Many interesting study about arsenic and its cycling in environment has been extensively
conducted by researcher in the world. One factor that makes it important to be a focus research
is because of arsenic (As) can occur in many different physicochemical form, red-ox state and
chemicals speciation such as volatile, water-soloble and lipid soluble. This different red-ox states
and chemical form that was varied depend on environmental condition and organism metabolic;
determine the toxicity level of the compound would be. The inorganic form of As [arsenite (As III)
and arsenate (As V)], for example, is more toxic than its organic forms. MMAA and DMAA (Mono
and Dimethyl arsenic acid), the methylated form of As, is less toxic and dominate in biomass and soil.
Arsenobetaine and arsenocholine are relatively non-toxic and have been identified to be the major
arsenical in variety of seafood products (Branch, et al. 1994). Other factors, the occurrence of As
or other its form in high level in environment, microbial interaction or sometime biotransformation
in such microorganism still remains unknown, for example how the organism or microorganism
still tolerate with the high concentration of As compound or it became one of their needs in their
metabolism.
Arsenic comes into environment through both naturally (one third of occurrence in
atmosphere) and due to certain human activities (the rest). In seawater, level of arsenic is the lowest.
However, research reported the high levels of total arsenic were detected in marine organisms, such
as phytoplankton, Phaeophyta and Rhodophyta (Bu-Olayan, et al. 2001; Maher, et al. 2003). Because
of the toxicity of arsenic highly depend on its chemical speciation, the determination of total arsenic
is not sufficient and thus, attempts to analysis each speciation have been developed by many scientist.
Recent result showed that in all seafood sample obtained from market in Canada the majority of
arsenic present was in the form of arsenobetaine, a non toxic arsenic species (Ackley, et al. 1999).
Arsenate (As (V)) ion in marine environment has closeness in the physicochemical or mimetic effect
with phosphate ion which difficulty of membrane cell of some organism, as insufficiently distinguish
them. Thus it is taken up by marine organisms via phosphate transporter by a number of organisms
(including phytoplankton, algae, crustaceans, and mollusk), methylated and further metabolized
into organic compounds, some of which enters the food chain as organoarsenic compounds
(arsenobetaine). In soil, arsenic can occur in arsenate, arsenite, MMAA, DMAA, arsenobetaine, and
arsenocholine. Transformation of arsenate to arsenite and further methylated to MMAA and in another
step to DMAA. This methylation is the process base in environmental cycle of arsenic. However,
predominant species of arsenic is arsenate and transformation of arsenate only takes place in small
amount (Pongratz, 1998).
In the bad condition, high concentration of arsenic and its form can detect in
drinking water and groundwater. However, because of EPA (2002) standard had decided that
the level of arsenic must below 10 μg/L. This make research on attempt to bio-remediate
contaminated place (marine and soil) by microorganisms has extensively studied. One of
microorganisms model for the bioremediation of arsenic are Corynebacterium glutamicum
(Mateos, et. al. 2006). However, mix method of bioremediation and phytoremediation has
been considered to be a novel method for detoxification of arsenic in environment. This is
because once arsenic and also other heavy metals released into environment, they cannot be
destroyed but possible to detoxification by using change their red-ox state or make as a non-
toxic. In case of arsenic, the organic form in non-toxic form, but it is completely different with
mercury that the organic form is more toxic than inorganic forms. Therefore, it is important to
understand the toxicity of different state and chemical speciation of arsenic to human. The
same important also to find the suitable method for detoxification of this metal(oid)s because it
is well known that the methylation mechanisms by microorganism is also including the
transformation from As (III) to As (V), not only from As(V) to As(III). So, clear information
for this transformation led us considered the effect of As in environment. But, in my opinion,
microorganism of organisms has suitable way for them to adapt with their environment, by
which they use As as metabolism or the try to detoxificate it as long as the concentration is still
lower than their capability to convert them.
I am very thanks for your lecture on February 10, 2012. It was very informative study
that I ever get. I actually, work in bioremediation of crude oil and PAHs in environment.
Information about arsenic contamination and it cycling in environment from this lecture has
opened my mind that the red-ox state, chemical speciation, environmental condition, and
detoxification ability of microorganisms should be considered.
Refferences:
