water contamination, affects of arsenic on human health, reactivity of arsenic, sources of arsenic, natural and human induced sources of arsenic, arsenic bearing minerals, rocks containing arsenic, health affects of arsenic, redox and oxidation of arsenic
Ground water Arsenic Contamination in IndiaDr Sayan Das
Extent, related research and remedication meassures
Chemistry of arsenic, Use of arsenic, reference value , Oxidation method, Ion exchange method, Membrane method
Ground water Arsenic Contamination in IndiaDr Sayan Das
Extent, related research and remedication meassures
Chemistry of arsenic, Use of arsenic, reference value , Oxidation method, Ion exchange method, Membrane method
Arsenic problem in Bangladesh can be seen as an example of how quick fix contribue to a policy failure and result in disaster. Sustainable policy intervention and mainstreaming the mitigation strategies can be the only effective sollution to this problem. The presentation is the answer of the question set at the outset of the slides.
The term heavy metal refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations.
Heavy metals are Globally distributed
pollutants
This slide is about Dissolved Oxygen and its importance and also it contains winkler's method for determining dissolved oxygen.There is a video attached to the slide.It contain the principle,interference,reagents and procedure for determination by winklers method
The chemical stability of tailings from mineral processing is important subject for study within the research field regarding the possible impacts for the environment, especially groundwater pollution and acid mine drainage (AMD). Tailings generated from processing metal ores can be classified as fined-grained sediment-water slurry. The solids are composed of minerals such as silicates, oxides, hydroxides, carbonates, and sulphides. The mineralogical and geochemical studies of tailings from metals ores are key factors used in the investigation of the chemical reactions and chemical systems that results in AMD. The scope of the study is to investigate tailing dams as a potential source of Arsenic (As) in Dokyiwa tailing dam which is an abandoned together with Pompora tailing dam and one active tailing dam which is the Sansu tailing dam at obuasi municipality and its dissolution into adjoining environmental media. The scope of this work is confined to Dokyiwa tailing dam in Obuasi municipality.
Arsenic problem in Bangladesh can be seen as an example of how quick fix contribue to a policy failure and result in disaster. Sustainable policy intervention and mainstreaming the mitigation strategies can be the only effective sollution to this problem. The presentation is the answer of the question set at the outset of the slides.
The term heavy metal refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations.
Heavy metals are Globally distributed
pollutants
This slide is about Dissolved Oxygen and its importance and also it contains winkler's method for determining dissolved oxygen.There is a video attached to the slide.It contain the principle,interference,reagents and procedure for determination by winklers method
The chemical stability of tailings from mineral processing is important subject for study within the research field regarding the possible impacts for the environment, especially groundwater pollution and acid mine drainage (AMD). Tailings generated from processing metal ores can be classified as fined-grained sediment-water slurry. The solids are composed of minerals such as silicates, oxides, hydroxides, carbonates, and sulphides. The mineralogical and geochemical studies of tailings from metals ores are key factors used in the investigation of the chemical reactions and chemical systems that results in AMD. The scope of the study is to investigate tailing dams as a potential source of Arsenic (As) in Dokyiwa tailing dam which is an abandoned together with Pompora tailing dam and one active tailing dam which is the Sansu tailing dam at obuasi municipality and its dissolution into adjoining environmental media. The scope of this work is confined to Dokyiwa tailing dam in Obuasi municipality.
Introduction, images of Arsenic, Industrial Uses and pollution sources, Speciation of Arsenic, Environmental levels and ecological effects, Biochemical effects, toxicology and toxicity, Treatment for Arsenic poisoning, Control measures.
Arsenic is a heavy metal occurring naturally in the environment. It's low concentration is important for various life processes on the Earth but the misuse and overexploitation of mineral resources caused the arsenic contamination to natural resources, which in turn get exposed to living beings causing various toxicity problems and severe health issues. Arsenic has not remained an important mineral for sustaining life but it becomes a category pollutant for which heavy precautions should be taken to avoid an exposure.
