exposure previously reported were further supported by a majority of the recent
studies. Nevertheless, harmonization of the study designs would contribute to
upgrade the confidence level of the evidence and identify the biological mechanisms
potentially involved in the reported associations. There were fewer investigations on
the risk of neurodevelopmental deficits following exposure to pyrethroids during
childhood. The data were contradictory and evidence on a causal relationship is
currently insufficient.
A major shortcoming of the available epidemiologic data is the lack of a detailed
and consistent exposure assessment, capturing all the various sources and routes of
pyrethroid exposure over long time periods. Many studies used urinary levels of
nonspecific metabolites to quantitatively estimate individual pyrethroid exposure.
When use and outcome were frequent enough, they could provide valuable
exposure-response information, particularly regarding the lower environmental
levels encountered by the general public. However, pyrethroids are nonpersistent
chemicals which are rapidly metabolized and excreted, and a single measure of their
urinary metabolites may only reflect current or recent exposures. Furthermore, the
use of cross-sectional data in a majority of studies may not account for peak or
duration of exposures. Characterization of extended and integrated exposure might
be improved by combining reiterate urine sampling and specific pyrethroid biomarker measurements with other relevant information, for example, other indicators
of long-term exposure (e.g., residential address history), occupational and domestic
uses of pesticide compounds (e.g., frequency, intensity, duration, life period), use of
protective equipment, diet and possible supplements intake, and occurrence of
co-exposures [30, 51, 56, 70, 103].
In most studies statistical analyses included common potential confounding
factors linked to the parameter of interest (e.g., maternal race/ethnicity, age, and
smoking). Pesticides are often used as complex mixtures of chemicals belonging to
the same or different classes (e.g., pyrethroid and organophosphate insecticides or
pyrethroid and the synergist piperonyl butoxide). Workers and the general adult and
child population are potentially exposed to multiple chemicals, with temporal and
spatial variations. Co-exposure or use of pyrethroids with other pesticides was
controlled in several studies (e.g., [61]). Although challenging, the possibility of
join effects and interactions would deserve more consideration in future large
epidemiological studies with longitudinal data collection [34, 43].
In conclusion, there is accumulating evidence that chronic exposure to the
pyrethroids may have potential negative effects on human health, especially during
pregnancy. Despite constant knowledge enhancement, this review also highlights
the critical need of valid epidemiological studies for a broader and more reliable
assessment of the risks associated with pyrethroids.
296
A.-M. Saillenfait and S. Malard
studies. Nevertheless, harmonization of the study designs would contribute to
upgrade the confidence level of the evidence and identify the biological mechanisms
potentially involved in the reported associations. There were fewer investigations on
the risk of neurodevelopmental deficits following exposure to pyrethroids during
childhood. The data were contradictory and evidence on a causal relationship is
currently insufficient.
A major shortcoming of the available epidemiologic data is the lack of a detailed
and consistent exposure assessment, capturing all the various sources and routes of
pyrethroid exposure over long time periods. Many studies used urinary levels of
nonspecific metabolites to quantitatively estimate individual pyrethroid exposure.
When use and outcome were frequent enough, they could provide valuable
exposure-response information, particularly regarding the lower environmental
levels encountered by the general public. However, pyrethroids are nonpersistent
chemicals which are rapidly metabolized and excreted, and a single measure of their
urinary metabolites may only reflect current or recent exposures. Furthermore, the
use of cross-sectional data in a majority of studies may not account for peak or
duration of exposures. Characterization of extended and integrated exposure might
be improved by combining reiterate urine sampling and specific pyrethroid biomarker measurements with other relevant information, for example, other indicators
of long-term exposure (e.g., residential address history), occupational and domestic
uses of pesticide compounds (e.g., frequency, intensity, duration, life period), use of
protective equipment, diet and possible supplements intake, and occurrence of
co-exposures [30, 51, 56, 70, 103].
In most studies statistical analyses included common potential confounding
factors linked to the parameter of interest (e.g., maternal race/ethnicity, age, and
smoking). Pesticides are often used as complex mixtures of chemicals belonging to
the same or different classes (e.g., pyrethroid and organophosphate insecticides or
pyrethroid and the synergist piperonyl butoxide). Workers and the general adult and
child population are potentially exposed to multiple chemicals, with temporal and
spatial variations. Co-exposure or use of pyrethroids with other pesticides was
controlled in several studies (e.g., [61]). Although challenging, the possibility of
join effects and interactions would deserve more consideration in future large
epidemiological studies with longitudinal data collection [34, 43].
In conclusion, there is accumulating evidence that chronic exposure to the
pyrethroids may have potential negative effects on human health, especially during
pregnancy. Despite constant knowledge enhancement, this review also highlights
the critical need of valid epidemiological studies for a broader and more reliable
assessment of the risks associated with pyrethroids.
296
A.-M. Saillenfait and S. Malard