Lecture 05A TOXINS IN ENVIRONMENT: EVOLUTIONARY RESPONSES? Pg. 508-512
MAJOR CONCEPTS:
Toxins are poisons that kill by interfering with physiology of organisms.
Each toxic hits organisms in a unique way.
Toxins accumulate as they move through the food chain →
carnivores affected more than herbivores.
Some organisms evolve resistance to (or tolerance of) toxins.
Humans are using bioremediation to accumulate dispersed toxins and removing them from the
landscape.
1) Acids
a) coal mining → S; if aerobic → SO4 + H20 → HsS04; acid mine drainage
b) acid rain from burning fossil fuels: NO2 + SO4 → acid rain
pH =conc. of H+ ions; H+ extremely reactive; affects activities of enzymes
lakes and rivers lack bases to buffer acid input → disrupt aquatic ecosystems
lower soil pH → increase leaching of nutrients and precipitate P –unavailable
2) Heavy Metals (Hg, Ar, Pb, Cu, Ni, Au)
a) mining and mining smelting (e.g. gold), industry, fungicides, leaded gas
b) interfere with neurologic function
c) kill fungi → slow decomposition
3) Organic Compounds
a) oil spills coat surface of organism; impair respiration
hydrocarbons act as organic solvent → disrupt membranes
bioremedication – use of microbes, plants, fungi, or their enzymes to detoxify
contaminants
b) pesticides (DDT, malathione, tiazine)
evolution of resistance by insects
c) herbicides (atrazine, Roundup, Select, Squadron)
evolution of resistance by weeds
4) Radiation
a) nuclear power plant accidents
b) waste products cause disposal problems
c) radiation cause DNA damage; damages photosynthetic machinery
5) Plastics
Vast vortex of plastic trash size of Texas in the middle of the Pacific Ocean
267 species – including seabirds, turtles, seals, sea lions, whales and fish –
suffer from entanglement or ingestion of marine debris.
Invertebrates attach to plastic and ride on it → invade other areas of ocean
Many plastics break down physically, but are non bio-degradable
Persist as small particles (thinner than hair) of chemicals
Ubiquitous
3000,000 particles per sq km of sea surface; 100,000 per sq km of seabed.
Can they get into food chains in oceans?
Filter-feeding invertebrates ingest as feed on seabed
Do they release chemicals in guts of larger animals?
Do their chemicals leach into seawater as they degrade?
Plastic absorbs other contaminants, such as PCBs; accumulate on sea surface and latch
onto plastic debris that is eaten by sea organisms
6) Atmospheric Pollution
Circulation of air and oceans is global
Effects extend far beyond source of problem
a) CO2 and Greenhouse effect
b) Ozone layer and Ultraviolet Radiation
1. at surface
O2 with NO2 with light → O3
NO2 from burning gas – tailpipes so high levels in cities
Highly reactive as oxidant of organic molecules → destroy function → toxic
2. in upper atmosphere
+ = shields from UV radiation; absorbs short wavelengths of sunlight
+ = chorine atoms break down ozone → decrease in stratospheric ozone
→ ozone hole at high latitudes; lose protection from UV
chlorine comes from CFCs (chlorofluoro-carbons (spray cans/coolants)
(treaty caused CFCs to be phased out by 2000; hole smaller but persists)
UV increases DNA damage → skin cancer
Damages PS machinery → decreases plant productivity