The Estuarine System consists of deepwater tidal habitats and adjacent tidal wetlands that are usually semienclosed by land but have open, partly obstructed, or sporadic access to the open ocean, and in which ocean water is at least occasionally diluted by freshwater runoff from the land. The salinity may be periodically increased above that of the open ocean by evaporation. Along some low-energy coastlines there is appreciable dilution of sea water. Offshore areas with typical estuarine plants and animals, such as red mangroves (Rhizophora mangle) and eastern oysters (Crassostrea virginica), are also included in the Estuarine System.
A harmful algal bloom (HAB) is an algal bloom that causes negative impacts to other organisms via production of natural toxins, mechanical damage to other organisms, or by other means. HABs are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisonings.
Similar to Arsenic contamination of Groundwater (20)
Critical analysis of Hydraulic stimulation of geothermal reservoirs: fluid fl...Umer Bhatti
Critical analysis of Hydraulic stimulation, geothermal reservoirs, fluid flow, electric potential and microseismicity, the Soultz-Sous-Forets Hot Dry Rock Site
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
2. ABSTRACT
Arsenic water contamination is a big problem in today’s time. Arsenic is present on earth naturally
and is added into ground water and stream both naturally and due to human activities also. Major
three types of rocks Igneous, Metamorphic and sedimentary all contain arsenic in different
proportion. Many individual minerals also contain arsenic. Upon certain conditions (redox and
oxidation) naturally occurring arsenic is freed and is dissolved into water. Many human activities
including mining, agricultural and industrial waste also adds arsenic into water. This water
contamination causes serious health issue and has affected millions of people all across the globe.
3. 1. ARSENIC CONTAMINATION
Arsenic contamination is groundwater pollution which is due to presence of naturally occurring
high concentrations of arsenic in groundwater. It has become a big issue due to the use of deep tube
wells for water supply for drinking, food etc., causing serious arsenic poisoning to large numbers
of people. In 2007, a study found that over 137 million people are affected by water contamination
in more than 70 countries. Mass poisoning of water in Bangladesh made everyone aware of the
issue of arsenic contamination. Arsenic contamination of ground water has affected countries all
across the globe, including Pakistan. 20 major incidents of groundwater arsenic contamination
have been reported uptil now, including 4 major in Thailand, Taiwan, Asia, and Mainland China.
1.1. Introduction
Arsenic is a natural component of the earth’s crust and it is widely distributed throughout the
environment in the air, water and land. It is highly toxic when in its inorganic form. People are
exposed to high levels of inorganic arsenic through drinking contaminated water, using
contaminated water in food preparation and irrigation of food crops, industrial processes, eating
contaminated food and smoking tobacco. Exposure to inorganic arsenic for too long, mainly
through drinking water and food, can lead to chronic arsenic poisoning. Skin lesions and skin
cancer are the most characteristic effects.
1.2. Exposure to Arsenic
The exposure of public to arsenic originates from using contaminated groundwater. Inorganic
arsenic is naturally present at high levels in the groundwater of a number of countries, including
Argentina, Bangladesh, Chile, China, India, Mexico, and the United States of America. Arsenic
contamination is higher in areas where there is geothermal activity. Drinking contaminated
water, crops irrigated with contaminated water and food prepared with contaminated water are
the sources of exposure. Fish, shellfish, meat, poultry, dairy products and cereals can also be
dietary sources of arsenic, although exposure from these foods is generally much lower
compared to exposure through contaminated groundwater. In seafood, arsenic is mainly found
in its less toxic organic form. Main and direct exposure of humans to arsenic is through drinking
contaminated water.
1.3. Effects of Arsenic
4. Arsenic appears to be essential for some plant and animal species. A possible safe dose for humans
as a dietary mineral is 15-25 μg. This amount could be absorbed from food without any trouble.
The total amount of arsenic in a human body is about 0.5-15 mg. Many arsenic compounds are
absorbed 60-90%, but they are also easily excreted. Humans can develop resistance to certain
arsenic concentrations. Shortly after absorption arsenic can be found in liver, spleen, lungs and
digestive tract. Most arsenic is excreted, and residues may be found in skin, hair, nails, legs and
teeth. Under conditions of prolonged exposure, many organs may be damaged, skin pigmentation
may occur, hair may fall out and nail growth may stop. Arsenic poisoning is a medical condition
that occurs due to elevated levels of arsenic in the body.
