Risk Assessment of Environmental Pollution From Arsenic

CH 515: Risk Assessment Paper

Abstract/Summary:

Environmental contamination related to arsenic is a global issue. Arsenic is toxic contaminant and carcinogen. Arsenic occurs naturally in the environment and can be found organically in shellfish and fish, and inorganic arsenic can be found in compounds in minerals and is released into the environment by certain industries. Multiple sources contribute to the amount of arsenic in the environment, including volcanic activity, anthropogenic sources, and microorganisms. Arsenic can be transported through the environment attached to airborne particles, in runoff, through leaching, the flow of water, and precipitation. Chronic exposure to arsenic in humans can result in cancer, peripheral neuropathy, lethargy, hyperkeratosis, peripheral vascular disease, gastrointestinal upset, and hematological abnormalities. Acute exposures in trace amounts is not harmful, but generally leads to mortality and adverse effects. Uptake of arsenic by humans can occur via ingestion, inhalation, and maternal transfer. Aquatic organisms uptake arsenic in a similar fashion. Policy and environmental regulation have reduced the impact of the contaminant on the environment, but arsenic-contaminated ground water has become a global issue and is causing health issues around the world.

Introduction/Background

Arsenic is a known toxin and carcinogen that is present in industrial settings and in the environment. It is believed that arsenic was discovered by a German chemist by the name of Albertus Magnus in 1250. Arsenic is an element that occurs naturally in the environment, and organic arsenic can be found in shellfish and fish, whereas most inorganic arsenic can be found in compounds in minerals such as arsenopyrite, realgar, and orpiment. Some plants such as ferns and soil bacteria are capable of removing arsenic from the environment through biodegradation, but then this potentially becomes a concern for other organisms relative to their likelihood to consume these plants and bacteria. Multiple sources contribute to the amount of arsenic in the environment, including: volcanoes, run-off, human involvement and interference, and microorganisms, according to Centers for Disease Control and Prevention [CDC], 2009. Historically, inorganic arsenic has been used for a variety of purposes, including pesticides, wood preservation, desiccant, glass manufacturing, non-ferrous alloys, treating lumber, and as early as the eighteenth century arsenic was used as a curative compound. Successful medicinal use of arsenic has resulted in the remission of patients suffering from chronic myelogenous leukemia and acute promyelocytic leukemia, but treatment was ceased after discovering that many of the patients had developed acute arsenic toxicity and skin cancers. (Atman, 2001) Arsenic use also used to be prevalent in the wine and beer industries.  Because inorganic arsenic was commonly sprayed in the past on grapes used to make wine, even organic wine can potentially be susceptible to contamination as a result of residual arsenic in the soil in which the grapes are grown on. This can be seen as a result of the soil being saturated with arsenic for years before changing to an organic method. According to the world health organization (WHO), arsenic can be found at relatively high levels in the groundwater of some countries. This is becoming a major public health concern of global proportions. Chronic exposure to inorganic arsenic via the oral route has been known to cause kidney and liver damage, peripheral neuropathy, anemia, skin lesions, gastrointestinal effects, tumor growth, DNA damage, tumor production, and central an peripheral nervous system disorders. Contaminated groundwater typically contains arsenic in the form of arsenous acid or arsenic acid and their derivatives. Arsenic is relatively scarce in the earth’s crust, Some notably rich sources of arsenic include, clays, phosphate rocks, and sedimentary iron and manganese oxides. Arsenic could also be considered highly mobile, as evidenced by the higher average contents of arsenic found in shales, coals, and sandstones associated with uranium mineralization in Utah, Wyoming, South Dakota, and Colorado. This high mobility contributes to the difficulty to convert arsenic into a water-soluble or volatile product. As a result of its high mobility, arsenic is not likely to be found in high concentrations in one specific site. This could be seen as a benefit, but it is also important to note that this high mobility can contribute to arsenic pollution becoming a more widespread issue. Immobilized Arsenic can be mobilized by human activities such as mining, and smelting, but it is important to note that arsenic cannot be mobilized easily when it is immobile. Due to human activities, mainly through mining and smelting, coal firing power plants, and the process of purifying industrial gasses, naturally immobile arsenics have also mobilized and can now be found on many more places than where they existed naturally. Some uncombined arsenic can also occur naturally as microcrystalline masses. These can be found in Italy, the United States, France, Romania, and Germany.

