Estimation of cumulative exposure to organophosphate sheep dips in a study of chronic neurological health effects among United Kingdom sheep dippers

21-Day dermal exposure to aircraft engine oils: effects on esterase activities in brain and liver tissues, blood, plasma, and clinical chemistry parameters for Sprague Dawley rats

This dermal study tested the potential toxicity of grade 3 (G3) and 4 (G4) organophosphate-containing aircraft engine oils in both new (G3-N, G4-N) and used states (G3-U, G4-U) to alter esterase activities in blood, brain and liver tissues, clinical chemistry parameters, and electrophysiology of hippocampal neurons. A 300 µl volume of undiluted oil was applied in Hill Top Chamber Systems®, then attached to fur-free test sites on backs of male and female Sprague Dawley rats for 6 hr/day, 5 days/week for 21 days. Recovery rats received similar treatments and kept for 14 days post-exposure to screen for reversibility, persistence, or delayed occurrence of toxicity. In brain, both versions of G3 and G4 significantly decreased (32-41%) female acetylcholinesterase (AChE) activity while in males only G3-N and G4-N reduced (33%) AChE activity. Oils did not markedly affect AChE in liver, regardless of gender. In whole blood, G3-U decreased female AChE (29%) which persisted during recovery (32%). G4-N significantly lowered (29%) butyrylcholinesterase (BChE) in male plasma, but this effect was resolved during recovery. For clinical chemistry indices, only globulin levels in female plasma significantly increased following G3-N or G4-N exposure. Preliminary electrophysiology data suggested that effects of both versions of G3 and G4 on hippocampal function may be gender dependent. Aircraft maintenance workers may be at risk if precautions are not taken to minimize long-term aircraft oil exposure.

Biomarkers of occupational exposure to pesticides: Systematic review of insecticides

INTRODUCTION

Pesticides are widely used around the world, and rural workers have greater risk of poisoning. The use of biomarkers for insecticides can contribute to the diagnosis and prevention of poisoning.

OBJECTIVE

To identify, in the scientific literature, the biomarkers of occupational exposure to insecticides of different insecticide classes.

METHODS

The PubMed, Lilacs and Embase databases were analyzed using a systematic search strategy and in accordance with the criteria established by the PRISMA methodology. Articles with information related to the use of biomarkers to identify active ingredients, or insecticide metabolites, or effects on the human biological matrices were analyzed.

RESULTS

A total of 840 studies was found, and 30 met the selection criteria. The search identified 118 results for insecticide biomarkers, of which 45% were of exposure, 42% of effect, and 14% of susceptibility. Additionally, 78 were possible biomarkers, and only 67 confirmed to be different biomarkers for insecticides. Acetylcholinesterase (AChE), butyrylcholinesterase (BuChE) and 3,5,6-trichloro-2-pyridinol (TCP-y), specific for Chlorpyrifos, were among the most common biomarkers identified; however, most metabolites found were non-specific.

CONCLUSION

Various insecticide biomarkers were mentioned; nonetheless, only a few are specific and used to identify the wide range of insecticides to which farm workers are exposed.

Pesticide Application Practices and Knowledge among Small-Scale Local Rice Growers and Communities in Rwanda: A Cross-Sectional Study

Background: Agriculture contributes a third of Rwanda’s GDP and is the main source of income for rural households, with 80% of the total population involved in crop and/or livestock production. The Government of Rwanda established the Muvumba rice project in 2011 amidst a policy shift towards rice as a national staple crop. However, the indiscriminate use of pesticides by local, low-income rice growers has raised concerns about potential human, animal and ecosystem health impacts as pesticide distribution and application are not strictly regulated. Although pesticide use can directly influence farmer health and ecosystems, little is known about small-scale farmers’ pesticide application practices and knowledge. We aimed to assess local application practices and understanding of pesticides to identify gaps in farmers’ knowledge on safe pesticide use and deviations from established standards and recommended practices. Methods: We conducted a cross-sectional study consisting of observations of pesticide practices and interviews with 206 small-scale rice growers in Nyagatare District, Rwanda, in March 2017. Descriptive statistical analyses (sample means, standard deviation and range) were performed, and we evaluated the association between farmers’ personal protective equipment (PPE) use and their education level and literacy status. Results: Over 95% of observed farmers did not comply with minimum standards for safe pesticide use, and 80% of respondents reported that they stored pesticides in their homes without personal protection measures. Education and literacy level were not significantly associated with PPE use. Additionally, 90% of respondents had experienced adverse health effects after using pesticides including intense headache, dizziness, stomach cramps, skin pain and itching, and respiratory distress. All respondents also reported animals in and around the rice scheme (cattle, birds, and fish) behaving abnormally or with signs consistent with pesticide exposure in the six months preceding the study, which may be linked to pesticide-contaminated water. Conclusions: Our study demonstrates potential for high exposure to pesticides for farmers, their families, and animals sharing rice-growing or downstream environments and points to the need for training on safe and effective pesticide use.

