A faithful reader pointed me to the Rivanna Regional Stormwater Education Partnership website and specifically asked me to post information about cigarette butts.

From the site:

Many smokers discard their cigarette butts by the roadside or on the ground when they are driving or walking around out doors. Perhaps the prevailing view is that cigarette litter is too small to have a significant effect on water quality. Nothing could be farther from the truth.

Cigarette litter is often carried into storm drains when it rains, where it is deposited in local streams and rivers. Nationwide, smokers litter about 4.5 trillion cigarette butts annually. About 95% of cigarette filters are composed of cellulose acetate, a plastic that persists in the environment for years and even decades. Cigarette filters concentrate a number of very toxic substances, which are released into our waterways when they are washed off roads and sidewalks into storm drains.