Bioaerosols may contain pathogenic microbiologic agents, such as those that can cause Legionnaires’ disease, viral pneumonia, and the common cold, as well as allergens derived from pet dander, dust mites, and fungi and molds, which can cause rhinitis, eye irritation, and even asthma.
Environmentaldiseasesareconditionscausedbyexposuretochemicalorphysicalagentsintheambient,workplace,andpersonalenvironments.
Exogenouschemicals,knownasxenobiotics,enterthebodythroughinhalation,ingestion,andskincontact,andcaneitherbeeliminatedoraccumulateinfat,bone,brain,andothertissues.
Xenobioticscanbeconvertedintonontoxicproductsortoxiccompoundsthroughatwo-phasereactionprocessthatinvolvesthecytochromeP-450system.
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Themostcommonairpollutantsareozone(whichincombinationwithoxidesandparticulatematterformssmog),sulfurdioxide,acidaerosols,andparticleslessthan10µmindiameter.
COisanairpollutantandanimportantcauseofdeathfromaccidentsandsuicide;itbindshemoglobinwithhighaffinity,leadingtosystemicasphyxiationresultinginCNSdepression.
Lead, mercury, arsenic, and cadmium, the heavy metals most commonly associated with harmful effects in human populations, are considered here.
Lead is a readily absorbed metal that binds to sulfhydryl groups in proteins and interferes with calcium metabolism, leading to hematologic, skeletal, neurologic, GI, and renal toxicities. Lead exposure occurs through contaminated air, food, and water. For most of the 20th century the major sources of lead in the environment were house paints and gasoline. Although the use of lead-based paints and leaded gas has greatly diminished, many sources of lead persist in the environment, such as mines, foundries, batteries, and spray paints, all of which constitute occupational hazards. However, flaking lead paint in older houses and soil contamination pose the major hazards for youngsters. Blood levels of lead in children living in older homes containing lead-based paint or lead-contaminated dust often exceed 5 µg/dL, the level at which the Centers for Disease Control and Prevention (CDC) recommends that measures be taken to limit further exposure. A dramatic case of lead contamination of drinking water occurred in the U.S. city of Flint, Michigan, in 2014–2016. The so-called “Flint water crisis” occurred when the source of water supply to the city was changed from Lake Huron to the Flint River. Because water from the Flint River had a higher chloride concentration than the lake waters, it leached lead from century-old lead pipes. This caused an increase in lead levels in tap water above the acceptable limit of 15 parts per billion (ppb) in about 25% of the homes and in some cases as high as 13,200 ppb. As a result 6000 to 12,000 residents developed very high lead levels in their blood. Ingested lead is particularly harmful to children because they absorb more than 50% of lead from food, whereas adults absorb approximately 15%. A more permeable blood–brain barrier in children creates a high susceptibility to brain damage. The clinical features of lead poisoning are shown in
Fig. 8.4