Gene silencing by RNA interference in the ectoparasitic mite, Psoroptes ovis

The presence of components of the RNA interference (RNAi) pathway in Psoroptes ovis, an ectoparasitic mite responsible for psoroptic mange, was investigated through interrogation of the P. ovis genome. Homologues of transcripts representing critical elements for achieving effective RNAi in the mite, Tetranychus urticae and the model organisms Caenorhabditis elegans and Drosophila melanogaster were identified and, following the development of a non-invasive immersion method of double stranded RNA delivery, gene silencing by RNAi was successfully demonstrated in P. ovis. Significant reductions in transcript levels were achieved for three target genes which encode the Group 2 allergen (Pso o 2), mu-class glutathione S-transferase (PoGST-mu1) and beta-tubulin (Poβtub). This is the first demonstration of RNAi in P. ovis and provides a mechanism for mining transcriptomic and genomic datasets for novel control targets against this economically important ectoparasite.

Mechanism for the acute effects of organophosphate pesticides on the adult 5-HT system

The neurotransmitter serotonin (5-HT) is involved in mood disorder aetiology and it has been reported that (organophosphate) OP exposure affects 5-HT turnover. The aim of this study was to elucidate the mechanism underlying OP effects on the adult 5-HT system. First, acute in vivo administration of the OP diazinon (0, 1.3, 13 or 39 mg/kg i.p.) to male Hooded Lister rats inhibited the activity of the cholinergic enzyme acetylcholinesterase in blood and in the hippocampus, dorsal raphe nucleus (DRN), striatum and prefrontal cortex. Diazinon-induced cholinesterase inhibition was greatest in the DRN, the brain's major source of 5-HT neurones. Second, acute in vivo diazinon exposure (0 or 39 mg/kg i.p.) increased the basal firing rate of DRN neurones measured ex vivo in brain slices. The excitatory responses of DRN neurones to α₁-adrenoceptor or AMPA/kainate receptor activation were not affected by in vivo diazinon exposure but the inhibitory response to 5-HT was attenuated, indicating 5-HT_1A autoreceptor down-regulation. Finally, direct application of the diazinon metabolite diazinon oxon to naive rat brain slices increased the firing rate of DRN 5-HT neurones, as did chlorpyrifos-oxon, indicating the effect was not unique to diazinon. The oxon-induced augmentation of firing was blocked by the nicotinic acetylcholine receptor antagonist mecamylamine and the AMPA/kainate glutamate receptor antagonist DNQX. Together these data indicate that 1) acute OP exposure inhibits DRN cholinesterase, leading to acetylcholine accumulation, 2) the acetylcholine activates nicotinic receptors on 5-HT neurones and also on glutamatergic neurones, thus releasing glutamate and activating 5-HT neuronal AMPA/kainate receptors 3) the increase in 5-HT neuronal activity, and resulting 5-HT release, may lead to 5-HT_1A autoreceptor down-regulation. This mechanism may be involved in the reported increase in risk of developing anxiety and depression following occupational OP exposure.

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Organophosphate exposure inhibits dorsal raphe nucleus cholinesterase activity.

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Organophosphate oxon exposure activates 5-HT neurones in the dorsal raphe nucleus.

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Nicotinic and AMPA receptors mediate the oxon-induced activation of 5-HT neurones.