If arsenic exposure occurs over a brief period of time symptoms may include vomiting, abdominal
pain, encephalopathy, and watery diarrhea that contains blood, these are also called acute effects
of arsenic.
Long-term exposure can result in thickening of the skin, darker skin, abdominal pain,
diarrhea, heart disease, numbness, and cancer. The most common reason for long-term exposure
is contaminated drinking water.
Recommended levels in water are less than 10–50 µg/l (10–50 parts per billion). Other routes of
exposure include toxic waste sites and traditional medicines. Most cases of poisoning are
accidental. Arsenic acts by changing the functioning of around 200 enzymes. Diagnosis is by
testing the urine, blood, or hair. Prevention is by using water that does not contain high levels of
arsenic. This may be achieved by the use of special filters or using rainwater. There is not good
evidence to support specific treatments for long-term poisoning
2. ARSENIC BEARING MINERALS
Pure arsenic is found in lesser amounts, but most of it is found combined with the atoms of other
elements. Most arsenic is obtained as a byproduct when rock containing other metals is processed.
There are several common arsenic minerals.
2.1. Arsenopyrite
The main arsenic containing mineral is arsenopyrite (also called mispickel), in which arsenic is
combined with iron and sulfur. Arsenopyrite is found in high temperature hydrothermal veins, in
pegmatites, and in areas of contact metamorphism or metasomatism. Much of the arsenopyrite that
5. has been mined formed as a high-temperature mineral in hydrothermal veins. Arsenopyrite has
also been mined from sulfide deposits formed by contact metamorphism.
2.2. Orpiment
Orpiment is another arsenic mineral, in which arsenic is combined with sulfur. The name orpiment
comes from Latin meaning “gold pigment”. Orpiment is very poisonous, and it also discolored the
other pigments that artists used. Orpiment is found in volcanic fumaroles, low temperature
hydrothermal veins, and hot springs.
2.3. Realgar
Realgar, also known as "ruby Sulphur" or "ruby of arsenic". Realgar most commonly occurs as a
low-temperature hydrothermal vein mineral associated with other arsenic and antimony minerals.
It also occurs as volcanic sublimations and in hot spring deposits.
2.4. Cobaltite
Cobaltite is a sulfide mineral composed of cobalt, arsenic, and sulfur, Co As S. It contains up to
10% iron and variable amounts of nickel. It occurs in high-temperature hydrothermal deposits and
contact metamorphic rocks.
2.5. Proustite
Proustite is a sulfosalt mineral consisting of; silver sulfarsenide, Ag3AsS3, known also as light red
silver or ruby silver ore, and an important source of the metal. Proustite occurs in hydrothermal
deposits as a phase in the oxidized and supergene zone.
2.6. Tennantite
Tennantite is a copper arsenic sulfosalt mineral with an ideal formula Cu12As4S13. It is found in
hydrothermal veins and contact metamorphic deposits in association with other Cu–Pb–Zn–Ag
sulfides and sulfo-salts, pyrite, calcite, dolomite, siderite, barite, fluorite and quartz.
3. ARSENIC BEARING ROCKS
3.1.Earth’s crust
Few estimates exist for the concentration of arsenic in the earth’s crust. However, the concentration
is generally taken to be low with average arsenic concentration in the lithosphere as about 2 mg/kg.
6. 3.2. Igneous rocks
Arsenic concentrations in igneous rocks are generally similar to those found in the crust, with
average value of 1.5 mg/kg. Volcanic glasses are only slightly higher with an average of around
5.9 mg kg–1. Despite not having exceptional concentrations of Arsenic, volcanic rocks (especially
ashes) are often implicated in the generation of high Arsenic waters. This may relate to the reactive
nature of recent acidic volcanic material, especially fine-grained ash and its tendency to give rise
to sodium rich high-pH groundwater.
3.3.Metamorphic rocks
Arsenic concentrations in metamorphic rocks tend to reflect the concentrations in their igneous
and sedimentary precursors. Most contain around 5 mg/kg or less. Pelitic rocks (slates, phyllites)
typically have the highest concentrations with on average 18 mg/kg.
