3 Results
The recent epidemiological studies on the influence of chronic exposure of adults to
pyrethroids have mainly focused on four areas of health effects, providing new
information on reproductive-, thyroid-, respiratory-, and neurological-related outcomes. In addition, a great and increasing number of studies have investigated the
possible association between prenatal and/or postnatal childhood exposures and
child health, especially neurodevelopment. Exposures could be occupational or
environmental, and most studies analyzed many pesticides and/or insecticides at
once (e.g., organophosphate and pyrethroid classes). Exposure assessment relied on
survey data (e.g., residential proximity to pesticides agricultural applications using
Californian Pesticide Use Reports-CPU), self-reported exposure mostly with a
dichotomous answer (e.g., user/no user in occupational settings), or measurement
of biomarkers, allowing possible evaluations of exposure-response patterns (e.g., by
stratifying exposures into a few levels). The most commonly used biomarkers were
pyrethroid urinary metabolites, primarily 3-phenoxybenzoic acid (3-PBA). It is a
general metabolite of several pyrethroids, and associations with 3-PBA implied
more the pyrethroid class than a specific parent chemical. Its detection frequency
in urine was generally in a range from 70 to 100% of the studied populations.
3.1 Respiratory Outcomes
All identified studies on respiratory health used cross-sectional analyses (Table 1).
Respiratory symptoms were assessed in agricultural or farm workers and their
families following occupational exposures to specific or different subclasses of
pesticides, including pyrethroid insecticides. They essentially consisted in selfreported rhinitis, wheeze, and asthma. Two large-scale studies have been conducted
in the USA. In an updated analysis of the Agricultural Health Study data, Hoppin
et al. [5] reported a slight increase in wheezing with exposure to three individual
pyrethroids. Of the 22,134 male applicators who had been interviewed, 6% had both
wheeze and allergy and 18% reported wheeze only. In the Farm and Ranch Safety
Survey, 30.8% of an estimated 2.1 million farm operators reported lifetime allergic
rhinitis, and 5.1% had current asthma [4]. A positive association was found between
lifetime allergic rhinitis and pyrethroids and other insecticides. However, in both
studies, pesticide uses and outcomes were self-reported. The potential relationship
between asthma and the pyrethroid class has not been specifically analyzed [4].
Information on the impact of non-occupational exposure to pyrethroids on respiratory health is scarce. Lung function was examined in a single study which
suggested association between urinary concentrations of pyrethroid metabolites
and changes in lung functions in children and adolescents from the Canadian general
population [10]. No association with respiratory symptoms and diseases was
observed in this population-based study.
Human Risk Associated with Long-Term Exposure to Pyrethroid Insecticides
261
The recent epidemiological studies on the influence of chronic exposure of adults to
pyrethroids have mainly focused on four areas of health effects, providing new
information on reproductive-, thyroid-, respiratory-, and neurological-related outcomes. In addition, a great and increasing number of studies have investigated the
possible association between prenatal and/or postnatal childhood exposures and
child health, especially neurodevelopment. Exposures could be occupational or
environmental, and most studies analyzed many pesticides and/or insecticides at
once (e.g., organophosphate and pyrethroid classes). Exposure assessment relied on
survey data (e.g., residential proximity to pesticides agricultural applications using
Californian Pesticide Use Reports-CPU), self-reported exposure mostly with a
dichotomous answer (e.g., user/no user in occupational settings), or measurement
of biomarkers, allowing possible evaluations of exposure-response patterns (e.g., by
stratifying exposures into a few levels). The most commonly used biomarkers were
pyrethroid urinary metabolites, primarily 3-phenoxybenzoic acid (3-PBA). It is a
general metabolite of several pyrethroids, and associations with 3-PBA implied
more the pyrethroid class than a specific parent chemical. Its detection frequency
in urine was generally in a range from 70 to 100% of the studied populations.
3.1 Respiratory Outcomes
All identified studies on respiratory health used cross-sectional analyses (Table 1).
Respiratory symptoms were assessed in agricultural or farm workers and their
families following occupational exposures to specific or different subclasses of
pesticides, including pyrethroid insecticides. They essentially consisted in selfreported rhinitis, wheeze, and asthma. Two large-scale studies have been conducted
in the USA. In an updated analysis of the Agricultural Health Study data, Hoppin
et al. [5] reported a slight increase in wheezing with exposure to three individual
pyrethroids. Of the 22,134 male applicators who had been interviewed, 6% had both
wheeze and allergy and 18% reported wheeze only. In the Farm and Ranch Safety
Survey, 30.8% of an estimated 2.1 million farm operators reported lifetime allergic
rhinitis, and 5.1% had current asthma [4]. A positive association was found between
lifetime allergic rhinitis and pyrethroids and other insecticides. However, in both
studies, pesticide uses and outcomes were self-reported. The potential relationship
between asthma and the pyrethroid class has not been specifically analyzed [4].
Information on the impact of non-occupational exposure to pyrethroids on respiratory health is scarce. Lung function was examined in a single study which
suggested association between urinary concentrations of pyrethroid metabolites
and changes in lung functions in children and adolescents from the Canadian general
population [10]. No association with respiratory symptoms and diseases was
observed in this population-based study.
Human Risk Associated with Long-Term Exposure to Pyrethroid Insecticides
261