Elsevier

NeuroToxicology

Volume 24, Issues 4–5, August 2003, Pages 577-591
NeuroToxicology

Neurobehavioral Effects of Pesticides: State of the Art

https://doi.org/10.1016/S0161-813X(03)00055-XGet rights and content

Abstract

The authors have reviewed the literature on neurobehavioral toxicity of pesticides to assess the status of knowledge on this matter. Some data suggest that exposure to DDT and fumigants may be associated with permanent decline in neurobehavioral functioning and increase in psychiatric symptoms, but, due to the limited number of studies available and the scarce knowledge on exposure levels, no firm conclusion can be drawn. Data on subjects acutely poisoned with organophosphorous compounds suggest that an impairment in neurobehavioral performance and, in some cases, emotional status may be observed as a long-term sequela, but the possibility still remains that these effects were only an aspecific expression of damage and not of direct neurotoxicity. Studies carried out on subjects chronically exposed to organophosphates, but never acutely poisoned, do not provide univocal results but the slight changes consistently observed in sheep dippers suggest the need of focusing on activities characterized by relatively higher exposure levels. In general, the main limits of existing knowledge are the variability of the testing methods used, which makes it difficult to compare the results of single studies, and the scarce knowledge on exposure levels. A promising approach may be the conduction of prospective longitudinal or cohort studies, where exposure and dose assessment can be more easily controlled, or the evaluation of cohorts of workers a priori selected for the availability of environmental and biological monitoring data. The follow up of the populations under study may give an answer at the problem of the prognostic significance of the observed changes. Also the protocols used to assess neurobehavioral functioning need to be standardized.

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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