Heavy Metals in Sediments of the Rivers Aviles And

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

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

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

434 Water Pollution

Table 3. Concentrations of metals Q^g/g) in sediments of the River Avil6s (Feb. 1993)

Points Fraction Depth Pb Cd Zn Cu Ni Fe Cr Overo Unsieved 00-10 77.89 5.27 154.70 18.30 146.10 56,219 40.19 Oveio Sand 00-10 51.99 4.32 136.60 18.24 121.60 32,304 39.64 Overo Mud 00-10 87.43 6.07 205.90 27.79 193.30 38,675 63.87 Overo Unsieved 10-20 62.34 4.80 153.20 22.87 20.42 23,154 30.53 Overo Sand 10-20 73.75 4.25 156.80 21.01 19.74 21,370 27.38 Overo Mud 10-20 69.83 6.99 217.50 30.16 21.06 30,462 40.02 Viaducto Unsieved 00-07 82.00 5.63 441.00 36.62 160.20 47,567 52.19 Viaducto Sand 00-07 79.91 5.16 473.80 33.85 163.00 46,098 44.01 Viaducto Mud 00-07 107.00 8.30 936.70 68.65 255.10 53,515 55.61 Viaducto Unsieved 07-14 149.40 8.03 611.30 46.38 38.57 25,907 116.80 Viaducto Sand 07-14 65.02 5.62 478.50 51.10 35.71 22,248 104.80 Viaducto Mud 07-14 187.90 8.01 649.90 59.51 37.71 25,966 90.91 Zeluan Unsieved 00-10 68.75 7.97 237.60 20.67 15.43 11,446 15.27 Zeluan Sand 00-10 93.63 6.33 270.50 24.04 18.38 11,752 16.34 Zeluan Mud 00-10 199.10 12.31 1,010.00 70.72 31.35 25,197 26.36 Zeluan Unsieved 10-20 87.22 7.06 314.80 24.47 22.67 11,746 13.39 Zeluan Sand 10-20 100.80 7.20 330.30 39.74 27.16 11,917 14.85 Zeluan Mud 10-20 231.50 14.96 1,745.00 99.04 46.02 37,116 39.64 Arafi6n Unsieved 00-08 67.73 5.66 1,338.00 15.17 7199 30,780 10.00 Arafi6n Sand 00-08 68.02 5.62 2,557.00 9.45 78.05 22,794 8.28 Aran6n Mud 00-08 196.60 21.07 1,142.00 130.10 128.30 51,633 11.59 Arafi6n Unsieved 08-20 39.88 5.01 243.90 9.87 1195 10,332 16.07 Aran6n Sand 08-20 55.64 5.07 281.50 10.88 13.87 10,094 16.86 Aran6n Mud 08-20 103.40 17.89 521.50 97.41 6.63 22,644 46.72

The results show that the highest concentration of chromium corresponds to the mud fraction at point 3 (Zeluan) whilst the maximum concentrations in the sand and unsieved fractions were obtained at point 2 (Viaducto). These concentrations are below the

concentrations found in the sediments of the River Qishon (Kronfeld [7]). The maximum iron concentrations at the two depths correspond to sampling point 2 (Viaducto). The iron concentrations in the sediments of this river are below the concentrations found in the sediments of the river Tin to (Huelva, Andalucfa), an extremely polluted river in

Spain, but are higher than the concentrations found in the sediments of other highly polluted rivers, such as some in the Basque Country and in Cataluna (Ruiz [13], Casas [3], Cordon[4]). With respect to nickel, the greatest concentrations at the two depths and in all the

fractions studied were obtained at sampling point 2 (Viaducto); being also highly significant at sampling point 3 (Zeluan). The maximum concentrations of copper were obtained at point 3 (Zeluan) in all the fractions and depths studied. The concentrations found for copper as well as those obtained for

zinc at this point clearly imply a high level of pollution, due to proximity to the pollution source. The concentrations of zinc in the River Avil6s reach very high values that exceed even the highest values found in the bibliography for rivers in Spain. Maximum concentrations of cadmium, although lower than the concentrations of other metals, correspond as in the previous metals, to sampling point 3 (Zeluan). The concentrations

at the other sampling points were more uniform than the values found for the rest of the metals.. The cadmium concentrations found are higher than values found by other authors,

Water Pollution 435

Ortiz et al. [11], Ramos et al. [12], Ruiz et al. [13] and Sola et al. [14] in different rivers of the Basque Country, but are lower than concentrations found in the River Tinto in Huelva

[2]. With regard to lead, the highest concentrations were found at point 2 (Viaducto) but concentrations are also very high at point 3 (Zelu&i), as is the case for other metals. However, cadmium concentrations are lower than those found by (Campos et al. [2]) in the River Tinto.

