In conclusion, heavy metals are an important part of our environment and a growing threat to our health. As I have explored over the course of my blog, heavy metals, such as mercury, have been influencing us since we first began to evolve and pose a significant threat to our well being when their emissions are not monitored. Consumption is the most common route of poisoning. As seen with Minimata and the USA, mercury is primarily ingested through fish and other sea food. It is successfully transferred up the tropic levels and thus reaches toxic levels at higher tropic levels. Similarly cadmium, passes into the food chain through plants and crops, which have a higher tolerance for the metal than animals or humans. Arsenic has similar properties to cadmium, it readily moves through the soil or rock and displays a high tolerance in vegetation yet when ingested by humans can have severe health implications, as seen in the case of Bangladesh, where the main source of poisoning was water resources in the Ganges.
One cannot ignore the importance of industry in the global contamination of heavy metals. Industry as far back as the classical era, during the Greeks and Romans, is responsible for high levels of heavy metal emissions. The main source of poisoning at Minimata was industrial actions and many marine polluted areas are near industrial outputs. Understanding their harmful effects and past emissions is crucial to being able to understand the current threat and how to mitigate potential harmful effects in the future. In many cases, the lesson at Minimata and in other parts of the world, has still not been learnt or is ignored for economic gain. Evidence found in ice cores shows that heavy metal pollution is not a new phenomena and has the potential to topple entire empires and as such it should be taken seriously.
Writing this blog has been an interesting experience where I have been able to explore a wide range of material and research. The topic chosen was broad and looked at a very interesting aspect of environmental pollution that is not always fully portrayed in modern forms of media, unlike climate change or deforestation. I believe it has been a valuable experience that has allowed me to develop key skills in both analytical and research fields. I would have enjoyed to have explored the other metals considered toxic and have gone into more depth about the modern roles of copper and lead.
I hope you enjoyed Highway to Bad Hell-th: Heavy Metal Pollution.
Tuesday, 3 May 2011
Monday, 2 May 2011
Ancient Civilisation Contributions to Heavy Metal Pollution
Almost everywhere we look we are told that our activities are harming our environment. We are lead to believe that climate change and pollution are relatively recent phenomena started by the industrial revolution but there is a lot of evidence to suggest that we have been shaping and polluting out surroundings for far longer than the last one hundred years or so.
The Greeks and Romans were some of the most prolific civilisations in ancient history and have been revered and studied for hundreds of years. Our understanding of literature and archaeological evidence shows they had a very sophisticated use for many heavy metals still in heavy industry and use today, the most common of which is lead (Pb) and Copper (Cu). As discussed in my previous post, there is significant evidence in Greenland ice cores showing that these metals have been highly variable in the atmosphere for many millennia and have significant natural sources. Yet peaks could be observed at certain points throughout the last few thousand years, most notable, during the existence of early civilisations.
Hong et al. (1994) wrote a research paper detailing the Greenland ice evidence supporting lead pollution specifically by the Greeks and Romans. They estimate that anthropogenic lead pollution started almost 6 millennia ago and primarily came from the smelting of lead-silver alloys. The ice core results they found suggested that during the Roman era the emissions reached 800,000 metric tonnes per year, similar to those found during the industrial revolution. This lead was sourced from Spain, the Balkans, Greece and Asia. Most smelting was done in Spain in open air furnaces with no emissions controls.
Yet this was not sustained, it declined to only a few hundred metric tons per year during the medieval era, it only increased following the discovery of new mines in central Europe. Perhaps the most astounding claim that Hong and his colleagues make is that lead was an integral part to the fall of the Roman Empire. It was suggested that mass poisoning was due to mass regional deposits of lead and further evidence can be gained from peat bogs in Britain. The high level usage of lead in smelting the Romans is also responsible for one of the largest hemispheric pollutions on record, with large deposits of lead making it into the troposphere and to remote areas of the Arctic.
