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Burden of Proof

What we don't know about the toxic chemicals in our

bodies

by Elizabeth Sawin

19 Mar 2003

 

http://www.gristmagazine.com/soapbox/sawin031903.asp?source=daily

 

Scientists call the accumulation of chemical

contaminants (such as PCBs, mercury, and pesticides)

within a person's body the " body burden. " Body burden

is just a number, a concentration in parts per billion

or micrograms per liter. But the term calls forth an

image too, of a body bent over and struggling beneath

a heavy load. When scientists start taking about body

burden, I think about real bodies -- my own and my

children's.

 

Thanks to a new report from the Centers for Disease

Control and Prevention, we have a better sense than

ever before of the body burden of the typical U.S.

citizen. In the Second National Report on Human

Exposure to Environmental Chemicals, CDC scientists

measured the levels of 116 chemicals in the blood and

urine of 2,500 volunteers. The study found detectable

levels of 89 chemicals, including pesticides,

phthalates, herbicides, pest repellents, and

disinfectants.

 

Chemical by chemical, the report documents the average

concentration of contaminants in the bodies of the

people studied. But what does all this data mean? At

what concentration do these chemicals become

dangerous?

 

For all but a handful of chemicals, nobody knows the

answer to this question. The report acknowledges as

much, in one understated sentence: " Research studies,

separate from the Report, are required to determine

which blood or urine levels are safe and which cause

disease. "

 

This is not easy research. The questions involved are

complex. What do you measure to determine safety? How

relevant are animal studies to questions about human

health? Do safe levels differ for children, who eat

and respire more per pound of body weight than adults?

 

These have always been the questions of toxicology,

but new questions are emerging, too. The website

associated with the book Our Stolen Future, which

introduced the idea of endocrine disruptors to the

general public in 1996, collects scientific papers and

news stories that track discoveries about the health

effects of chemical

exposures. The papers collected there make it clear

that we need to add three new questions to the way we

think about safe levels of chemicals.

 

1. Could a given chemical have health effects a long

time after exposure? For chemicals that interfere with

cell-signaling systems, such as hormone systems,

subtle impacts during early development can cause

trouble after a long latency. Traditional tests for

the safety

of chemicals look for immediate effects, not those

that emerge years after exposure.

 

2. Has a given chemical been tested for low-dose

effects?

Traditionally, chemicals are tested for safety at

lower and lower doses, until a concentration is

discovered that has no ill effects.

All doses below that threshold are usually assumed to

be harmless.

But for some chemicals, the dose-response relationship

is not that simple. Unexpected effects can appear at

lower concentrations than the " safe dose " as a

biologically active chemical " hijacks " cellular

processes. Because it focuses on testing for outright

damage by toxic chemicals, traditional toxicology may

miss this low-dose effect.

 

3. Is a given chemical safe when mixed with other

chemicals? Most studies of chemical safety examine the

effects of one chemical at a time, but in real life,

people are exposed to complex mixtures of

contaminants. New studies, such as one on the impact

of a commercially available weed-killer mixture on

pregnant mice, suggest that mixtures of chemicals can

have effects that none of the chemicals have on their

own.

 

No wonder the CDC report can't say much about the safe

levels of the chemicals it measured. Looking for

effects from very low doses over very long time

periods is difficult enough. Try to do that for all

possible real-world combinations of chemical exposure

and the task grows exponentially.

 

Maybe some day our science will reach a level of

sophistication that can give us solid assurances about

chemical safety. But that's a distant goal, not a

current reality. Until then, we are all walking,

breathing experiments in toxicology. Until then, we

are all living with risk.

 

However, there was one definitive and telling finding

in the CDC report: The body burdens of lead, DDT,

PCBs, and hexachlorobenzene have all decreased since

the last CDC study. Guess what? These are all

chemicals that have been banned or strictly regulated

in the U.S.

That's great news. It means that the pollution of our

bodies, like the pollution of our rivers or our air,

is reversible.

 

But a river doesn't come back to life until the

pollution is cut off at the source, and the same will

be true for our bodies. So the CDC finding gives us a

clear mandate of where to go from here: If a lower

body burden seems like a sensible, desirable thing,

then we need to limit the chemicals to which we are

exposed. That's no small task.

The number of artificial chemicals in our environment

is astounding.

The CDC tested for the presence of 116, but the U.S.

EPA estimates that at least 80,000 chemicals -- 690

times the number tested by the CDC -- are produced and

used today.

 

If we keep assuming that all chemicals are harmless

until we uncover the exact doses, combinations, and

lag-times that will make us sick, our bodies are going

to remain polluted for a long, long time.

Wouldn't it make more sense to put the burden of proof

of safety on the chemical manufacturers, rather than

the burden of the chemicals on our bodies?

 

- - - - - - - - -

 

Elizabeth Sawin is a mother, biologist, and systems

analyst. A member of Cobb Hill Cohousing, she lives on

an organic farm in Hartland, Vt.

She works at the Sustainability Institute, a think-do

tank founded by Donella Meadows.

 

Live Simply So That

Others May Simply Live

Yoga-With-Nancy/

SignSoFla/

SoFlaVegans/

SoFlaSchools/

 

________

Have a burning question?

Go to www.Answers. and get answers from real people who know.

[Guest guest]

Note: forwarded message attached.Ronald A. Fells

N3VPU

Amateur Radio Operator

Need Mail bonding?Go to the Mail Q&A for great tips from Answers users.

