**1. Introduction**

Environmental pollution with heavy metals is caused by anthropogenic and natural actions. Discharges of wastewater from various industrial activities such as electroplating, mining, paint factory, plastics, coating metal cables, and automotive radiators, and certain industries producing energy, metal engineering industry and producers of welding materials contain high concentrations of metals. Several heavy metals are highly toxic and ingestion of these metals by drinking contaminated water or breathing polluted air can cause serious health problems in human beings. Several metals are considered toxic at certain levels of concentra‐ tions in wastewater, such as arsenic, cadmium, cobalt, copper, chromium, nickel, lead and mercury. Unlike the organic compounds, heavy metals cannot be biodegraded or destroyd, therefore they must be removed. There are several methods for removal of heavy metals: ion exchange, membrane separation, and separation and electrochemical adsorption on various adsorbents. [1].

Chromium (Cr) is one of the major environmental pollutants coming from industrial effluents and tannery. It is considered the major pollutant cataloged by the United States Environmental Protection Agency (EPA: www.epa.gov), since it is stable in aqueous solution and hence high in mobility in different environments. Chromium is a metal element in the periodic table. It is odorless and tasteless; is found in rocks, plants, soil, and volcanic dust, humans and animals; and exists in the environment most commonly as the trivalent [(chromium (III))], hexavalent [(chromium (VI))] and metallic [(chromium (0))]. Chromium (III) is generally contained in many vegetables, fruits, meats, grains and yeast. Industrial processes generally produce chromium (VI) and chromium (0). The main sources of chromium (VI) in drinking water are discharges from steel and pulp, and erosion of natural deposits of chromium (III). In many places, chromium compounds have been scattered to the environment through leaks, poor storage or improper disposal practices. The chromium compounds are very persistent in water and sediment [2].

Chromium is regarded as an environmental pollutant due to its wide use in various industrial activities, such as electrolytic plating, leather tanning, explosives manufacturing etc. The stable forms of chromium in the environment are trivalent (Cr (III)) and hexavalent chromium (Cr (VI)). Further, Cr (VI) is highly soluble, making it mobile in soil and aquatic environments, with consequent toxicity ecosystems. Chromium in their different forms can be use in the production of steel alloys and other metals chromed, for dyes and pigments, and the preser‐ vation of leather and wood. It can also be find naturally in the soil. The primary forms of chromium found in nature are chromium (III) and chromium (VI) and these forms are converted to each other depending on environmental conditions [2]. Cr (VI) is consider the most toxic form of chromium, and is usually associated with oxygen as chromates (CrO4 –2) and dichromates (Cr2O7 –2) [3], which due to its high solubility are highly mobile in soil environ‐ ments and water [4]. Moreover, Cr (III) is in the form of oxides, hydroxides or poorly soluble sulfates, by which it is much less mobile, and there joined organic matter in the soil and aquatic environments [5, 6]. Cr (VI) is a strong oxidizing agent, and in the presence of organic matter is reduced to Cr (III); this transformation is faster in acidic environments [3]. However, high levels of Cr (VI) may exceed the reducing capacity of the environment and thus can persist as a contaminant. It has been established now that various chromium compounds as oxides, chromates and dichromates, are environmental contaminants in water, soil, and industrial effluents, because this metal is widely used in various manufacturing, such as electrolytic plating, explosives manufacturing, leather tanning, metal alloy, dyes and pigments manufac‐ turing, etc. [1, 5].

**1. Introduction**

166 Advances in Bioremediation of Wastewater and Polluted Soil

adsorbents. [1].

and sediment [2].

dichromates (Cr2O7

Environmental pollution with heavy metals is caused by anthropogenic and natural actions. Discharges of wastewater from various industrial activities such as electroplating, mining, paint factory, plastics, coating metal cables, and automotive radiators, and certain industries producing energy, metal engineering industry and producers of welding materials contain high concentrations of metals. Several heavy metals are highly toxic and ingestion of these metals by drinking contaminated water or breathing polluted air can cause serious health problems in human beings. Several metals are considered toxic at certain levels of concentra‐ tions in wastewater, such as arsenic, cadmium, cobalt, copper, chromium, nickel, lead and mercury. Unlike the organic compounds, heavy metals cannot be biodegraded or destroyd, therefore they must be removed. There are several methods for removal of heavy metals: ion exchange, membrane separation, and separation and electrochemical adsorption on various