4. ARSENIC BEARING MINERALS IN SED. ROCKS
The concentration of Arsenic in sedimentary rocks is typically in the range 5–10 mg/kg, slightly
above average terrestrial abundance. Average sediments are enriched in Arsenic relative to igneous
rocks.
4.1. Sandstone
Sands and sandstones tend to have the lowest concentrations, reflecting the low Arsenic
concentrations of their dominant minerals, quartz and feldspars. Average sandstone Arsenic
concentrations are around 4 mg/kg.
4.2. Argillaceous
Argillaceous deposits have a broader range and higher average Arsenic concentrations than
sandstones, typically an average of around 13 mg/kg. The higher values reflect the larger
proportion of sulphide minerals, oxides, organic matter and clays. Black shales have Arsenic
concentrations typically at the high end of the range principally because of their enhanced pyrite
content. Marine argillaceous deposits have higher concentrations than non-marine deposits. This
may also be a reflection of the grain-size distributions, with potential for a higher proportion of
fine material in offshore pelagic sediments as well as systematic differences in sulphur and pyrite
contents. Marine shales tend to contain higher sulphur concentrations. Sediment provenance is also
7. a likely important factor. Particularly high Arsenic concentrations have been determined for shales
from mid-ocean settings. Atlantic Ridge gases may in this case be a high Arsenic source.
4.3. Organic Coals
Concentrations in coals and bituminous deposits are variable but often high. Samples collected of
organic-rich shale from Germany have Arsenic concentrations of 100–900 mg/kg. Some coal
samples have been found with extremely high concentrations up to 35,000 mg/kg but generally
low concentrations of 2.5–17 mg/kg are also reported.
4.4. Carbonates
Carbonate rocks typically have low concentrations, reflecting the low concentrations of the
constituent minerals. Some of the highest observed Arsenic concentrations, often several thousand
mg/kg, are found in ironstones and Fe-rich rocks. Phosphorites are also relatively enriched in
Arsenic (values up to ca. 400 mg/kg having been measured).
4.5. Unconsolidated Sediments
Concentrations of Arsenic in unconsolidated sediments are not notably different from those in their
indurated equivalents, muds and clays having typically higher concentrations than sands and
carbonates. Values are typically 3–10 mg/kg, depending on texture and mineralogy. Elevated
concentrations tend to reflect the amounts of pyrite or Fe-oxides present. Increases are also
typically found in mineralized areas. Placer deposits in streams can have very high concentrations
as a result of the abundance of sulphide minerals.
Average Arsenic concentrations for stream sediments are in the range 5– 8 mg/kg. Similar
concentrations have also been found in river sediments where groundwater-arsenic concentrations
are high: Datta and Subramanian (1997) found concentrations in sediments from the
River Ganges averaging 2.0 mg kg–1 (range 1.2–2.6 mg/kg),
Brahmaputra River averaging 2.8 mg kg–1 (range 1.4–5.9 mg/kg)
Meghna River averaging 3.5 mg kg–1 (range 1.3–5.6 mg/kg).
Arsenic concentrations in lake sediments ranges between 0.9–44 mg/kg (median 5.5 mg/kg) with
highest concentrations present down-slope of mineralized areas. The upper baseline concentration
for these sediments is likely to be around 13 mg/kg.
8. Arsenic concentrations in glacial till ranges from 1.9–170 mg/kg (median 9.2 mg/kg) and highest
concentrations down-ice of mineralized areas. Relative arsenic enrichments have been observed
in reducing sediments in both near shore and continental-shelf deposits noted concentrations
increasing with depth (up to 30 cm) in continental shelf sediments as a result of the generation of
increasingly reducing conditions.
4.6. Soils
Baseline concentrations of Arsenic in soils are generally of the order of 5–10 mg/kg. Peats and
bog soils can have higher concentrations with average 13 mg/kg, principally because of increased
prevalence of sulphide mineral phases under the reduced conditions.
