independent chambers, each chamber being equipped with a 450 mm 2 PIPS detector, model A450-18AM, manufactured by Canberra Co. Only two chambers were used for 210 Po measurements, two other chambers were used for Thorium-isotopes measurements and the remaining four chambers were used for Uranium-isotopes determinations. Activity determinations were performed by applying the isotope-dilu- tion technique. 3. Results and discussion The U-isotopes and 210 Po results obtained in the analysis of the water samples are listed in Table 2. 238 U activity concentrations range from 9.4 to 203 mBq/l (Upper Moulouya river), from 6.6 to 22.8 mBq/l (Middle Moulouya River), and from 235 to 1979 mBq/l (pit lakes of abandoned mines), while the 234 U/ 238 U activity ratios range from 1.9 to 3.4 (Upper Moulouya river), from 1.8 to 2.0 (Middle Moulouya river), and 4.3–5.4 in the pit lake water samples. The 210 Po activity concentrations in the same waters were in the range of 0.7–2.7 mBq/l (Upper Moulouya River), 1.5–13.2 mBq/l (Middle Moulouya river), and 2.3–4.7 mBq/l (pit lake water samples). Mining has previously been considered a source of contamination in the Moulouya river and pit lakes, in the zone of Zaida, when trace metals were only considered ((Bounakhla et al., 2012). The results obtained in this work indicate that this last conclusion can be extended to include U-isotopes. The evidence that mining activities can be a potential source of uranium in to the nearby environment is reflected in the higher activity concentrations found for 238 U and 234 U in the waters of the Moulouya river located near Zaida (a mining area), which reached one order of magnitude higher than typical levels of uncontaminated rivers (Martínez-Aguirre & García-León, 1992)(Table 2). Additionally, the U-isotope activity concentrations in the three pit lakes are one to two orders of magnitude higher than in uncontaminated waters collected in rivers of southern Spain (the high levels of uranium in dissolution in the pit lakes is an indication of the potential tendency of this radionuclide to leach from wastes, tailings and residues located in the surroundings that can finish in the river). In summary, mining can be considered as a U source that is impacting on the Moulouya aquatic system as this can be deduced from the results obtained in sampling points HM03 and HM06 located in Zaida City, in the vicinity of abandoned mines, where the 238 U activity concentrations reach 203 ± 4 mBq/l. Similar conclusions can be deduced from the analysis of the 238 U results corresponding to the sampling points located in the Aouli mines area (particularly HM13). However, according to Table 1, pH and conductivity have similar values in all the samples analyzed and a relationship between U-isotope activity concentration to pH or conductivity is not observed. The high radionuclide levels can therefore only be related to former mining activities. The presence of U in dissolution is favored by the formation of soluble uranium carbonated complexes when there is a leaching process from the treated substratum. The presence of Uranium dissolved in water can thus be explained by the formation of carbonates (Broecker, 1974). The existence of U impact in the Upper Moulouya river is reinforced by observing the obtained 234 U/ 238 U activity ratios in the waters analyzed. In the river samples with higher Uranium concentrations, such as HM06 the value of this activity ratio (3.45 ± 0.09) is in good agreement with the 234 U/ 238 U activity ratios found in the pit lake waters which were in the range of 4.3–5.4. 