A follow up paper can be found in a later issue of 'Science', also written by Hong, in 1996. This article outlined the pollution of copper (Cu) because of it's use in Roman and Medieval times from the analysis of another Greenland ice core. Hong states that copper pollution and emissions was actually higher before the industrial revolution that in was afterwards. This is mainly due to the techniques employed during the pre-industrial copper industries, smelting and mining practices were far less cleaner and less efficient.
Copper was first produced around 7000 years ago and production reached it's peak around 5000 years ago after smelting was developed and demand for tin bronze rose during the Bronze Age. The technique of smelting was modified with the introduction of sulphide around 45000 years ago causing production to increase again. From the ice core, Hong estimates that between 4000 and 2700 years ago, half a million metric tonnes of copper was produced. The demand for coinage during the Roman era 2000 years ago meant a record high of 15,000 metric tons was produced in one year. Hong also commented that between 2250 and 1650 years ago Spain and Cyprus were the main producers and exporters of copper, resulting in 5 million metric tons being created between them during this time period.
The smelting of copper didn't just mean that copper pollution became a problem in the classical era. When smelting copper for weapons, high levels of arsenic were used in the process that was then disposed of irresponsibly. This meant that many ground water reservoirs in areas producing copper reported high levels of arsenic and thus arsenic poisoning of water resources. Copper production finally declined with the fall of the Roman empire, it was picked back up again in Medieval times but the production was not on the same scale as those found in the ice core during Roman times.
Both of Hong's papers are highly informative and give a comprehensive overview of the production of heavy metals in Roman, Greek and Medieval times. The paper's show the scale of production and plenty of numerical evidence for the scale of pollution during these times in comparison to more recent industry. They are another contribution to the argument that heavy metals are indeed an important aspect we should be considering in environmental pollution. Having said that, I feel the methodology and science behind the examples and figures was not fully explained and I would have liked to have read more about it.
The Greeks and Romans were some of the most prolific civilisations in ancient history and have been revered and studied for hundreds of years. Our understanding of literature and archaeological evidence shows they had a very sophisticated use for many heavy metals still in heavy industry and use today, the most common of which is lead (Pb) and Copper (Cu). As discussed in my previous post, there is significant evidence in Greenland ice cores showing that these metals have been highly variable in the atmosphere for many millennia and have significant natural sources. Yet peaks could be observed at certain points throughout the last few thousand years, most notable, during the existence of early civilisations.
Hong et al. (1994) wrote a research paper detailing the Greenland ice evidence supporting lead pollution specifically by the Greeks and Romans. They estimate that anthropogenic lead pollution started almost 6 millennia ago and primarily came from the smelting of lead-silver alloys. The ice core results they found suggested that during the Roman era the emissions reached 800,000 metric tonnes per year, similar to those found during the industrial revolution. This lead was sourced from Spain, the Balkans, Greece and Asia. Most smelting was done in Spain in open air furnaces with no emissions controls.
Yet this was not sustained, it declined to only a few hundred metric tons per year during the medieval era, it only increased following the discovery of new mines in central Europe. Perhaps the most astounding claim that Hong and his colleagues make is that lead was an integral part to the fall of the Roman Empire. It was suggested that mass poisoning was due to mass regional deposits of lead and further evidence can be gained from peat bogs in Britain. The high level usage of lead in smelting the Romans is also responsible for one of the largest hemispheric pollutions on record, with large deposits of lead making it into the troposphere and to remote areas of the Arctic.
A follow up paper can be found in a later issue of 'Science', also written by Hong, in 1996. This article outlined the pollution of copper (Cu) because of it's use in Roman and Medieval times from the analysis of another Greenland ice core. Hong states that copper pollution and emissions was actually higher before the industrial revolution that in was afterwards. This is mainly due to the techniques employed during the pre-industrial copper industries, smelting and mining practices were far less cleaner and less efficient.
