Environmental Health Perspectives Volume 108, Number 7, July 2000
There is no such thing as a "national" environment.
Our growing economic interdependence provides the context for
global cooperation in dealing with the global ecosystem.
John Naisbitt, Utne Reader, November-December 1989
New Grounds for Drinking Coffee
New information suggests that your morning cup of coffee may be a healthy
part of a nutritious breakfast. Research by an international team of
scientists published in the April 2000 issue of Human and Ecological Risk
Assessment has shown that automatic drip coffee makers can remove up to 85%
of both copper and lead in tap water. Team leader Herbert E. Allen, a
professor of civil and environmental engineering at the University of
Delaware in Newark, speculates that coffee grounds retain heavy metals
through surface chelation, a chemical reaction in which metals form
complexes with organic matter. After looking at ion exchange or adsorption
as possible filtering mechanisms, Allen says that due to coffee's
nature--coffee grounds having uncharged or negatively charged
molecules--surface chelation most likely explains the large percentage of
metals removed. Because dissolved heavy metals are positively charged, the
metal ions bind strongly to the coffee, he says.
The study was conducted by Allen, graduate student Christopher
Impellitterri, Michael McLaughlin of the division of soils at the
Commonwealth Scientific and Industrial Research Organisation in Adelaide,
Australia, and Gustavo Lagos, a scientist at the Pontificia Universidad
Católica de Chile in Santiago. After attending a seminar about copper in the
human diet presented by Lagos, the group speculated that the amount of
copper in prepared coffee would be less than the amount present in the water
used to make the coffee, and they decided to conduct a study to test their
idea.
In order to simulate home coffee brewing as closely as possible, the team
studied three commercial coffee brands using a coffee maker with a
basket-type paper-lined filter and a 12-cup-capacity glass carafe. For the
first batch of each brand, the team began with the standard amount of coffee
recommended by the manufacturer (one teaspoon per cup) and then adjusted
that amount to 30 grams of coffee per liter of water, a strength they agreed
was satisfactory. From each first batch, four samples were taken for both
metal and pH analysis to establish a baseline value for the amount of copper
and lead in an average pot of each brand of brewed coffee. The team prepared
additional batches at different volumes (but maintaining the coffee-to-water
ratio) and using different concentrations of coffee to produce stronger
brews. They also ran normal and metal-spiked solutions through the coffee
maker both with and without a paper filter to assess sorption by the coffee
maker and the filter.
The results of the team's research suggest several reasons for the lead and
copper removal. When increasingly stronger batches of coffee were brewed, an
increase in metal removal was observed, probably because of the increased
contact time between the coffee and the water as it seeped through a thicker
bed of grounds. People who prefer stronger coffee may be enjoying a greater
decrease of the metals, the team says, since the stronger the coffee is
brewed, the more metals may be removed. But after comparing the strongest
batches and noting no additional removal of metals, they decided to continue
the search for additional factors.
The team then varied the coffee grounds' consistency. They found that coarse
coffee grounds removed 73% of the copper and 79% of the lead. In comparison,
finely ground coffee powder removed 90% of copper and 91% of lead,
suggesting that the increased surface area of the smaller grounds enhances
removal of the metals. A moister bed of coffee also increased how much metal
was adsorbed, as demonstrated by collecting samples of the coffee as it
passed through the coffee bed and comparing their metal concentrations to
those of the finished pot. Allen says that sorption of the metals may also
occur on interior surfaces of the coffee maker, paper filter, or glass
carafe.
Although Allen says that the metal removal could actually be much higher
worldwide for those who drink coffee, depending on cultural and personal
tastes in coffee preparation, he says that the team's findings are important
to current human exposure assessment estimates of copper and lead in tap
water. Current estimates for metal exposure could be much higher than actual
levels for people whose main tap water intake is through coffee.
-Lindsey A. Greene
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