environment chapter 4

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University of Toronto Scarborough
Environmental Science
Zachariah Campbell

Environmental Chapter 4 • Exception to metals being natural is plutonium • Metals are notable for wide environmental dispersion from such activity, tendency to accumulate in select tissues of the body, and overall potential to be toxic even at minor levels of exposure • Xenobiotics; have no useful role in physiology and may be toxic even at trace levels of exposure • even metals that are essential are toxic at high levels of exposure • metals may be inhaled as dust or fume -some can be vaporized and inhaled -may be ingested involuntarily through food or drink • excretion occurs through kidneys and digestive tract, but some can persist in liver, bones, and kidneys for years or decades • toxicity involves brain and kidney • chronic exposure to metals at a high enough level can also occur in individuals who have no symptoms • most important metal toxins from a global and US perspective; lead, mercury, arsenic, and cadmium Lead • most widely used Exposure • dominant source of worldwide dispersion of lead into the environment and people for the past 50 years is use of lead organic compounds as antiknock motor vehicle fuel additives • since leaded gasoline was introduced in 1923, its combustion and resulting contamination of the atmosphere has increased background levels everywhere, including ice cap covering Northern Greenland • some segments of the population in developed countries remain at high risk of exposure because of the persistence of lead paint, lead plumbing, and lead-contaminated soil and dust, particularly in old urban housing • number of factors can modify impact of lead exposures -water with a lower pH will leach more lead out of plumbing connected by lead solder than more alkaline water will -lead from soil tends to concentrate in root vegetables -individuals will absorb more lead if their diets are deficient in calcium, iron or zinc Toxicity • depending on the dose, lead exposure in children and adults can cause a wide spectrum of health problems, ranging from convulsions, come, renal failure, and death and the high end to subtle efforts on metabolism and intelligence developed at the low end of exposures • children appear to be particularly vulnerable to the neurotoxic effects of lead • low-level lead exposure in children less than five years of age results in deficits in intellectual development, as manifested by lost IQ points • maternal bone-lead stores are mobilized at an accelerated rate during pregnancy and lactation and are associated with decrements in birth weight, growth rate, and mental development • adults are generally allowed by regulations to be exposed to higher amounts of lead • blood-lead levels in the range of 7-40 μg/dL is toxic in adults Mercury Exposure • in pure form ,metallic mercury is liquid • not hazardous if ingested • if left standing or aerosolized, metallic mercury will volatize into a vapour that if well absorbed by the lungs • mercurous and mercuric mercury form inorganic and organic compounds with other chemicals that can readily be absorbed through ingestion • mercury dispersion through atmospheric deposition has increased markedly through waste incineration • when deposited in soil, organic mercury compounds are slowly broken down into inorganic compounds; conversely, inorganic mercury can be converted by microorganisms in soil and water into the organic compound methyl mercury, which is then bioconcentrated up the food chain • fish can concentrate methyl mercury at high levels Toxicity • high levels of mercury ex
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