Copper was first produced around 7000 years ago and production reached it's peak around 5000 years ago after smelting was developed and demand for tin bronze rose during the Bronze Age. The technique of smelting was modified with the introduction of sulphide around 45000 years ago causing production to increase again. From the ice core, Hong estimates that between 4000 and 2700 years ago, half a million metric tonnes of copper was produced. The demand for coinage during the Roman era 2000 years ago meant a record high of 15,000 metric tons was produced in one year. Hong also commented that between 2250 and 1650 years ago Spain and Cyprus were the main producers and exporters of copper, resulting in 5 million metric tons being created between them during this time period.
The smelting of copper didn't just mean that copper pollution became a problem in the classical era. When smelting copper for weapons, high levels of arsenic were used in the process that was then disposed of irresponsibly. This meant that many ground water reservoirs in areas producing copper reported high levels of arsenic and thus arsenic poisoning of water resources. Copper production finally declined with the fall of the Roman empire, it was picked back up again in Medieval times but the production was not on the same scale as those found in the ice core during Roman times.
Both of Hong's papers are highly informative and give a comprehensive overview of the production of heavy metals in Roman, Greek and Medieval times. The paper's show the scale of production and plenty of numerical evidence for the scale of pollution during these times in comparison to more recent industry. They are another contribution to the argument that heavy metals are indeed an important aspect we should be considering in environmental pollution. Having said that, I feel the methodology and science behind the examples and figures was not fully explained and I would have liked to have read more about it.
Monday, 25 April 2011
Ice Core evidence for Cadmium pollution
It's a commonly known fact that ice cores, whether they be from Greenland or Antartica, are an important part of our understanding of past conditions. Until recently, our understanding of heavy metal pollution in the planet's history has been intermittent. In 1996 the first reliable time series of four heavy metal pollutants, Lead (Pb), Zinc (Zn), Cadmium (Cd) and Copper (Cu) was published after closely studying a GRIP ice core. Hong et al. (1996) found that concentrations of these metals had been highly variable and there was early large scale pollution before the industrial revolution in the Greek, Roman and medivial eras.
Having been the first time series published of heavy metal pollution from an ice core, it was found that the climatic variability of these metals was strongly anti-correlated with those of the oxygen isotope, O18. As seen in the figure below, in the first half of the GRIP core, 0-80 kyr B.P., the high frequency observed for Cu, Pb, Cd and Zn was in contrast to the low and steady concentrations of O18. In the subsequent years, 80-160 kyr B.P., the concentrations of Cd, CU, Pb and Zn were very low but concentrations of O18 were very high and more variable. More O18 in the ice is a common indicator of a colder climate, this would allow one to conclude that heavy metals are more persistent and variable in the atmosphere when the climate is warmer, such as in the first half of the record and recent history.
Hong et al. (1006) look closely at the climatic record portrayed in their GRIP ice core before turning to analyse the sources of heavy metal pollution in the atmosphere. It was found that large scale pollution could be attributed to wind-bourne soil and rock particles, sea salt spray, volcanoes and wild fires. Cu and Pb were likely to be the product of soil and rock dust during the study time period (0-160 kyr B.P.). Hong discussed that the large variations depicted in the time series in the most recent inter-glacial, the holocene, was most likely the product of dramatic changes in environmental conditions. The retreat of northern ice sheets, such as the Eurasian and American, meant opening up and exposure of large areas of fresh rock and land. This would account for the variation in Pb and Cu which originated from rock and soil particles. Sea ice also retreating leaving more exposed ocean and coastal areas, thus more sea spray.
As far as cadmium goes, the variation is mainly accountable because of more dust and soil particle sources being exposed, which is a significant source, but also large contributions from the growing continental biosphere. The progressive expansion of vegetation and northward advance with retreating ice sheets meant that the Cd ratios increase observed between 13,000 to 9300 years ago was primarily a result of increasing plant matter on the continent. From reading my previous post one can presume this is because more plants means a larger Cd potential reservoir on the continent. Cadmium levels increased until 9300 kmyr B.P. but then decreased despite further advance of vegetation, this has been attributed to changes in atmospheric circulastio influencing the movement of air-bourne cadmium.
