The
results of the PISA International and National studies on
mental capacities of school children worldwide in 2000 are
a matter of intensive debates, especially concerning a surprisingly
bad outcome in various Western countries with a high socioeconomic
status, e.g. Germany. Mainly, different school and preschool
systems are held responsible for it, interacting with family
matters of course. However, mental capacities are in general
not only a result of learning possibilities but of learning
capabilities, a so far rarely considered aspect with regard
to PISA.
Dichlorodiphenyl trichloroethane (DDT) is a chlorinated phenyl
derivative and was worldwide used as a pesticide. Interestingly,
there are some indications for negative long-term effects
on mental capacities of chlorinated phenyl compounds, observed
in animal experiments and human studies.
Therefore,
we aimed to investigate a possible lasting impact of DDT exposure
in early (neonatal) life on mental capacities in school age.
Statistical relationships were evaluated by correlation and
regression analysis between total DDT concentrations in human
breast milk in the birth years of 1984/85 and PISA 2000 results
on mental capacities in 15-year-old pupils worldwide as well
as percentages of backward school children in Germany in 1994/95.
DDT concentrations were extrapolated in the best possible
way from available publications on worldwide DDT levels. Thereby,
estimations were possible for eleven international countries
out of three continents as well as fourteen Federal States
of Germany which participated in PISA 2000.
Thus, comparing the mental capacities of 15-year-old school
children with population based total DDT levels in human breast
milk in eleven international countries (PISA International),
an inverse correlation was found, even under consideration
(adjustment) of the socioeconomic status (see Figure 1).
Furthermore,
a significant inverse relationship could be observed between
the mental capacities of pupils born in 1984/85 and the total
DDT concentrations in ten international countries (PISA International)
plus fourteen Federal States of Germany (PISA National). Finally,
a significant relationship was found between the total DDT
contents in human milk in 1984/85 and the percentages of backward
school children in evaluated German Federal States in 1994/95.
In conclusion, these observations speak for a dose-dependent
deleterious impact of DDT exposure in early life on mental
health and mental capacities in later life.
As
DDT is a hormonally active substance, it is noteworthy that
hormones are important organizers of the brain, recognized
by our group since the 1970s. Obviously, these chemical messengers
are capable of "programming" fundamental processes
of life dose-dependently during critical developmental periods.
In view of extensive studies, mental disorders and important
diseases of reproduction, metabolism, information processing
and immune responsiveness may therefore be preventable, at
least in part, by avoiding abnormal hormone concentrations
during critical developmental periods of the organism. It
should also be mentioned that total DDT concentrations in
human breast milk are an indirect indicator of the offspring's
exposure not only in early postnatal life but also in prenatal
life.
In
summary, our data -in association with additional experimental
and epidemiological findings- suggest that DDT exposure in
early life may lead to harmful effects on brain development
and, therefore, mental capacities in later life. Thus, a neuroendocrine
prophylaxis -as recommended by our group for many years- during
critical developmental periods appears to be most important
not only for primary preventive medicine but also for "preventive
pedagogics". The validity of these theses should be re-tested
in future PISA studies.
Fig. 1. Linear regression plots for DDT concentrations
in human breast milk (log-transformed) in the years of birth
(1984/85) vs mean mental capacities in school children according
to PISA International 2000.
Scheduled
for publication in October
Vol. 23 No.5, 2002
Neuroendocrinology Letters www.nel.edu
More
information available: publisher@nel.edu
