SAUD S. AL-OUD Department of Soil Water Science College of Agric. & Vet. Medicine KING SAUD UNIVERSITY

Contamination of soil may be indirectly responsible for the greatest human exposures to heavy metals through uptake of plants to these metals. If heavy metal contamination exceeds the binding capability of the soil, there is a danger that heavy metal compounds can percolate into the groundwater

Cd used in metal plating, pigments, batteries, and plastics. Igneous rocks ( mg/Kg) Metamorphic ~.3 &Sedimentary rocks g/kg ZnS minerals, ZnCO3 Up to 5% Fertilizers in cultivated soils

Health risk (direct exposure specially children e.g Pb in paint and playground. Plant grown in contaminated soil can accumulate a lethal dosage when consumed by human. Heavy metals can percolate into the groundwater. Soil contaminated with heavy metal need many years for remediation and clean up

Siet (1): ALmota. Is industrial waste, home garbage and auto wrecks. This site used by Buriedah city as a landfill from early 1950s until late 1970s. The land surrounding this site is a semi- rural, residential and faming field.

Siet (2): ALdahy The site used to disposal excess rain from the Buriedah city streets and overflow of municipal water. This site used as a landfill from early late 1960s to late 1970s. The land surrounding this site is residential community.

Siet (3): ALsnaeeah This site is being used to infiltrate and evaporate industrial solid and liquid wastes since late 1970 until now. -It surrounded by mainly factories and a farming fields.

To survey soil contamination by heavy metals in AL-Qassin area. To determine relative mobility of heavy metals in soil profile. To evaluate heavy metals uptake by native plants.

Surface and subsurface soil samples were collected from three different sites. Soils in the three sites classified as Coarse sandy, thermic Typic Torrifluvent. These soils represent most of the major agric. soils in AL-Qassim reigmn,Saudi Arabia. Total heavy metals were obtained by Mobile forms of heavy metals were extracted with 1 M HNO 3 and DTPA. and were determined by ICP-XL Native plant grown in the contaminate soil were collected and its heavy metal content were analyzed

Range of general characteristics of soils. Sample no. ALmotaALdahyALsnaeeah Sand % Silt % Clay % PH 1: O.M (%) CaCO 3 (%) E.C (ds/m)

Distribution of Pd. Zn, Cu and Co in soil profile

Distribution of Ni and Mn in soil profile

Relative mobility of heavy metals in soil

MetalRange Range Pb Ni Mn Zn Cu CO Fe Range of mobile form of heavy metals (μg g -1 ) extracted with 0.5 N HNO 3

Effect of pollution sources on of heavy metal mobility as extracted with 0.5 N HNO 3.. SitePbNiMnZnCuCoFe ALmota23.23 ALdahy36.72 ALsnaee ah 28.75

MetalRange Range Pb Ni Mn Zn Cu CO Fe Range of plant available form metals (μg g -1 ) as extracted with DTPA

Effect of pollution sources on of heavy metal availability. SitePbNiMnZnCuCoFe ALmota ALdahy ALsnaee ah

FeMnZnCuCdNi Malvaparviflora Rumex Vesicarias Solanumnigrum Lactuca Serviola Chenopodium marale Sisymbrium irio Pulicaria crispa Phrgmites australis Accumulation of heavy metals in native plants leaves (μg g -1 ) extracted by DTPA (Site (1) Almota).

FeMnZnCuCdNi Chenopodi umAlbum Brassicato rnefortil Sisymbrium irio Malvaparviflora Accumulation of heavy metals in native plants leaves (μg g -1 ) extracted by DTPA (Site (3) Alsnaeeah)..

At ( ppm) Cd Load & Unadjusted pH: The Cd 2+ in the soils varied M It increased with increasing total Cd added. At (12.8 ppm ) & different levels of pH (5-8) The Cd 2+ activities ranged from M The Cd 2+ were inversely related to soil pH.

Cd2+ activities as a function of pH for soils (1, 2, 4, 6, and 10).

Solubility diagram for the Cd-soil equilibrium for soils (1, 2, 4, 6, 10)

IAP of Cd(OH)2 as a function of soil pH

SAC of Cd Adsorbed (Unadjusted pH and varied Cd loads). IAP of increased with Cd addition&IAP<Ksp The IAP  2.3x M to 5.6x M. The SAC of Cd(OH) 2  8.2x10 -5 to 470 The single ion SAC Cd2+  0.02 to 7.8

SAC of Cd Adsorbed (pH 5-8 &12.8 ppm Cd) IAP of is strongly pH dependent. The SAC of Cd(OH) 2  3.9x10 -6 to 4.6 SAC increased with pH The SAC indicate that Cd adsorption increase with increasing iron (Feo-Fep, Feo, and Fed), CEC, and O.M in soils.

Cadmium speciation for the non electrostatic and the diffuse layer models,where [H 2 A] T = 1.66x10 -3 M, [H 2 B] T =7.44 x10 -4 & [FeOOH] T =3.76x M.

Measured and predicted Cd adsorption (Aridic Soils)

Measured and predicted Cd adsorption (Andisols Soils )

Log Rcd versus pH for two different amounts of HFO in a soil/water system.

1) The complexation model prediction values for the% of adsorbed Cd are within 5% of the batch data at the pH 8 2) Soils have high contents of O.M & hydrous ferric oxides showed relatively good agreements with the batch data. 3) The Humic materials are important in Cd retentionat pH>3 & HFO surfaces at pH>7. 3)

4) The relationship between Cd activity and soil pH was highly significant 5) Small change in pH can cause a dramatic change in the adsorption capacity of the soil specially at pH below 6. 6). The correlation between SAC Cd2+ and soil properties suggests that soil adsorption capacity for Cd would increase with increasing Iron Fraction and O.M in 7) The Rcd values increased with increasing amounts of the iron oxide fractions.

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