The paper by Hong et al. (1996) was another good indicator review of heavy metal pollution during the last glaciation and during deglaciation, they offered explanations for the reasons behind the variablitily to pollution. Yet the paper lacked a comprehensive discussion of the differnt sources of heavy metals into the atmosphere or how changes in atmospheric transport could influence heavy metal content in the ice core.
These results show that cadmium has indeed been an integral part of our environment for thousands of years and has been collecting in soils and plants before the industrial revolution. Although crops have only recently become a health threat it is important to recognise natural sources and past aptterns of cadmium pollution to better understand future fluctuations and their role in our health.
Reference: Hong, S., J-P. Candelone, C. Turetta and C.f. Boutron (1996) 'Changes in natural lead, copper, zinc and cadmium concetrations in central Greenland ice from 8250 to 149,100 years ago: their association with climatic changes and resultant variations of dominant source contributions,' Earth and planetary science letters 143: 233-244.
Having been the first time series published of heavy metal pollution from an ice core, it was found that the climatic variability of these metals was strongly anti-correlated with those of the oxygen isotope, O18. As seen in the figure below, in the first half of the GRIP core, 0-80 kyr B.P., the high frequency observed for Cu, Pb, Cd and Zn was in contrast to the low and steady concentrations of O18. In the subsequent years, 80-160 kyr B.P., the concentrations of Cd, CU, Pb and Zn were very low but concentrations of O18 were very high and more variable. More O18 in the ice is a common indicator of a colder climate, this would allow one to conclude that heavy metals are more persistent and variable in the atmosphere when the climate is warmer, such as in the first half of the record and recent history.
Hong et al. (1006) look closely at the climatic record portrayed in their GRIP ice core before turning to analyse the sources of heavy metal pollution in the atmosphere. It was found that large scale pollution could be attributed to wind-bourne soil and rock particles, sea salt spray, volcanoes and wild fires. Cu and Pb were likely to be the product of soil and rock dust during the study time period (0-160 kyr B.P.). Hong discussed that the large variations depicted in the time series in the most recent inter-glacial, the holocene, was most likely the product of dramatic changes in environmental conditions. The retreat of northern ice sheets, such as the Eurasian and American, meant opening up and exposure of large areas of fresh rock and land. This would account for the variation in Pb and Cu which originated from rock and soil particles. Sea ice also retreating leaving more exposed ocean and coastal areas, thus more sea spray.
As far as cadmium goes, the variation is mainly accountable because of more dust and soil particle sources being exposed, which is a significant source, but also large contributions from the growing continental biosphere. The progressive expansion of vegetation and northward advance with retreating ice sheets meant that the Cd ratios increase observed between 13,000 to 9300 years ago was primarily a result of increasing plant matter on the continent. From reading my previous post one can presume this is because more plants means a larger Cd potential reservoir on the continent. Cadmium levels increased until 9300 kmyr B.P. but then decreased despite further advance of vegetation, this has been attributed to changes in atmospheric circulastio influencing the movement of air-bourne cadmium.
The paper by Hong et al. (1996) was another good indicator review of heavy metal pollution during the last glaciation and during deglaciation, they offered explanations for the reasons behind the variablitily to pollution. Yet the paper lacked a comprehensive discussion of the differnt sources of heavy metals into the atmosphere or how changes in atmospheric transport could influence heavy metal content in the ice core.
These results show that cadmium has indeed been an integral part of our environment for thousands of years and has been collecting in soils and plants before the industrial revolution. Although crops have only recently become a health threat it is important to recognise natural sources and past aptterns of cadmium pollution to better understand future fluctuations and their role in our health.
Reference: Hong, S., J-P. Candelone, C. Turetta and C.f. Boutron (1996) 'Changes in natural lead, copper, zinc and cadmium concetrations in central Greenland ice from 8250 to 149,100 years ago: their association with climatic changes and resultant variations of dominant source contributions,' Earth and planetary science letters 143: 233-244.
