Geochemical features of topsoils in the Gaza Strip: Natural occurrence and anthropogenic inputs

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Abstract

The aims of this study were to establish the current contents of trace metals and major elements in agricultural soils of the Gaza Strip and to identify the main anthropogenic inputs affecting trace metal contents. An extensive soil survey was conducted in agricultural and nonagricultural areas. One hundred and seventy sites that represent a broad range of soil types and locations were selected. The results revealed that soils in the Gaza Strip fall within the range of uncontaminated to slightly contaminated. Up to 90% of the tested soils had trace metal contents equal to the international background values. Ten percent showed slight contamination, primarily by Zn, Cu, As, and Pb, due to anthropogenic inputs, and the mean concentrations of these elements were 180, 45, 13, and 190 mg/kg, respectively. The trace metal contents varied, with the highest contents detected in the southern regions (where one finds clay soil and low precipitation) and the lowest in the northern areas (where are sandy soil and high precipitation). The soil geochemistry is dependent on soil type and location and to a lesser extent on crop pattern and fertilizer and fungicide application. Anthropogenic inputs lead to the enrichment of Zn, Pb, Cu, and Cd in the agricultural soils. The pollution of several investigated sites was found to be most severe for Zn, Pb, Cu, Cd, and, to a somewhat lesser extent, for As, whereas anthropogenic input of Hg, Ni, and Co seemed to be less important. The application of Cd-containing phosphate fertilizers coupled with Cu-containing fungicides may be an important source of Cd and Cu in several soils. High Zn levels (1000 ppm) in several soils may be caused by sewage sludge, which has an average Zn content of 2000 ppm. Saline-sodic soils were found in the central and southern regions, where the soils are characterized by high contents of Na and salty groundwater. Elevated Cl, Na, Zn, and Pb contents in some areas need further investigation to determine their ecological and health implications.

Introduction

Owing to the scarcity of land and rapid urbanization in the Gaza Strip, most agricultural areas are located near industrial areas and the environmental hotspots of wastewater treatment plants and solid waste dumping sites. The soils of these agricultural areas are subject to potential pollution from various sources (Abrahams, 2002). Soils are prone to contamination from atmospheric and hydrological sources, but direct waste disposal causes a major impact on this natural resource, posing serious environmental concern (Navas and Machin, 2002). At the current rates of atmospheric deposition, concentrations of potentially toxic trace metals in soils of several countries worldwide may already be close to exceeding their critical capacity for pollution (Nriagu, 1990). Most trace metal contamination in the surface environment is associated with a cocktail of contaminants rather than one metal (Jung, 2001). It has been noted that roadside soils near heavy traffic and urban soils are polluted by Cd, Cu, Pb, Zn, and other metals (Li et al., 2001). In the polluted soil, the trace metal concentrations in crop plants have been found to vary between plant species (Lee et al., 2001). Balances between removed and supplied quantities of trace elements indicate slow depletion of the micronutrients Zn, Cu, and Mn in farming based on cash crops and conventional fertilization. The soil levels of Cd, Hg, and Pb are slowly increasing due to additions of commercial fertilizers (Andersson, 1992; Bowen, 1979).

Soil salinity and sodicity can have a major effect on the structure of soils. Soil structure, or the arrangement of soil particles, is critical in affecting permeability and infiltration (Sparks, 1995). Saline irrigation water, low soil permeability, inadequate drainage, low rainfall, high potential evapotranspiration, and poor irrigation management all have caused salts to accumulate in several soils of Gaza, which deleteriously affects crop growth and yields (Sparks, 1995).

In the Gaza Strip, there is not enough water to leach soluble salts from soil. Consequently, the soluble salts accumulate, resulting in salt-affected soils. The major cations of concern in saline soils and waters are Na+, Ca2+, Mg2+, and K+ and the primary anions are Cl, SO42−, HCO3, CO32−, and NO3. Carbonate ions are normally found only at pH⩾9.5.

Crop rotation and fertilization vary between different regions depending on climate and soil conditions, and, similarly, there is a variation in the rate of precipitation from south (250 mm/acre) to north (400 mm/acre) over the Gaza Strip.

The main goal of this study was to establish the topsoil geochemistry in the Gaza Strip. A secondary objective was to identify the major anthropogenic inputs affecting soil geochemistry.

Section snippets

Soil types

The Gaza Strip is 360 km2 and has several major soil types (Fig. 1). Arenosolic, Calcaric, Rhegosolic, and Calcaric Fluvisolic soils are examples of these soils (Table 1). Arenosolic (sandy) soils of dune accumulations are Regosols without a marked profile. The soils are moderately calcareous (5–8% CaCO3), with low organic matter, and are physically suitable for intensive horticulture.

Calcaric Arenosols (loessy sandy soils) can be found some 5 km inland in the central and southern part of the

Results

Owing to the large data set obtained from the analysis of 170 soil samples, each having 20 parameters, this section will cover mostly elements that are environmentally significant in Gaza. Mercury was detected in 56 samples, while Sb was detected only in 8 of them. The levels of Ti, Br, Rb, Sr, Y, and Zr were low to very low, and consequently data from these elements are not presented in Table 2. The statistical median of similar soils was considered and 11 soil categories were used to

Discussion

The Palestinian environmental strategy (MEnA, 2000) has established that several threats cause the deterioration of soil quality in the Gaza Strip. The accumulation of solid and hazardous wastes, discharge of untreated wastewater, extensive use of fertilizers and fungicides, overgrazing, soil salinization, urbanization, vegetation removal, and soil erosion are examples of these threats. The agricultural areas are exposed to one or more of these threats.

The average content of AOX in the sludge

Conclusions

  • 1.

    The soil types, crop patterns, and specific location factors largely control the distribution of trace metals (Pb, Cu, Zn, Cd, and Mn) in soils. Linear regression analysis found a correlation coefficient of r=0.85 between Zn and Cd concentrations in soils with highways nearby.

  • 2.

    The irrigation water, the applied fertilizers and fungicides, and the nearby sludge and wastewater have played a major role in and contributed significantly to the enrichment of several soils with Zn, Pb, Cu, and Fe. Soils

Acknowledgments

Thanks are expressed to Dr. Andriy Cheburkin for the analyses of the soil, fertilizers, and fungicide samples by EMMA-XRF. The authors acknowledge Prof. Dr. Bernd Lottermoser (James Cook University–Australia) and Prof. Dr. R.D. Schuiling (University of Utrecht-The Netherlands) for their critical reading of and comments on the manuscript.

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