artificial compounds are made, they become pollutants
because they cannot decompose and recombine into other
useful, non-toxic substances.

 Naturally-occurring substances can be broken
 / down efficiently into simple elements by nature;
 these substances are biodegradable. However,
 the word biodegradable is often misused it is
 applied to products that generally aren't
biodegradable (like detergents and plastics) and not used
to describe those that usually are biodegradable (like
soap and paper). Everything will break down (or
biodegrade) eventually, but the important consideration
is not whether a substance will eventually break down,
but how fast and how easily the environment can break
down that chemical.

Persistent chemicals that are not easily broken down
accumulate in soils, plants, animals and other
organisms. These are then eaten by other
animals, which are eaten by predators even
higher in the food chain, and so on. Each I
higher organism in the food chain contains a
greater accumulation of that chemical in its body.
Humans are at the top of the food chain, so our body's
fatty tissues can accumulate large levels of harmful
substances that occur in much lower levels in the
environment. These chemicals can then be passed on to
our children,