Friday, 22 April 2011
Cadmium Toxicity
Cadmium is a non-essential element that is found in naturally occurring high abundance in fertilizers. Cadmium has been able to monopolize similar reservoirs as mercury by collecting in tropic levels. This bioaccumulation is due to wide use of cadmium rich fertilizers, sewage sludge and industrial uses of cadmium, as well as the plants possessing a naturally high tolerance for the substance, unlike mercury. Similar to arsenic, cadmium moves readily within the soil, resulting in wide distribution and easy absorption into plants. The high tolerance in plants means their cadmium levels are greater than those found in animals or humans and thus only a small amount of contaminated plant matter needs to be ingested for a toxic dose (Satarug et al., 2003).
In 2003, Soisungwan Satarug and associates published a detailed paper discussing the effects of cadmium pollution and toxicity in the non-occupationally exposed population. They reviewed several studies and trials that documented the effects of cadmium toxicity on the body, which was then compared with their own study on liver and kidney samples that had been exposed through major food groups. Tabacco, willow and the sunflower plant have all been found to have high tolerance levels against cadmium. This means their bio-reservoirs are larger and thus allow cadmium to be readily passed up the food chain. In Australia, a study in the early 90s found that sheep grazing on fertilized pasture had high levels of cadmium in their kidneys compared to those grazing on unfertilized pasture. Correspondingly, Taiwanese and Japanese rice grown on contaminated soils was documented as having 0.21-2.16 and 1.67-5.38 mg/kg of cadmium, respectively, compared with rice grown in Queensland which only had 0.05mg/kg of cadmium.
Satarug et al. (2003) moves on from a review of studies to look at WHO/FAO cadmium health regulations. They establish that any crop grown on coils that are either contaminated or naturally rich in cadmium are the main source of toxic exposure in the general population. In Australia, the recommended daily allowances of cadmium are 0.1 ug/kg body weight per day. The WHO and FOA recommend no more than 70 ug per day and considering that most indiciduals ingest and average of 30 ug per day (based on estimates typical food products and diets) this fall within safe limits. However, in some areas and products where food items were reported to contain higher levels, ingestion was estimated to be as high as 90 ug per day, way above the safe levels. These food products were identified as primarily vegetables and cereals.
A detailed list of problems that were caused as a result of cadmium exposure were included in the paper, these incorporated diabetic renal complications, hypertension, osteoporosis, leukemia and cancer in several other organs; lung, kidney, breast, bladder, pancreas to name a few. They conclude that cadmium has a profound effect on the burden of health and the connections have now been well established and documented. In Japan, cadmium exposure in contaminated areas was found to increase mortality by 40-80%. A follow up study, 15 years later, showed researchers that the higher standardized mortality rate for cardiovascular disease was higher in contaminated areas of the Kakehashi river basin in a sample size of 2840 residents, the large sample of residents in this area meant minimizing the risk of anomalies and give a clear picture of cadmium pollution in the basin.
The paper contains a plethora of example studies to reinforce the impact of cadmium on the human body at high levels. Many of the example studies are reinforced by multiple studies and have large sample sizes meaning a higher quality of results. It is comprehensive in its review of the risk cadmium poses to health burden and the consequences of cadmium exposure. Regions of the world including, Australasia, have been identified as having high levels of cadmium. On the other hand, despite the comprehensive overview and arguments for the significant role of cadmium in the non-occupationally exposed population, there is no mention of how these risks can be monitored, controlled or even prevented. The journal article is a good foundation for future developments in both research and policy.
