S.K.T. Nasar
[Please see http://www.fao.org/biotech/logs/C14/020407.htm;
FAO Forum Conference (Water) – 2 April 2007]
Sanyal and Nasar (2002, 2003 and 2005) showed that arsenic contamination in agriculture is a water-related disaster jointly with droughts, floods or other unwanted conditions. Nasar et al. (2003) indicated how arsenic-contaminated hazardous agricultural products lose marketability under Sanitary and Phytosanitary Measures. (References to these articles are given below). Developing countries oblivious of the consequences focus chiefly on additional rather than on clean food in the face of the globalised open market economy and their rising populations. We firmly believe that both the quantity and quality of irrigation water-to-food continuum warrant equal importance.
The widespread arsenic (mainly As III) contamination of groundwater-irrigation water-soil-crop-animal-human continuum is a global concern. Soil is an effective sink and absorbs arsenic thereby reducing its entry into the food web. A number of weedy flowering and nonflowering plant species, crop varieties, bacteria and cyanobacteria that absorb high amounts of As III are recorded. Published work and our experience propose that arsenic contamination of soil is reduced by hyperaccumulator species of plants. Pteris vittata, a fern, is a well-known example. Developing countries can and should identify location-specific hyperaccumulators as we are doing in West Bengal, India, for use in phytoremediation options for contaminated soils.
We recommend the use of green water for irrigation purposes. Where there is no alternative to using As-contaminated ground water for irrigation, it is recommended that this blue water should first be ponded for 24-72 hours before use in irrigation. Arsenic sinks to the benthos during ponding. The mechanism is unclear. Empirical evidence indicates that suspended soil particles, organic matter, phytoplankton and zooplankton hyperaccumulate arsenic from the ponded water thereby leaving it with substantially reduced contaminant load. Suspended particles and dead plankton settle to the bottom taking along the absorbed or adsorbed arsenic compounds. [The term 'benthos' refers to the organisms that live on or in the bottom of a body of water...Moderator].
There are, however, pitfalls in such non-rDNA (recombinant DNA) technologies. The toxic arsenite species is very slowly, if at all, converted into the less toxic arsenate compounds or to the least toxic volatile arsine forms. Most developing countries lack adequate resources of infrastructure and expertise for large scale monitoring of arsenic species in ecosystem components. Dumping of the after-use hyperaccumulating organisms or the filtrates where arsenic filters have been used is another predicament. Toxic arsenic is thrown back to the ecosystem if not dumped properly. Dumping by deep burial of after-use hyperaccumulating organisms in steel capsules is too costly for developing countries. Other protocols are required.
Large-scale affordable rDNA technology application for remediation of arsenic contamination is not available. Genes and genetic systems vis-a-vis arsenic resistance and conversion in bacterial species are well documented. Sporadic reports on higher plants and humans are appearing with a rising frequency. It is now noticeably possible that large-scale application protocols of gene construct, transformant and transgenic plant for conversion of toxic arsenic compounds will soon become globally available. At present, developing countries should opt for collection, identification and large scale use of organisms that hyperaccumulate and convert arsenic species. More efficient microbes should be selected and put back together into arsenic-contaminated ecosystems for horizontal gene transfers (HGT; equivalent to naturally occurring rDNA processes) to work. A gene hunt for desirable genomes of reharvested microbes from time to time will yield gene reconstructs that will be location specific and in the public domain. It is well documented that different bacterial species contain genes for resistance to arsenic while some are also known to convert arsenic species, say from As 3 to As 5. I believe that if these (species) genomes are placed together in high-arsenic environments, HGT will naturally create over time new genomes harboring both resistance and conversion genes together. This may not appear to be much of a science but has been happening in nature throughout evolutionary history of organisms. HGT happens among bacterial species in just hundred to thousand generations. Dhankher et al. 2002-reported rDNA engineered Arabidopsis thalliana for arsenic phytoremediation (http://www.genetics.uga.edu/rbmlab/pubs.html). This opens up the possibility of producing plant species for a similar purpose. However, in the present context, I recommend current non-rDNA options for developing countries and that they should simultaneously create infrastructure and expertise in rDNA technology options.
