Pesticides
in
Groundwater
Care to guess how
many pounds of pesticides the United States used in 1964? How about in 1993?
If you ask your grandparents what life was
like when they were kids, the answer will probably be that things were simpler,
slower, less automated, and that people did not move around the country so
often.
But since your grandparents' time two major
things have happened:
(1) the population
of the United States has increased greatly, and
(2) technology and
scientific innovations have come to play a major role in our lives.
Pesticide use has grown because not only
must our exploding population be supplied with food, but crops and food are
grown for export to other countries.
The United States has become the largest
producer of food products in the world, partly owing to our use of modern
chemicals (pesticides) to control the insects, weeds, and other organisms that
attack food crops.
But, as with many things in life, there's a
hidden cost to the benefit we get from pesticides. We have learned that
pesticides can potentially harm the environment and our own health.
Water plays an important role here because
it is one of the main ways that pesticides are transported from the areas where
they are applied to other locations, where they may cause health problems.
Pesticides can contaminate groundwater
Pesticide
contamination of groundwater is a subject of national importance because
groundwater is used for drinking water by about 50 percent of the Nation's
population.
This especially concerns people living in
the agricultural areas where pesticides are most often used, as about 95
percent of that population relies upon groundwater for drinking water.
Before the mid-1970s, it was thought that
soil acted as a protective filter that stopped pesticides from reaching
groundwater. Studies have now shown that this is not the case.
Pesticides can reach water-bearing aquifers
below ground from applications onto crop fields, seepage of contaminated
surface water, accidental spills and leaks, improper disposal, and even through
injection waste material into wells.
Chemicals can take a long time to appear in groundwater
The effects of past
and present land-use practices may take decades to become apparent in
groundwater.
When weighing management decisions for
protection of groundwater quality, it is important to consider the time lag
between application of pesticides and fertilizers to the land and arrival of
the chemicals at a well.
This time lag generally decreases with
increasing aquifer permeability and with decreasing depth to water.
In response to reductions in chemical
applications to the land, the quality of shallow groundwater will improve
before the quality of deep groundwater, which could take decades.
Pesticides are mostly modern chemicals.
There are many hundreds of these compounds, and extensive tests and studies of
their effect on humans have not been completed. That leads us to ask just how
concerned we should be about their presence in our drinking water.
Certainly it would be wise to treat
pesticides as potentially dangerous and, thus, to handle them with care.
We can say they pose a potential danger if
they are consumed in large quantities, but, as any experienced scientist knows,
you cannot draw factual conclusions unless scientific tests have been done.
Some pesticides have had a designated
Maximum Contaminant Limit (MCL) in drinking water set by the U.S. Environmental
Protection Agency (EPA), but many have not.
Also, the effect of combining more than one
pesticide in drinking water might be different than the effects of each
individual pesticide alone.
It is another situation where we don't have
sufficient scientific data to draw reliable conclusions.
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https://water.usgs.gov/edu/pesticidesgw.html
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