In 2003, Soisungwan Satarug and associates published a detailed paper discussing the effects of cadmium pollution and toxicity in the non-occupationally exposed population. They reviewed several studies and trials that documented the effects of cadmium toxicity on the body, which was then compared with their own study on liver and kidney samples that had been exposed through major food groups. Tabacco, willow and the sunflower plant have all been found to have high tolerance levels against cadmium. This means their bio-reservoirs are larger and thus allow cadmium to be readily passed up the food chain. In Australia, a study in the early 90s found that sheep grazing on fertilized pasture had high levels of cadmium in their kidneys compared to those grazing on unfertilized pasture. Correspondingly, Taiwanese and Japanese rice grown on contaminated soils was documented as having 0.21-2.16 and 1.67-5.38 mg/kg of cadmium, respectively, compared with rice grown in Queensland which only had 0.05mg/kg of cadmium.
Satarug et al. (2003) moves on from a review of studies to look at WHO/FAO cadmium health regulations. They establish that any crop grown on coils that are either contaminated or naturally rich in cadmium are the main source of toxic exposure in the general population. In Australia, the recommended daily allowances of cadmium are 0.1 ug/kg body weight per day. The WHO and FOA recommend no more than 70 ug per day and considering that most indiciduals ingest and average of 30 ug per day (based on estimates typical food products and diets) this fall within safe limits. However, in some areas and products where food items were reported to contain higher levels, ingestion was estimated to be as high as 90 ug per day, way above the safe levels. These food products were identified as primarily vegetables and cereals.
A detailed list of problems that were caused as a result of cadmium exposure were included in the paper, these incorporated diabetic renal complications, hypertension, osteoporosis, leukemia and cancer in several other organs; lung, kidney, breast, bladder, pancreas to name a few. They conclude that cadmium has a profound effect on the burden of health and the connections have now been well established and documented. In Japan, cadmium exposure in contaminated areas was found to increase mortality by 40-80%. A follow up study, 15 years later, showed researchers that the higher standardized mortality rate for cardiovascular disease was higher in contaminated areas of the Kakehashi river basin in a sample size of 2840 residents, the large sample of residents in this area meant minimizing the risk of anomalies and give a clear picture of cadmium pollution in the basin.
The paper contains a plethora of example studies to reinforce the impact of cadmium on the human body at high levels. Many of the example studies are reinforced by multiple studies and have large sample sizes meaning a higher quality of results. It is comprehensive in its review of the risk cadmium poses to health burden and the consequences of cadmium exposure. Regions of the world including, Australasia, have been identified as having high levels of cadmium. On the other hand, despite the comprehensive overview and arguments for the significant role of cadmium in the non-occupationally exposed population, there is no mention of how these risks can be monitored, controlled or even prevented. The journal article is a good foundation for future developments in both research and policy.
Saturday, 16 April 2011
Summary and Introduction to Cadmium
One can deduce so far that heavy metals are commonly found in our environment yet are found in concentrations to small to cause adverse effects to public health. That is until commercialisation of resources of the local environment takes place. In the case of Mercury, mercury poisoning was a little occurring problem until fish become exposed to the toxic substance through industrial waste. The USA has large problems with mercury causing neurological damage and infertility, it was only decades after the Minimata disaster that many authorities woke to the grave realisation that mercury had dire health, and ultimately economic, consequences.
On a similar scale to Minimata, Bangladesh, predominantly the Ganges delta, has suffered mass arsenic poisoning with many people becoming critically ill and unable to support families. Both arsenic and mercury are responsible for mass poisoning from natural sources. Arsenic was the result of years of deposition in the Ganges aquifer during the last glaciation and was not correctly checked before being cleared for domestic water use. Mercury, on the other hand, was responsible for an early mass extinction of early species during the evolution of our current atmosphere causing the evolution of toxic metal defences in the biology of modern day animals.
The next metal that will be discussed is Cadmium, a naturally occurring heavy metal that is commonly found. Levels of dangerous cadmium have started to appear in the environment, like mercury, since industrialisation and its main sources are sewage, fertilisers and other agricultural products. Similar to mercury, cadmium's most effective poisoning method is via the food chain, this is because plants generally have a much higher cadmium tolerance level than animals and as such create cadmium reserves. The next post will discuss the work by Satarug et al. (2002) where cadmium was studied in the non-occupationally exposed population.
