What is the role of GMAC?
To ensure public safety in Singapore while allowing for the commercial use of GMOs and GMO-derived products by companies and research institutions, in compliance with international standards.
What are some of the guidelines for release of sgriculture-related Genetically Modified Organisms (GMOs)?
Notification and approval of GMAC is required before GMOs can be used. Proposal is also required to be submitted to GMAC, whereby informations such as Species of organisms, Eventual use of GMO, Location for release, Habitat and ecology, Genetics of the GMO, Data from contained work and other studies, Experimental procedures, monitoring and contingency planning needs to be provided. (Section A of Appendix 1) http://www.gmac.gov.sg/guidelines/agriculture_appendix_1_a.html
What are the objectives of the guidelines?
1. To ensure the safe movement and use in Singapore of agriculture-related GMOs.
2. To provide a common framework for:(a) assessment of risks of agriculture-related GMOs to human health and the environment; and(b) approval mechanisms for their release in Singapore.
3. These Guidelines address issues related to food safety based on the concept of substantial equivalence.
Adapted from : http://www.gmac.gov.sg/guidelines/agriculture_guidelines.html
Monday, July 30, 2007
Friday, July 20, 2007
Atomic absorption spectroscopy
In analytical chemistry, Atomic absorption spectroscopy is a technique for determining the concentration of a particular metal element in a sample. Atomic absorption spectroscopy can be used to analyse the concentration of over 62 different metals in a solution.
Although atomic absorption spectroscopy dates to the nineteenth century, the modern form was largely developed during the 1950s by a team of Australian chemists. They were lead by Alan Walsh and worked at the CSIRO (Commonwealth Science and Industry Research Organisation) Division of Chemical Physics in Melbourne, Australia. The technique typically makes use of a flame to atomize the sample, but other atomizers such as a graphite furnace are also used. Three steps are involved in turning a liquid sample into an atomic gas:
Desolvation – the liquid solvent is evaporated, and the dry sample remains
Vaporisation – the solid sample vaporises to a gas
Volatilisation – the compounds making up the sample are broken into free atoms.
The flame is arranged such that it is laterally long (usually 10cm) and not deep. The height of the flame must also be monitored by controlling the flow of the fuel mixture. A beam of light passes through this flame at its longest axis (the lateral axis) and hits a detector.
The light that is focused into the flame is produced by a hollow cathode lamp. Inside the lamp is a cylindrical metal cathode containing the metal for excitation, and an anode. When a high voltage is applied across the anode and cathode, the metal atoms in the cathode are excited into producing light with a certain emission spectra. The type of hollow cathode tube depends on the metal being analysed. For analysing the concentration of copper in an ore, a copper cathode tube would be used, and likewise for any other metal being analysed. The electrons of the atoms in the flame can be promoted to higher orbitals for an instant by absorbing a set quantity of energy (a quantum). This amount of energy is specific to a particular electron transition in a particular element. As the quantity of energy put into the flame is known, and the quantity remaining at the other side (at the detector) can be measured, it is possible to calculate how many of these transitions took place, and thus get a signal that is proportional to the concentration of the element being measured.
Background correction methods
The narrow linewidths of hollow cathode lamps make spectral overlap rare. That is, it is unlikely that an absorption line from one element will overlap with another. Molecular emission is much broader, so it is more likely that some molecular absorption band will overlap with an atomic line. This can result in artificially high absorption and an improperly high calculation for the concentration in the solution. Three methods are typically used to correct for this:
Zeeman correction - A magnetic field is used to split the atomic line into two sidebands (see Zeeman effect). These sidebands are close enough to the original wavelength to still overlap with molecular bands, but are far enough not to overlap with the atomic bands. The absorption in the presence and absence of a magnetic field can be compared, the difference being the atomic absorption of interest.
Smith-Hieftje correction (invented by Stanley B. Smith and Gary M. Hieftje) - The hollow cathode lamp is pulsed with high current, causing a larger atom population and self-absorption during the pulses. This self-absorption causes a broadening of the line and a reduction of the line intensity at the original wavelength.
Deuterium lamp correction - In this case, a separate source (a deuterium lamp) with broad emission is used to measure the background emission. The use of a separate lamp makes this method the least accurate, but its relative simplicity (and the fact that it is the oldest of the three) makes it the most commonly used method..
