Ask A Scientist Chemistry Archive

name         Maggie W.
status       student
age          11

Question -   Do lawn chemicals severely hurt our environment? What
kinds of animals are they life-threatening to?
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Lawn chemicals can damage the environment.  They can affect the area around
the house--they are usually designed to kill weeds, so they may cause
problems for small animals like birds and squirrels.  Most people keep
children away from newly-sprayed lawns also.  One of the big problems with
lawn chemicals is that they often end up far from where they started because
it rains and the chemicals get washed into the sewers, lakes and streams.
Sometimes the chemicals cause problems there, also.  For example, some plants
may grow too much, blocking light to other animals and plants. It  probably
takes a lot of chemicals to do this.  One lawn's chemicals may not be enough
to cause problems, but hundreds or thousands may be.

Pat Rowe
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This is a controversial subject and one that does not have a single answer.
It depends upon what chemicals are present in the lawn treatment. The basic
fertilizer contains potassium, phosphate ion in some form, and nitrogen
usually present as the nitrate or as urea. Runoff of these chemicals can
cause algae blooms in streams and lakes and could potentially contaminate
well water used for drinking. On the other hand, these chemicals have been
standard ingredients of both lawn and crop lands for years.

However, lawn chemicals may also contain a variety of weed killers and
insecticides. These pose a greater threat of acute toxicity to animals (and
people) especially in the first 24 hours after application. Some states
require the commercial applicators to put small flags bordering treated
lawns to warn people to stay off. Unfortunately, small children and pets
don't read.

Culturally, Americans are rather "lawn-crazy-lazy". Many want their lawn to
look like the green of a golf course and will go to extremes to achieve that
goal. Few are willing to "spot" treat weeds to minimize over-spray. And
often "treating" one lawn in fact treats several depending on the wind speed
and direction.

The answer to your question is a not-too-satisfactory maybe, it is not clear
cut. It depends on the proximity of streams and lakes, how much treatment is
applied, if the treatment is applied correctly, and so on.

A potentially greater hazard is posed by commercial runoff from farms, golf
courses, and the like-- where many acres are treated at a time, and which
use chemicals that are prohibited for use on domestic lawn applications.

Most lawns do not need annual "feeding". And by cutting the grass "high",
that is about 2 1/2 to 3 inches, most lawns will become weed-free in about
three seasons. The grass itself prevents weeds (which are mostly annuals)
from germinating -- but it does take time.

Vince Calder
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