Arsenic And Old Lace: Recall The Observations Made By Marco Polo During .

Selenium-Related Illness Arsenic and Old Lace: Examples of Trace Metal-Related Illnesses (with emphasis on selenium and arsenic) Marco Polo (1254-1324) Su-chau During his travels to China, Marco Polo noted a curious affliction in imported European horses that grazed on vegetation in Su-chau; symptoms only showed up in imported horses and were absent among horses that were raised in the area. Recall the observations made by Marco Polo during his travels in China Observations Made by Marco Polo in Su-chau “Travellers passing this way do not venture to go among these mountains with any beast except those of the country, because a poisonous herb grows here, which makes beasts that feed on it lose their hoofs; but beasts born in the country recognize this herb and avoid it.” Geological investigations made much later indicated high concentrations of selenium in the soil of the Su-chau regions. Certain varieties of plants (including grasses) concentrate selenium in their tissues without ill effect. But herbivores cannot cope with very high concentrations of selenium Common symptoms of selenium poisoning: Weakening of hoofs/nails and hair (plus others that we will look at later on in course). So Marco Polo’s observations (together with geological evidence) suggest selenium poisoning. 1

Selenium Poisoning Other effects of selenium poisoning Marco Polo’s observations were made on horses only Humans have also been affected by high selenium Toxicity problems have been recognized in parts of China, where excessive intake of selenium resulted from eating local vegetables and corn grown on soil rich in selenium from weathering of coal and organic-rich shale One of the worst cases of selenium poisoning occurred in the Humbei Province of China during the 1960s. Residents of three villages routinely ate plants containing 3,000-5,000 micrograms of selenium. They developed brown splotches on their bodies, their fingernails fell out and some suffered severe damage to their central nervous system (normal daily allowance on the order of 60 micrograms) Bioavailability Closer to home, cases of severe selenium poisoning have been documented in California Soils in the San Joaquin Valley in California are developed on salt-rich, and organic-rich sedimentary rocks that contain high concentrations of selenium. Groundwater here is high in selenium. But concentrations in soil water are further increased by high evaporation rates in hot, arid areas. Irrigation washes selenium from soil and rock and concentrates it in wetland water Selenium replaces sulphur in some amino acids (amino acids) are the building blocks for protein molecules. Selenium is known to scramble genetic signals in developing embryos Bird chicks in San Joaquin Valley have been found to show gross deformities. Some individuals lack beaks, eyeballs or feet. Are we next ? Like mercury, selenium is passed upward through the food chain, accumulating in higher organisms 2

Low Selenium Belt But too little is bad too ! In the 1930s, China was later to be found to host widespread heart disease among humans (also related to selenium- but in this case, deficiency in that element) In 1935, incidences of a disease that later became known as “Keshan Disease” became apparent Thus far, Keshan Disease has been documented in over 300 counties in China. Causes weakening of heart muscle tissue, particularly in children and young women Abnormally low concentrations of selenium occur in a welldefined, northeast to southwest-trending belt across China. Soils in this region are developed on thick deposits of loess (windblown silt, composed almost entirely of quartz) Where did the loess come from ? Occurrences of Keshan Disease Mostly from the Gobi Desert to north and Tibetan Plateau to west. Low concentrations of selenium and other metals reflects lengthy period of mechanical weathering (combined with chemical weathering) Quartz is most resistant to weathering, and is the last mineral to break down This is why loess is composed almost entirely of quartz grains Tibetan Plateau Very close correspondence of Keshan Disease occurrences and very low concentrations of selenium Strongly suggests causal relationship 3

Kashin-Beck Disease Occurrences of Kaschin-Beck Disease Another disease widespread in same region is Kashin-Beck disease. This disease produces enlarged joints and muscular weakness Is there a link with geology ? You bet there is ! Very close correspondence of Kashin-Beck Disease occurrences and very low concentrations of selenium Again, strongly suggests causal relationship Acute Arsenic Poisoning Arsenic is a lethal toxin in high doses (acute arsenic poisoning usually accidental and rare). Early symptoms of acute arsenic poisoning include: a metallic taste in the mouth, excessive saliva production and problems swallowing. -followed by vomiting and diarrhea coupled with garlic-like breath, stomach cramps and excessive sweating. -as the effects of arsenic progress, the affected person will suffer seizures and go into shock, dying within a few hours. -if death does not occur at this stage, it will happen a few days when the kidney fails. Arsenic Poisoning: Slightly Lower Levels of Exposure Prolonged exposure to arsenic in lower doses appears to lead to a higher incidence of skin diseases: Changes in skin pigmentation Skin thickening Lesions (sores), leading to gangrene Cancer Common household sources of arsenic-rich substances include: slug bait and other insecticides, weed killers, rodenticides (avoid leaving these out on the kitchen counter, o.k. ?) 4

Arsenic poisoning in West Bengal (India) and Bangladesh Traditionally, Bangladeshis living in rural areas obtained drinking water from ponds and rivers Arsenic poisoning has reached epidemic proportions in West Bengal and Bangladesh As population increased, pollution from sewage rendered surface waters in many parts of the country unfit for consumption (by early 1970s). Cause of widespread poisoning is actually due to natural factors However, the circumstances leading to poisoning is somewhat political Case study of arsenic poisoning in Bangladesh In the 1970s, international agencies headed by the United Nations Children’s Fund (UNICEF) began spent millions of dollars to install groundwater wells to provide clean drinking water. West Bengal Use of this water has, unfortunately led to the poisoning of thousands of people (up to 5 million tube wells in the country are believed to have toxic concentrations of arsenic). What is the source of arsenic ? Arsenic poisoning in Bangladesh The first recorded cases of arsenic poisoning in Bangladesh and West Bengal date back to the mid1980s. Incidence of arsenic-related illness continues to increase. It is estimated that between 35 and 77 million Bangladeshis may be drinking water containing more than the safety limit of 10-50 parts per billion of arsenic (water from some wells have been found to contain up to 4,000 ppb arsenic). In this case, the source of arsenic is natural Sedimentary rocks underlying the region (mostly shale), contain seams of pyrite (iron sulphide) originally formed under low-oxygen conditions Arsenic substitutes for iron and is incorporated into the sulphide mineral (pyrite acquires arsenic to form arsenopyrite) Lowering of the water table has introduced oxygen into the groundwater, oxidizing the pyrite and releasing dissolved iron and associated arsenic into the groundwater. Similar incidences of natural arsenic poisoning have been documented from Taiwan, Chile and Mexico 5

Alleviation of Arsenic Problem The solution to the arsenic problem in India and Bangladesh is not simple. Note that surface water supplies are already badly polluted in many areas END OF LECTURE and Bangladesh is an economically deprived nation It is possible for wells to be dug to deeper levels where water is not contaminated, but this requires Who is going to pay the bill ? 6

-as the effects of arsenic progress, the affected person will suffer seizures and go into shock, dying within a few hours.-if death does not occur at this stage, it will happen a few days when the kidney fails. Common household sources of arsenic-rich substances include: slug bait and other insecticides, weed killers, rodenticides (avoid leaving