Ubiquity of Arsenic
|Arsenic is even more widespread than is suggested by the foregoing list of minerals. It is to be found in small quantities in many other metallic ores, especially those of copper, lead, iron and antimony. Although the arsenic content may be very small, the flue dusts obtained during the smelting of these ores constitute an important source of arsenic compounds. Iron pyrites generally contains 1 to 2 per cent., although more than 4 per cent, has been found in samples from Freiberg. It is consequently often present with pyrites in coal and anthracite, and the combustion of these leads to its presence in the atmosphere. That this occurs to an appreciable extent in large industrial cities has been shown by the examination of atmospheric dusts gathered from office shelves, porticoes, etc., in the centre of Newcastle-on-Tyne, revealing the presence of 65 to 530 parts of As2O3 per million. A similar examination of dusts from turret floors in public buildings of Leeds yielded 120 to 350 p.p.m. As2O3, whilst samples from churches at Harehills, two miles from the city centre, and Whitkirk, on the extreme outskirts, gave 200 and 40 p.p.m. respectively. |
Spectroscopic examination of the carbon arc light usually reveals the presence of arsenic.
Arsenic is present in many primitive rocks, in limestones and marls, clays, sands and gravels. It has been estimated that the percentage amount in the earth's crust is 0.000011, while the atomic proportion may be 0.00005. Analysis of a composite sample of 329 rocks available in the United States yielded 0.00074 per cent. As2O5; while analyses of 46 samples of the common types and grades of phosphate rock from the same country gave a range of 0.0005 to 0.0163 per cent. As2O5. Native sulphur frequently contains arsenic. Javan sulphur containing about 30 per cent, arsenic is known as sulphurite.
Owing to the prolonged action of air and moisture on arsenical ores, soluble compounds of arsenic find their way into the soil, into subterranean waters, streams, and eventually the sea. Thus virgin soils in Colorado have been found to contain 2.5 to 5 p.p.m. of arsenic, while the underlying marl contained 4 to 15 p.p.m. Sulphides of arsenic occur in the waters of the Norris Geyser and of other hot springs at Yellowstone National Park. Arsenic is frequently reported present in mineral waters. For the Choussy Well water, La Bourboule, 5.8 to 6.5 mg. As per litre was recorded for the season 1928 to 1929. Water from the brackish shore lakes of East Prussia contains 1 to 4 mg. As per 1000 litres; the muds from these lakes are found to be much richer in arsenic, containing from 2 to 30 g. per ton of dry weight; this is probably due to the extraction of arsenic from the water by minute water organisms. Samples of Baltic Sea water from nearby contained about 1 mg. As per 1000 litres. Chapman examined 16 samples of sea water from points within 4 miles of the Nore lightship and found 0.14 to 1.0 part of arsenic per million. According to Atkins and Wilson, the element is present in sea water principally in the form of arsenite, in amounts equal to, or greater than, the phosphate content; if this be so, previous determinations of phosphates in sea water by methods involving preliminary treatment with nitric acid have included also arsenates. The arsenic content of sea water varies with the depth, owing to absorption by algae. Gautier examined water of the Atlantic Ocean taken at various depths in the neighbourhood of the Azores, and found the arsenic content at depths of 10, 1335 and 5943 metres respectively to be 25, 10 and 80 parts per million. These high values are attributed to volcanic actions which take place thereabout.