The data compiled in the previous tables show that concentrations of lead, cadmium, zinc and copper are higher at sampling point 3 (Zelu&n) whilst concentrations of nickel, iron and chromium are higher at point 2 (Viaducto). In both cases, the values found were both higher in the surface layer as well as in the sub-surface layer.

3.2 Results corresponding to the samples of the River Abono The concentration of heavy metas in sediments of the river Abono at the four sampling points and for the two different depths are shown in Tables 4, 5 and 6.

Table 4. Concentrations of metals (j^g/g) in sediments of the River Abono (Dec. 1992)

Points Fraction Depth Pb Cd Zn Cu Ni Fe Cr Arroyo Unsieved 00-10 36.53 330 48.02 17.35 115.40 8,415 16.91 Arroyo Sand 00-10 36.64 119 46.97 13.28 107.07 8,525 15.42 Arroyo Mud 00-10 75.52 5.70 248.10 76.22 179.90 26,418 37.08 Arroyo Unsieved 10-20 37.19 3.64 55.29 14.75 121.40 6,324 17.84 Arroyo Sand 10-20 37.45 3.64 57.16 16.70 137.30 8,229 21.58 Arroyo Mud 10-20 50.61 548 127.90 64.23 206.40 17,165 36.45 Verina Unsieved 00-10 250.00 5.20 6,420.00 68.82 97.30 160,703 60.07 Verina Sand 00-10 202.00 5.18 5,425.00 43.45 93.92 192,838 50.16 Verina Mud 00-10 240.70 8.19 5,885.00 64.51 136.00 363,251 78.05 Verina Unsieved 10-20 224.70 5.26 7,054.00 49.77 94.98 86,856 45.95 Verina Sand 10-20 207.80 5.70 7,135.00 44.95 86.69 83,186 43.42 Verina Mud 10-20 280.60 9.39 8,592.00 71.57 116.40 160,152 81.24 Pervera Unsieved 00-06 50.62 3.25 127.90 35.14 18.35 14,742 16.78 Pervera Sand 00-06 52.96 3.44 135.40 41.49 17.97 19,895 15.43 Pervera Mud 00-06 90.23 5.86 406.90 87.35 30.93 83,699 41.49 Pervera Unsieved 06-16 55.40 4.09 127.50 39.74 152.90 33,241 30.02 Pervera Sand 06-16 45.58 4.22 111.70 42.83 132.60 16,813 28.49 Mud Pervera 06-16 107.00 698 348.70 74.43 189.23 54,066 61.23 Abono Unsieved 00-10 46.00 5.82 2,389.00 54.93 161.30 71,051 66.21 Abono Sand 00-10 95.23 549 2,463.00 57.53 168.70 73,205 60.56 Abono Mud 00-10 116.30 8.05 2,734.00 71.25 231.40 109,440 80.38

Abono Unsieved 10-20 94.46 4.29 1,067.00 58.75 174.70 49,329 42.30 Abono Sand 10-20 98.95 4.15 2,172.00 54.78 179.60 93,481 43.46 Abono Mud 10-20 146.40 6.63 2,064.00 81.64 230.50 167,801 70.73

436 Water Pollution

Table 5. Concentrations of metals (Hg/g) in sediments of the River Abono (Jan. 1993)

Points Fraction Depth Pb Cd Zn Cu Ni Fe Cr Arroyo Unsieved 00-09 34.36 2.59 9.63 17.59 40.56 5,674 11.83 Arroyo Sand 00-09 44.37 2.39 11.62 19.26 39.82 4,882 10.87 Arroyo Mud 00-09 71.43 4.65 56.45 65.34 58.39 12,415 20.90 Arroyo Unsieved 09-17 48.79 3.46 5.87 20.84 47.67 5,987 11.08 Arroyo Sand 09-17 53.00 3.70 4.71 19.68 55.91 5,314 12.25 Arroyo Mud 09-17 74.93 5.86 32.00 68.18 73.54 13,407 24.45 Verina Unsieved 00-10 155.20 5.22 2,387.00 46.25 57.46 174,669 63.25 Verifia Sand 00-10 169.30 443 2,516.00 43.67 54.05 126,480 63.90 VeriOa Mud 00-10 149.30 6.71 2,222.00 57.60 61.33 221,730 82.05 Verina Unsieved 10-20 195.20 4.97 2,472.00 55.46 62.93 279,572 76.94 Verina Sand 10-20 192.30 4.57 2,487.00 51.78 61.28 242,870 69.33 Verifia Mud 10-20 269.30 6.49 1,246.00 54.60 61.19 426,840 91.04 Pervera Unsieved 00-09 52.64 363 144.70 52.43 21.56 21,035 17.77 Pervera Sand 00-09 53.99 3.67 144.70 55.98 21.43 25,352 17.30 Pervera Mud 00-09 70.69 548 319.50 68.07 25.17 44,822 30.52 Pervera Unsieved 09-17 50.16 3.93 188.90 56.49 166.00 32,362 14.41 Pervera Sand 09-17 25.96 2.54 195.10 36.57 98.04 24,540 11.74 Pervera Mud 09-17 96.96 7.50 398.50 131.00 330.10 76,286 27.86 Abofio Unsieved 00-07 75.35 5.06 947.00 51.61 117.30 31,745 33.70 Abofio Sand 00-07 72.97 439 773.60 61.89 124.60 34,371 33.51 Abofio Mud 00-07 90.20 7.60 1,246.00 83.48 172.00 82,586 56.39 Abono Unsieved 07-18 65.95 3.20 788.30 43.07 78.12 1,517 36.99 Abofio Sand 07-18 57.28 3.16 381.30 35.47 80.56 1,396 25.07 Abono Mud 07-18 87.22 5.99 1,284.00 76.12 136.70 1,121 70.57