Acid sulphate soils which are generated by the oxidation of pyrite in sulphide-rich terrains such as
pyrite-rich shales, mineral veins and dewatered mangrove swamps can also be relatively enriched
in Arsenic. Arsenic concentrations up to 45 mg/kg has been noticed in the acid sulphate soils
derived from the weathering of pyrite-rich shales in Canada.
Although the dominant source of Arsenic in soils is geological, and hence dependent to some
extent on the concentration in the parent rock material, additional inputs may be derived locally
from industrial sources such as smelting and fossil-fuel combustion products and agricultural
sources such as pesticides and phosphate fertilizers.
4.7. Contaminated Surficial Deposits
Arsenic concentrations much higher than baseline values have been found in sediments and soils
contaminated by the products of mining activity, including mine tailings and effluent.
Concentrations in tailings piles and tailings-contaminated soils can reach up to several thousand
mg/kg. The high concentrations reflect not only increased abundance of primary arsenic rich
sulphide minerals, but also secondary iron arsenates and iron oxides formed as reaction products
of the original ore minerals. The primary sulphide minerals are susceptible to oxidation in the
tailings pile and the secondary minerals have varying solubility in oxidizing conditions in ground
waters and surface waters. Scorodite (FeAsO4.2H2O) is a common sulphide oxidation product
and its solubility is considered to control arsenic concentrations in such oxidizing sulphide
environments. Scorodite is metastable under most groundwater conditions and tends to dissolve
incongruently, forming iron oxides and releasing arsenic into solution. There is some confusion in
9. the analysis of these solubility relationships between congruent dissolution, incongruent
dissolution and sorption/desorption reactions. Secondary arsenolite (As2O3) is also relatively
soluble. Arsenic bound to iron oxides is relatively immobile, particularly under oxidizing
conditions.
5. SOURCES
The contamination of groundwater by naturally occurring Arsenic is much more serious, it is
urgently necessary to understand and investigate the major geochemical pathways involved in
the transformation and mobilization of Arsenic in aquifer sediments. The geochemistry of
Arsenic is a complex phenomenon found in the environment, and it generally is a function of
multiple oxidation states, speciation, and redox transformation. The contamination of a drinking
water source by arsenic can result from either natural or human activities. Arsenic is an element
that occurs naturally in rocks and soil, water, air, plants, animals and is used for a variety of
purposes within industry and agriculture. It is also a byproduct of copper smelting, mining, and
coal burning. Volcanic activity, the erosion of rocks and minerals, and forest fires are natural
sources that can release arsenic into the environment. Arsenic is used for wood preservative
purposes, paints, drugs, dyes, soaps, metals, semi-conductors and agricultural applications.
Arsenic can enter the water supply from natural deposits in the earth or from industrial and
agricultural pollution. It is widely believed that naturally occurring arsenic dissolves out of certain
rock formations when ground water levels drop significantly. Once released, arsenic remains in
the environment for a long time. Arsenic is removed from the air by rain, snow, and gradual
settling. Once on the ground or in surface water, arsenic can slowly enter ground water. High
arsenic levels in water wells may come from certain arsenic containing fertilizers used in the past
or industrial waste. It may also indicate improper well construction or overuse of chemical
fertilizers or herbicides in the past.
5.1. How Arsenic enters water
In the absence of oxygen, some bacteria living in deposited sediments can use arsenic and iron
oxide particles as an alternative means of respiration. The microbes separate the arsenic and iron
oxides and transfer the toxin into underlying groundwater.
10. Arsenic is present in many minerals, which further forms rocks and different formation. In
sedimentary rocks, matrix contain arsenic bearing minerals (e.g. Iron oxide and Pyrite) in them.
Arsenic can be released from iron oxides if groundwater has these characteristics:
neutral to slightly alkaline pH (a pH of about 7 or slightly greater),
“Reducing” redox conditions (indicated by low oxygen and high iron concentrations).
5.2. Speciation of Arsenic
Arsenic is unique among trace metalloids and oxyanion forming metals. It is very sensitive to
change in pH of water (6.5-8.5). It mostly exist as inorganic form in water as trivalent arsenite [As
(III)] or pentavalent arsenate [As (V)], although it can occur in (-3, 0, +3 and +5) forms. Organic
forms are formed by biological activity but are not quantitatively important, they can be significant
in industrial polluted area.
