Journal of Soil Science and Plant Nutrition, 2011, 11 (3), 125-145 Spatial distribution of copper, organic matter and pH in agricultural soils affected by mining activities R. Aguilar1, C. Hormazábal1, H. Gaete2, A. Neaman1,3,* 1Laboratorio de Suelos y Análisis Foliar, Facultad de Agronomía, Pontificia Universidad Católica de Valpa- raíso, Casilla 4-D, Quillota, Chile. 2Departamento de Biología y Ciencias Ambientales, Facultad de Ciencias, Universidad de Valparaíso, Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile. 3Centro Regional de Estudios en Alimentos Saludables (CREAS), Región de Valparaíso. * Corresponding author: E-mail: alexander.nea- [email protected], Phone: 56-32-2274537, Fax: 56-32-2274570 Abstract The Aconcagua River Basin, located in north-central Chile, is an important agricul- tural region of the country. However, several copper mining industries are also lo- cated in this basin. A total of 103 topsoil samples were collected at varying distances from mining industries. There were no statistically significant differences between the sampling areas with regard to organic matter content and copper concentration. However, the sampling areas were significantly different with regard to soil pH. Soils of the Putaendo sampling area exhibited the lowest pH values (mean of 6.3), while the highest pH values (mean of 7.1) were measured in the Catemu – Chagres sampling area. In the sampling areas where mining activities were absent, the to- tal copper concentrations ranged from 70-155 mg kg-1. These concentrations are a result of the geological setting and/or of applications of copper-containing fungi- cides. High copper concentrations (above 700 mg kg-1, with a maximum of 4000 mg kg-1) were generally observed near mining activities or in areas where mining activities were located nearby and upstream. In these sampling areas, the copper concentrations differed by an order of magnitude in nearby locations. These high and heterogeneously-distributed copper concentrations most likely resulted from either modern or former mining activities. Keywords: trace elements, metals, agriculture, mining, smelting. 125 126 R. Aguilar et al. 1. Introduction The Aconcagua River Basin (ARB) is located in ARB. The most important of these industries are the north-central Chile in the Valparaíso Region, be- El Soldado (near Nogales) and Andina complexes tween 32º30’ and 33º07’ latitude south (Figure 1), (near Saladillo, in the high Andes, ~3500 m above sea with an area of ~7600 km2. The ARB is one of the level). These complexes include mines and ore con- most important agricultural regions of Chile (ODE- centration/leaching plants. In addition, there are sev- PA-CIREN, 2002; IGM, 2003). However, Chile is eral smaller mines, concentration/leaching plants, and the foremost copper producer in the world (Comisión mine dumps distributed throughout the basin, and a Chilena del Cobre, www.cochilco.cl), and several copper smelter at Chagres (near the town of Catemu) important copper mining industries are located in the (Arancibia, 2002; Lara and Romo, 2002). Figure 1. Location of the Aconcagua River Basin. The study was limited to arable soils located on landforms with slopes of less than 15%. Journal of Soil Science and Plant Nutrition, 2011, 11 (3), 125-145 Distribution of Coper, organic matter and pH 127 The environmental problems historically associated risk from those that, at similar total concentrations of with copper mining are widely known, particularly in metals, do represent significant ecological risks (Ávila relation to the contamination of agricultural soils by et al., 2009). In other words, future legislation should metals (González et al., 1984; Ginocchio, 2000; De consider soil properties that affect metal bioavailability, Gregori et al., 2003). Copper is the main contaminant such as soil pH and organic matter content (Adriano, in the soils of copper mining areas in Chile (Goecke et 2001; Sauvé, 2003; Kabata-Pendias, 2004). al., 2011). Copper is an essential micronutrient to all To establish the maximum permissible concen- organisms but is toxic at certain concentrations (Mc- trations of copper in soils, its bioavailability can be Bride, 1994; Adriano, 2001). assessed by exposing organisms, e.g., plants, micro- Environmental (or ecological) risk is defined as organisms, and invertebrates, to soil to monitor the “the potential for adverse effects on living organ- effects of bioavailable copper (ISO 17402, 2008). In isms associated with pollution of the environment such types of experiments, care should be taken so by effluents, emissions, wastes, or accidental chemi- that soils have wide ranges of copper concentration, cal releases; energy use; or the depletion of natural pH, and organic matter content. However, little