A Step in the Wrong Direction on Arsenic A Step in the Wrong Direction on Arsenic A Step in the Wrong Direction on Arsenic

aubrey stimola stimola at acsh.org
Wed Oct 20 13:55:28 EST 2004

A Step in the Wrong Direction on Arsenic 

According to a study in the August 2004 issue of Chemical Research in
Toxicology, arsenic could be toxic at much lower levels than
previously thought, raising the alarm that the new EPA drinking water
standard of 10 parts per billion (ppb), to take effect in 2006, might
still be too high.(1) But don't dump the glass of tap water yet; the
conclusions of this newest study were based on an in vitro study of a
rat cell line. 

While animal experiments play a crucial role in many fields of
research, there has been much scientific debate about how heavily we
can rely on high-dose, single-species animal tests as indicators of
human toxins and carcinogens.  Over-reliance on such studies as the
basis for increasingly stringent regulations of various chemicals
lacks scientific credibility and often results in unnecessary health
scares.  The scares draw energy and financial resources away from
actual health dangers.  The current study, conducted by researchers at
Dartmouth Medical School, takes the issue of relying on animal tests
another step in the wrong direction. 

The term in vitro -- literally, "in glass" -- refers to any biological
process that takes place in an artificial environment such as a Petri
dish or a test tube.  An essential part of medical research, in vitro
procedures are most useful in the early or intermediate stages of
experimentation to study the effects of a substance in isolation,
without interference from natural bio-mechanisms involving hormones,
enzymes, and immune responses.  They have been used to understand
mechanisms of toxicity, to identify cellular target sites of action,
and to characterize cellular and molecular changes prompted by
exposure to toxicants.  They reduce variability, allow for greater
control of the experimental environment, and are quicker and cheaper
than their in vivo -- "in life" -- counterparts. 

However, extrapolating in vitro results to whole animal situations --
even animals of the same species that provided the cell cultures --
has many limitations.  These studies cannot take into account toxicant
distribution in a whole organism, route of administration, or
metabolism of the substance.  Further, cells in culture are not
exposed to circulatory, nervous, or endocrine system functions, or to
the millions of cells, thousands of enzymes, hundreds of chemical
messengers, and dozens of organs that work in concert within a whole
organism.  In other words, the biochemical processes leading from
toxicant exposure to toxic effect in vivo are too complicated to be
duplicated in vitro.  This is very much the case when it comes to
cancer forma......

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