(Chapter 6) Toxic Metals and Elements
heavy metals
–has a high atomic weight with a specific gravity that exceeds the specific gravity of water by 5 or more times at 4 degrees celcius

–lead, mercury, nickel, cadmium

other toxic metallic compounds
aluminum, iron, tin
CERCLA priority list of hazardous substances
Agency for Toxic Substances and Disease Registry (ATSDR) has identified a list of the top 20 hazardous substances known as the CERCLA Priority List of Hazardous Substances. This list is revised every 2 years
Characteristics of hazardous substances on the CERCLA priority list
–pose the most significant threat to human health because they have known or suspected toxicity and have potential for human exposure at NPL sites

–A substance can be on the NPL if there is a high frequency of occurrence and a potential for human exposure, even if it is not among the most toxic substances

Some hazardous substances from 2011 CERCLA Priority List of Hazardous Substances
arsenic, lead, mercury, cadmium, chromium (hexavalent), phosphorus (white), benzene, DDT, chloroform, dieldrin
Major toxic metals with multiple effects
arsenic, beryllium, cadmium, chromium (VI), lead, mercury, nickel
Essential metals with potential for toxicity
Co, Cr (III), Cu, Fe, Mg, Mn, Mo, Se, Zn
Metals related to medical therapy
Al, Bi, Ga, Au, Li, Pt
Minor toxic metals
Sb, Ba, Ge, In, Ag, Te, Tl, Sn, Ti, U, V
Bioaccumulation
toxic substances (such as heavy metals) become more concentrated and potentially more harmful as they move up the food chain
high and low level contacts
–contact with high concentrations of toxic metals is most likely to occur in an occupational setting (among persons who work with metals)

–lower level exposures may result from contact with the ambient environment (children ingesting toxic metals present in paint)

acute toxic metal poisoning
–symptoms generally have rapid onset (a few minutes – an hour)

–GI effects (vomiting and stomach pain), and neurological effects (headaches, suppression of normal breathing, and convulsions)

symptoms of long-term exposure at lower levels
–reduced cognitive functioning

–mimicking of chronic disease symptoms

–in terms of human environmental health, long-term exposure presents more risk for the greater number of people

potential exposure media
air (particulate), soil/dust, water, biota/food
Gender differences and heavy metal exposure effects
–health effects of exposure to heavy metals are different for women than for men
–differences have been attributed to hormonal and metabolic processes related to menstruation, pregnancy, and menopause
children and exposure to heavy metals
–for fetuses, infants, and children (esp. young children), heavy metals are known to present serious hazards, which can include impairment of physical and mental development, damage to internal organs and the nervous system, some forms of cancer, and even mortality.

–nervous system damage (memory impairment, difficulty in learning, range of behavioral problems, such as hyperactivity syndrome and overt aggressiveness)

Heavy metal exposure among children vs. adults
–children have a smaller body weight, consume more food in proportion to body weight, and thus receive higher doses of heavy metals that may be present in their food

–kids do stupid things (eating paint chips)

