Chemicals and the environment lectures 13-15

Humans cannot

create or destroy elements (except through nuclear chemistry)

Humans CAN

influence the amount of elements in the environment

Humans can readily create compounds through

chemistry - compounds are composed of elements, and chemistry ca rearrange the order of elements within compounds

Elements are

atoms

Compounds are

molecules

Polychlorinated biphenyls (PCBs)

persistent, unreactive viscous liquids with low volatility

PCBs were

used as hydraulic fluids, coolants, fluids in transformers, lubricants and plasticizers.

Most are now banned but

because they are so persistent in the environment (e.g. the Housatonic River) and are fat soluble, they tend to biomagnify within the biosphere.

Four phases of chemical movement

atmosphere, water, soil, biosphere

Chemicals enter the biosphere depending on their

bioavailability

Hydrocarbons

carbon and hydrogen only, major source form petroleum, natural gas and incomplete combustion of nearly all organic materials

ex: oil spills, cigarette ,smoke, grilled meat and combustion of fossil fuels

__ is a known human carcinogen

3,4-Benzo(a)pyrene

Oil spill events

Largest oil spills

Environmental impact of oil spills

Impact of oil on organisms

Interactions between oil and plastic pollution

Ecological impact of oil spills

Organochlorine insecticides

DDT and similar chlorinated compounds (lindane still use din some countries for head lice) - very persistent compounds, very fat solutbe

Most now banned in US but still used in some countries

Organophosphates and carbamate insecticides

also used as nerve gases/agents against humans, relatively water soluble, short lived in the environment so chronic toxicity is not typically an issue, some still used, mostly acute toxicity concerns

Phenoxy Herbicides (plant growth regulators)

2,4-D and 2,4,5-T. 2,4-D is still commonly used to kill weeds, but 2,4,5-T is banned. These chemicals readily degrade in the environment. 2,4-D is classified as “possibly carcinogenic to humans” which puts it in the same risk category as red meat.

Agent Orange

defoliant in Vietnam war to expose enemy troop movement in jungles

mixture of 2,4,-D and 2,4,5-T

may have caused cancer in exposed soldiers, but causality has been difficult to demonstrate, though rodent studies are suggestive of carcinogenicity

also contained TCDD (dioxin) as trace contaminant

Glyphosate herbicide (Roundup)

generally not demonstrated to cause acute toxicity or cancer risk in humans (several studies), though there has been a proliferation of lawsuits based on cancer concerns (mostly related to failure to adequately warn consumers)

Glyphosate-resistant crops widely used (GMOs), along with agricultural use of glyphosates

Some concern about bee toxicity

Pyrethroid insecticides

derived from chemical in chrysanthemums, low water solubility, acute toxicity to fish and non-target invertebrates

blocks sodium channels in nerves

Dioxins

Polychlorinated dibenzodioxins (PCDDs)-best known is TCDD (dioxin) very toxic (LD50 = 10 ug/kg = 10 ppb) in rodents (not acutely toxic in humans); Carcinogenic in rodents (at high doses) & humans. Is a by product of combustion of organic matter.

Causes chloracne in humans at high doses and is possibly an EDC.

1976 explosion at chemical plant near Seveso, Italy

resulted i highest TCDD exposure know in human population —> chloracne in humans

human carcinogens and endocrine disruptors

Current concerns for organic compounds in plastic

Dynamics and movement of organic compounds in plastics

Flamme retardants - polybrominated diphenyl ethers (PBDEs)

June 2008: U.S. EPA set safe daily human exposure level ranging from 0.1 to 7 ug/kg (ppb) body weight per day for common PBDEs

Currently found everywhere in the environment.

Mechanisms of potential toxicity are unknown

Perfluoroacids (PFAs)

Scotchgard for clothing and used to make non-stick (Teflon) pans. These are being phased out but are currently found everywhere in the environment.

5.4 year half life in humans

What does PFA look like?

What have PFAs been replaced with?

The modern human environment - bedroom/bathroom, living room

Human bioaccumulation - what’s in all of us?

The modern human environment - kitchen/dining room, outdoors

Correlation and proof of causation

What are the environmental/human health effects of long-term low dose exposure to persistent environmental compounds?

Many studies show correlations between exposure and toxicity. But can correlations sometimes be misleading?

Pharmaceuticals most commonly found in the environment

A. Anti-inflammatory drugs/analgesics (ibuprofen,

diclofenac)

B. Lipid Regulators (to lower cholesterol, lipitor, crestor)

C. Antibiotics (penicillin, doxycycline)

D. Steroids/hormones (birth control)

Environmental transport of pharmaceuticals

Diclofenac and vultures in india

Toxic chemicals can be present in both ___ and ___ compartments and can move between them.

abiotic, biotic

Correlation between Co2 and temperature

Greenhouse gases - how greenhouse gases warm our planet

Greenhouse effect

Greenhouse gases, their atmospheric concentration, lifetime, and global warming potential

Climate tipping points