It will readily be understood that traces of arsenic are found in many plants and plant products, and consequently may be assimilated by animals and man. If the quantities of arsenic present are considerable, as they may be when artificial application of insecticidal dust or sprays has been resorted to, an important problem arises owing to the physiological action of arsenical compounds. The element has been detected in the ashes of many plants, and in wood charcoal. Amounts up to 0.025 part As in 100,000 have been found in many vegetables and nuts; fruits generally contained less, 0.005 to 0.012, while mushrooms contained 0.006 part per 100,000. Almonds, red haricot beans, lettuce and celery were richest in arsenic, with 0.020 to 0.025 part per 100,000. Arsenic appears to be present always in hops grown under natural conditions. Thus Lindemann found 0.004 to 0.025 part per 100,000 in untreated hops, this arsenic being derived apparently from the soil. In strongly sulphured hops there was 0.07 to 0.13 part per 100,000. Some of this arsenic passes to the wort on boiling and is adsorbed by the yeast during fermentation. Wine yeasts exhibit this adsorptive power to a somewhat greater degree than brewing yeasts. Both beer and wines are liable to contain arsenic. In the former it may be derived largely from glucose used in production, as was shown to be the case after an outbreak of arsenical poisoning in 1900. Malts may become contaminated with arsenic from the coal or coke used as fuel in the drying operations. Examination of five samples of red wines from Baden showed the presence of 0 to 0.66 mg. As per litre, and traces of the element have been detected in Californian wines, but it is not a normal constituent and the amounts are insignificant.
In tobacco small quantities of arsenic also occur; the following contents of samples from various sources are due to Popp: from the Palatinate 5.1, from Brazil 4.6, from Macedonia 0.70, and from Java 0.33 parts As per million. These quantities are sufficiently small to be harmless, but Remington found 6.0 to 28.9 parts As per million (i.e. 0.05 to 0.27 grains As2O3 per lb.) in American manufactured plug and smoking tobaccos - this quantity exceeds the accepted legal limit for foods. About half the arsenic in pipe tobacco, however, is evolved in smoke, and about half that in plug tobacco is soluble in water.
The presence of arsenic in animal organisms has been widely demonstrated, but there has been considerable controversy as to whether it may be regarded as a normal constituent. The quantity present undoubtedly depends to a high degree on the amount of the element available in the environment of the organism. Thus, whereas freshwater crustaceans and shellfish from rivers containing only minute traces of arsenic were found by Chapman to contain only about 0.4 to 1.5 parts per million, marine crustaceans and shellfish contained amounts up to 174 parts per million, estimated as As2O3 on the wet substance. The following maximum quantities were found: in British oysters, 10 parts; Portuguese oysters, 70 parts; escallops, 85 parts; mussels, 119 parts; cockles, whelks and periwinkles, 40 parts; prawns, 174 parts; shrimps, 50 parts. The boiled edible portion of lobster contained 36 to 40 parts As2O3 per million for three specimens, but a fourth specimen gave 105 parts. Experiments with American large-mouth black bass showed that whereas no arsenic could be detected in the normal domesticated fish, bass from Rock River contained 0.106 to 1.60 parts per million (estimated as As2O3), and from the Mississippi 0.066 to 0.156 parts per million, while those kept in arsenic-treated water contained 0.58 to 0.96 part per million. It was observed that bass retained in arsenic-bearing water appeared to develop the power of eliminating the element from their bodies. An examination of cod and herring gave the following results expressed in parts of As per million: cod, muscular tissue 0.4 to 0.8, liver 0.7 to 3.2, cod-liver oil 3.0 to 4.5; herring, muscular tissue 2.0, oil 9.0. Thus the concentration is higher in the oily liver than in the muscular tissue. The arsenic appears to be present as fat-soluble compounds, probably acidic since they may be extracted with dilute alkaline solutions. Chapman concluded that in lobster the element occurs in a complex organic substance or mixture of substances since it is not readily reducible by hydrogen and can be extracted by alcohol or acetone.