 

 

 

 

Burden of Proof

What we don't know about the toxic chemicals in our

bodies

by Elizabeth Sawin

19 Mar 2003

 

http://www.gristmagazine.com/soapbox/sawin031903.asp?source=daily

 

Scientists call the accumulation of chemical

contaminants (such as PCBs, mercury, and pesticides)

within a person's body the " body burden. " Body burden

is just a number, a concentration in parts per billion

or micrograms per liter. But the term calls forth an

image too, of a body bent over and struggling beneath

a heavy load. When scientists start taking about body

burden, I think about real bodies -- my own and my

children's.

 

Thanks to a new report from the Centers for Disease

Control and Prevention, we have a better sense than

ever before of the body burden of the typical U.S.

citizen. In the Second National Report on Human

Exposure to Environmental Chemicals, CDC scientists

measured the levels of 116 chemicals in the blood and

urine of 2,500 volunteers. The study found detectable

levels of 89 chemicals, including pesticides,

phthalates, herbicides, pest repellents, and

disinfectants.

 

Chemical by chemical, the report documents the average

concentration of contaminants in the bodies of the

people studied. But what does all this data mean? At

what concentration do these chemicals become

dangerous?

 

For all but a handful of chemicals, nobody knows the

answer to this question. The report acknowledges as

much, in one understated sentence: " Research studies,

separate from the Report, are required to determine

which blood or urine levels are safe and which cause

disease. "

 

This is not easy research. The questions involved are

complex. What do you measure to determine safety? How

relevant are animal studies to questions about human

health? Do safe levels differ for children, who eat

and respire more per pound of body weight than adults?

 

These have always been the questions of toxicology,

but new questions are emerging, too. The website

associated with the book Our Stolen Future, which

introduced the idea of endocrine disruptors to the

general public in 1996, collects scientific papers and

news stories that track discoveries about the health

effects of chemical

exposures. The papers collected there make it clear

that we need to add three new questions to the way we

think about safe levels of chemicals.

 

1. Could a given chemical have health effects a long

time after exposure? For chemicals that interfere with

cell-signaling systems, such as hormone systems,

subtle impacts during early development can cause

trouble after a long latency. Traditional tests for

the safety

of chemicals look for immediate effects, not those

that emerge years after exposure.

 

2. Has a given chemical been tested for low-dose

effects?

Traditionally, chemicals are tested for safety at

lower and lower doses, until a concentration is

discovered that has no ill effects.

All doses below that threshold are usually assumed to

be harmless.

But for some chemicals, the dose-response relationship

is not that simple. Unexpected effects can appear at

lower concentrations than the " safe dose " as a

biologically active chemical " hijacks " cellular

processes. Because it focuses on testing for outright

damage by toxic chemicals, traditional toxicology may

miss this low-dose effect.

 

3. Is a given chemical safe when mixed with other

chemicals? Most studies of chemical safety examine the

effects of one chemical at a time, but in real life,

people are exposed to complex mixtures of

contaminants. New studies, such as one on the impact

of a commercially available weed-killer mixture on

pregnant mice, suggest that mixtures of chemicals can

have effects that none of the chemicals have on their

own.

 

No wonder the CDC report can't say much about the safe

levels of the chemicals it measured. Looking for

effects from very low doses over very long time

periods is difficult enough. Try to do that for all

possible real-world combinations of chemical exposure

and the task grows exponentially.

 

Maybe some day our science will reach a level of

sophistication that can give us solid assurances about

chemical safety. But that's a distant goal, not a

current reality. Until then, we are all walking,

breathing experiments in toxicology. Until then, we

are all living with risk.

 

However, there was one definitive and telling finding

in the CDC report: The body burdens of lead, DDT,

PCBs, and hexachlorobenzene have all decreased since

the last CDC study. Guess what? These are all

chemicals that have been banned or strictly regulated

in the U.S.

That's great news. It means that the pollution of our

bodies, like the pollution of our rivers or our air,

is reversible.

 

But a river doesn't come back to life until the

pollution is cut off at the source, and the same will

be true for our bodies. So the CDC finding gives us a

clear mandate of where to go from here: If a lower

body burden seems like a sensible, desirable thing,

then we need to limit the chemicals to which we are

exposed. That's no small task.

The number of artificial chemicals in our environment

is astounding.

The CDC tested for the presence of 116, but the U.S.

EPA estimates that at least 80,000 chemicals -- 690

times the number tested by the CDC -- are produced and

used today.

 

If we keep assuming that all chemicals are harmless

until we uncover the exact doses, combinations, and

lag-times that will make us sick, our bodies are going

to remain polluted for a long, long time.

Wouldn't it make more sense to put the burden of proof

of safety on the chemical manufacturers, rather than

the burden of the chemicals on our bodies?

 

- - - - - - - - -

 

Elizabeth Sawin is a mother, biologist, and systems

analyst. A member of Cobb Hill Cohousing, she lives on

an organic farm in Hartland, Vt.

She works at the Sustainability Institute, a think-do

tank founded by Donella Meadows.

 

Live Simply So That

Others May Simply Live

Yoga-With-Nancy/

SignSoFla/

SoFlaVegans/

SoFlaSchools/

 

________

Have a burning question?

Go to www.Answers. and get answers from real people who know.