234 U/ 238 U activity ratios higher than unity are usually explained by the nucleus recoil after alpha particle emission. In a lixiviation process 238 U daughters ( 234 Th, 234 Pa and 234 U) would have enough energy to break the chemical bonds (Coward Table 2 U-isotopes and 210 Po activity concentrations (mBq/l) in water samples. Sample Code 238 U 234 U 234 U/ 238 U activity ratio 210 Po Upper Moulouya: river water samples HM01 9.4 ± 0.5 21.4 ± 0.8 2.28 ± 0.15 0.9 ± 0.2 HM02 17.9 ± 1.1 34.3 ± 1.6 1.92 ± 0.15 2.0 ± 0.3 AN1 3.6 ± 0.4 7.6 ± 0.6 2.13 ± 0.29 2.7 ± 0.3 HM03 177 ± 5 57 ± 13 3.25 ± 0.11 1.1 ± 0.2 HM06 203 ± 4 702 ± 12 3.45 ± 0.09 2.5 ± 0.3 HM13 56 ± 2 117 ± 3 2.07 ± 0.09 2.3 ± 0.3 HM20 14 ± 1 27.6 ± 1.4 1.92 ± 0.16 0.7 ± 0.1 Middle Moulouya: river water samples MM01 21 ± 1 38.2 ± 1.4 1.80 ± 0.11 4.0 ± 0.4 MM02 10.9 ± 0.7 20.1 ± 1.0 1.85 ± 0.15 13.2 ± 0.8 MM03 6.6 ± 0.6 10.5 ± 0.8 1.60 ± 0.18 12.0 ± 0.8 MM04 14.7 ± 0.9 28.5 ± 1.3 1.94 ± 0.14 3.8 ± 0.5 MM05 22.8 ± 0.9 46.1 ± 1.5 2.02 ± 0.10 1.5 ± 0.2 Pit lake water samples HM04-3 1979 ± 169 8564 ± 671 4.33 ± 0.50 2.7 ± 0.3 HM05-3 443 ± 8 1921 ± 32 4.34 ± 0.11 2.3 ± 0.3 HM07 235 ± 14 1267 ± 62 5.40 ± 0.41 4.7 ± 0.5 Typical uncontaminated level range Uncontaminated 11–32 a 13–40 a 1.0–1.6 a 3 b a Martínez-Aguirre & García-León, 1992. b Persson & Holm, 2011. G. Manjón, et al. Journal of Sustainable Mining 18 (2019) 45–51 47 & Osmond, 1974). In the case of 210 Po, the activity concentrations found along the entire water course were similar to the ones found in uncontaminated rivers (Persson & Holm, 2011). Quite low activity levels are found in the pit lakes waters and in all the Moulouya river waters regardless of the place of sampling collection. Undetectable enhanced levels were observed in the upper Moulouya river waters collected in the vicinity of the former mining activities. This lack of 210 Po environmental impact is not surprising due to the tendency of this radionuclide to be present in aquatic systems associated with particulate matter and its very low tendency to leach (Barbero et al., 2014). In all the waters the activity concentration of Th-isotopes ( 232 Th and 230 Th) was also determined and the results are shown in Table 3. The activity concentrations of 232 Th found were to be in the range of 0.2–1.3 mBq/l, while the activity concentrations of 230 Th were from 0.1 to 8.4 mBq/l across the whole set of water samples. This set of results reflects a lack of this element's impact in the Moulouya river. Similarly to Po, the tendency of Th is to remain associated to solid fractions in aquatic systems. The distribution coefficient of this element, in surface waters, is usually one or two orders of magnitude higher than those observed for U. Even in carbonated solutions the Th did not form soluble compounds. In surface aquatic systems the 230 Th/ 234 U activity ratio is usually very low (Ku, 1976). The 238 U, 234 U, 210 Po, 230 Th and 232 Th activity concentrations determined in sediment samples are listed in Tables 4 and 5. The U levels found were, in general, quite moderate (with the exception of the HM03 sample) with 238 U activity concentrations ranging from 4.0 to 15.2 mBq/g in Upper Moulouya, from 8.8 to 11.9 mBq/g in Middle Moulouya and from 28 to 39 mBq/g in pit lakes. The corresponding 234 U/ 238 U activity ratios were in the range of 1.1–2.2 in sediments collected along the whole of Moulouya river, while this activity ratio ranges from 2.5 to 3.8 in the pit lake sediments. The U impact observed in the waters is not unambiguously distinguishable in the sediments, which is in agreement with the hypothesis that the U incorporated in to the Moulouya river is mostly dissolved after leaching in the abandoned mining area and afterwards is transported to the river's watercourse where is diluted. The activity concentrations of 210 Po in the same sediments were in the range of 31–71 mBq/g along the Upper Moulouya river, 28–72 mBq/g along the Middle Moulouya river and 16–62 mBq/g in the pit lake sediments. In the case of 230 Th the activity concentrations along the Moulouya river were between 8.5 and 17.5 mBq/g, whereas the range in the pit lake samples was 26–39 mBq/g. For both elements, Th and Po, the activity levels found are in the range of values observed in riverbed sediments worldwide which are not affected by anthropogenic