Chapter 2: Human Exposure to Chemicals

Most susceptible contact sites and target organs
MAJOR ROUTES1.

skin –> percutaneous2. lungs –> respiratory3. mouth –> digestiveMINOR ROUTES1. rectal2. vaginal3.

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Crucial physiological elements to the study of human exposure to chemicals
1. skin2. vascular system3. respiratory system4. digestive system5. circulatory system6. liver7. kidneys
skin
–highly organized–serves as a protective barrier–dynamic living tissue whose pemeability may change–stratum corneum major barrier to absorption–permeability coefficient (Kp) key in estimating dermal absorption
vascular system
–represents the blood stream–distributor of absorbed chemicals–to become part of circulation, a contaminant must penetrate to the dermis
respiratory system
–prime site for absorption and distribution–inhaled air enters the lungs and encounters a huge area of tissue that allows exchange of gas in the lungs with gas in the blood–suspended particles present a unique problem in that they tend to collect on the bronchial tubes and interfere with gas exchanges
digestive system
–absorption occurs in the stomach and intestines (most important is the small intestine)–can have some absorption in the stomach, but mostly in the small intestine–large intestine stores undigested/unaborbed food for excretion later
circulatory system
–distribution and removal of chemicals after absorption–very important route of distribution–the human body contains 3-6 liters of blood (adults typically have 5-6 liters)
liver
–filter for blood–control system for levels of chemicals–place where toxic substances can be transformed via detoxification reactions–most important in facilitating chemical transformations
kidneys
–blood passing through deposits substances not needed by the body–these are generally separated and excreted in the urine–kidney facilitates excretion from the body
target organ toxicity
1.

hematotoxicity (blood cell toxicity)2. hepatotoxicity (toxic effects in the liver)3. nephrotoxicity (toxic effects in the kidney)4. neurotoxicity (toxic effects to the nervous system)5. dermatotoxicity (adverse effects produced by toxicants in the skin)6. pulmonotoxicity (disease states in the respiratory system resulting from inhalation of toxicants

Inhalation exposures
–indoor air (volatile constituents and fugitive dust)–outdoor air (volatile constituents and fugitive dust)
ingestion exposures
–drinking water, swimming, soil ingestion, crop consumption, dairy and meat consumption, seafood consumption
dermal exposures
–showering, swimming, soil contact
airborne chemical toxicants
–can travel great distances (DDT in beluga whales in the Arctic)–chemical concentrations are a combination of ground-level concentration and dilution factor–some contaminants have a direct effect on the body’s ability to transport oxygen
chemicals in water
–surface water contamination given high priority early on–groundwater contamination is the “hidden” pollution problem–another “hidden” water problem is eutrophication
chemicals on land
–contamination in soils can impact several other environmental matrices (migration, volatilization, runoff)–exposures via direct inhalation of vapors or respirable particles, dermal absorption, ingestion, food chain (crops grown in contaminated soils, grazing activities, dairy), leaching into waterways, uptake in aquatic organisms
chemicals in food
–major source of human exposure to chemicals–dietary exposures are a function of consumption and chemical concentration–complex to estimate chemical amounts in food
public health and socio-economic implications
–potential exposures are enough for public outcry–reduction of life expectancy–reduced quality of life–averted by carefully implementing risk management strategies or corrective action
General nature of human health effects
MAJOR CATEGORIES1.

carcinogenicity2. genetic and chromosomal mutation (heritable)3. developmental toxicity and teratogenesis4. reproductive toxicity5.

neurotoxicity6. alterations of immunobiological homeostasis7. congenital abnormalities

assessing public health risks
1. problem definition2.

identification of the principal hazards3. design of sampling and analysis programs4. collection or reporting lab results for further evaluation5.

analysis of results6. interpretation