Heavy Metals in Sediments of the Rivers Aviles And
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Transactions on Ecology and the Environment vol 7, © 1995 WIT Press, www.witpress.com, ISSN 1743-3541 Heavy metals in sediments of the Rivers Aviles and Abono, Spain R. Garcia*, M. Rionda*, E. Maranoif "Escuela Superior de Marina Civil, ^E.T.S. Ingenieros Industrials, University ofOviedo, 33203 Gijon, Spain Abstract In this work the concentrations of the metals Cr, Fe, Ni, Cu, Zn, Cd and Pb in sediments of the Rivers Avil6s and Abono in Asturias were studied. Samples were taken at four points of said rivers from December 1992 to February 1993. These rivers were chosen because they flow trough highly industrialized zones and the most densely populated area of Asturias. Sediments were digested with acids in closed reactors in a microwave oven. The results show significant levels of pollution in some areas due to the disposal of untreated industrial effluents, the mud fraction of the sediments having the highest concentration values. 1 Introduction The continuous disposal of untreated industrial and urbane effluents into rivers is the cause of important accumulations in river beds of non-biodegradable substances, such as heavy metals, which are then transported towards the sea. Sediments are traditionally considered as a "drain" for heavy metals and can be used as pollution indicators in rivers as well as in the littoral. Retention of metals in sediments depends on various factors but there is a high correlation between metal concentration and organic matter content (Oakley et al [10]). Industrialization in Asturias developed in the Central Area of the region where 70% of the total population lives, the Rivers Avil6s and Abono bearing the major part of industrialization in the province. 2 Materials and Methods Samples of sediments were taken during the months of December 1992, January and February 1993 by driving tubes of PVC of 6 cm diameter down to a depth of about 20 cm in order to obtain two samples at different depths so as to investigate the vertical distribution of metals Transactions on Ecology and the Environment vol 7, © 1995 WIT Press, www.witpress.com, ISSN 1743-3541 432 Water Pollution in each sediment column. The metals determined were Or, Fe, Ni, Zn, Cd and Pb using an Atomic Aborption Spectrophotometer Instrumentation Laboratory Mod. 551. 2.1 Localization of the sampling points Four sampling points were selected in both rivers: one point upstream, presumably unpolluted, and the other three along the river course in the industrialized zones. In the River Avil6s, the selected points were: 1 (Overo), just downstream of the Trasona reservoir; 2 (Viaducto), in the industrialized zone; 3 (Zeluan), the name of the village and beach and 4 (Aranon), the name of the beach at the east of the river mouth, as can be seen in figure 1. In the River Abono, the samples were taken at: 1 (Arroyo), just upstream of the reservoir of San Andre's de los Tacones; 2 (Verina), where the Rivers Abofio and Pinzales join; 3 (Pervera) and 4 (Abono), near to the mouth of the river (see figure 2). Figure 1: Avil6s River and sampling points Figure 2: Abono River and sampling points 2.2 Determination of metals in sediments The concentration of heavy metals increases as the size of the grain decreases, due fundamentally to the fact that the adsorption surface increases (Garcia et al. [6], Nombela et al [9]). Therefore, it is necessary to standardize the size of the grains and to determine the concentrations in the different fractions. In our case, after eliminating particles larger than 2 mm, we have considered the two most important fractions as well as the raw sample: mud (0<63 |J.m), sand (0>63 jj.m) and unsieved (0<0<2 mm). The sediments were dry-sieved. Digestion of sediments with strong acids such as HNO^ or aqua regiae, although used very often, is sometimes incomplete. The quantity of metals disolved depends upon the type of samples, the matrix and the element (Arjonilla et al. [1]). Samples of approximately one gram of the different fractions of the sediments were digested in Teflon reactors with 10 ml of fluorhydric acid and 2 ml of regiae water, according to an adaptation of Loring & Rantala's method (Loring [8], Garcia [5]). The addition of HF has to be made very slowly via the reactor wall so as to avoid the formation of foam. The digestion period was 120 s using a microwave oven. Once cooled, the solutions were transferred to a 100 ml polyethylene flask, adding 50 ml of saturated solution of HgBOg. The flasks were levelled off and the black carbonized residue, which does not interfere in the determination of the metals, was allowed to settle. 