Calcium arsenate
Encyclopedia
Calcium arsenate is an extremely poisonous chemical compound
that most commonly exists as a colorless to white amorphous solid. It was originally used as a pesticide
and as a germicide. It is highly soluble in water, as compared with lead arsenate, which makes it more toxic.
. The resulting solution is then made alkaline by adding sodium hydroxide. This reaction occurs via ion exchange
and the resulting precipitate is calcium arsenate.
2Na2H[AsO4] + 3CaCl2 → 4NaCl + Ca3[AsO4]2 +2HCl
The solubility of this compound was found by Tartar, et al. to be 0.014g in 100g of water at 25˚ C. This molecule is fairly reactive. When placed in an aqueous solution and heated, H2AsO4 gas is released.
ic and systematic health effects. This compound, considered non-combustible, gives off irritating or toxic fumes when heated (H2AsO4 as outlined above). The compound also reacts with strong acids to form toxic arsine gas
(AsH3). The substance is normally absorbed into the body by inhalation of its aerosol form or by ingestion.
Hazardous Class/Division: 6.1 – meaning the material, when not in its gas form, is known to be so toxic to humans to afford a hazard to health during transportation.
Oral LD50: 298 mg/kg in rats
In cases of exposure, symptoms include cough, sore throat, headache, labored breathing, weakness, redness of eyes, abdominal pain, diarrhea, vomiting, burning sensation in throat and chest, and shock or collapse.
In the 1920s Calcium Arsenate was considered a “very important agricultural insecticide,” made in large manufacturing vats by mixing 4 moles of Calcium Oxide with 1 mole of Arsenic Oxide. In the United States, 1360 metric tons were produced in 1919, 4540 in 1920, and 7270 in 1922. The total arsenic content was calculated from the total Ca3(AsO4)2 in order to obtain the percentage of the active ingredient, but even then it was speculated that a considerable portion of the product was basic arsenate. In a study in 1931, 16 brands of pesticides were tested for basic arsenic content and it was found that “the presence of basic arsenate in undetermined compositions was definitely established."
Article the data acquired was inadequate for correlation studies. Toxicity-level doses of arsenic affect all the steroid receptors and signal transduction pathways, which may lead to dysfunction of osteoclast signaling and differentiation. Human cells are. more susceptible than animal cells to arsenic, but this is based on studies of non-bone cells. It is speculative that arsenic may be a factor in the abnormal variation in prevalence rates of Paget’s disease in Lancashire. This hypothesis is not yet a general theory in Paget’s disease of the bone.
Calcium Arsenate has also been proven to have tumorigenic tendencies in male Syrian Golden Hamsters when given in 15 intratracheal instillations weekly in doses of 3 mg/kg of body weight. It is also theorized to remain in tissue for longer periods of time when compared to arsenic trioxide.
Arsenic poisoning is given as the latest reason for the widespread prevalence of kidney disease in north central province of Sri Lanka.Thousands of lives have fallen victim to various kidney ailments in the province during the past two decades or so. At present, around 20,000 patients are seeking treatment at state hospitals.All the patients have symptoms of arsenic poisoning, and an analysis of their drinking water has found high arsenic and mercury contents.The two, and the high salinity of the water in the north central province, has make it more toxic. The researcher said further details would be released in the coming weeks.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
that most commonly exists as a colorless to white amorphous solid. It was originally used as a pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
and as a germicide. It is highly soluble in water, as compared with lead arsenate, which makes it more toxic.
Synthesis
The synthesis of calcium arsenate is commonly prepared by adding disodium hydrogen arsenate in excess to calcium chlorideCalcium chloride
Calcium chloride, CaCl2, is a salt of calcium and chlorine. It behaves as a typical ionic halide, and is solid at room temperature. Common applications include brine for refrigeration plants, ice and dust control on roads, and desiccation...
. The resulting solution is then made alkaline by adding sodium hydroxide. This reaction occurs via ion exchange
Ion exchange
Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...
and the resulting precipitate is calcium arsenate.
2Na2H[AsO4] + 3CaCl2 → 4NaCl + Ca3[AsO4]2 +2HCl
The solubility of this compound was found by Tartar, et al. to be 0.014g in 100g of water at 25˚ C. This molecule is fairly reactive. When placed in an aqueous solution and heated, H2AsO4 gas is released.
Toxicity
Calcium arsenate is considered highly toxic, having both carcinogenCarcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
ic and systematic health effects. This compound, considered non-combustible, gives off irritating or toxic fumes when heated (H2AsO4 as outlined above). The compound also reacts with strong acids to form toxic arsine gas
Arsine
Arsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is one of the simplest compounds of arsenic...
(AsH3). The substance is normally absorbed into the body by inhalation of its aerosol form or by ingestion.
Hazardous Class/Division: 6.1 – meaning the material, when not in its gas form, is known to be so toxic to humans to afford a hazard to health during transportation.