Selenium contamination together with arsenic contamination in groundwater is reported. Multiple contaminations are fast appearing as the rule rather than the exception. This creates complexity for rDNA technology application in this context. Reduced quantity of irrigation water, selection of varieties containing lesser amounts of embedded water and the combined use of traditional and rDNA biotechnologies form the current option for developing countries. We believe that similar strategies are applicable for different contaminants and locations.
Prof. S.K.T. Nasar,
Visiting Professor (Genetics),
Department of Environmental Science,
University of Burdwan
West Bengal
India
skt.nasar @ gmail.com
References:
S.K. Sanyal and S.K.T. Nasar. 2002. Arsenic contamination of groundwater in West Bengal (India): Build-up in soil-crop systems. Paper presented to the International Conference on Water Related Disasters held in Kolkata on 5-6 December 2002.
S.K. Sanyal and S.K.T. Nasar. 2002. Arsenic contamination of groundwater in West Bengal (India): Build-up in soil-crop systems. In Analysis and Practice in Water Resource Engineering for Disaster Mitigation, New Age (P) Publishers, New Delhi, pp. 216-222.
S.K. Sanyal and S.K.T. Nasar. 2002. Arsenic contamination of groundwater in West Bengal (India): build-up in soil-crop systems. Jalvigyan Sameeksha (Hydrology Review), Volume 17, Number 1-2, pp. 49-63.
Nasar, S.K.T., Sanyal, S.K. and Bagchi, B. 2003. Negation of marketable quality and rice by arsenic contamination: mitigation options for Bengal-Delta Basin; Paper presented: International Symposium on Emerging Strategies for Reliability; December 12-14, 2003; Organised by Indian Association for Productivity, Quality and Reliability, Kolkata, India
S.K. Sanyal and S.K.T. Nasar. 2005. Arsenic Contamination in Groundwater of the Bengal Delta Basin: Implications in Agricultural Systems. In arsenic pollution in west Bengal; 5-6 August 2005, Organised by Srikrishna College Bagula. Nadia
[Please see http://www.fao.org/biotech/logs/C14/020407.htm;
FAO Forum Conference (Water) – 2 April 2007]
Sanyal and Nasar (2002, 2003 and 2005) showed that arsenic contamination in agriculture is a water-related disaster jointly with droughts, floods or other unwanted conditions. Nasar et al. (2003) indicated how arsenic-contaminated hazardous agricultural products lose marketability under Sanitary and Phytosanitary Measures. (References to these articles are given below). Developing countries oblivious of the consequences focus chiefly on additional rather than on clean food in the face of the globalised open market economy and their rising populations. We firmly believe that both the quantity and quality of irrigation water-to-food continuum warrant equal importance.
The widespread arsenic (mainly As III) contamination of groundwater-irrigation water-soil-crop-animal-human continuum is a global concern. Soil is an effective sink and absorbs arsenic thereby reducing its entry into the food web. A number of weedy flowering and nonflowering plant species, crop varieties, bacteria and cyanobacteria that absorb high amounts of As III are recorded. Published work and our experience propose that arsenic contamination of soil is reduced by hyperaccumulator species of plants. Pteris vittata, a fern, is a well-known example. Developing countries can and should identify location-specific hyperaccumulators as we are doing in West Bengal, India, for use in phytoremediation options for contaminated soils.
We recommend the use of green water for irrigation purposes. Where there is no alternative to using As-contaminated ground water for irrigation, it is recommended that this blue water should first be ponded for 24-72 hours before use in irrigation. Arsenic sinks to the benthos during ponding. The mechanism is unclear. Empirical evidence indicates that suspended soil particles, organic matter, phytoplankton and zooplankton hyperaccumulate arsenic from the ponded water thereby leaving it with substantially reduced contaminant load. Suspended particles and dead plankton settle to the bottom taking along the absorbed or adsorbed arsenic compounds. [The term 'benthos' refers to the organisms that live on or in the bottom of a body of water...Moderator].