Chromium (Cr) is one of the major environmental pollutants coming from industrial effluents and tannery. It is considered the major pollutant cataloged by the United States Environmental Protection Agency (EPA: www.epa.gov), since it is stable in aqueous solution and hence high in mobility in different environments. Chromium is a metal element in the periodic table. It is odorless and tasteless; is found in rocks, plants, soil, and volcanic dust, humans and animals; and exists in the environment most commonly as the trivalent [(chromium (III))], hexavalent [(chromium (VI))] and metallic [(chromium (0))]. Chromium (III) is generally contained in many vegetables, fruits, meats, grains and yeast. Industrial processes generally produce chromium (VI) and chromium (0). The main sources of chromium (VI) in drinking water are discharges from steel and pulp, and erosion of natural deposits of chromium (III). In many places, chromium compounds have been scattered to the environment through leaks, poor storage or improper disposal practices. The chromium compounds are very persistent in water

Chromium is regarded as an environmental pollutant due to its wide use in various industrial activities, such as electrolytic plating, leather tanning, explosives manufacturing etc. The stable forms of chromium in the environment are trivalent (Cr (III)) and hexavalent chromium (Cr (VI)). Further, Cr (VI) is highly soluble, making it mobile in soil and aquatic environments, with consequent toxicity ecosystems. Chromium in their different forms can be use in the production of steel alloys and other metals chromed, for dyes and pigments, and the preser‐ vation of leather and wood. It can also be find naturally in the soil. The primary forms of chromium found in nature are chromium (III) and chromium (VI) and these forms are converted to each other depending on environmental conditions [2]. Cr (VI) is consider the most toxic form of chromium, and is usually associated with oxygen as chromates (CrO4

ments and water [4]. Moreover, Cr (III) is in the form of oxides, hydroxides or poorly soluble sulfates, by which it is much less mobile, and there joined organic matter in the soil and aquatic environments [5, 6]. Cr (VI) is a strong oxidizing agent, and in the presence of organic matter is reduced to Cr (III); this transformation is faster in acidic environments [3]. However, high

–2) [3], which due to its high solubility are highly mobile in soil environ‐

–2) and

There are studies of many methods for removal of chromium ion present in water industrial waste, for example: ion exchange on resins, coagulation-flocculation, adsorption on activated carbon, reduction, chemical precipitation, sedimentation, etc., [7], which in most cases are expensive or inefficient, especially when the concentration of these ions is very low [8]. Therefore arise emerging technologies such as biosorption, the process of attracting various chemical species by biomass (live or dead), by physicochemical mechanisms as adsorption or ion exchange [9].

Fungal cells interact with chromium at different levels from the cell wall and, from the periplasm to the cytoplasm and cell organelles. These microorganisms require detecting and regulating intracellular levels of chromium through homeostasis systems that maintain a balance between the incorporation, expulsion, and arrest of metal [1]. It is common for native microorganisms of sites contaminated with chromate ion, show resistance because they have asset or liability mechanisms that allow them to remove from detoxification. In certain species these mechanisms are know in detail, some of which are of basic interest and biotechnological importance, the latter in the context of developing new technologies for the treatment of industrial effluents and for bioremediation of contaminated sites. These mechanisms generally include biotransformation of Cr (VI) reduced species (chemical reduction), which may be direct (enzymatic) or indirect (enzyme); incorporation and bioaccumulation; biosorption of Cr (III), and Cr (VI); and immobilization [1, 9]. Some filamentous fungi reduce Cr (VI) to Cr (III), by different mechanisms of Cr (VI) detoxification, like reducing power generated by carbon metabolism [10, 11, and 12]. *Aspergillus niger* var. *tubingensis* Ed8, has demonstrated the ability to both biotransform Cr (VI) and accumulate it in the biomass, by a reduction and a sorption processes, using electron microscopy techniques [13].