Table 6. Concentrations of metals (}ig/g) in sediments of the River Abono (Feb. 1993)

Points Fraction Depth Pb Cd Zn Cu Ni Fe Cr Arroyo Unsieved 00-10 34.88 3.55 59.81 29.91 138.20 6,683 9.42 Arroyo Sand 00-10 39.19 3.70 52.52 27.08 161.70 7,432 9.89 Arroyo Mud 00-10 51.62 5.95 111.50 75.11 214.70 16,227 14.18 Arroyo Unsieved 10-20 50.77 3.90 61.28 20.60 50.12 6,135 12.20 Arroyo Sand 10-20 54.21 4.02 19.23 20.77 58.64 5,888 14.61 Arroyo Mud 10-20 87.85 6.35 163.40 65.12 76.80 15,472 24.88 Verina Unsieved 00-10 441.50 5.40 1,653.00 37.12 39.68 53,571 48.72 Verina Sand 00-10 378.10 5.51 4,941.00 38.38 40.78 43,816 40.67 Verina Mud 00-10 560.90 9.44 6,417.00 98.30 62.39 80,357 66.10 Verina Unsieved 10-20 383.70 5.83 8,646.00 39.06 97.89 83,637 47.62 Verifia Sand 10-20 482.70 6.67 10,808.00 39.20 96%) 179,705 49.37 Verifia Mud 10-20 615.70 8.99 12,353.00 45.07 122.90 286,959 72.06 Pervera Unsieved 00-10 58.32 2.90 139.80 59.80 78.39 57,624 12.11 Pervera Sand 00-10 64.67 2.97 175.30 51.17 73.44 62,284 11.31 Pervera Mud 00-10 72.93 3.67 235.50 82.95 97.86 60,924 28.67

Pervera Unsieved 10-20 55.88 2.90 109.20 60.14 78.25 44,179 10.31 Pervera Sand 10-20 56.91 2.93 107.50 46.68 82.57 65,377 9.52 Pervera Mud 10-20 89.94 4.53 231.80 92.65 101.90 61,066 19.98 Abono Unsieved 00-10 44.14 5.00 78.07 28.42 18.37 14,654 8.73 Abono Sand 00-10 46.51 2.74 89.91 35.56 15.58 12,977 7.73 Abono Mud 00-10 46.77 5.83 270.20 78.59 36.44 40,015 21.38 Abono Unsieved 10-18 36.00 2.67 31.50 19.20 30.29 30,037 13.81 Abono Sand 10-18 39.67 3.13 45.11 20.86 36.48 19,104 13.87 Abono Mud 10-18 81.23 5.50 212.00 69.20 69.46 108,792 44.38

Water Pollution 437

Maximum concentrations of chromium were found at sampling point 2 (Verina) and were below most of the levels found in the bibliography for Spanish rivers. Iron concentrations in the sediments from upstream of the River Abono are also, below the concentrations found in the bibliography for other rivers, although the values found at point 2 (Verina) were higher than the values found in some Basque rivers and even surpass the values found in the River Tinto.

Concentrations of nickel are maximum at the mouth of the river in the surface sediments but in the sub-surface layer the highest levels are found at point 3 (Pervera). Concentrations of copper are more uniform at all the sampling points and, as expected, the highest values are found in the mud fraction. The highest mean values are found at the mouth of the river. The concentrations values found for copper, as well as for nickel, fall within the range of the values determined in the Basque rivers and in the River Gardener, Cataluna, and are lower than those found in the River Tinto. Zinc concentrations in the River Abono are low upstream but at Verina surpass the values found by Campos et al. in the River Tinto, which are the highest amongst the values quoted in the literature. Cadmium reaches the maximum concentration at point 2 (Verina), but the values show a uniform (regular) distribution along the bed of the river. The concentrations are similar to the values found in the Rivers Tinto and Gardener and do not represent a significant level of pollution. With respect to lead, maximum levels were also found at sampling point 2 (Verina) at the two different depths and the concentrations of lead founded are similar to the values quoted in the literature for Spanish rivers which support industrial effluents, with the

exception of the river Tinto that shows higher concentrations. From the data obtained, sampling point 2 (Verina) is the most polluted zone for all the metals studied, but also point 4 (Abono) in the mouth of the River Abono clearly indicate a significant level of pollution for chromium and zinc; these results correspond to the two

different depths studied.

