|
•
<br />scientific literature. How does the recent
<br />toxicology compare with the existing
<br />toxicology, and what, if anything, did we
<br />learn?
<br />2,4-D toxicology
<br />The latest studies confirm what existing
<br />toxicology hes shown for some time. For
<br />example, the new toxicology and
<br />environmental toxicology (114 studies)
<br />confirms:
<br />I. 2,4-D has moderate to (ow acute
<br />toxicity. The LD50 (rats) ranges
<br />from 699 mg per kg of body weight
<br />(2,4-D acid) to 896 mg/kg for the
<br />ester. From an LD50 standpoint,
<br />2,4-D is less toxic than caffeine and
<br />slightly more toxic than aspirin.
<br />2. 2,4-D has low reproductive toxicity.
<br />3. 2,4-D does not cause birth defects.
<br />4. Based on the extensive toxicology, it
<br />is highly improbable that 2,4-D
<br />causes cancer.
<br />5. 2,4-D has low potential to cause
<br />neurotoxicity in both short- and long-
<br />term exposures.
<br />6. 2,4-D does not cause genetic
<br />damage.
<br />7. At the concentrations which may be
<br />found in the environment, 2,4-D is
<br />highly unlikely to present a threat to
<br />wildlife.
<br />Environmental fate
<br />The seventy-eight environmental fate
<br />studies again confirm that 2,4-D has a
<br />relatively short half-life and is rather
<br />immobile in the soil. In thirty-five
<br />studies across the U.S., the average
<br />lowest depth ranged from six to twelve
<br />inches in soils of the Southern United
<br />States to sixteen to twenty-four inches in
<br />tow organic-matter soils. Soils were
<br />
<br />sampled to a depth of forty~ight inches.
<br />Its average half-life in soils ranged from
<br />6.4 days in Southern soils to 8.3 days in
<br />high organic- matter soils. As a result,
<br />2,4-D is unlikely to get into ground
<br />water. The average half-life in grass was
<br />6.1 days and 6.9 days in thatch. The half-
<br />life in natural water was two to four
<br />weeks, although in areas where soil
<br />microbes were conditioned to 2,4-D,
<br />such as a treated rice paddy, the half-life
<br />was as short as one day. The acid form
<br />of 2,4-D, as wel[ as the amine and ester
<br />chemical groups, metabolized to
<br />compounds of nontoxicological
<br />significance and ultimately to form of
<br />cazbon. Thus, 2,4-D is considered a
<br />biodegradable compound, and under
<br />normal conditions, 2,4-D residues are not
<br />persistent in soil, water, or vegetation.
<br />2,4-D and past problems
<br />ff the toxicology of 2,4-D has always
<br />been essentially clean, why aze there still
<br />per+eeived problems? Any suggestions
<br />that 2,4-D may cause cancer, for
<br />example, were never based on controlled,
<br />laboratory-animal feeding studies.
<br />Rather, they came from what are known
<br />as case-control studies in the field of
<br />epidemiology. These studies are based on
<br />interviews, often by telephone, with
<br />populations of cancer cases who may
<br />have had an exposure of interest. The
<br />results of these interviews are then
<br />compared to interviews with non-cancer
<br />cases.
<br />There aze more than 100 epidemiologic
<br />studies pertinent to 2,4-D. Taken
<br />together, the results aze equivocal or
<br />ambiguous, with some studies suggesting
<br />a relationship between 2,4,-D and non-
<br />Hodgkins lymphoma (NHL.), a form of
<br />
|