Although atomic absorption spectroscopy dates to the nineteenth century, the modern form was largely developed during the 1950s by a team of Australian chemists. They were lead by Alan Walsh and worked at the CSIRO (Commonwealth Science and Industry Research Organisation) Division of Chemical Physics in Melbourne, Australia. The technique typically makes use of a flame to atomize the sample, but other atomizers such as a graphite furnace are also used. Three steps are involved in turning a liquid sample into an atomic gas:
Desolvation – the liquid solvent is evaporated, and the dry sample remains
Vaporisation – the solid sample vaporises to a gas
Volatilisation – the compounds making up the sample are broken into free atoms.
The flame is arranged such that it is laterally long (usually 10cm) and not deep. The height of the flame must also be monitored by controlling the flow of the fuel mixture. A beam of light passes through this flame at its longest axis (the lateral axis) and hits a detector.
The light that is focused into the flame is produced by a hollow cathode lamp. Inside the lamp is a cylindrical metal cathode containing the metal for excitation, and an anode. When a high voltage is applied across the anode and cathode, the metal atoms in the cathode are excited into producing light with a certain emission spectra. The type of hollow cathode tube depends on the metal being analysed. For analysing the concentration of copper in an ore, a copper cathode tube would be used, and likewise for any other metal being analysed. The electrons of the atoms in the flame can be promoted to higher orbitals for an instant by absorbing a set quantity of energy (a quantum). This amount of energy is specific to a particular electron transition in a particular element. As the quantity of energy put into the flame is known, and the quantity remaining at the other side (at the detector) can be measured, it is possible to calculate how many of these transitions took place, and thus get a signal that is proportional to the concentration of the element being measured.
Background correction methods
The narrow linewidths of hollow cathode lamps make spectral overlap rare. That is, it is unlikely that an absorption line from one element will overlap with another. Molecular emission is much broader, so it is more likely that some molecular absorption band will overlap with an atomic line. This can result in artificially high absorption and an improperly high calculation for the concentration in the solution. Three methods are typically used to correct for this:
Zeeman correction - A magnetic field is used to split the atomic line into two sidebands (see Zeeman effect). These sidebands are close enough to the original wavelength to still overlap with molecular bands, but are far enough not to overlap with the atomic bands. The absorption in the presence and absence of a magnetic field can be compared, the difference being the atomic absorption of interest.
Smith-Hieftje correction (invented by Stanley B. Smith and Gary M. Hieftje) - The hollow cathode lamp is pulsed with high current, causing a larger atom population and self-absorption during the pulses. This self-absorption causes a broadening of the line and a reduction of the line intensity at the original wavelength.
Deuterium lamp correction - In this case, a separate source (a deuterium lamp) with broad emission is used to measure the background emission. The use of a separate lamp makes this method the least accurate, but its relative simplicity (and the fact that it is the oldest of the three) makes it the most commonly used method..
Saturday, July 14, 2007
Toxin detection: GC-MS
GC-MS stands for Gas Chromatography-Mass Spectrometer
How does the GCMS work?
The GCMS instrument is made up of two parts. The gas chromatography (GC) portion separates the chemical mixture into pulses of pure chemicals and the mass spectrometer (MS) identifies and quantifies the chemicals.
The GC separates chemicals based on their volatility, or ease with which they evaporate into a gas. It is similar to a running race where a group of people begin at the starting line, but as the race proceeds, the runners separate based on their speed. The chemicals in the mixture separate based on their volatility. In general, small molecules travel more quickly than larger molecules.
The MS is used to identify chemicals based on their structure. Let’s say after completing a puzzle, you accidentally drop it on the floor. Some parts of the puzzle remain attached together and some individual pieces break off completely. By looking at these various pieces, you are still able to get an idea of what the original puzzle looked like. This is very similar to the way that the mass spectrometer works.
Gas chromatography (GC)
Injection port – One microliter (1 µl, or 0.000001 L) of solvent containing the mixture of molecules is injected into the GC and the sample is carried by inert (non-reactive) gas through the instrument, usually helium. The inject port is heated to 300° C to cause the chemicals to become gases.
Oven –The outer part of the GC is a very specialized oven. The column is heated to move the molecules through the column. Typical oven temperatures range from 40° C to 320° C.
Column - Inside the oven is the column which is a 30 meter thin tube with a special polymer coating on the inside. Chemical mixtures are separated based on their votality and are carried through the column by helium. Chemicals with high volatility travel through the column more quickly than chemicals with low votality.
Mass Spectrometer (MS)
Ion Source: After passing through the GC, the chemical pulses continue to the MS. The molecules are blasted with electrons, which cause them to break into pieces and turn into positively charged particles called ions. This is important because the particles must be charged to pass through the filter.
