Date of Award

1-1-2001

Thesis Type

PhD

Document Type

Thesis

Divisions

Institute for Advanced Studies

Department

-

Institution

Universiti Malaya

Abstract

Heavy metals contaminated soils pose a continuing and increasing threat to human health, the increased inputs of heavy metals from the widespread disposal of industrial wastes have created an Increased attention on the issue of their fate. bioavailability and environmental significance. These Investigations were carried mainly to study the solid - solution phase distribution, chemical speciation and plant uptake of cadmium (Cd), lead (Pb), nickel (Ni) and zinc (Zn) in three contrasting soils amended with Cd, Pb. Ni and Zn nitrate sails at rates of 5-40 mmol/kg for incubation time varied between 3-15 month. Although heavy metal cations adsorbed to the soils at low concentrations, increasing their mass loading resulted in positive correlations with the adsorption values of these metal cations to the soil solid particles. Soil type had significant effect on the solid - solution equilibrium of the added metals. The studied metals are varied in their adsorption and desorption characteristics. Zn reported the highest solution concentration than that of Ni. Cd and Pb In the three soils while Pb was the most adsorbed metal. Metals concentration In soil solution and are positively correlated with residence rime. The speciation of metals In soils Is essential in understanding their chemical and biological interactions in the soil environment. The solid phase speciation of Cd. Pb. Ni and Zn In soils amended with such metals at rare of 5mmol/kg was estimated by sequentially extracting the treated soils with IM NH₄OAc to dissolve the water soluble and the exchangeable metals, with 0.125 M Cu (OAc)₂ 110 dissolve complexed metals and with IM HNO₃ to dissolve the precipitated and residual metals. The speciation of the added metals was greatly influenced by soil type and residence time. The soil solution chemistry of heavy metal is of great importance in assessing their bioavailability and estimates their toxicity. MINTEQA2 version 3.0 used to explore the

speciarion of the studied metals the in solution of the three soils revealed the majority of metals as the free ionic Cd²⁺, Pb²⁺, Ni²⁺, Zn²⁺ forms with varying proportions of the other different inorganic species. The bioconcentration of heavy metals by plants is the major route for metal contaminants to enter the human body. Greenhouse experiments were conducted to study Cd, Pb, Ni and Zn uptake from soils amended with these metals at levels from 0-20mmol/kgsoils, using lettuce (lactuce sativa) as bio-monitor. This concentration range was chosen based on the ability of lettuce to tolerate such metal rates. Significant positive correlations were obtained between the bioconcentration of Cd, Pb, Ni and Zn by plant and the metal amendments, the exchangeable chemical fraction and the residence time. The relative bioavailability of the studied heavy metals is in this order Zn> Ni> Pb>Cd. The soil-plant-man exposure pathway Is identified as the major exposure pathway to contaminants. The estimated plant-soil bioconcentrationfactor for Cd, Pb, Ni and Zn was found to be slightly elevated with the residence time of the contaminant. Thus the study concluded that amount of Cd, Pb, Ni and Zn contaminants available for human intake is subjected to gradual elevation in response to the metal mass loading and the length of time soils are exposed to the specific contaminants.

Initial

snms

Additional Information

Thesis (PhD) -- Institute for Advanced Studies, Universiti Malaya, 2001.

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