I chose this as a topic because of our proximity to a coal burning power plant, and the fact that groundwater contamination related to high levels of arsenic in coal ash (related to burning coal and releasing trace amounts of arsenic, and also arsenic particles binding to the coal ash throughout coal-burning process) which leads to elevated concentrations of arsenic at coal ash disposal sites. This arsenic then makes its way into groundwater via some of the processes mentioned above. For the aforementioned reasons this is seriously concerning to anyone who may be ingesting the groundwater in local areas in proximity to the power plants, especially in the case of drinking unprocessed and untreated water such as that from streams and rivers. As someone who is passionate about being outdoors, this is a situation I actually find myself in quite often, as my friends or my wife and I spend our time camping and inevitably have to drink potentially contaminated water while on our adventures.

Hazard identification

 Arsenic is a known carcinogen and chronic exposure to arsenic via ingestion can result in kidney and liver damage, peripheral neuropathy, anemia, skin lesions, gastrointestinal effects, tumor growth, DNA damage, tumor production, and central an peripheral nervous system disorders. Inhalation of arsenic, as a result of burning wood products treated with arsenic, can cause severe arsenic toxicity leading to a sore throat, irritated lungs, and lung cancers. A study by Smith, Ercumen, Yuan, and Steinmaus found that the risk for developing lung cancer actually didn’t vary much when exposed to arsenic through the inhalation versus the ingestion route. Dermal exposure is also possible when considering airborne arsenic. Acute exposure to high concentrations of airborne arsenic can cause skin irritation, redness, and swelling, but in most cases dermal exposure is unlikely to result in any serious internal effects. Most of the other aforementioned effects are directly related to ingestion, and could be considered to be related, at least in part, to the issue of contaminated ground water containing arsenic. Arsenic in the environment is naturally occurring in soil and minerals. As a result, wind-blown dust, runoff, and leaching can lead to the contaminant being dispersed across land, sea, and air. Volcanic eruptions are believed to account for roughly one third of the arsenic in the atmosphere. The mining and smelting of metal-containing ores also contributes to the amount of arsenic in the environment. As mentioned before, coal-firing power plants that produce coal ash which subsequently makes its way into ground water and is then transported to bodies of water and other areas by advection. Arsenic takes many forms in the environment, including arsenous acid in groundwater, arsenates in soil that are capable of dissolving in groundwater, attached to the small particles released in coal ash and from other combustion processes, large arsenic particles in wind-borne soil, arsenic release from iron oxide, and it can be found most often in rocks, soil, and sediment. Airborne arsenic can travel long distances, and because common arsenic compounds are capable of dissolving in water, the contaminant is able to travel through groundwater, lakes, and rivers by dissolving in precipitation. These arsenic particles then either settle to the bottom of the water and bind to particles in the sediment at the bottom of the body of water, or are transported by the flow of water. There are bacteria capable of using enzymatic activity to break down iron. Arsenic can bind to the surface of solid iron and render it unavailable, but when the iron is broken down by these bacteria, any arsenic that was bound to the iron will now be released into groundwater.

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According to American Society for Microbiology (2005), When arsenic is attached to small particles the toxicant may stay airborne for days and be transported across great distances. Most of the common arsenic compounds are capable of dissolving in water, which leads to arsenic contamination in groundwater, rivers, and lakes, possibly as a result of dissolving in precipitation and industrial waste. While oftentimes, arsenic will adhere to particles in aquatic ecosystems or sediment on the bottom of rivers and lakes, certain amounts of the contaminant will be transported via the water. Bacteria capable of reducing iron, such as ps. stutzeri and Bacillus cereus are able to thrive without oxygen and can transform (Fe(III)) to (Fe(II)), which is water soluble. Solid Fe(III) has the potential to immobilize arsenic by binding to it. This arsenic can be released into groundwater whenever the aforementioned bacteria transform the iron. An organic form of arsenic can also be found in fish and shellfish. This form of arsenic is known as arsenobetaine.

Arsenic is constantly moving in the environment, and is thus not persistent relative to some pollutants (PCBs, DDT). Arsenic compounds are generally non-volatile, so environmental factors such as wind patterns would have a less significant effect on distribution than the advection of ground water. According to Vahter, M. (2002), Inorganic arsenic in the body is methylated via alternating between the reduction of pentavalent adding a methyl group from S-adenosylmethionine. In terms of importance relative to arsenic methylation, the liver is the most important site. However, most organs do present at least some form of arsenic methylating activity. Metabolites of arsenic include methylarsonic acid (MMA) and dimethylarsenic (DMA), which, when compared to inorganic acid, are less reactive with tissues and are readily excreted in urine. Global warming and climate change can also have an effect on the transportation of arsenic in the environment. With increasing temperatures and the lack of rainfall in certain areas as a result of climate change, arsenic that would previously have made its way into the soil and water with the falling precipitation can now be blown into the wind along with dust particles. This can lead to an increased risk of airborne arsenic causing adverse effects in areas where arsenic is a part of the geological landscape this can lead to serious problems and respiratory health issues for anyone local to the area.