*Aspergillus niger* strains have been described as coping with chromium mainly via the bio‐ sorption of the metal into the cells, rather than via the use of reducing activity [14]. Extracellular reduction of Cr (VI) to Cr (III) was observed during the growth of *Candida utilis* by mechanisms independent from the intensity of culture growth or initial chromium concentration [15], and they hypothesized that Cr (VI) reduction in *C. utilis* could be partly dependent on pH changes of broth during the exponential phase or on exo-enzymatic activities during stationary phase. Also, the biosorption of this metal has has been investigated in different fungi and yeast: *Cyberlindnera fabianii, Wickerhamomyces anomalus* and *Candida tropicalis* in aqueous solutions at different pH conditions. Cr (VI), and pH range between 2 and 4 where the most effective for the three species [16]. Secondly, *Candida maltosa*, isolated from tanning liquors from a leather factory has the capacity to reduce Cr (VI) both in the presence of viable intact cells and in cellfree extracts [17]. This ability was related to NADH-dependent chromate reductase activity associated with soluble proteins and, to a lesser extent, with the membrane fraction [17]. Recently, the reduction of Cr (VI) to Cr (III) through an enzymatic mechanism has been observed in *Pichia*. Both in intact cells and in cell-free extracts of *P. jadinii* M9 and *P. anomala* M10 strains, chromate was reduced, suggesting the presence of a chromate reductase activity possibly associated with the cytosolic or membrane proteins [18]. In the bacteria *Pseudomonas putida* F1, challenged with Cr (VI) in minimal médium (instead of in the complex LB medium), an ATPase involved in DNA repair-like protein (Pput 2963) was overexpressed compared with untreated cultures, suggesting that DNA damage occurs [19], and a non-enzymatic mechanism of Cr (VI) reduction has been described for *A. niger* [20]. The purpose of this chapter is to elucidate the characteristics of removal of chromium (VI) by *Penicillium* sp. IA-01cells.

#### **2. Materials and methods**

#### **2.1. Screening of the microorganism showing the resistant to Chromium (VI) and chromate resistance test**

We isolate a chromate resistant mycelial fungus from polluted air near the Faculty of Chemical Science, UASLP (San Luis Potosí, México), and this was used for the screening. The chromate resistant filamentous fungus contained in the air was grown on the Petri dish containing modified Lee's minimal medium (LMM) (with 0.25% KH2PO4, 0.20% MgSO4, 0.50% (NH4)2SO4, 0.50% NaCl, 0.25% glucose, and 2% agar) supplemented with 500 mg/L K2CrO4; the pH of the medium was adjusted and maintained at 5.3 with 100 mmol/L citrate-phosphate buffer. The plates were incubated at 28<sup>∘</sup> C for seven days. The strain was identified based on characteristic macroscopic and microscopic observation [21]. Fungal cultures grown in thioglycolate broth were used as primary inoculums. Chromate-resistant tests of the isolated strain, filamentous fungus *Penicillium* sp IA-01, were perform on liquid LMM containing the appropriate nutritional requirements and different concentrations of Cr (VI) (as potassium chromate), and the dry weight was determined.

#### **2.2. Biosorption tests by using dry cells**

The fungal cells was grown at 28°C in an stirred and aerated liquid media containing thiogly‐ colate broth at a concentration of 8g/L (p/v). After five days of incubation, the cells were recovered by centrifugation (3000 rpm/10 min), and washed twice in the same conditions with deionized wáter, and subsequently it was dry (80°C/24 h) in an oven. Solutions of Cr (VI) for analysis, were prepared by diluting 71.86mg/L of stock metal solution. The concentration range of chromium (VI) solutions was 50-1000mg/L. The pH of each solution was adjusted to the required value by adding 1M H2SO4 solution before mixing with the microorganism. The biosorption of the metal by fungal dry cells was determined at different concentrations (50– 1,000mg/L) of 100 mL Cr (VI) solution, with 1g of fungal biomass, at 120 rpm, and the sample was filtered. The filtrate containing the residual concentration of Cr (VI) was determined spectrophotometrically. For the determination of rate of metal biosorption, 200, 400, 600, 800, and 1,000mg/L of Cr (VI) solution was used. The supernatant was analyzed for residual Cr (VI) after the contact period at different times. For determination of the effects of pH and temperature, four solutions (pH 1, 2, 3, and 4) and temperatures (28, 40, 50, and 60℃) were respectively used.

Moreover, biosorption to the contaminated soil and water was examined. Four Erlenmeyer glass flasks containing 5g of fungal biomass and 20g of contaminated soil and 20 mL of water (297mg Cr (VI)/g soil or 155mg Cr(VI)/L water), of tannery (Celaya, Guanajuato, México), was completed to 100 mL with trideionized water, were incubated during seven days at 120 rpm, and filtered in Whatman filter paper No. 1, and the concentration of Cr (VI) of the filtrate analyzed with 1, 5 diphenylcarbazide [22].