Oral LD50: 298 mg/kg in rats
In cases of exposure, symptoms include cough, sore throat, headache, labored breathing, weakness, redness of eyes, abdominal pain, diarrhea, vomiting, burning sensation in throat and chest, and shock or collapse.
Effects of short-term exposure
Calcium arsenate irritates skin, eyes, and the respiratory tract. It may affects the gastrointestinal tract, cardiovascular system, central nervous system and kidneys, resulting in severe gastroenteritis, loss of fluid and electrolytes, cardiac disorders, shock and kidney impairment. Exposure above OEL(**) may result in death, though effects may be delayed.Effects of long-term exposure
Repeated or prolonged contact with skin may cause dermatitis. The substance may have effects on the skin, mucous membranes, peripheral nervous system, bone marrow and liver, resulting in pigmentation disorders, perforation of nasal septum, neuropathy, lesions of blood cells and liver impairment. This substance is carcinogenic to humans. Animal tests show that this substance possibly causes malformations in human babies.Use as an Herbicide
Once commonly used as an herbicide, Calcium Arsenate use is now banned in the UK, and its use is strictly regulated in the United States. It is currently the active ingredient in TURF-Cal manufactured by Mallinckrodt, it is one of the few herbicides – used mainly for the control of Poa annua and crabgrass- that hinders earthworm activity. Its label states that it will “reduce and inhibit earthworm activity and survival” and is only recommended against serious earthworm infestations in places such as golf course greens.In the 1920s Calcium Arsenate was considered a “very important agricultural insecticide,” made in large manufacturing vats by mixing 4 moles of Calcium Oxide with 1 mole of Arsenic Oxide. In the United States, 1360 metric tons were produced in 1919, 4540 in 1920, and 7270 in 1922. The total arsenic content was calculated from the total Ca3(AsO4)2 in order to obtain the percentage of the active ingredient, but even then it was speculated that a considerable portion of the product was basic arsenate. In a study in 1931, 16 brands of pesticides were tested for basic arsenic content and it was found that “the presence of basic arsenate in undetermined compositions was definitely established."
Mechanism of Toxicity
Arsenic’s mechanisms as a successful herbicide and germicide and in its toxicity to humans are very similar. Arsenic forms very stable bonds with sulfur, and is therefore able to bind with many sulfhydryl groups on proteins – causing non-specific toxic effects. It is able to both weaken the structural integrity of proteins, and inactivate some enzymes. The lethal risk of arsenic exposure comes from its ability to interfere with cellular metabolism. Arsenic binds to sulfur groups present on pyruvate dehydrogenase complex, an enzyme responsible for converting pyruvate into acetyl-CoA, inactivating it. Without this conversion, the cell is unable to proceed into the Citric Acid cycle, which along with oxidative phosphorylation provide 90% of the cell’s biochemical energy. The loss of function of the Citric Acid cycle is detrimental to the cell. In plants, Arsenic is often mistaken for silicon because of its similar size and solubility. Arsenic enters via phosphate channels and is toxic because of its ability to form a stable bond with ADP (Adenine Di-Phosphate) and prevent the formation of ATP – a vital energy source within the plant’s cells.Recent Findings
Recent hypotheses have been made possibly linking exposure to Arsenic pesticides to Paget’s disease of bone – a condition affecting how bones break down and rebuild, which over time results in bones that are brittle and fragile. A cluster of six small towns in Lancashire County in North west England, which have a high prevalence of the disease have a noted links with the cotton industry – where calcium arsenate pesticide as used intensely to combat the boll weevil and imported to Lancashire in cotton bails from 1917 to 1945. This era of Calcium Arsenate use is consistent with the high prevalence of the disease until 1974 and its decline in numbers in 1993, given appropriate time for lags. Geochemical arsenate is widespread within the local environment and could possibly account for the geographical variations of the disease’s prevalence, although according this 2002Article the data acquired was inadequate for correlation studies. Toxicity-level doses of arsenic affect all the steroid receptors and signal transduction pathways, which may lead to dysfunction of osteoclast signaling and differentiation. Human cells are. more susceptible than animal cells to arsenic, but this is based on studies of non-bone cells. It is speculative that arsenic may be a factor in the abnormal variation in prevalence rates of Paget’s disease in Lancashire. This hypothesis is not yet a general theory in Paget’s disease of the bone.
Calcium Arsenate has also been proven to have tumorigenic tendencies in male Syrian Golden Hamsters when given in 15 intratracheal instillations weekly in doses of 3 mg/kg of body weight. It is also theorized to remain in tissue for longer periods of time when compared to arsenic trioxide.
Arsenic poisoning is given as the latest reason for the widespread prevalence of kidney disease in north central province of Sri Lanka.Thousands of lives have fallen victim to various kidney ailments in the province during the past two decades or so. At present, around 20,000 patients are seeking treatment at state hospitals.All the patients have symptoms of arsenic poisoning, and an analysis of their drinking water has found high arsenic and mercury contents.The two, and the high salinity of the water in the north central province, has make it more toxic. The researcher said further details would be released in the coming weeks.