fetal exposure effects
lead and mercury have the capacity to cross the placental barrier, causing potential fetal brain damage
Arsenic
–varies in toxicity depending upon its chemical form
–byproduct of refining gold and other metals
–used in pesticides, wood preservatives, and in manufacturing processes
–exposure can come from ingestion and inhalation
standards for arsenic
EPA announced the standard of 10 ppb of drinking water in 2001 (lowered from 50 micrograms of arsenic per liter)
potential health effects of arsenic exposure
–skin, bladder, kidney and liver cancer when ingested; lung cancer when inhaled
–cerebrovascular disease
–cardiovascular disease (hypertensive heart disease)
–diabetes (long-term exposure)
–adverse pregnancy outcomes (spontaneous abortions, stillbirths, and preterm births)
–acute poisoning (vomiting, diarrhea, seizures, and death)
beryllium
–used widely in industry because of its special properties (lighter than aluminum and stronger than steel)
–employees in the metal processing industry most likely to be exposed
–inhalation is most common method of exposure
–Class A carcinogen
Cadmium
–primary sources of exposure are cigarette smoke and dietary cadmium
–bioaccumulates in shellfish and is found in some species of mushrooms
–occupational exposure comes from the production of nickel cadmium batteries, zinc smelting, manufacture of paint pigments, soldering, and from employment in metal factories
–effects of cadmium exposure are osteoporosis (brittle bones, joint and spine pain–“itai-itai disease”), height loss in men, kidney damage, elevated blood pressure, cardiovascular diseases
mercury
–naturally occurring, highly toxic metal
–released into environment as a by-product of industrial processes
–at low levels, it becomes deposited in the beds of lakes, rivers, and other bodies of water
–microorganisms ingest these small amounts of mercury
–the process of bioaccumulation causes the mercury to become more concentrated in aquatic invertebrates
–minimata disease
–water contamination around the New Almaden mine in California
chromium
naturally occurring element in the earth’s crust (in rocks, soils, and materials of volcanic origin)
–most common forms are chromium(0), chromium(III) (an essential nutrient), and chromium(VI) (a carcinogen)
Erin Brockovich
advocated for residents of Hinkley, California against an electric power company accused of contaminating the town’s water with chromium
Effects of hexavalent chromium(VI) exposure
–digestive problems and damage to organs such as the kidney and liver when ingested
–produces skin ulcers when applied to the skin
–inhaling Cr(VI) in high concentrations may cause respiratory problems (nose bleeds, perforation of nasal septum, runny nose)
lead
–sources of environmental lead include leaded gasoline, tap water from soldered pipes, imported pottery used in food service, gun ranges, and painted surfaces in older buildings
–lead exposure: CNS effects and other adverse consequences occur even when ingested at low levels
–lead poisoning is one of the most common environmental problems in the U.S.
nickel
–one of constituents of earth’s crust
–exposure to low levels is probably universal and unavoidable
–employed in the production of many appliances and tools used in everyday life
–effects: nickel allergy (manifested as contact dermatitis), cardiovascular-related and renal diseases, fibrosis of the lungs, potential carcinogenic action
essential metals with potential for toxicity
–Cu, Zn, and Fe are essential for human nutrition, but can be toxic if ingested in excessive amounts
–a narrow range of these essential metals is necessary to maintain health
Copper
–appears in electrical wires, pipes, in combination with other metals to form alloys, as a mildew inhibitor, and as a wood and leather preservative
–ATSDR estimates that in the year 2000 alone, approx. 1.4 billion pounds of copper were released into the environment during industrial processing
–exposure occurs by inhalation, ingestion, and direct contact with skin (small amounts may dissolve into tap water, causing Cu levels to become more concentrated when the water remains in the pipes overnight)
–effects: concentrated amounts can produce respiratory and GI disturbances, respiratory effects from dust include irritation of the respiratory tract (nose and mouth), very high levels are known to cause liver damage, renal damage, and death
Zinc
–frequently occurring element found in earth’s crust, permeating air, soil, water, and (to some degree) all foods
–used commercially as a coating for rust inhibition, as a component of batteries, and in combination with other metals to make brass, bronze, and other alloys
–a nutritional element that is important for maintaining health
–consumption of large quantities is associated with GI problems (stomach cramps, nausea, and vomiting)
–can cause anemia and damage to pancrease
–breathing high concentrations in the workplace causes a disease known as metal fume fever (appears to be an immune-mediated response that originates in the lungs)
Iron
–one of the most ubiquitous metals in the earth’s crust
–vital to human health (important for the growth of cells and the transport of oxygen with in circulatory system)
–acute iron intoxication (accidental iron poisoning) is among the most common childhood poisonings (causes stomach pain, nausea, vomiting, death from liver failure)
–other groups at risk from iron overload (iron toxicity) include adult men and postmenopausal women
aluminum
–silver-white metal used widely in food and beverage containers, in pots and pans, and in construction sites
–ingredient in various medicines and cosmetics (buffered aspirin and antiperspirants)
–concern about possible association with Alzheimer’s disease
sources of metal
burning of fossil fuels, smelting of metals, natural levels, other industry, mining operations, burning of wood and vegetation
movement of metals
atmospheric transport, metals in oceans, metals in pristine environments (artic, amazon)
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