Filter– As the ions continue through the MS, they travel through an electromagnetic field that filters the ions based on mass. The scientist using the instrument chooses what range of masses should be allowed through the filter. The filter continuously scans through the range of masses as the stream of ions come from the ion source.
Detector – A detector counts the number of ions with a specific mass. This information is sent to a computer and a mass spectrum is created. The mass spectrum is a graph of the number of ions with different masses that traveled through the filter.
Computer
The data from the mass spectometer is sent to a computer and plotted on a graph called a mass spectrum.
Adapted from: http://www.unsolvedmysteries.oregonstate.edu/GCMS_05.shtml
(A Flash is avaliable at this site to give a idea of how it works)
How does the GCMS work?
The GCMS instrument is made up of two parts. The gas chromatography (GC) portion separates the chemical mixture into pulses of pure chemicals and the mass spectrometer (MS) identifies and quantifies the chemicals.
The GC separates chemicals based on their volatility, or ease with which they evaporate into a gas. It is similar to a running race where a group of people begin at the starting line, but as the race proceeds, the runners separate based on their speed. The chemicals in the mixture separate based on their volatility. In general, small molecules travel more quickly than larger molecules.
The MS is used to identify chemicals based on their structure. Let’s say after completing a puzzle, you accidentally drop it on the floor. Some parts of the puzzle remain attached together and some individual pieces break off completely. By looking at these various pieces, you are still able to get an idea of what the original puzzle looked like. This is very similar to the way that the mass spectrometer works.
Gas chromatography (GC)
Injection port – One microliter (1 µl, or 0.000001 L) of solvent containing the mixture of molecules is injected into the GC and the sample is carried by inert (non-reactive) gas through the instrument, usually helium. The inject port is heated to 300° C to cause the chemicals to become gases.
Oven –The outer part of the GC is a very specialized oven. The column is heated to move the molecules through the column. Typical oven temperatures range from 40° C to 320° C.
Column - Inside the oven is the column which is a 30 meter thin tube with a special polymer coating on the inside. Chemical mixtures are separated based on their votality and are carried through the column by helium. Chemicals with high volatility travel through the column more quickly than chemicals with low votality.
Mass Spectrometer (MS)
Ion Source: After passing through the GC, the chemical pulses continue to the MS. The molecules are blasted with electrons, which cause them to break into pieces and turn into positively charged particles called ions. This is important because the particles must be charged to pass through the filter.
Filter– As the ions continue through the MS, they travel through an electromagnetic field that filters the ions based on mass. The scientist using the instrument chooses what range of masses should be allowed through the filter. The filter continuously scans through the range of masses as the stream of ions come from the ion source.
Detector – A detector counts the number of ions with a specific mass. This information is sent to a computer and a mass spectrum is created. The mass spectrum is a graph of the number of ions with different masses that traveled through the filter.
Computer
The data from the mass spectometer is sent to a computer and plotted on a graph called a mass spectrum.
Adapted from: http://www.unsolvedmysteries.oregonstate.edu/GCMS_05.shtml
(A Flash is avaliable at this site to give a idea of how it works)
Saturday, July 7, 2007
What is Bioremediation and phytoremediation?
Bioremediation can be defined as any process that uses microorganisms, fungi, green plants or their enzymes to return the environment altered by contaminants to its original condition
Phytoremediation describes the treatment of environmental problems (bioremediation) through the use of plants.
Advantages and limitations
Advantages:
- the cost of the phytoremediation is lower than that of traditional processes both in situ and ex situ
- the plants can be easily monitored
- the possibility of the recovery and re-use of valuable metals (by companies specializing in “phytomining”)
- it is the least harmful method because it uses naturally occurring organisms and preserves the natural state of the environment.
Limitations:
- phytoremediation is limited to the surface area and depth occupied by the roots.
- slow growth and low biomass require a long-term commitment
- with plant-based systems of remediation, it is not possible to completely to prevent the leaching of contaminants into the groundwater (without the complete removal of the contaminated ground which in itself does not resolve the problem of contamination)
- the survival of the plants is affected by the toxicity of the contaminated land and the general condition of the soil.
- possible bio-accumulation of contaminants which then pass into the food chain, from primary level consumers upwards.
The role of genetics
Breeding programs and genetic engineering are powerful methods for enhancing natural phytoremediation capabilities, or for introducing new capabilities into plants. Genes for phytoremediation may originate from a micro-organism or may be transferred from one plant to another variety better adapted to the environmental conditions at the cleanup site.
