HEALTH & GEOLOGY

There can be a relationship between the geology of an area and certain diseases of people, plants & animals, due to abundance or shortage of certain elements, or presence of certain minerals or radon gas.

Anthropogenic activities may increase the natural level of toxic elements by mining, manufacturing, usage or disposal of waste.

Medical geology

multidisciplinary field of science to study the effect of geological interactions between rocks, soil, water and air on the health of people.

It includes:

(1) Natural hazards such as the effect of volcanic gases, toxic elements in ground water, land slides etc.

(2) Enhanced hazards due to anthropogenic activity such as acid mine drainage and the release of Hg due to gold mining in Brazil.

Toxicology: study of toxins Effect of substance on population as a whole, but individual

reactions may varyElements may work together to enhance or reduce the

effectiveness or toxicity of an element.

Epidemiology: study of epidemicStudy of the statistical occurrence of diseases and factors

such as trace elements in diet or smoking. May find areas with high or low concentrations of an

element have high or low occurrence of certain disease. Epidemiological hypotheses must be proved with controlled

laboratory experiments to discover the actual effect of the element either alone or in conjunction with other factors.

TRACE ELEMENTS

Detrimental to Health

TRACE ELEMENTSEssential for the production of living tissue:

H, Na, Mg, K, Ca, C, N, O, P, S, ClNecessary in trace amounts:

F, Cr, Cu, Zn, Se, Mo, I, Mn, CoCause health problems in high concentrations:

As, Ba, B, Cd, Cu, Cr, F, Pb, Hg, nitrates, Se, Ag, Na

All trace elements are available in rocks but amount may depend on: the type of rock and geological environment the dominant weathering processes the soil cover.

Trace element problems improve as we eat food from many different areas but drinking water is usually local

CONCENTRATIONS in NATURE

DOSE RESPONSE CURVE Many elements essential for health in small doses, become toxic and even

lethal in higher concentrations.Threshold A: Less than this value is harmful

A-B: increasing benefitB-C: maximum benefitC-D: declining benefitD: threshold of increasing harm, toxicE: noticeable harmF: death

Values of ABCDEF notnecessarily known for each element or form of lifeFor each element the thresholds are different

FLUORINEF- is smaller with the same

charge as OH- Has a higher charge to mass

ratio so repels anions efficiently.

F- can replace OH- in minerals Bones & teeth made of apatite Ca5(PO4)3(F,Cl,OH)Fluoro-apatite grows larger and

stronger crystals than hydroxy-apatite.

F can make bones and teeth stronger and more dense

Helps with osteoporosis and tooth decay

Dental Caries

% of decreasedbone density in areas of high or low F in drinking water

Osteoporosis

Greater than 8 ppm can cause excessive bone formation and calcification of ligaments,

Often seen in cattle eating F-rich grass and in people drinking from confined aquifers high in fluoride

B, Mo, Li reinforce the effect of F; Se reduces the effect

School girl in Sri Lanka in a region with high F in ground water

Geological Occurrence of Fluorine

Igneous rocks and clays Less common in

sandstones and limestone

F added to drinking water in areas of low abundance.

(ppm)

IODINE and SELENIUM

Similar biogeochemical cycling including concentration in ocean water and atmospheric transport

Released from oceans by (1) seasalt aerosols (e.g NaI)

(2) biogenic gases (e.g. CH3I)

Marine plants and animals have higher Se and I than ocean water which causes the surface to have higher concentrations due to the abundance of biota.

I & Se concentrated in the upper layers of soil by atmospheric precipitation from ocean spray or by biological action in soils, then be remobilized into surface water.

Iodine Cycle

IODINEis an essential trace elementLack of iodine causes Iodine Deficiency Disorders (IDD): (1) goitre (enlargement of the thyroid gland).(2) stunted growth and mental development in children

whose mothers have iodine deficiency. WHO estimates >1 billion people at risk from IDD

Woman with a goitre from Sri lanka

Relationship between low iodine and IDD

Low iodine concentrations are linked with a high incidence of goitre in areas where glaciation removed the topsoil

e.g. goitre belt in northern US states & S. Canada.

Iodised table salt or iodized cooking oil supplements drinking water

Winnipeg

131I released after nuclear explosion (e.g. Chernobyl) moves rapidly into food chain and may lead to thyroid cancer. People given iodine tablets to saturate thyroid with non radiogenic iodine.

SELENIUMO.04 ppm Se essentialSe deficiency causes muscular degeneration, impeded growth, fertility

problems, anaemia, liver disease0.04-0.1 ppm Se beneficial4 ppm toxic: Cattle eating plants rich in selenium (loco-weeds) get the

"blind staggers" muscular dystrophy and appear drugged. e.g. in San Joaquin Valley,

California

0.04 4.0 (ppm)0.1

Dose ResponseCurve for Se

Geological environment of selenium

Primary source: volcanic activity

Concentrated in:hydrothermal sulphide veins U deposits.in soils by plants and animals

Concentration ranges from 0.1 to 1200ppm.

Solubility depends on pH and Eh

Se has 4 oxidation states:-2 H2Se: toxic and reactive gas0 Elemental Se: insoluble &

unreactive+4 SeO3

2- selenite: toxic but easily reduced to elemental Se0

+6 SeO42- selenate: very soluble and

toxic

(ppm)

MERCURY, CADMIUM, LEAD toxic enzyme inhibitors.

Can be methylated by bacteria, cross the blood/brain boundary

High Cd, Pb & Hg in the brain cause impairment of neurological functions and congenital defects.

Bioaccumulate: become concentrated in plants, animals, fish

Geological Occurrence

Cd, PbConcentrated in economic hydrothermal sulphide mineral deposits and released during mining and mineral processing, and industrial use

Geological Formation of Hg

Hydrothermal ore formationNote the natural emissions of Hg to the atmosphere from volcanoes and fumaroles

Toxicity of mercury

Knowledge of toxicity from miners. Roman slaves and Spanish convicts had an

average life expectancy in the Hg mines of 3 years

Causes loss of teeth, tremors, loss of strength, psychological problems.

Mad Hatter disease due to use of mercuric nitrate in felting of fur for hats

Methyl mercury extremely toxic

Minamata, Japan1956: People in a fishing village of Minamata developed

blurred vision & speech, numbness of limbs (Minamata Disease)

This was caused by the release of methyl mercury in industrial waste water from the Chisso Chemical factory upstream

1959: the pollution problem and source were identified but the dumping continued until 1971.

By 2001, 2,265 victims had been officially recognized (1,784 of whom had died) and over 10,000 had received financial compensation from Chisso.

Mining

Cinnabar mined at Amaden Spain since 430 BCE.

HgS heated to release elemental Hg as a gas which is condensed

Historical uses of mercurySince 4000 BCE Cinnabar used for the preservation of human bones including EgyptiansSince Egyptian/Roman times cinnabar used as paint pigment, cosmetic, pottery glaze, anti

fouling on ships, red ink. Romans: Extraction of elemental Hg by distillation and amalgamation with goldMiddle ages: Hg amalgamation used in alchemy and early chemistry leading to the

discovery of 22 elementsMedicinal use since 460 BCE (Hippocrates) and since 16th century as a cure for syphilis,

and as a diuretic, antiseptic, contraceptiveStill used in dental amalgam, preservative in flu vaccines (Thimerosal), herbal remedies