1. Acklye, K/ L., et. al. J. Anal. At. Spectrom., 1999, 14. 845-850.
2. Mateos, L.M., et. al. International microbiology, 2006, 9. 207-2015
3. Pongratz, R. J. The Sci. of The Tot. Environ. 1998. 224. 133-141
4. Pletsch, M. et. al. Biotechnol. Adv. 1999. 17. 679-687
5. Lloyd. J. R. et. al. Elements. 2006. 2. 85-90
6. Qin, J. et. al. PNAS. 2009.106. 5213-5217
7. Cullen, W. et. al. Chem. Rev. 1989. 89. 713-764
8. Francesconi, K. A. Pure Appl. Chem. 2010. 82. 373-381
9. Bu-Olayan. A. H. et. al. The Environmentalist. 2001. 21. 71-75
10. Turpeinen, R. The Sci. of The Tot. Environ. 1999. 236. 173-180
11. Zouboulis A. I. et. al. Envrion. Intern. 2005. 31. 213-219
12. Kaise, T. et. al. Appl. Organometal. Chem. 1999. 13. 107-111
13. EPA. 2002.
Many interesting studies about arsenic and its cycling in environment have been extensively conducted by researchers in the world. One factor that makes it important to be a focus research is because of arsenic (As) can occur in many different physicochemical form, red-ox state and chemicals speciation such as volatile, water-soloble and lipid soluble. This different red-ox states and chemical form that was varied depend on environmental condition and organism metabolic; determine the toxicity level of the compound would be. The inorganic form of As [arsenite (As III) and arsenate (As V)], for example, is more toxic than its organic forms. MMAA and DMAA (Mono and Dimethyl arsenic acid), the methylated form of As, is less toxic and dominate in biomass and soil. Arsenobetaine and arsenocholine are relatively non-toxic and have been identified to be the major arsenical in variety of seafood products (Branch, et al. 1994). Other factors, the occurrence of As or other its form in high level in environment, microbial interaction or sometime biotransformation in such microorganism still remains unknown, for example how the organism or microorganism still tolerate with the high concentration of As compound or it became one of their needs in their metabolism.
Arsenic comes into environment through both naturally (one third of occurrence in atmosphere) and due to certain human activities (the rest). In seawater, level of arsenic is the lowest. However, research reported the high levels of total arsenic were detected in marine organisms, such as phytoplankton, Phaeophyta and Rhodophyta (Bu-Olayan, et al. 2001; Maher, et al. 2003). Because of the toxicity of arsenic highly depend on its chemical speciation, the determination of total arsenic is not sufficient and thus, attempts to analysis each speciation have been developed by many scientist. Recent result showed that in all seafood sample obtained from market in Canada the majority of arsenic present was in the form of arsenobetaine, a non toxic arsenic species (Ackley, et al. 1999). Arsenate (As (V)) ion in marine environment has closeness in the physicochemical or mimetic effect with phosphate ion which difficulty of membrane cell of some organism, as insufficiently distinguish them. Thus it is taken up by marine organisms via phosphate transporter by a number of organisms (including phytoplankton, algae, crustaceans, and mollusk), methylated and further metabolized into organic compounds, some of which enters the food chain as organoarsenic compounds (arsenobetaine). In soil, arsenic can occur in arsenate, arsenite, MMAA, DMAA, arsenobetaine, and arsenocholine. Transformation of arsenate to arsenite and further methylated to MMAA and in another step to DMAA. This methylation is the process base in environmental cycle of arsenic. However, predominant species of arsenic is arsenate and transformation of arsenate only takes place in small amount (Pongratz, 1998).
In the bad condition, high concentration of arsenic and its form can detect in drinking water and groundwater. However, because of EPA (2002) standard had decided that the level of arsenic must below 10 μg/L. This make research on attempt to bio-remediate contaminated place (marine and soil) by microorganisms has extensively studied. One of microorganisms model for the bioremediation of arsenic are Corynebacterium glutamicum (Mateos, et. al. 2006). However, mix method of bioremediation and phytoremediation has been considered to be a novel method for detoxification of arsenic in environment. This is because once arsenic and also other heavy metals released into environment, they cannot be destroyed but possible to detoxification by using change their red-ox state or make as a non-toxic. In case of arsenic, the organic form in non-toxic form, but it is completely different with mercury that the organic form is more toxic than inorganic forms. Therefore, it is important to understand the toxicity of different state and chemical speciation of arsenic to human. The same important also to find the suitable method for detoxification of this metal(oid)s because it is well known that the methylation mechanisms by microorganism is also including the transformation from As (III) to As (V), not only from As(V) to As(III). So, clear information for this transformation led us considered the effect of As in environment. But, in my opinion, microorganism of organisms has suitable way for them to adapt with their environment, by which they use As as metabolism or the try to detoxificate it as long as the concentration is still lower than their capability to convert them.
References:
1. Acklye, K/ L., et. al. J. Anal. At. Spectrom., 1999, 14. 845-850.
2. Mateos, L.M., et. al. International microbiology, 2006, 9. 207-2015
3. Pongratz, R. J. The Sci. of The Tot. Environ. 1998. 224. 133-141
4. Pletsch, M. et. al. Biotechnol. Adv. 1999. 17. 679-687
5. Lloyd. J. R. et. al. Elements. 2006. 2. 85-90
6. Qin, J. et. al. PNAS. 2009.106. 5213-5217
7. Cullen, W. et. al. Chem. Rev. 1989. 89. 713-764
8. Francesconi, K. A. Pure Appl. Chem. 2010. 82. 373-381
9. Bu-Olayan. A. H. et. al. The Environmentalist. 2001. 21. 71-75
10. Turpeinen, R. The Sci. of The Tot. Environ. 1999. 236. 173-180
11. Zouboulis A. I. et. al. Envrion. Intern. 2005. 31. 213-219
12. Kaise, T. et. al. Appl. Organometal. Chem. 1999. 13. 107-111
13. EPA. 2002.