On a similar scale to Minimata, Bangladesh, predominantly the Ganges delta, has suffered mass arsenic poisoning with many people becoming critically ill and unable to support families. Both arsenic and mercury are responsible for mass poisoning from natural sources. Arsenic was the result of years of deposition in the Ganges aquifer during the last glaciation and was not correctly checked before being cleared for domestic water use. Mercury, on the other hand, was responsible for an early mass extinction of early species during the evolution of our current atmosphere causing the evolution of toxic metal defences in the biology of modern day animals.
The next metal that will be discussed is Cadmium, a naturally occurring heavy metal that is commonly found. Levels of dangerous cadmium have started to appear in the environment, like mercury, since industrialisation and its main sources are sewage, fertilisers and other agricultural products. Similar to mercury, cadmium's most effective poisoning method is via the food chain, this is because plants generally have a much higher cadmium tolerance level than animals and as such create cadmium reserves. The next post will discuss the work by Satarug et al. (2002) where cadmium was studied in the non-occupationally exposed population.
Monday, 11 April 2011
Arsenic around the world
World population is reaching record highs, 6 billion and counting, and the most sought after resource of the 21st century will not be oil but clean water. In 1990 the WHO revised its estimates of access to safe drinking water, they concluded that 43% of the world's population is lacking adequate sanitation and 22% do not have access to clean drinking water. Heavy reliance is beginning to come from underground aquifers as surface water begins to become scarce.
Nordstrom (1998) discussed the risks associated with groundwater and heavy metal pollution. His review in the policy forum outlined that groundwater utilization comes with high risks, such as the 36 million people in the Bengal Delta now suffering from arsenic. Arsenic is not found in high abundance in the Earth's crust and is strongly associated with pyrite, a prolific mineral. Areas that have high levels of arsenic are Kamchatka, New Zealand, Japan, Alaska, California and Wyoming, areas where there are young basalt rocks. Environments such as closed basins in arid and semi arid climates and areas that have aquifers with strong reduction properties are all prone to arsenic collections. Nordstrom does, however, highlight that although these environments are condusive to arsenic it doesn’t help us to predict a high or low concentration, primarily due to the heterogeneous spread in the aquifers. Arsenic is highly soluble and as such its concentrations and distributions in aquifers can change within a few years. This results in constant monitoring to pre-empt arsenic entry into ground water enterprises in high risk areas.
Nordstrom (1998) discussed the risks associated with groundwater and heavy metal pollution. His review in the policy forum outlined that groundwater utilization comes with high risks, such as the 36 million people in the Bengal Delta now suffering from arsenic. Arsenic is not found in high abundance in the Earth's crust and is strongly associated with pyrite, a prolific mineral. Areas that have high levels of arsenic are Kamchatka, New Zealand, Japan, Alaska, California and Wyoming, areas where there are young basalt rocks. Environments such as closed basins in arid and semi arid climates and areas that have aquifers with strong reduction properties are all prone to arsenic collections. Nordstrom does, however, highlight that although these environments are condusive to arsenic it doesn’t help us to predict a high or low concentration, primarily due to the heterogeneous spread in the aquifers. Arsenic is highly soluble and as such its concentrations and distributions in aquifers can change within a few years. This results in constant monitoring to pre-empt arsenic entry into ground water enterprises in high risk areas.
Thursday, 7 April 2011
Review of Arsenic
So far, I have discussed the role of Mercury and its affects on our health, I now wish to look briefly at Arsenic. Arsenic is classed as a metalloid which means it shares both metal and non-metal qualities and is ranked the 20th most common element in the Earth's crust.
Arsenic and humans have had a fairly dark relationship for centuries. It was immortalised by Plato when he described the use of Hemlock (a natural resource of arsenic) in the death of Socrates. Due to its lack of odour or smell, and small qunatities being fatal, it is a highly effective killer.
