Arsenic, a persistent and bio-accumulative poisonous element, has potential to pollute land, water, crops and the overall environment; ultimately affecting human and animal health. Arsenic has become a common contaminant in the environment and particularly ground water arsenic contamination has become a global issue. Higher concentrations of arsenic in the environment, due to its toxicity and induced carcinogenetic effect, is considered a serious problem for human health, especially in countries like Bangladesh, India, Vietnam, China, Canada, USA, Mexico and Chile. In Pakistan, a joint research conducted by PCRWR, UNICEF and National Water Quality Monitoring Program (2002-2006) revealed the presence of arsenic in Punjab and Sind provinces. According to PCRWR report (2005-2006), in Punjab out of 11559 ground water samples, 38% contained arsenic concentration more than permissible limit (>10 ppb), 17% contained >50 ppb and 4% contained >100 ppb. In Sindh out of 5991 samples, 11% contained arsenic concentration >10 ppb, 3% contained >50 ppb & 1.42% contained arsenic concentration > 100 ppb. Similarly, in another joint study conducted by Tokyo Institute of Technology and National Institute of Advanced Industrial Science and Technology (AIST), Pakistan, it was observed that the water samples in the Southern and other areas of Punjab had arsenic level up to five times higher than permissible limit (10 ppb) of the WHO standards. Significant research has been carried out to provide arsenic free drinking, municipal and industrial waste water using conventional techniques based on principles of precipitation-coagulation, oxidation, membrane separation, electro coagulation/flocculation and adsorption. The applicability of these procedures is limited on account of their high operational and capital costs, expensive reagents, high energy requirements, low selectivity and presence of interfering species from sludge and waste products. Among others, adsorption principle for arsenic remediation has been extensively exercised using a wide range of adsorbents. Adsorbents used may range from naturally occurring and synthetic minerals to agricultural products and wastes. Bio-sorbent like fungi, algae and bacteria are considered environment friendly and can be used as alternate sorbents. Bio-sorption is a passive immobilization of arsenic by biomass and cell surface sorption mechanisms are independent of cell metabolism. The process is based upon physicochemical interactions between arsenic and functional groups of the cell walls mainly composed of polysaccharides, lipids and proteins and other binding sites. The use of fungi for bioremediation of water contaminated with toxic compounds has gathered unusual attention as they are found everywhere in the natural environment and are mostly the dominant organisms, particularly over a wide range of pH. Cell walls of fungi contain sufficient quantities of polysaccharides and proteins, which contains a number of functional groups (such as hydroxyl, carboxyl, phosphate, sulphate, and amino groups) that help in binding of metal ions. Many fungal species such as Aspergillus fumigatus, Aspergillus niger, Penicillium sp., Rhizopus arrhizus, Mucor miehei, Phanerochaete chrysosporium, have been studied for As sorption. Keeping in view the potential threat of As(III) to environment and importance of fungi in bioremediation, this thesis research was designed. For this study, fungal isolates were obtained from contaminated soils collected from peri-urban areas of Multan and Gujranwala under untreated industrial and/municipal effluents irrigation. The fungal strains were also obtained from nonpolluted soil of Islamabad. Eighteen (18) prominent fungal isolates (5 from Multan, 6 from Gujranwala and 7 isolated from Islamabad) were tested for arsenic (III) tolerance by growing on Potato Dextrose Agar (PDA) medium amended with increasing As(III) concentrations (50 to 5600 mg kg-1). Fungal isolates tolerance was evaluated by measuring Tolerance Index (TI), Minimum Inhibitory Concentrations (MIC) and tolerance level. Out of 18 isolates, 12 were belonged to genus Aspergillus, 3 to Fusarium, 2 to Curvularea and one to Penicillium. Fusarium oxysporum and Aspergillus fumigatus appeared to be most tolerant. Fungal strains isolated from Gujranwala soil exhibited more As(III) tolerance than those from Multan and Islamabad. Maximum fungal growth was observed at temperature 30 to 35 oC, pH 6 to 7 over a period of 96-120 hrs. Most of the isolates (11 out of 18) showed exponential reduction in radial growth with increase in As concentration from 0 to 300 mgL-1. Afterwards, these isolates showed gradual reduction in growth and after 2000 mg L-1, no growth was observed in these strains. While four strains (two from Gujranwala - A. fumigatus and F. oxysporum; one from Multan - A. fumigatus and one from Islamabad - A. fumigatus) grew even up to As (III) concentration of 5600 mg L-1. The four isolates, G-2, G-5, M-4 and I-5, were observed most arsenic resistant and out of the four isolates, three,G-2, M-4 and I-5 were identified as Aspergillus fumigatus and one, G-5, was identified as Fusarium oxysporum. These four As