Neurobehavioral Effects of Pesticides: State of the Art
Section snippets
INTRODUCTION
Pesticides differ from other chemical substances because they are toxic chemicals deliberately spread into the environment with the aim of controlling undesired living species. Since their toxicity may be not completely specific for the target organisms, their use may pose a risk to human health.
The mechanism of action of pesticides frequently involves a neurotoxic effect: organophosphorous compounds and carbamates act through the inhibition of central nervous system cholinesterase (Jeyaratnam
ORGANOCHLORINE COMPOUNDS
Available data regarding organochlorine compounds are summarized in Table 1.
In a USA study, 859 children were tested at the ages of 3, 4, or 5 years to evaluate the effects of DDT absorbed either through transplacental route or during breast-feeding (Gladen and Rogan, 1991). This study indicated that DDT did not affect either psychomotor and mental behavioral patterns, or school performance in English and mathematics, even when the provisional tolerated daily intake was exceeded. Six hundreds
ORGANOPHOSPHOROUS COMPOUNDS
Organophosphorous compounds represent the chemical group of pesticides most extensively investigated for their neurobehavioral toxicity. The first reports of neurobehavioral changes, such as memory impairment, confusion, anxiety, drowsiness, labile emotion, fatigue, depression, irritability in subjects heavily exposed to OP compounds date back to the 1950s and 1960s (Dille and Smith, 1964, Gerson and Shaw, 1961, Grob et al., 1950, Metcalf and Homes, 1969, Durham et al., 1965). Even if these
SYNTHETIC PYRETHROIDS
Synthetic pyrethroids are insecticides becoming more and more important in agriculture, public health and for the struggle against vector born disease in the developing world because of their low acute toxicity and very short environmental half-lives. They also find a significant use indoors (home, restaurants, offices and also airplanes), therefore the definition of the health risk associated with the use of these compounds is of great public health interest. No extended studies are available
FUMIGANTS
One of the most toxic fumigants is methyl bromide, a compound widely used for soil fumigation and seed treatment.
Two studies suggested the capacity of methyl bromide and another fumigant, sulfuryl fluoride, to cause neurobehavioral effects (Table 5). Calvert et al. (1998) studied a group of 123 fumigation workers through the measurement of nerve conduction, vibration, neurobehavioral, visual, and olfactory functions. The study showed a reduction of the performance at the pattern memory tests
MIXTURES
In several retrospective studies, the active ingredients used by the studied subjects could not be defined, and, given that the use of many different active ingredients is very common in agriculture, data were referred to “use of mixtures”. Also the so-called “Gulf War syndrome” has been sometimes attributed to exposure to mixtures of pesticides.
A reduction in cognitive tests was observed when comparing 96 Hispanic adolescents working in agriculture with 51 contemporaries engaged in
CONCLUSIONS AND PERSPECTIVES
Although most pesticides have a known neurotoxic potential, the evidence of their capacity to cause neurobehavioral impairment in man in the absence of a previous acute poisoning episode is very limited. Even in the past-poisoned subjects, the often observed reduction of verbal attention, visual memory and attention, motricity, affectivity, and flexibility of thinking, may be the result of a generic brain injury, for example, anoxia consequent to the cholinergic crisis, and not necessarily to
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