data resources” (U.S. Environmental Protection Agency, are available on the spatial distribution of these soil Terms of Environment: Glossary, Abbreviations and characteristics in agricultural soils of the ARB. There- Acronyms, www.epa.gov/OCEPAterms). It is well fore, the main objective of the present study was to known that the total concentration of a metal in a soil determine the spatial distribution of copper, pH, and is not sufficient to predict the potential ecological risk organic matter in the agricultural soils of the ARB. that it represents (McBride, 1994; Sauvé et al., 1998; Additionally, for metal bioavailability tests with or- ISO 17402, 2008). Ecological risk is more related to ganisms, it is important to sample soils with differ- the bioavailability of the metal that, in turn, is relat- ent sources of contamination because different types ed to the chemical form in which it is found in the of mine wastes have different solubilities (Ginocchio soil (Adriano, 2001). The National Research Council et al., 2006). Therefore, the second objective of the (2003) defines bioavailability as the fraction of the to- present study was to estimate the possible sources of tal element that is available to the receptor organism. contamination. The information generated from this Although the total metal concentration in the soil study will form the basis for choosing locations for is not a good indicator of the elements bioavailability, soil sampling in future studies aimed at assessing cop- total concentrations are still used by legislations in per bioavailability. many countries (Ewers, 1991). In some cases, legis- lations consider soil properties that affect metal bio- 2. Materials and methods availability. For instance, the Council of the European Communities (2009) and the UK (1989) consider the Using a Geographical Information System (GIS) and soil pH for maximum concentrations of metals in soils available GIS databases, the agricultural soils of the on which sewage sludge is applied. ARB were clustered into 8 sampling areas (Table 1). Chile currently does not have any legislation on The study was limited to arable soils located on land- the maximum permissible concentrations of metals in forms with slopes less than 15% (Figure 1). These soils. Any future legislation should distinguish between boundaries included the agricultural soils that have tra- soils where metals are present but do not represent a ditionally been irrigated by gravity. Journal of Soil Science and Plant Nutrition, 2011, 11 (3), 125-145 128 R. Aguilar et al. Table 1. Sampling locations and chemical properties of the studied soils. Different letters in the pH column indicate significant differences between the sampling areas (Tukey test, p < 0.001). There were no differences (ANOVA, p > 0.05) between the sampling areas with regard to organic matter (OM) content and total copper concentration. WGS 1984 Coordinates Total copper, Sample UTM H19S Crop pH OM, % mg kg-1 W S E N Quillota sampling area 106 70°29’15’’ 32°51’19’’ 294404 6363683 Fallow 7 5.4 96 107 70°30’32’’ 32°50’53’’ 287993 6356616 Cabbage 6.9 5.9 100 108 70°32’25’’ 32°49’59’’ 289484 6355597 Fallow 7.3 5.1 91 109 70°33’50’’ 32°44’1.5’’ 291200 6358418 Fallow 7.1 5.6 98 110 70°33’44’’ 32°44’5’’ 291987 6359551 Fallow 6.8 5.7 154 Median 7.0 5.6 98 Mean 7.0 ab 5.5 108 STD 0.2 0.3 26 CV, % 3 6 24 Nogales sampling area 68 71°11’40’’ 32°38’59’’ 294161 6385402 Avocado 6.8 2.4 115 70 71°11’47’’ 32°39’3’’ 293979 6385277 Bean 7 3.2 111 72 71°11’56’’ 32º38’51’’ 293771 6385618 Bean 6.9 4.8 253 73 71°11’14’’ 32°38’39’’ 294841 6386016 Bean 6.8 4.4 401 74 71°11’56’’ 32°38’35’’ 293732 6386139 Lemon 7.9 0.8 4087 76 71°12’12’’ 32°39’41’’ 293355 6384094 Walnut 6.8 3.9 670 82 71°7’5’’ 32°42’58’’ 301480 6378195 Lemon 7.1 4.7 122 83 71°6’38’’ 32°42’44’’ 302192 6378638 Alfalfa 6.5 4.3 128 84 71°6’43’’ 32°42’33’’ 302038 6378951 Fallow 6.9 6.1 130 85 71°6’36’’ 32°42’32’’ 302232 6379007 Beans 6.3 3.2 90 120 70°33’48’’ 32°44’5’’ 297663 6370833 Avocado 7.2 4.7 151 121 70°37’46’’ 32°44’55’’ 294947 6376708 Cabbage 6.8 4.5 116 122 71º11’17’’ 32º43’41’’ 294949 6376705 Tomato 6.1 6.6 159 123 71º10’16’’ 32º44’23’’ 296563 6375439 Fallow 6.8 4.1 270 124 71º9’49’’ 32º44’59’’ 297301 6374337 Fallow 6.6 4.2 192 Median 6.8 4.3 151 Mean 6.8 ab 4.1 466 STD 0.4 1.4 1013 CV, % 6 34 217 Journal of Soil Science and Plant Nutrition, 2011, 11 (3), 125-145 Distribution of Coper, organic matter and pH 129 Continued... WGS 1984 Coordinates Total copper, Sample UTM H19S Crop pH OM, % mg kg-1 W S E N Catemu – Llay-Llay sampling area 53 70°54’30’’ 32°51’42’’ 321434 6362426 Fallow 6.9 3.4 114 54 70°53’34’’ 32°51’41’’ 322898 6362461 Peach 6.9 2.8 131 55 70°53’35’’ 32°51’52’’ 322861 6362136 Lemon 6.7 0.6 746 56 70°53’18’’ 32°51’34’’ 323304 6362691