The most infamous aresenic poisoning that occured on a large scale, is the case of Bangladesh. Shallow aquifers, less than 300m deep, supply more than 90% of the drinking water to Bangladesh and West Bengal. It has been known for years that up to one million wells using these water reserves contain dangerous levels of arsenic. In many of these wells the arsenic content reaches 1000 mg l-1, 9950 mg l-1 above the bangladeshi limit and the WHO limit (Nickson et al., 1998).
Arsenic occurs in the Bangladesh and West Bengal aquifers due to reductive disolution of arsenic rich iron oxyhydroxides, which originate from the reduction of sulphate based metals after weathering. Though it is important to note that the arsenic rich wells are primarily isolated to the ganges delta aquifers. This suggests that weathering upstream of Bangladesh transported the arsenic-rich oxyhydroxides in sediments downstream to the delta in the late pliestocene, an epoch covering the last glaciation (Gibbard and van Kolfschoten, 2004). The sediments displaced by glaciation and de-glaciation have accumulated and been chemically reduced for centuries in the genges delta to produce arsenic rich water reserves.
Nickson et al. (1998) discuss how understanding the past geological structure of arsenic depisits and transport allow a better understanding of arsenic distribution in Bangladesh. They propose a predictive model to help influyence and advise future water developments on the aquifer to minimise the risk of future poisoning.
References:
Nickson, R., J. McArthur, W. Burgess, K.M. Ahmed, P. Ravenscroft and M. Rahman (1998) 'Arsenic Poisoning of Bangladesh Grounwater,' Nature 395: 338.
Gibbard, P. and van Kolfschoten, T. (2004) 'The Pleistocene and Holocene Epochs' in Gradstein, Ogg, Smoth and Gilbert (eds.) A geological time scale, Cambridge Press, Cambridge.
Arsenic and humans have had a fairly dark relationship for centuries. It was immortalised by Plato when he described the use of Hemlock (a natural resource of arsenic) in the death of Socrates. Due to its lack of odour or smell, and small qunatities being fatal, it is a highly effective killer.
The most infamous aresenic poisoning that occured on a large scale, is the case of Bangladesh. Shallow aquifers, less than 300m deep, supply more than 90% of the drinking water to Bangladesh and West Bengal. It has been known for years that up to one million wells using these water reserves contain dangerous levels of arsenic. In many of these wells the arsenic content reaches 1000 mg l-1, 9950 mg l-1 above the bangladeshi limit and the WHO limit (Nickson et al., 1998).
Arsenic occurs in the Bangladesh and West Bengal aquifers due to reductive disolution of arsenic rich iron oxyhydroxides, which originate from the reduction of sulphate based metals after weathering. Though it is important to note that the arsenic rich wells are primarily isolated to the ganges delta aquifers. This suggests that weathering upstream of Bangladesh transported the arsenic-rich oxyhydroxides in sediments downstream to the delta in the late pliestocene, an epoch covering the last glaciation (Gibbard and van Kolfschoten, 2004). The sediments displaced by glaciation and de-glaciation have accumulated and been chemically reduced for centuries in the genges delta to produce arsenic rich water reserves.
Nickson et al. (1998) discuss how understanding the past geological structure of arsenic depisits and transport allow a better understanding of arsenic distribution in Bangladesh. They propose a predictive model to help influyence and advise future water developments on the aquifer to minimise the risk of future poisoning.
References:
Nickson, R., J. McArthur, W. Burgess, K.M. Ahmed, P. Ravenscroft and M. Rahman (1998) 'Arsenic Poisoning of Bangladesh Grounwater,' Nature 395: 338.
Gibbard, P. and van Kolfschoten, T. (2004) 'The Pleistocene and Holocene Epochs' in Gradstein, Ogg, Smoth and Gilbert (eds.) A geological time scale, Cambridge Press, Cambridge.
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