4. Conclusions

1. The concentration of heavy metals in the sediments of the Rivers Avil6s and Abono clearly indicate a significant level of pollution, the maximum values being found in industrial zones.

2. The mud fraction shows the highest concentrations in all the samples due to the fact that it has a greater adsorption area as the particle size is smaller than that of the sand fraction. The mud fraction also has a greater capacity of transport along the

bed of the rivers and contributes to the dispersion of the contaminants towards the mouth of the rivers.

3. The steel working industry developed since the middle of this century in Asturias

is the main cause of pollution of these river due to the continuous disposal of their effluents without adequate previous treatment.

438 Water Pollution

5 References

01. Arjonilla, M. et al. Comparaci6n de diferentes me"todos de extracci6n de metales pesados en sedimentos marines (ed U.N.E.D.) /// Seminario de Quimica Marina, Cadiz 1987, pp. 199-212. 02. Campos Lissen, J.M. et al. Contaminaci6n por metales en los sedimentos del rio Tinto, Tecnologia del Agua, 2* Monografico, 1990, pp. 49-57. 03. Casas, J.M. et al. Estudio de los sedimentos del rio Gardener II. Contamination por metales pesados, Tecnologia del Agua, 1990,74, pp. 17-24. 04. Cordon R. et al. Concentraciones de metales pesados en aguas, sedimentos y tres especies animales (Crassostrea angulata, Dicentrarchus labrax y Mugil auratus) de los estuarios de los rios Barbate y Guadalquivir (ed U.N.E.D.) pp. 65-71,7/7 Seminario de Quimica Marina, Cadiz, 1987. 05. Garcia,R., Marandn, E., Sastre, H. Heavy Metal Pollution in Seawater and Marine Sediments off the Coast of Gijdn (Cantabrian Sea), (ed L.C. Wrobel & C.A. Brebbia) Water Pollution II: Modelling, Measuring and Prediction, pp. 657-654. Southampton, UK. 1993. 06. Garcia,R., Maran6n,E., Sastre, H. Seawater Pollution by Heavy Metals (Fe, Cu, Cd and Pb) in the bay of Gij6n (Cantabrian Sea), (ed P.A. Bogdanov) IMAM'93, VI Congress, Vol. 3., 1993, Varna (Bulgaria). 07. Kronfeld J. & NavrotJ. Transition Metal Contamination in the Qishon River System, Israel, Environ. Pollut. 1974,6. 08. Loring D.H. & Rantala R.T.T. Manual for the Geochemical Analysis of Marine Sediments and Suspended Paniculate Matter, Marine Chemistry Division, Dpt. of Fisheries and Oceans, Bedford Institute of Oceanography, Darmputh, Canada, 1989. 09. Nombela, M.A. et al. Metales pesados en el registro sedimentario reciente en la ensenada de San Simdn, parte interna de la riade Vigo - Spain, (ed Museo National de Historia Natural) pp 149-56, Revista de Geociencias GAIA, ler. Simpdsio sobre a margem continental Iberica Atlantica, Lisboa, 1994. 10. Oakley, S.M. et al. Model of Trace-Metal Partitioning in Marine Sediments, Environ. Sci. Technol, 1981, 15, No. 4, pp 474-480. 11. Ortiz, M.I. et al. Evaluaci6n del impacto de los metales pesados en sedimentos e indices bio!6gicos en el estuario del Urdaibai, Retema, Nov.-Die. 1992, pp 99-105. 12. Ramos, A. et al. Distribution de microcontaminantes en los sedimentos superficiales de la bahiade Zarautz (Guipuzcoa), (ed. U.N.E.D.) 255-265, V Seminario de Quimica Marina,, pp Cadiz, 1990 13. Ruiz, E. & Romero, F. Composition y cracteristicas de sedimentos de rios del pais vasco: el rio Lea como nivel de fondo de contaminantes, Tecnologia del Agua, 1991, 81, pp 56-64. 14. Sola, M.J. et al. Metales pesados en sedimentos del litoral de Guipuzcoa (ed. UJSF.E.D.), pp 205-213, V Seminario de Quimica Marina, Cadiz, 1990.