Past form of the verb: Pollute
polluted
Past form of the verb: save
saved
Past form of the verb: waste
wasted
Past form of the verb: Produce
Produced
Past form of the verb: change
changed
Past form of the verb: recycle
recycled
Past form of the verb: decide
decided
Past form of the verb: conserve
conserved
Past form of the verb: use
used
Past form of the verb: collect
collected