Gautier examined a large number of animals and found no arsenic in the muscles or adipose tissue, but it was always present in small quantity in the thyroid gland, of which he concluded it was a normal constituent. Kunkel, however, denied this, not finding the element as a normal constituent of any animal organ, and many investigators have put forward evidence as to its presence or absence normally in the human body, the problem having been the subject of much discussion. It appears to be established that arsenic is not normally present in the liver of man or of the domestic animals, although in the case of arsenic poisoning it is in the liver that the element is largely concentrated. But it is frequently found to be present in all parts of the human body, and if the element does play any physiological role in the organism, the part is not confined to any one organ. Arsenic is not necessarily present in healthy human blood, but Gautier observed its presence in the blood of women during the menstrual period. Guthmann and Grass, however, found that in the intermenstrual period the venous blood of normal women contained, as an average value, 63.8×10-6 g. As per 100 c.c., the range being from 20.5 to 113.4, with little variation in the individual. During menstruation there is an increase of 50 per cent, to an average of 92.5, and during pregnancy it further increases, reaching a maximum value (average 220) between the fifth and sixth months and then gradually falling, although at the full term the value is still above the normal intermenstrual value.
The examination of the urine of a large number of hospital patients subject to the same diet gave the following results: 16 per cent., no arsenic present; 43 per cent., 0.01 to 0.06 mg. As per litre; 33 per cent., 0.07 to 0.20 mg. per litre; 8 per cent., 0.21 to 0.69 mg. per litre. In four cases there was a variation from 0 to 0.23 mg. As per litre over periods of 4 to 6 days. Traces of arsenic may be found in the bones, the skin, and in the hair and nails. The arsenic content of human hair for normal persons not engaged in any arsenical industry or undergoing medication was stated by van Itallie to be 0.01 to 0.03 mg. per 100 grams, and the same observer found that the content in finger and toe nails varies between wide limits. The presence of traces of arsenic in urine, lungs and hair is usual for people living in districts where, owing to industrial operations, the atmosphere is contaminated with arsenic.
Bertrand found arsenic present in hens' eggs, to the extent of 0.005 mg. in one egg chiefly concentrated in the yolk. On the other hand, Gautier could not detect the element in birds' eggs.
The wide distribution of arsenic in so many natural products results in the contamination of a great variety of industrial products. Thus the use of pyrites, or even sulphur which may be slightly arsenical, in the manufacture of sulphuric acid, leaves the element as a common impurity in the acid, and although methods are applied to remove the arsenic as completely as possible, traces are still liable to remain. The use of sulphuric acid on an immense scale in the manufacture of hydrochloric and nitric acids, and the further employment of these acids in chemical industry, result in a widespread distribution of arsenic, so that it is frequently found in phosphorus, phosphoric acid and phosphates, hydrobromic acid, calcium chloride, ferric chloride, caustic alkalies, alkali chlorides and carbonates, bismuth compounds, ammonia and ammonium compounds, hydrogen sulphide, chloroform, glycerine, beers, vinegars, flour, sugars and many foodstuffs. The ubiquity of arsenic in artificial materials is undoubtedly a cause of the conflicting evidence, discussed above, as regards its presence as a normal constituent of the organism. It is only in recent years that analytical methods have been sufficiently refined to guard against accidental introduction of the element.
Traces of arsenic may occur in many metals, e.g. antimony, bismuth, copper, iron, lead, nickel, tin and zinc, and in alloys derived from such metals. Its presence generally results from the use of arseniferous ores and inadequate purification of the metals. It is found as an impurity in many dyes and colouring matters, and some arsenic compounds constitute important pigments. Wines coloured with aniline dyes have been found to contain arsenic. Printing inks generally contain it, as do many writing materials. Kappeller examined fourteen samples of violet carbon paper and found arsenic in five; three of German origin contained 0.95 to 3.8 g. As per 100 grams, while two American samples contained 0.9 to 3.0 g. As per 100 grams. Two English violet typewriter ribbons contained 0.5 to 1.1 g. As per 100 grams, or 5.8 to 15.4 mg. per metre. On the other hand, aniline ink powders and violet pencils did not contain arsenic. It is seldom nowadays that arsenic is found in wallpapers 4 and window curtains in excess of the permissible limit of 5 mg. per sq. metre, and the same is to be said of coloured papers and boards used for wrappings,5 the agreed limit for these being 10 parts per million. Arsenic is sometimes found in wall plaster,6 however, in dangerous quantity.