Adapted from http://en.wikipedia.org/wiki/Phytoremediation
Phytoremediation describes the treatment of environmental problems (bioremediation) through the use of plants.
Advantages and limitations
Advantages:
- the cost of the phytoremediation is lower than that of traditional processes both in situ and ex situ
- the plants can be easily monitored
- the possibility of the recovery and re-use of valuable metals (by companies specializing in “phytomining”)
- it is the least harmful method because it uses naturally occurring organisms and preserves the natural state of the environment.
Limitations:
- phytoremediation is limited to the surface area and depth occupied by the roots.
- slow growth and low biomass require a long-term commitment
- with plant-based systems of remediation, it is not possible to completely to prevent the leaching of contaminants into the groundwater (without the complete removal of the contaminated ground which in itself does not resolve the problem of contamination)
- the survival of the plants is affected by the toxicity of the contaminated land and the general condition of the soil.
- possible bio-accumulation of contaminants which then pass into the food chain, from primary level consumers upwards.
The role of genetics
Breeding programs and genetic engineering are powerful methods for enhancing natural phytoremediation capabilities, or for introducing new capabilities into plants. Genes for phytoremediation may originate from a micro-organism or may be transferred from one plant to another variety better adapted to the environmental conditions at the cleanup site.
Adapted from http://en.wikipedia.org/wiki/Phytoremediation
Friday, June 22, 2007
How is ADI set and what it is based on?
Principle for permitted level based on ADI
Acceptable Daily Intake (ADI) is defined as an estimate of the amount of a food additive, expressed on a body weight basis, which can be ingested daily over a lifetime without appreciable health risk. (CFSAN, 1993) The ADI is expressed in a range, which is considered to be the zone of acceptability of the substance.
The acceptable daily intake (ADI) is generally estimated by dividing the no-observed-effect level (NOEL) of a test substance by the safety factor. NOEL is the highest exposure that does not produce adverse effect. NOEL may be expressed as mg test substance per kg body weight of the test animal or as percent or ppm (parts per million) of the test diet for the animal. The ADI is usually expressed in mg additive per kg body weight of humans. A food additive generally is considered safe for its intended use if the estimated daily intake (EDI) of the additive is less than, or close to, the ADI. This is because the ADI is calculated to protect against the most sensitive adverse effect, it also protects against other adverse effects occurring at higher exposures to the ingredient.
Safety factor is used in calculation of ADI because even though the toxic substances at the NOEL level might not affect animals, it might affect humans. Thus the safety factor is to account for the differences between animals and humans and differences in sensitivity among humans and also to ensure consumer’s safety by providing an adequate margin of safety. A general rule of safety factor of 100 is used. However, there are exceptions to which the safety factor of 100 is used. For example, if the food additive is going to be used in infant formulas, a higher safety factor would need to be used to ensure safety.
http://www.cfsan.fda.gov/~acrobat/rediiabc.pdf
Estimated daily intake of an additive (x) is calculated based on the following formula:
Where:
F = Total number of foods in which substance "x" can be found
Acceptable Daily Intake (ADI) is defined as an estimate of the amount of a food additive, expressed on a body weight basis, which can be ingested daily over a lifetime without appreciable health risk. (CFSAN, 1993) The ADI is expressed in a range, which is considered to be the zone of acceptability of the substance.
The acceptable daily intake (ADI) is generally estimated by dividing the no-observed-effect level (NOEL) of a test substance by the safety factor. NOEL is the highest exposure that does not produce adverse effect. NOEL may be expressed as mg test substance per kg body weight of the test animal or as percent or ppm (parts per million) of the test diet for the animal. The ADI is usually expressed in mg additive per kg body weight of humans. A food additive generally is considered safe for its intended use if the estimated daily intake (EDI) of the additive is less than, or close to, the ADI. This is because the ADI is calculated to protect against the most sensitive adverse effect, it also protects against other adverse effects occurring at higher exposures to the ingredient.