Arsenic may be solubilized when pH is high, arsenic can be released from surface binding sites
that lose their positive charge. When water level drops and sulfide minerals are exposed to air,
trapped arsenic in sulfide minerals can be released into water. In organic carbon presence in water,
bacteria are fed by directly reducing As (V) to As (III) or by reducing the element at the binding
site, releasing inorganic arsenic.
5.3. Mobilization and Redox Transformation of Arsenic
Natural geochemical and biologic processes play a vital role in controlling the mobilization and
transformation of Arsenic in the surface and subsurface environment. In groundwater,
mobilization of Arsenic takes place in the range of pH 6.5 to 8.5 under both oxidizing and
reducing conditions. Both abiotic and biotic processes favor the natural redox transformation
and mobilization of Arsenic in humid as well as arid environments.
5.4. Redox transformation of Arsenic in water
Under reducing conditions in natural environments, deltaic and alluvial sediments usually are
associated with the mobilization of Arsenic. Aquifer sediments, along with a layer of clay or silt,
may act as a cap, which effectively restricts the penetration of atmospheric oxygen to the aquifers,
thereby creating an anaerobic environment. Highly reducing conditions (anaerobic) also may be
developed in the presence of natural organic matter deposited with sediments. These highly
11. reducing conditions facilitate the release of Arsenic adsorbed on amorphous Fe oxides commonly
occurring in the aquifer sediments. Reductive dissolution of As-bearing amorphous Fe (III) oxides
plays a key role in the mobilization of Arsenic from aquifer sediments to ground waters. Dissolved
organic carbon (DOC) deposited in sediments and anaerobic metal-reducing bacteria also play a
vital role in Arsenic mobilization. The Arsenic concentration in ground waters is more in reducing
environment depends on several factors, including areal and vertical distributions of peat deposits,
the degradation of which is the major redox controller, the redox driver in the groundwater system,
groundwater movement, pH, HCO3
−, Fe, Mn, and Al oxides, and DOC concentrations of
sediments.
5.4.1. Reductive Dissolution of Iron Oxide
Iron hydroxides Fe (OH)3 are one of the most common phases associated with aquifer sediments.
The desorption mechanisms of As from Fe (OH)3 are directly responsible for the existing high
concentrations of mobile As(III) in ground waters
5.5. Oxidation of Arsenite
The form of As (III) is thermodynamically unstable in aerobic conditions; hence, it oxidizes easily
to the less mobile form of As (V). However, this reaction is a slow process, when oxygen becomes
the only oxidant. The presence of some other redox-sensitive species, such as ferric iron [Fe (III)],
manganese oxides (MnO2), clay minerals, and some microorganisms, can intensively increase the
rate of As (III) oxidation converting into the less toxic As (V) form. These oxidation reactions are
highly favorable in arid and semiarid areas as a result of extensive mineral reactions and
evaporation. In the presence of Fe (III) in aqueous solutions, the rate of As (III) oxidation is
accelerated below pH 7. Manganese oxides commonly associated with aquifer solids have been
recognized as an important oxidant to oxidize As (III) to As (V), and this reaction is
thermodynamically feasible over a wide range of pH values.
5.5.1. Oxidation of Sulfide Minerals
The primary source of Arsenic in the environment is the oxidation of Arsenic sulfides, such as
FeAsS and FeS2 minerals. Oxidation of As-bearing sulfides is recognized as an important cause
of Arsenic contamination of groundwater due to production of acid drainage containing toxic
12. inorganic pollutants at higher levels. In oxygen-rich waters, Arsenic is released predominantly
through pyrite and FeAsS minerals
5.5.2. Arsenic Release from Pyrite
FeS2 oxidation takes place via several reaction pathways; the first step involves the chemical
oxidation of FeS2 in the presence of dissolved oxygen (DO), resulting in a certain amount of
Arsenic in ground waters.