3 Results and discussion Transactions on Ecology and the Environment vol 7, © 1995 WIT Press, www.witpress.com, ISSN 1743-3541 Water Pollution 433 3.1 Results corresponding to the samples of the River Aviles Tables 1,2 and 3 show the heavy metal concentrations obtained in the sediments of the River Avil6s for the three different fractions studied and at the two different depths. Table 1. Concentrations of metals (ng/g, ) in sediments of the River Aviles (Dec. 1992) Points Fraction Depth Pb Cd Zn Cu Ni Fe Cr Overo Unsieved 00-10 104.00 4.46 497.90 28.70 31.48 16,726 35.05 Overo Sand 00-10 91.97 347 195.60 47.69 26.03 13,667 20.01 Overo Mud 00-10 181.90 630 543.20 69.64 61.20 32,362 39.17 Overo Unsieved 10-20 82.33 4.58 278.80 37.68 18.56 21,059 25.98 Overo Sand 10-20 71.03 432 270.90 28.06 21.59 20,505 31.97 Overo Mud 10-20 132.10 9.25 486.30 4732 39.51 35,529 55.03 Viaducto Unsieved 00-07 78.09 4.51 1,329.00 27.01 109.90 55,222 42.60 Viaducto Sand 00-07 79.63 4.49 972.00 23.22 11130 43,627 35.84 Viaducto Mud 00-07 96.10 7.26 1,756.00 38.69 147.70 73,177 56.17 Viaducto Unsieved 07-17 57.04 5.19 181.10 15.21 131.30 52,652 32.02 Viaducto Sand 07-17 #33 449 16430 14.15 12730 31,444 29.82 Viaducto Mud 07-17 79.89 7.12 307.70 2338 177.50 52,151 4033 Zeluan Unsieved 00-08 60.21 539 215.80 18.80 145.70 11,660 22.17 Zeluan Sand 00-08 60.82 4.22 196.10 13.92 125.60 11,286 19.59 Zeluan Mud 00-08 123.30 9.73 438.60 61.70 278.60 27,357 50.86 Zeluan Unsieved 08-17 60.29 4.04 190.20 16.09 136.70 15,995 19.51 Zeluan Sand 08-17 58.22 4.54 190.80 1763 165.60 20,658 19.09 Zeluan Mud 08-17 111.00 945 43830 38.99 246.90 31,978 43.77 Arandn Unsieved 00-07 48.04 2.68 180.60 11.15 7030 16,549 3.27 Aran6n Sand 00-07 45.88 2.40 151.00 9.26 62.14 16,867 2.15 Arandn Mud 00-07 66.16 3.07 245.70 43.11 8339 26,499 3.62 Arafidn Unsieved 07-18 45.61 3.16 196.00 9.09 78.23 17,566 1033 Arandn Sand 07-18 46.00 330 218.50 9.16 89.93 15,183 8.91 Arandn Mud 07-18 112.40 745 504.50 156.60 142.40 28,515 19.50 Table 2. Concentrations of metals (jig/g) in sediments of the River Aviles (January 1993) Points Fraction Depth Pb Cd Zn Cu Ni Fe Cr Overo Unsieved 00-10 47.16 3.23 77.13 12.44 89.51 15,490 725 Overo Sand 00-10 #48 3.56 105.70 942 103.60 33,074 945 Overo Mud 00-10 125.10 935 369.50 67.21 184.50 116,153 50.29 Overo Nil 10-20 - - - - - - - Viaducto Unsieved 00-10 308.10 8.89 298.30 103.80 13430 151,582 135.20 Viaducto Sand 00-10 326.90 9.14 264.00 85.47 112.10 180,592 137.40 Viaducto Mud 00-10 206.50 8.96 197.80 128.30 213.60 252,797 137.10 Viaducto Unsieved 10-18 225.10 8.05 320.10 8436 122.10 174,120 136.40 Viaducto Sand 10-18 297.40 830 753.70 72.74 126.80 144,901 159.50 Viaducto Mud 10-18 174.00 9.35 136.60 12630 193.10 210,282 136.60 Zeluan Unsieved 00-09 633.20 40.95 3,157.00 748.80 38.51 76,501 96.75 Zeluan Sand 00-09 33030 25.08 2,185.00 637.80 31.04 56,453 57.60 Zeluan Mud 00-09 996.60 64.84 6,248.00 531.50 5633 12,797 152.10 Zeluan Unsieved 09-19 1,672.00 36.99 9,167.00 97430 107.90 71,963 78.04 Zeluan Sand 09-19 1,688.00 30.57 7,901.00 705.40 114.90 106,820 62.66 Zeluan Mud 09-19 3,437.00 53.97 13,300.00 1,065.00 162.60 120,196 125.80 Aran6n Unsieved 00-10 5138 2.77 204.50 7.67 31.18 42,916 10.74 Arandn Sand 00-10 49.05 2.56 186.10 7.50 29.42 28,782 10.95 Aran6n Mud 00-10 12740 5.60 434.20 102.40 44.26 116,845 29.03 Aran6n Unsieved 10-20 51.52 3.27 20730 932 42.45 21,150 12.00 Aran6n Sand 10-20 51.11 3.41 214.00 8.60 37.95 24,498 11.77 Aran6n Mud 10-20 73.10 4.88 383.10 65.47 50.36 46,553 24.55 Transactions on Ecology and the Environment vol 7, © 1995 WIT Press, www.witpress.com, ISSN 1743-3541 434 Water Pollution Table 3.