Safety factor is used in calculation of ADI because even though the toxic substances at the NOEL level might not affect animals, it might affect humans. Thus the safety factor is to account for the differences between animals and humans and differences in sensitivity among humans and also to ensure consumer’s safety by providing an adequate margin of safety. A general rule of safety factor of 100 is used. However, there are exceptions to which the safety factor of 100 is used. For example, if the food additive is going to be used in infant formulas, a higher safety factor would need to be used to ensure safety.
http://www.cfsan.fda.gov/~acrobat/rediiabc.pdf
Estimated daily intake of an additive (x) is calculated based on the following formula:
Where:
F = Total number of foods in which substance "x" can be found
Freqf = Number of eating occasions of food "f" over "N" survey days
Portf = Average portion size for food "f"
Concxf = Concentration of the substance "x" in food "f"
N = Number of survey days
The sources of data can be collected from food consumption survey, food/ingredient disappearance figures, total diet study and body burden/excretion measurements: “Biomakers”. Food consumption data may be collected at the national, household, or individual level. Consumption surveys at the level of the individual provide information on mean food intakes and the distribution of food intakes within sub-populations of individuals defined by demographic factors (e.g., age, gender) and health status (e.g., pregnancy, lactation). These surveys measure food intake by one or more methods: i.e., food records or diaries, 24-hour recalls, food frequency questionnaires (FFQ), and diet history. The data collected from these surveys can then be used to calculate the EDI. This would help to determine the safety of an additive as the EDI should be lower or close to the ADI if the food additive is generally safe.
http://www.cfsan.fda.gov/~dms/opa2cg8.html#Bfoo
Sunday, June 10, 2007
Analytical method used by PDP to measure the amount of pesticide residues in food
PDP stands for Pesticide Data Program, which is a national pesticide residue database program, is responsible in management of collection, analysis, data entry, and reporting of pesticide residues on agricultural commodities. For more details, visit http://www.ams.usda.gov/science/pdp/what.htm
PDP uses the following analytical method to analyze fresh and processed fruit and vegetables, meat (beef and pork), poultry, and dairy products (milk, cream and butter).
http://www.ams.usda.gov/science/pdp/MethodAbstracts.pdf
PDP uses the following analytical method to analyze fresh and processed fruit and vegetables, meat (beef and pork), poultry, and dairy products (milk, cream and butter).
http://www.ams.usda.gov/science/pdp/MethodAbstracts.pdf
Saturday, June 2, 2007
Pesticides' Acceptable Daily Intake
4.1 Acephate (095) (T)**
4.2 Azocyclotin (067) and cyhexatin (129) (T, R)**
4.3 Benalaxyl (155) (T)**
4.4 Carbendazim (072) (D)**
4.5 Chlorpropham (201) (T)**
4.6 Clofentezine (156) (T)**
4.7 Dimethenamid-P (214)/Racemic dimethenamide (T, R)*
4.8 Ethoxyquin (035) (T)**
4.9 Fenhexamid (215) (T, R)*
4.10 Glyphosate (158) (R)**
4.11 Imazalil (110) (D)**
4.12 Indoxacarb (216) (T, R)*
4.13 Malathion (049) (R)**
4.14 Methiocarb (132) (R)**
4.15 S-Methoprene (147) (R)**
4.16 Novaluron (217) (T, R)*
4.17 Phorate (112) (R)**4
4.18 Propamocarb (148) (T)**
4.19 Pyrethrins (063) (R)**
4.20 Sulfuryl fluoride (218) (T, R)*
4.21 Terbufos (167) (R)**
Some of the pesticides residue that can be found in crops...the acceptable daily intake can also be found in annex 3 of this report :http://www.fao.org/docrep/009/a0209e/a0209e00.htm#Contents
4.2 Azocyclotin (067) and cyhexatin (129) (T, R)**
4.3 Benalaxyl (155) (T)**
4.4 Carbendazim (072) (D)**
4.5 Chlorpropham (201) (T)**
4.6 Clofentezine (156) (T)**
4.7 Dimethenamid-P (214)/Racemic dimethenamide (T, R)*
4.8 Ethoxyquin (035) (T)**
4.9 Fenhexamid (215) (T, R)*
4.10 Glyphosate (158) (R)**
4.11 Imazalil (110) (D)**
4.12 Indoxacarb (216) (T, R)*
4.13 Malathion (049) (R)**
4.14 Methiocarb (132) (R)**
4.15 S-Methoprene (147) (R)**
4.16 Novaluron (217) (T, R)*
4.17 Phorate (112) (R)**4
4.18 Propamocarb (148) (T)**
4.19 Pyrethrins (063) (R)**
4.20 Sulfuryl fluoride (218) (T, R)*
4.21 Terbufos (167) (R)**
Some of the pesticides residue that can be found in crops...the acceptable daily intake can also be found in annex 3 of this report :http://www.fao.org/docrep/009/a0209e/a0209e00.htm#Contents
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