There are, however, pitfalls in such non-rDNA (recombinant DNA) technologies. The toxic arsenite species is very slowly, if at all, converted into the less toxic arsenate compounds or to the least toxic volatile arsine forms. Most developing countries lack adequate resources of infrastructure and expertise for large scale monitoring of arsenic species in ecosystem components. Dumping of the after-use hyperaccumulating organisms or the filtrates where arsenic filters have been used is another predicament. Toxic arsenic is thrown back to the ecosystem if not dumped properly. Dumping by deep burial of after-use hyperaccumulating organisms in steel capsules is too costly for developing countries. Other protocols are required.
Large-scale affordable rDNA technology application for remediation of arsenic contamination is not available. Genes and genetic systems vis-a-vis arsenic resistance and conversion in bacterial species are well documented. Sporadic reports on higher plants and humans are appearing with a rising frequency. It is now noticeably possible that large-scale application protocols of gene construct, transformant and transgenic plant for conversion of toxic arsenic compounds will soon become globally available. At present, developing countries should opt for collection, identification and large scale use of organisms that hyperaccumulate and convert arsenic species. More efficient microbes should be selected and put back together into arsenic-contaminated ecosystems for horizontal gene transfers (HGT; equivalent to naturally occurring rDNA processes) to work. A gene hunt for desirable genomes of reharvested microbes from time to time will yield gene reconstructs that will be location specific and in the public domain. It is well documented that different bacterial species contain genes for resistance to arsenic while some are also known to convert arsenic species, say from As 3 to As 5. I believe that if these (species) genomes are placed together in high-arsenic environments, HGT will naturally create over time new genomes harboring both resistance and conversion genes together. This may not appear to be much of a science but has been happening in nature throughout evolutionary history of organisms. HGT happens among bacterial species in just hundred to thousand generations. Dhankher et al. 2002-reported rDNA engineered Arabidopsis thalliana for arsenic phytoremediation (http://www.genetics.uga.edu/rbmlab/pubs.html). This opens up the possibility of producing plant species for a similar purpose. However, in the present context, I recommend current non-rDNA options for developing countries and that they should simultaneously create infrastructure and expertise in rDNA technology options.
Selenium contamination together with arsenic contamination in groundwater is reported. Multiple contaminations are fast appearing as the rule rather than the exception. This creates complexity for rDNA technology application in this context. Reduced quantity of irrigation water, selection of varieties containing lesser amounts of embedded water and the combined use of traditional and rDNA biotechnologies form the current option for developing countries. We believe that similar strategies are applicable for different contaminants and locations.
Prof. S.K.T. Nasar,
Visiting Professor (Genetics),
Department of Environmental Science,
University of Burdwan
West Bengal
India
skt.nasar @ gmail.com
References:
S.K. Sanyal and S.K.T. Nasar. 2002. Arsenic contamination of groundwater in West Bengal (India): Build-up in soil-crop systems. Paper presented to the International Conference on Water Related Disasters held in Kolkata on 5-6 December 2002.
S.K. Sanyal and S.K.T. Nasar. 2002. Arsenic contamination of groundwater in West Bengal (India): Build-up in soil-crop systems. In Analysis and Practice in Water Resource Engineering for Disaster Mitigation, New Age (P) Publishers, New Delhi, pp. 216-222.
S.K. Sanyal and S.K.T. Nasar. 2002. Arsenic contamination of groundwater in West Bengal (India): build-up in soil-crop systems. Jalvigyan Sameeksha (Hydrology Review), Volume 17, Number 1-2, pp. 49-63.
Nasar, S.K.T., Sanyal, S.K. and Bagchi, B. 2003. Negation of marketable quality and rice by arsenic contamination: mitigation options for Bengal-Delta Basin; Paper presented: International Symposium on Emerging Strategies for Reliability; December 12-14, 2003; Organised by Indian Association for Productivity, Quality and Reliability, Kolkata, India
S.K. Sanyal and S.K.T. Nasar. 2005. Arsenic Contamination in Groundwater of the Bengal Delta Basin: Implications in Agricultural Systems. In arsenic pollution in west Bengal; 5-6 August 2005, Organised by Srikrishna College Bagula. Nadia
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