5.5.3. Arsenic Release from Arsenopyrite
Dissolution of FeAsS also is of environmental concern and therefore has received much attention
in recent years. FeAsS can be oxidized by Fe (III), a process more than 10 times faster than
oxidation of FeS2
6. NATURAL BARRIERS FOR ARSENIC MOBILIZATION IN DISSOLVED
PHASE
6.1. Geochemical Processes in Controlling Arsenic Mobility and Transformation
Adsorption is the most prominent geochemical process that controls the mobility and transport of
Arsenic in ground waters. Adsorption reactions between Arsenic and mineral surfaces generally
are the most critical phenomena in controlling the dissolved concentrations of Arsenic in ground
waters. Adsorption of Arsenic depends on several external factors, such as solid surface, pH, Eh,
concentration of Arsenic and competing ions, and Arsenic speciation. Redox-active oxide surfaces
of iron, aluminum, and manganese minerals are potentially the most important sources of Arsenic
in aquifer sediments
6.2. Arsenic Adsorption on Iron Oxides
The solubility of Arsenic in ground waters is strongly influenced by adsorption at the Fe (OH)3
surfaces, which exist as discrete particles or as coatings on other mineral surfaces. Both As (V)
and As (III) may be adsorbed and co-precipitated on Fe (OH)3, depending on several important
factors, including pH, the amount of Fe (OH)3 deposited, and the concentration of other competing
ions found in the medium. The adsorption of Arsenic onto Fe (OH)3 occurs mainly at the
oxic/anoxic boundary, referred to as ferrihydrite (Fe2O3·2H2O), which has a large specific area
resulting in an increased adsorption capacity.
13. 6.3. Arsenic Adsorption on Aluminum Oxides
Oxides and hydroxides of Al also have significant adsorption capacity for Arsenic. Because the Al
(III) atom has the same charge and a nearly identical radius as the Fe (III) atom, the common
hydrous Al oxide phases are structurally similar to hydrous ferric oxide. As(V) species such as
CH3AsO(OH)2 and (CH3)2AsOOH can be absorbed by amorphous Al(OH)3, crystalline
Al(OH)3 (gibbsite), α-Al2O3, and β-Al2O3 up to 7.0 pH, and adsorption decreases significantly
at higher pH values, whereas As(III) adsorption increases with increasing pH.
6.4. Arsenic Adsorption on Manganese Oxide
The oxidation of As (III) to As (V) by manganese oxide is an important process in the natural
cycling of Arsenic, as well as in reducing the concentration of dissolved As (III) in groundwater
systems. As (III) is oxidized by MnO2 followed by the adsorption of the As (V) reaction product
on the MnO2 solid phase. The As (V)–MnO2 complex likely is a bidentate binuclear corner-
sharing complex occurring at MnO2 crystallite edges and interlayer domains [100, 125].
Manganese oxides may act as an electron acceptor in the oxidation process and therefore can
adsorb significant amounts of As.
6.5. Arsenic Adsorption on Clay Minerals
Adsorption and oxidation/reduction reactions of Arsenic at clay mineral surfaces also play a crucial
role in the natural attenuation and transformation of Arsenic in groundwater systems.
Aluminosilicate clay minerals are composed of alternating layers of silica oxide and aluminum
oxide, providing several types of binding sites to adsorb a variety of metal ions. The OH groups
associated with Al ions bound on the surface of clay particles act as proton acceptors, forming
anionic species of Arsenic.
14. 7. SUMMARY
Arsenic contamination is a serious problem in this modern world. World population is increasing
and providing them clean water for drinking is becoming more difficult. We have to better
understand how ground water is contaminated by the arsenic naturally and how humans add up to
the contamination. With better understanding we can reduce, if not completely prevent, the water
contamination.
15. 8. References
Source and behavior of arsenic in natural waters Pauline L Smedley and David G
Kinniburgh British Geological Survey, Wallingford, Oxon OX10 8BB, U.K.
Mobilization of arsenic by dissolved organic matter from iron oxides, soils and sediments
by Markus Bauer T, Christian Blodau
https://link.springer.com/article/10.1007/s40726-016-0028-2
https://en.wikipedia.org/wiki/Arsenic_contamination_of_groundwater
https://www.lenntech.com/periodic/water/arsenic/arsenic-and-water.htm
https://www.cdc.gov/healthywater/drinking/private/wells/disease/arsenic.html