inputs (Gonzalez-Labajo, Bolívar, & García-Tenorio, 2001). Some additional information about the behavior of the natural radionuclides analyzed and the possible anthropogenic impact generated by the former mining activities in the Upper Moulouya catchment area can be obtained through the study of the distribution coefficients (K d ) found for the analyzed radionuclides along the whole Moulouya watercourse. The determinations performed at the same sampling point in both waters and sediments enables the determination of the distribution coefficients (K d, l/kg), defined as the quotient of 238 U activity concentration in sediment (mBq/kg) and water (mBq/l). In Fig. 2 the K d values for U and Po are shown for comparison, which led to the following comments: a) The K d obtained for Po-210, as expected, is clearly higher than the K d of Uranium due to the known tendency of the Po to be bound to particulate matter in opposition to the more conservative behavior of Uranium in aquatic systems. b) A good correlation is found between the K d (U) values and the Uranium concentrations determined in the waters, as shown in Fig. 3.K d decreases when the Uranium concentrations in the waters increase. Higher K d (U) values, reaching 10 3 , were determined in the sampling points less influenced by mining, while values as low as 10 1 were determined in the pit lakes, indicating the tendency of the uranium to be in dissolved form in environments rich in carbonates. The sediments in the pit-lakes show higher U activity concentration values than those in the riverbed sediments indicating that a fraction of anthropogenic U can accumulate, but it has a higher tendency to Table 3 232 Th, 230 Th and 234 U activity concentrations (mBq/l) in waters. Sample Code 232 Th 230 Th 234 U River water samples HM01 0.5 ± 0.2 1.7 ± 0.3 21.4 ± 0.8 HM02 0.4 ± 0.2 1.1 ± 0.3 34.3 ± 1.6 HM03 0.8 ± 0.4 1.6 ± 0.5 7.6 ± 0.6 AN1 0.8 ± 0.3 2.9 ± 0.6 576 ± 13 HM06 0.32 ± 0.14 2.4 ± 0.4 702 ± 12 HM13 1.3 ± 0.5 8.4 ± 1.1 117 ± 3 HM20 1.1 ± 0.3 4.2 ± 0.7 27.6 ± 1.4 MM01 1.4 ± 0.3 3.5 ± 0.5 38.2 ± 1.4 MM02 3.0 ± 0.6 7.0 ± 0.9 20 ± 1 MM03 0.12 ± 0.09 0.1 ± 0.05 10.5 ± 0.8 MM04 0.2 ± 0.1 1.2 ± 0.3 28.5 ± 1.3 MM05 0.9 ± 0.3 2.2 ± 0.4 46.1 ± 1.5 Pit lakes water HM04 0.2 ± 0.1 0.7 ± 0.2 8564 ± 671 HM05 < AMD ± 2.8 ± 0.2 1921 ± 32 Table 4 U-isotopes and 210 Po activity concentrations (Bq/kg) in sediment samples. Sample Code 238 U 234 U 234 U/ 238 U activity ratio 210 Po Upper Moulouya: river sediment samples HM01 4.0 ± 0.8 4.92 ± 0.9 1.46 ± 0.14 43.3 ± 2.3 HM02 7.9 ± 0.9 8.80 ± 1 1.2 ± 0.3 71 ± 8 AN1 7.6 ± 0.6 12.93 ± 0.8 1.7 ± 0.2 28.0 ± 1.2 HM03 52 ± 2 197.00 ± 7 1.1 ± 0.2 1.7 ± 0.5 HM06 8.8 ± 0.8 23.40 ± 1.4 2.16 ± 0.14 31 ± 5 HM13 9.8 ± 0.8 13.00 ± 0.8 1.2 ± 0.1 HM13F 11.1 ± 0.6 13.29 ± 0.7 1.20 ± 0.09 54 ± 2 HM20 15.2 ± 0.8 17.64 ± 0.9 1.16 ± 0.09 39.4 ± 1.4 Middle Moulouya: river sediment samples MM01 9.3 ± 0.6 11.04 ± 0.6 1.2 ± 0.1 40 ± 2 MM02 8.8 ± 0.5 11.22 ± 0.6 1.3 ± 0.1 46 ± 2 MM03 10.1 ± 0.6 12.27 ± 0.7 1.2 ± 0.1 52 ± 2 MM04 10.5 ± 0.6 12.63 ± 0.6 1.20 ± 0.09 72.5 ± 2.5 MM05 11.9 ± 0.7 13.87 ± 0.8 1.17 ± 0.09 29.0 ± 1.2 Pit lake sediment samples HM04 38.5 ± 1.7 97 ± 3 3.8 ± 0.2 62 ± 8 HM05 28 ± 1 44.5 ± 1.4 2.52 ± 0.14 HM07 16 ± 4 Table 5 232 Th, 230 Th and 234 U activity concentrations (Bq/kg) in sediments. Sample Code 232 Th 230 Th 234 U River sediment samples HM01 14.9 ± 0.9 9.6 ± 0.7 4.9 ± 0.9 HM02 24.5 ± 1.7 14.3 ± 1.2 8.8 ± 1.0 AN1 11.7 ± 1.1 8.5 ± 0.9 12.9 ± 0.7 HM03 18.4 ± 1.2 11.5 ± 0.9 197 ± 7 HM06 13.7 ± 1.2 10.6 ± 1.0 23.4 ± 1.4 HM13 14.9 ± 0.9 15.0 ± 0.9 13.0 ± 0.8 HM20 23.7 ± 1.6 16.2 ± 1.0 13.3 ± 0.7 MM01 12.7 ± 0.8 15.3 ± 0.9 11.0 ± 0.6 MM02 9.6 ± 0.7 14.3 ± 0.9 11.2 ± 0.6 MM03 13.4 ± 0.7 16.6 ± 0.8 12.3 ± 0.7 MM04 15.8 ± 0.8 17.8 ± 0.9 12.6 ± 0.6 MM05 17.1 ± 0.9 17.5 ± 0.9 13.9 ± 0.8 Pit lakes sediment samples HM04 13.7 ± 1.0 38.8 ± 1.9 97 ± 3 HM05 14.9 ± 0.9 26.2 ± 1.2 44.5 ± 1.4 G. Manjón, et al. Journal of Sustainable Mining 18 (2019) 