Etude de lʹinfluence du milieu environnant sur la composition minérale dʹune rivière marocaine en utilisant lʹactivation neutronique et lʹICP/MSEnvironmental control of Boufekrane river water basins by neutron activation analysis and ICP/MS

Instrumental neutron activation analysis (INAA) and inductively coupled plasma/mass spectrometry (ICP/MS) have been performed to study the degree of contamination due to toxic heavy metals and other pollutants in water and sediments of a Moroccan river. Water and sediments samples have been collected from seven locations from this river along 41 km, as shown in Fig. 1. The sediment samples were irradiated in the Osiris nuclear reactor in an epithermal neutron flux of 1013 n cm−2 s−1 for 2 h in high purity aluminium paper. The gamma-rays subsequently emitted were measured for 1 h, after a decay time of 1 and 15 days, with a coaxial GeLi detector coupled to a 4600 pulse-height analyser. The computational K0 method was used to determine the concentration of elements of interest (Elmir, 1994; El Nimr et al., 1981). As summarized in Table 1 and presented in Figs 2, 3 and 4, the results showed maximum concentrations for As, Ba, Br, Co, Cr, Cs, Fe, La, Rb, Sb and Zn in stations situated between 1 and 15 km below Meknes city. They also showed that the sedimentation takes place along 15 km and decreased at S7, 21 km below the city. The existence of toxic elements such as As, Br and Sb is detrimental to aquatic systems. Perhaps it could explain the absence of normal aquatic life in the river (Rodier et al., 1992; Phillips et al., 1993). A maximum concentration of Cr, Fe and Zn in S4 and S6 is correlated to the different utilization of these elements in human activities (tannery, textile and ceramic industries etc.) (Jenkins et al., 1992; Minear, 1982), and their origin is mainly anthropogenic. Water samples were decanted and placed in polythene bottles and stored at 4°C. All the samples have been analysed using the ICP/MS method (Fardy, 1992; Howard, 1992; Jarvis, 1992). The measurements were carried out using a PQ2-Plasma Quad system (Fisons) with a pneumatic nebulizer. Data acquisition was controlled using PQ-Vision software. The machine was calibrated with “SPEX” commercial solutions diluted at 10 ppb. Some elements such as Fe, Zn and Ca were analysed by INAA after evaporation on high purity aluminium at room temperature. Samples and standards were irradiated in the Orphee reactor in a thermal neutron flux of 1013 n cm−2 s−1. As summarized in Table 2 and presented in Figs 5, 6 and 7, the concentrations of Fe and Zn in water are maximum at S1 (Fig. 5). These values were confirmed with INAA, and the fluctuation is less than 10%. The results confirmed that the source is rich in Zn and deposits it along the course of the river. The concentration of Mn increased from S4 to S7 (Fig. 6). This may be explained by its utilization in ceramics, painting and agriculture as a fertilizer (Förstner, 1991; Minear, 1982). The high quantity of Pb in S6 can be explained by its use in industries involving accumulators, ceramics and caoutchouc. Other elements such as Co, Ni, Se and V were also detected. They increased from S4 onwards but the concentrations were low (≈ng/g). The high and quasi-constant concentration of Ca could be due to its natural geological origin (Abdellaoui, 1990). With the aim of detecting eventual diffusion of pollutants from the river to an adjacent well, three samples, namely Meknes city fresh water, water from station S6 and that from the well, were analysed using the ICP/MS method. The results are summarized in Table 3. They indicate a high concentration of Fe, Pb and Zn in the fresh water.