Perchlorate Will Accumulate

• Author: Samuel Kounaves
• Position: Professor in the Chemistry Department at Tufts University
• Pages: 41-41

MAY/JUNE 2010 ❧ Page 41

Copyright © 2010, Environmental Law Institute®, Washington, D.C. www.eli.org.

Reprinted by permission from The Environmental Forum®, May/June 2010

anoTher view

fection. Nearly $3 billion of sodium

hypochlorite bleach is sold globally

each year. In a 2008 study, perchlo-

rate contamination was found to

occur in more than 90 percent of

sodium hypochlorite samples.

e most recent part of the per-

chlorate source picture to come

to light is the volume of the com-

pound entering the United States

in f‌ireworks. Recent data from the

Department of Commerce indicate

a large increase in f‌irework imports

over a f‌ive-year span, from 174.7

million pounds in 2002 to 271.2

million pounds in 2006. Potas-

sium perchlorate constitutes up to

70 percent of the chemical fraction

in f‌ireworks. Based on these data,

the American Pyrotechnics Asso-

ciation estimates that 14.2 million

pounds of perchlorate entered the

country in f‌ireworks in 2002, and

21.8 million pounds in 2006. Im-

ports represent about 90 percent of

f‌ireworks used in the United States.

For 2006, the amount of perchlo-

rate imported in f‌ireworks repre-

sents nearly three times the amount

purchased by the military. While

importation does not necessarily

equate with amounts released into

the environment, these data high-

light an important potential non-

point source.

Recent f‌ield studies also support

focusing on perchlorate discharges

from f‌ireworks. EPA analyzed wa-

ter in an Oklahoma lake before

and after f‌ireworks displays. Testing

performed 14 hours after an event

showed that perchlorate levels rose

24 to 1,028 times above the pre-

display baseline. e agency found

that concentrations of perchlorate

peak about 24 hours after a display

and then decrease to the baseline

within 20 to 80 days. us, Fourth

of July activities and sporting events

may be important in future ef‌forts

to def‌ine sources and routes of ex-

posure. Ef‌forts to restrict and man-

age releases at the local level may be

able to control exposure.

e millions of emergency road

best explanation for its changing

distribution in the soil when mov-

ing from the upper to lower valleys

is the dif‌ference in the amount of

liquid water present and its ef‌fect,

leading to depletion or concentra-

tion of the perchlorate. In the high-

lands the atmospheric deposition

of perchlorate is left undisturbed,

while in the lower wet valleys its

distribution becomes chaotic.

Combining our f‌indings with

those for the Arctic, North Amer-

ica, and other regions provides an

emerging picture for the global

presence of natural perchlorate. In

addition, our results from Antarc-

tica clearly point to the conclusion

that even though natural perchlo-

rate is atmospherically

and homogeneously

deposited, over time it

will accumulate at high

levels at some locations

while it will be non-

existent at others.

Our results sup-

port the hypothesis

that perchlorate must

also have a variety of long-term,

widely, and irregularly distributed

sinks. Since aqueous perchlorate

is chemically stable in the natu-

ral environment, its lack of accu-

mulation in the ocean or aquifers

may also be attributable to micro-

bial utilization in anaerobic or low

nitrate media.

To help us understand the full

impact of perchlorate, we need to

more accurately determine its glob-

al distribution and accumulation

patterns, its interactions with ter-

restrial ecology, and its atmospheric

formation mechanisms.

Samuel Kounaves is a Professor in the

Chemistry Department at Tufts University.

For more information see: S. P. Kounaves,

et al., Environmental Science and Tech -

nolog y, 2010, 44, 236-2364, doi:10.1021/

es9033606.

In 2008 NASA’s Phoenix

Lander found perchlorate

in three dif‌ferent Martian

soil samples. at discovery

prompted a re-analysis of the

soil samples we had brought back

from an expedition a year earlier to

Antarctica’s Dry Valleys, a site used

as a Mars analogue for training be-

cause of the subzero temperatures

and extreme aridity. For both Earth

and Mars, the evidence implies that

given the right conditions and a

source of chlorine, perchlorate will

accumulate.

Free of anthropogenic inf‌luenc-

es, the Dry Valleys provide an ideal

location for such studies.e Ant-

arctic soil samples had been collect-

ed from pits dug in three

types of Dry Valley mi-

croclimate zones: coastal

(wet), inland (arid), and

highland (hyperarid).

Samples were collected

from every identif‌iable

soil horizon (boundaries

between dif‌ferent kinds

of soil) down to the ice-

cemented soil. All the samples were

reanalyzed for perchlorate.

To our amazement, perchlorate

was found in all the highland soils,

in all the horizons from the surface

to the ice-cemented soil. Its concen-

tration ranged up to 630 parts per

billion and in a continuous vertical

prof‌ile. In contrast, for the inland

valley soil horizons, it was found

to vary with a more heterogeneous

distribution, while in the coastal

valleys it appeared very randomly

distributed, approaching 1,100

ppb in one isolated soil horizon,

and totally absent in others, with

no regular or discernible pattern.

How the perchlorate is deposit-

ed in these valley soils is clearly evi-

dent from its correlation to nitrate

and chloride, both of which have

been shown to be atmospherically

formed and deposited. us, the

Perchlorate Will Accumulate

Samuel Kounaves