45–51 48 Fig. 2. Distribution coefficients (K d, l/kg) for U and Po, defined as the quotient of activity concentration in sediment (mBq/kg) and water (mBq/l). Fig. 3. K d (U) versus 238 U activity concentrations in the water samples. Fig. 4. K d (Po) versus 210 Po activity concentrations in the water samples. G. Manjón, et al. Journal of Sustainable Mining 18 (2019) 45–51 49 dissolve. Consequently, the sediments of the analyzed pit lakes cannot be considered a sink of U, in the sense that the majority of the U existing in the water ecosystem does not accumulate. c) The K d of Po is less sensitive to the concentrations found for this radionuclide in the waters, as can be observed in Fig. 4. These conclusions reinforce previous comments which state that nowadays the impact of former mining activities in the Moulouya river waters is restricted only to the presence of Uranium, due to its tendency to be in dissolved form as carbonates, while no influence is observed for 210 Po and Th isotopes. The analysis of the 230 Th/ 234 U activity ratios also reinforces the main conclusion of this work. This activity ratio has a value near unity in the majority of the samples (waters and sediments), particularly those from sampling points located far from the mining area (Fig. 5). However, the ratio is lower than 1 in the sediment pit lakes and in the sampling points near the abandoned mines, again indicating the presence of some anthropogenic Uranium. In the case of the river waters, the 230 Th/ 234 U activity ratio was in the range of 10 −2 to 1 with a tendency for activities ratios to decrease when the Uranium concentration in water increases. This activity ratio is in the range of 10 −4 to 10 −2 in the water samples collected in pit lakes and in a river water sample (HM06) located not far from the mines, reflecting the tendency of Uranium to be in dissolved form. 4. Conclusions Natural radionuclides (U-isotopes, 210 Po, 230 Th and 232 Th) activity concentrations were measured in samples of water and sediment collected along the Moulouya river (east Morocco) and in some pit lakes formed in abandoned mines nearby. High Uranium concentrations were found in the waters of pit lakes formed by former open air mines; these levels are associated with the presence of carbonates. In addition, relatively high levels of U were also observed in water taken from sampling points of the Moulouya river located in the vicinity of former mines, indicating the local impact of the former mining activities on the aquatic system. The impact of U in the waters of the Upper Moulouya region was confirmed through the analysis of the corresponding K d (U) values and the 230 Th/ 234 U activity ratios. Although the mining impact is not easily determined when U levels in the sediments of the Moulouya river are compared, the lower values of the 230 Th/ 234 U determined in the sediments collected in the vicinities of the abandoned mines could be considered as an impact evidence. However, nonenhanced levels in waters and sediments were found for 210 Po, 230 Th and 232 Th, reflecting the lower tendency of these radionuclides to be in dissolution even in solutions rich in carbonates. The impact of the former mining activities in relation to these last radionuclides should be considered as negligible. Conflicts of interest None declared. Ethical statement Authors state that the research was conducted according to ethical standards. Funding This work has been partially financed by the Spanish Agency of International Cooperation and Development (AECID) of the Government of Spain. Acknowledgments This work has been partially financed by the Spanish Agency of International Cooperation and Development (AECID) of the Government of Spain. The authors gratefully acknowledge the laboratory assistance of J. Díaz. References Barbero, L., Gázquez, M. J., Bolívar, J. P., Casas-Ruiz, M., Hierro, A., Baskaran, M., et al. (2014). 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