An epidemiological study of the relations between exposure to organophosphate pesticides and indices of chronic peripheral neuropathy and neuropsychological abnormalities in sheep farmers and dippers

Abstract

Objectives-To investigate the hypothesis that chronic low level exposure to organophosphates (OPs) in sheep dips is related to clinically detectable measures of polyneuropathy. Methods-The design was a cross sectional exposure-response study of sheep dippers and other non-exposed groups. The study group consisted of 612 sheep dipping farmers, 53 farmers with no sheep dipping experience, and 107 ceramics workers. Retrospective exposure information was obtained by questionnaire based on stable and easily identifiable features of sheep dipping found during the first phase of the study; in particular, estimates of handling concentrate and splashing with dilute dip. Neurological assessments were based on a standard neuropathy symptoms questionnaire, and thermal and vibration quantitative sensory tests. Results-Adjusted for confounders there was a weak positive association between cumulative exposure to OPs and neurological symptoms, the significance of which was dependent on the inclusion of a few individual workers with extremely high exposure. There was no evidence of an association between cumulative exposure and the thermal or vibration sensory thresholds. However, separating the effects of exposure intensity and duration showed a higher prevalence of symptoms, primarily of a sensory type, among sheep dippers who handled the OP concentrate. There was also evidence that sensory and vibration thresholds were higher among concentrate handlers, the highest exposed group of dippers. Conclusions-The findings showed a strong association between exposure to OP concentrate and neurological symptoms, but a less consistent association with sensory thresholds. There was only weak evidence of a chronic eVect of low dose cumulative exposure to OPs. It is suggested that long term health eVects may occur in at least some sheep dippers exposed to OPs over a working life, although the mechanisms are unclear. (Occup Environ Med 2001;58:702-710)

Low level exposures to organophosphorus esters may cause neurotoxicity

“…The study also provided important insight into the profile of neurotoxicity, which confirmed earlier findings and showed that there was a positive correlation between abnormal neurological tests and evidence of anxiety and depression in patients exposed to OP. In another study , the neuropathy profile confirmed earlier observations (Kaplan et al, 1993;Steenland et al, 1994;McConnell et al, 1994;Horowitz et al, 1999;Pilkington et al, 1999) that this neuropathy linked to LTLL exposure to OP, unlike OPIDN, was predominately involving the sensory nerve fibres and affected both small and large fibre populations. This neuropathy profile linked with LTLL exposure to OP was also compared with another one seen in chronic neurotoxicity following one or more acute cholinergic episodes ).…”

“…A number of complicating factors, which make exposure assessment extremely difficult (Table 7, may be responsible for absence of dose Á/response relationship in some studies. Furthermore, the high quality studies did show a doseÁ/response relationship (Stephens et al, 1995;Pilkington et al, 1999).…”

“…All of these high quality studies showed evidence of a positive link between LTLL exposure to OP esters and chronic neurotoxicity. The most accurate study available to date estimated the overall incidence of one form of neurotoxicity, distal axonal peripheral neuropathy, to be about 40 times in people exposed to OP compared to the incidence in the general population (Pilkington et al, 1999). This involved 612 subjects exposed to OP and they were compared with a large group of unexposed subjects of the same occupational group as well as with another large group of control subjects belonging to a different occupational group but with a similar physical effort, socio-economic background and geographical location.…”

Neurobehavioral performance and work experience in Florida farmworkers.

“…Acute pesticide poisoning is followed, sometimes after many years, by impaired neurobehavioral performance and decreased nerve conduction velocity as well as increased frequency of neurologic symptoms (London et al 1998;McConnell et al 1994;Rosenstock et al 1991;Savage et al 1988;Steenland et al 1994;Wesseling et al 2002). Chronic pesticide exposure has also been associated with neurologic deficits London et al 1997;Pilkington et al 2001;Ruijten et al 1994;Sack et al 1993; Environmental Medicine | Kamel et al 1770 VOLUME 111 | NUMBER 14 | November 2003 • Environmental Health Perspectives Table 3. The referent for all comparisons is the control group; the value is 1 for digit span and 0 for other tests.…”

Intoxicación por plaguicidas

“…En los últimos años se han descrito cuadros neuropsicológicos crónicos no bien definidos, incluyendo el Síndrome de fatiga crónica, relacionados, en unos casos, con efectos a largo plazo de intoxicaciones agudas y, en otros, con exposiciones acumulativas subclínicas [25][26][27][28] . Este tipo de efecto no ha sido confirmado por el momento.…”