Hazard Characterization and Dose Response Assessment

A study conducted by Hertz-Picciotto I, and Smith A.H. (1993) examined the dose-response behavior between arsenic and lung cancers in miners and smelters from various parts of the world. This study examined the chronic effects of exposure to arsenic in the workplace and the relationship of exposure to the development of lung cancer, and investigated the respiratory or inhalation route of exposure. The endpoint being studied in this case was the standardized mortality ratio, which utilized the death rates of a general population in the same region to derive the expected deaths of the cohort being studied. In one particular cohort, a large group of smelters from Tacoma, Washington, found that the standardized mortality rate increased by a third of the magnitude of the cumulative dose. Linearity between the dose and the observed adverse health effects was not consistent throughout the course of the study, but this was explained through the discussion of various confounding factors, such as exposure to other carcinogens, age, and smoking. This is clearly one of the most common routes of arsenic uptake for humans working at or living near mines or smelting facilities. According to the Environmental Protection Agency (EPA), concerning humans, for inorganic arsenic the per-day reference dose is 0.0003 mg/kg of body weight. This was decided relative to the adverse effects experienced when exposed to arsenic via the oral route, including vascular complications, keratosis, and hyperpigmentation. The reference dose is based on daily exposure of arsenic to humans that is unlikely to cause deleterious effects excluding cancer.

Due to the characteristics of arsenic that cause it to be so prevalent in aquatic ecosystems, freshwater organisms are continuously exposed to relatively low concentrations of arsenic, which will eventually bioaccumulate in the liver and kidney. A study completed by Kumari et al. (2016) examined the acute toxicity of arsenic to fish. Their findings, which included variations in the ninety-six hour LC50 values of differing fish species, examined the response of multiple species to metallic stress. One specific species, Danio rerio (Zebra fish), when exposed to concentrations of arsenic ranging from five to fifteen milligrams per liter would typically die within the first 48 hours of exposure. However, the fish that survived the first 48 hours of testing were typically able to tolerate subsequent exposures. These findings reveal that when exposed to arsenic, Zebra fish would either experience mortality or recover with an increased resiliency against arsenic toxicity. Mortality was not the only endpoint observed in this study. Behavioral endpoints such as loss of equilibrium, lateral swimming, jumping out of the test media, rapid opercular movement, and erratic swimming. The study also found that when fish are exposed to lower concentrations of arsenic, for example, concentrations as low as 0.08 mg/L, they do not show behavioral changes.

Exposure Assessment:

 In terms of exposure to arsenic, respiration and ingestion through the intake of contaminated water are the most likely to affect humans. Dermal absorption of arsenic is the least likely and prevalent route of exposure for humans. In situations that present high concentrations of arsenic in the air, trace amounts of the contaminant will actually be absorbed into circulation through the skin, but will cause irritation, swelling, and redness. There is much greater risk in these situations of respiratory exposure. Specifically, these exposure situations occur often in the mining and smelting industry and can be the source of chronic exposure to arsenic, but any profession which involves the use of arsenic, release through chemical processes, and volatilization of the contaminant can be at risk for chronic exposure.

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exposure. Chronic exposure to arsenic in humans can result in cancer, peripheral neuropathy, lethargy, hyperkeratosis, peripheral vascular disease, gastrointestinal upset, and hematological abnormalities. A study completed by Dartmouth college examining the placental arsenic levels of 652 women. These levels were compared to urinary levels of arsenic and the levels found in the women’s and children’s toenails. A positive correlation was found between the levels of arsenic found in the placenta and levels found in urine, maternal toenails, and infant toenails. While not the most prevalent, in utero exposure of arsenic is possible based on the exposure of the mother to arsenic. Because arsenic is such a toxic and dangerous contaminant, acute exposures typically result in mortality except in the case of extremely small doses. Frequency and magnitude of exposure, both chronic and acute, are relative to geographical location, occupation, and environmental regulation. Regions of the world that are subject to high amounts of volcanic activity, and those near mines, and smelting facilities are at significantly higher risk of exposure via the aforementioned routes. (Punshon, T. (2015))