tolerant isolates were selected for As removal capacity from aqueous solution and As sorption studies. Treated (with NaOH and FeCl3) and untreated arsenic tolerant fungal bio-mass of each strain was equilibrated with synthetic aqueous solutions of varying As(III) concentrations ranging from 0 to 1000 mg L-1 for a period of 240 minutes on a rotary shaker at 150 rpm at temperature of 28 + 2 oC. As(III) removal capacities were calculated using mass balance equation. FeCl3-treated G-2 (Aspergillus fumigatus) fungal biomass removed 3.2 mg As g-1 fungal biomass wheraeas NaOH-treated biomass removed 2.83 mg g-1 and untreated biomass removed 2.66 mg As g-1 fungal biomass. Maximum increase in As (III) removal due to FeCl3 treatment was 33.65 % over untreated whereas alkali (NaOH) treatment enhanced 22.27 % As(III) removal over untreated. As(III) removals by untreated, NaOH- and FeCl3-treated Fusarium oxysporum (G-5) biomass were up to 2.56 mg g-1, 3.02 mg g-1 and 3.39 mg g-1, respectively. FeCl3-treatment increased As(III) removal up to 28.16% over untreated, whereas increase due to alkali-treatment was low (up to 19.26%). As(III) removal capacity of untreated and treated wet biomass of M-4 (Aspergillus fumigatus), isolated from Multan also showed that FeCl3-treated biomass removed more As(III) than NaOH-treated and untreated biomass. The maximum As (III) removal with FeCl3- treated fungal (M-4) biomass was 3.27 mg g-1, followed by removal with NaOHtreated biomass (2.93 mg g-1) and untreated biomass (2.72 mg g-1). There was an increase in As(III) removal due to FeCl3-treatment up to 63.37% than untreated biomass. The increase in As(III) removal due to NaOH treatment was relatively less, i.e., 22.48 %. Arsenic (III) removal capacities of I-5 (Aspergillus fumigatus),obtained from non-contaminated soil of Islamabad, was also studied as a function of the initial As(III) solution concentration and like earlier isolates As(III) removal by biomass treated with NaOH and FeCl3 was higher than untreated biomass at higher concentrations (>300 mg L-1). The maximum As(III) removal was with FeCl3-treated biomass (3.20 mg g-1), while NaOH-treated removed 2.85 mg g-1 and untreated biomass removed 2.63 mg g-1. FeCl3-treatment increased up to 31.95% As(III) removal whereas alkali-treatment enhanced 27.91%. In general, a linear increase in As(III) removal up to the concentration of 300 mg L-1 was observed and then was gradual increase from 300 to 700 mg L-1 As(III) concentration and afterwards there was almost no increase. The results indicated that treated and untreated biomass of all the four selected fungal isolates removed significant amounts of As(III) from synthetic arsenic aqueous solutions. The treatment of biomass with NaOH and FeCl3 further enhanced the As(III) removal. The FeCl3-treated biomass removed more As from aqueous solution than that treated with NaOH. The results also indicate that fungal strains belonged to Aspergillus fumigatus,either isolated from heavy metals contaminated soils or non-polluted soil were capable to grow and remove As(III) at higher concentrations showing that the fungus specie is more important than site of isolation. Arsenic sorption parameters i.e. maximum sorption capacity and binding strength of the treated and untreated fungal biomasses were calculated using classical sorption models, Langmuir and Freundlich. High values of Langmuir regression coefficient (r2) (≥0.97) indicated its better fitness to adsorption data of than that of Freundlich model having regression coefficient values ≤0.90. The treatment of fungal biomass, either with NaOH or FeCl3, increased the maximum adsorption capacity of As (III) significantly over untreated fungal biomass; while the FeCl3 treatment increased As (III) sorption more than that of NaOH treatment. The maximum As (III) sorption capacity obtained by FeCl3-treated fungal biomass was 3.65 mg As (III) g-1 of wet fungal biomass followed by 3.55 mg As (III) g-1 by fungal biomass treated with NaOH and 3.37 mg As (III) g-1 of untreated fungal biomass. The Langmuir maximum sorption capacity of Fusarium oxysporum (G-5) was 3.85 mg g-1 biomass treated with FeCl3 and was 3.32 and 2.76 mg g-1 for NaOH treated and untreated biomasses, respectively. Relatively high maximum Langmuir sorption capacities were observed in case of Aspergillus fumigatus (M-4), i.e., 3.846 mg g -1 , 4.00 mg g-1, 3.953 mg g-1 for untreated, NaOH- and FeCl3-treated wet biomasses, respectively. The fungal strain isolated from non-contaminated soil, Aspergillus fumigatus (I-5), also showed equally good sorption capacity when treated with FeCl3 (4.149 mg g-1) and slightly less sorption was observed when treated with NaOH (3.521 mg g-1) but was better than untreated (3.125 mg g-1). The FeCl3 treatment of fungal biomass proved better and enhanced more As sorption than that of NaOH treatment. Results indicate that the tested arsenic tolerant fungal strains could remove significant amounts of arsenic from arsenic ammended media under laboratory conditions and the fungal strains may be used as an effective sorbent in arsenic removal technology from arsenic contaminated waters and soils." xml:lang="en_US