1. Chapter 19.1 Toxicology and Chemical Hazards
study of harmful effects of chemicals on human and environmental health
acute effects—might occur upon ingestion or contact with skin
chronic exposure—occurs over years
carcinogenic potential
data on toxic chemicals
(National Toxicology Program)
(Report on Carcinogens)
(EPA Integrated Risk Information System)
(Environmental Defense)

2. dose response and threshold
in investigating a suspect chemical, a toxicologist would conduct tests on animals, investigate human involvement with the chemical, and present information linking the dose with the response
dose: level of exposure multiplied by the length of time over which exposure occurs
response: acute or chronic effect, or the development of tumors
LDL0: lowest dose at which death occurred in animal testing

3. threshold level
in dose-response relationship, there is usually a threshold
organisms are able to deal with certain levels of many substances without suffering ill effects
threshold level: level below which no ill effects are observed
above this level, effect of a substance depends on concentration and duration of exposure
for carcinogens, EPA generally takes a zero-dose, zero-response approach
however, the lower the dose, the more likely it is that the response cannot be distinguished from the background level of cancers in a population

4. HAZMATs HAZMAT = hazardous material
categorized based on the following hazardous properties:
ignitability—catch fire readily
corrosivity—corrode storage tanks and equipment
reactivity—chemically unstable and may explode or create toxic fumes when mixed with water
toxicity—injurious to health when they are ingested or inhaled

5. sources of chemicals entering the environment
materials making up almost everything we use, from shampoo to toothpaste to TVs, are products of chemical technology
our use constitutes only one step in the total product life cycle
life cycle begins with obtaining raw materials and ends in the final disposal of the product
chemical wastes and by-products are inevitable in any production process, as is the potential for accidents and spills
when these steps are multiplied by the hundreds of thousands of products used by billions of people, the magnitude of hazardous materials becomes clear

6. toxics release inventory
introduction of chemicals into the environment may occur in every sector, from major industrial plants to small shops and individual homes
some idea of quantities of chemicals released can be obtained from Toxics Release Inventory (TRI)
since TRI has been in effect, total releases have decreased by 68%
Emergency Planning and Community Right-to-Know Act (EPCRA) of 1986 requires industries to report releases of toxic chemicals to the environment
Pollution Prevention Act of 1990 mandates collection of data on toxic chemicals that are treated on-site, recycled, or combusted for energy
TRI does not cover small businesses such as dry cleaners and gas stations (facilities do not need to report yearly releases under 500 lb), or household hazardous waste

7. threat from toxic chemicals
fortunately, a large portion of chemicals introduced into the environment are gradually broken down and assimilated by natural processes
once these chemicals are diluted, they pose no long-term human or environmental risk, although they may be toxic in acute doses
two major classes of chemicals do not readily degrade in the environment:
heavy metals
synthetic organics

8. heavy metals
most dangerous include lead, mercury, arsenic, zinc, cadmium, tin, chromium, and copper
common in metalworking or metal-plating shops, electronics, pesticides, and some medicines
once common in paint pigments, glazes, inks, and dyes due to brilliant colors
extremely toxic because, as ions in certain compounds, they are soluble in water and may be readily absorbed by the body (usually inhibit the function of enzymes)

9. organic compounds
chemical basis for all plastics, synthetic fibers, pesticides, wood preservatives, and hundreds of other products
because of their chemical structure, many are resistant to biodegradation (which is part of what makes them useful)
compounds are toxic because they are often readily absorbed into the body, where they interact with specific enzymes
high dose  acute poisoning and death
low doses over long periods  effects can be mutagenic, carcinogenic, or teratogenic (birth defect-causing)

10. dirty dozen
particularly troublesome class of synthetic organics is halogenated hydrocarbons
organic compounds in which one or more hydrogen atoms have been replaced by Cl, Br, F, or I
all are toxic to varying extents and most are known animal carcinogens
many are also suspected endocrine disruptors at very low levels
chlorinated hydrocarbons are most common
used in plastics (polyvinyl chloride), pesticides (DDT), solvents, electrical insulation (PCBs), and many other products

11. PERC tetrachloroethylene, also called perchloroetheylene (PERC)
major substance in dry cleaning fluid; effective solvent found in many industrial cleaners
evaporates readily when exposed to air, but can enter groundwater easily because it does not bind to soil particles
enters body most readily when breathed in with contaminated air
breathing PERC for short periods can bring on dizziness, fatigue, headaches, and unconsciousness
over long periods, can cause liver and kidney damage
Report on Carcinogens: “reasonably anticipated to be a carcinogen”
studies have shown higher risk of cancer along with neurological impairment in dry cleaner employees
EPA issued ruling to phase out PERC by 2020

12. Minamata
tragic episode in early 1970s revealed potential for biomagnification of mercury and other heavy metals
in the mid-1950s, cats in the small fishing village of Minamata, Japan began to show spastic movements, followed by partial paralysis, coma, and death
at first, most thought the syndrome was specific to felines
however, same symptoms began to appear in humans
chemical company near the village was discharging wastes containing mercury into a river that flowed into a bay where villagers fished
mercury settled with detritus, then absorbed and bioaccumulated by bacteria, then biomagnifed up the food chain
in the end, 50 died and 150 suffered bone and nerve damage