 Aquatic organisms can be continuously exposed to relatively low concentrations of arsenic due to the characteristics of the contaminant that cause it to be so prevalent in aquatic ecosystems. This arsenic will eventually bioaccumulate in the liver and kidney. The most likely routes of exposure to these organisms is dermal absorption, ingestion of water, and respiration. The exposure scenarios again, are dependent on geographical location and environmental regulation. Close proximity to volcanoes and facilities that use or release arsenic will result in significantly increased likelihood of exposure. Arsenic will move through the trophic levels, resulting in a greater risk of exposure to organisms that ingest plants that have been able to uptake arsenic, as well as to predators who may consume aquatic organisms and, of course, humans with diets that include potentially contaminated seafood. Sampling of groundwater and aquatic organisms (typically liver or kidney tissue samples) can be taken regularly, especially in geographical areas of concern based on proximity to sources of arsenic. If possible, samples can also be collected from local predators to assess the risk of exposure to arsenic to other organisms at higher trophic levels. Human exposure in these areas should also be measured to assess the risk of exposure via ingestion of contaminated organisms or groundwater. The biological process involved in elimination result in traceable levels of arsenic in urine and toenails, so both urine and toenail samples would be sufficient for exposure testing purposes. It could also be useful to take samples of arsenic levels in the air to assess the risk of dermal and inhalation-based exposure.

Risk Characterization:

 Environmental regulation, leading to the reduction of the global widespread use of arsenic in manufacturing and agriculture has reduced the risk of exposure for many organisms and regions significantly over the course of time. However, proximity to volcanoes, as well as to industrial sources of arsenic still presents significant risk to local biota. Contaminated groundwater containing significantly higher levels of arsenic than the EPA proposed guidelines of 0.01 mg/L can be found in many areas of the world, which can cause severe complications related to chronic exposure, such as cancer, hematological abnormalities, cancer, peripheral neuropathy, lethargy, hyperkeratosis, and peripheral vascular disease. Due to the high mobility of arsenic in water and the air, even areas that aren’t localized to these sources can be at risk for exposure via the same routes. Arsenic is an incredibly dangerous contaminant and has thus been studied extensively, so there is an abundance of data concerning exposure and risk. As a resident in an area that is in close proximity to a coal burning power plant, near which contaminated groundwater, soil, and sediment samples have been found to contain dangerous levels of arsenic (according to samples taken by Mobile Baykeeper that were found to be 80 times higher than background levels from nearby waterways) I would personally prefer to see more studies and research conducted concerning the risk of exposure to the local population, especially those that may live downstream from the plant. Groundwater samples localized to the powerplant can be taken as well as samples from the surrounding waterways in order to assess the risk of exposure to local residents. Samples of aquatic organisms local to the area can be taken regularly, and if possible, samples can also be collected from local predators to assess the risk of arsenic exposure to other organisms at higher trophic levels. Human exposure in these areas should also be measured to assess the risk of exposure via ingestion of contaminated organisms or groundwater.

Remediation/Solutions/Future Directions:

 Policy and environmental regulation has made an impact on the relative risk of exposure to arsenic when considering the historical context. That being said, arsenic is an incredibly toxic contaminant that can cause irreversible damage to organisms and argument could certainly be made that while the risk of exposure has been reduced since the implementation of these policies, arsenic levels in the environment are still too high to eliminate risk. Particularly problematic is the contamination of areas of concern from before these regulations were put into place. Oftentimes arsenic-based waste from power plants and other industries mentioned in this paper was allowed to seep into groundwater and contaminate the local environment with no measures being taken to prevent or slow this process. Whereas today, these industries are required to take preventative steps such as using protective liners for waste reservoirs, in the past arsenic waste has been free to enter and contaminate groundwater and pollute local environments. The wine example from earlier can express why this is such a concern. If arsenic can continue to contaminate wine even after its use is discontinued because of residual arsenic in the soil, then contamination and exposure in these areas is a major concern. More rigorous policy and regulation, as well as the enforcing of fines for environmental pollution will help to prevent future contamination on the scale of the pollution from the last century. Some plants such as Pteris vittata (Brake fern) are capable of removing arsenic from contaminated soil. These plants could be used as a possible solution for remediation in these areas. The most effective solution for future prevention of contamination would be the reduction of industry that is releasing massive amounts of the contaminant into the environment. 

References:

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Glossary-Appendix (2 points):

Anthropogenic- originating in human activity (Page 1, line 7)

Bioaccumulation- the accumulation of substances, such as pesticides or other chemicals in an organism

Boidegradation- the decomposition of organic materials by microorganisms

Carcinogen- a substance capable of causing cancer in tissues

Hematologic- of or relating to blood or hematology (Page 1, line 11)

Myelogenous- having to do with, produced by, or resembling bone marrow

Promyelocyte- a cell in bone marrow that is in an intermediate stage of development between a myeloblast and a myelocyte and has the characteristic granulations but lacks the specific staining reactions of a mature granulocyte of the blood