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Organophosphate exposure attenuates the response to 5-HT1A autoreceptor activation.

Low-level repeated exposure to diazinon and chlorpyrifos decrease anxiety-like behaviour in adult male rats as assessed by marble burying behaviour

Occupational exposure to organophosphate (OPs) pesticides is reported to increase in the risk of developing anxiety and depression. Preclinical studies using OP levels, which inhibit acetylcholinesterase activity, support the clinical observations, but little is known of the effects of exposure below this threshold. We examined the effects of low level OP exposure on behaviours and neurochemistry associated with affective disorders. Adult rats were administered either diazinon (1 mg/kg i.p.) which is present in sheep dip and flea collars, chlorpyrifos (1 mg/kg i.p.) which is present in crop sprays, or vehicle for 5 days. OP exposure did not affect acetylcholinesterase activity (blood, cerebellum, caudate putamen, hippocampus, prefrontal cortex), anhedonia-like behaviour (sucrose preference), working memory (novel object recognition), locomotor activity or anxiety-like behaviour in the open field arena. In contrast OP exposure attenuated marble burying behaviour, an ethological measure of anxiety. The diazinon-induced reduction in marble burying persisted after exposure cessation. In comparison to vehicle, dopamine levels were lowered by chlorpyrifos, but not diazinon. 5-HT levels and turnover were unaffected by OP exposure. However, 5-HT transporter expression was reduced by diazinon suggesting subtle changes in 5-HT transmission. These data indicate exposure to occupational and domestic OPs, below the threshold to inhibit acetylcholinesterase, can subtly alter behaviour and neurochemistry.

Incidence and prevalence of Parkinson's disease among Navajo people living in the Navajo nation

Parkinson's disease (PD) is largely unstudied among American Indians. Unique populations might harbor clues to elusive causes. We describe the incidence and prevalence of PD among Navajo people residing in the Navajo Nation, home to the largest American Indian tribe in the United States. We analyzed 2001-2011 inpatient and outpatient visit data for Navajo people obtained from the Indian Health Service, which provides health care to American Indian people living on the Navajo Reservation. Cases were defined by at least two inpatient or outpatient visits with the diagnosis of PD. Crude and age-adjusted incidence and prevalence rates were calculated overall as well as by age, sex, region of residence, and time period. Five hundred twenty-four Navajo people with median age-at-onset of 74.0 years were diagnosed with PD during the study period, yielding an average annual crude incidence rate of 22.5/100,000. Age-specific incidence was 232.0 for patients 65 years of age or older and 302.0 for 80 years of age or older. Age-adjusted incidence was 35.9 overall (238.1 for ≥65 years), was higher in men than in women (47.5 vs. 27.7; P<0.001), varied by region (P=0.03), and was similar between time periods (2002-2004 vs. 2009-2011). The age-adjusted point prevalence rate was 261.0. The rate of PD among Navajo People appears to be as high as or higher than rates reported in many other populations. Rates increased to the highest age group, consistent with population-based studies. Further investigation is warranted to examine risk factors for PD in this remote population.

Pesticide exposure and screen-positive neuropsychiatric disease in British sheep farmers

BACKGROUND

Epidemiological evidence linking low dose pesticide exposure and chronic ill-health in UK sheep farmers is limited. Our aim was to examine whether neuropsychiatric disorders were associated with low dose chronic and/or more acute pesticide exposure in sheep farmers.

METHODS

A cohort of British farmers working in the 1970s was sent a screening questionnaire which asked about their health and work history. The prevalence of screen-positive depression, dementia, Parkinsonism and neuropathy was determined using a priori algorithms. Self-reported pesticide exposure was assessed by whether the participant had ever handled the pesticide concentrate (for low dose chronic exposure) or sought advice for pesticide poisoning (acute exposure) and participants categorised into those with only acute or chronic exposure, those with both acute and chronic exposure and those with neither acute nor chronic exposure. Associations between acute and chronic pesticide exposure, and screen-positive ill-health were determined after adjustment for demographic, lifestyle, occupation and somatic severity scores and other variables.

RESULTS

In those participants, who had never sought advice for pesticide poisoning, handling the pesticide concentrate for treating sheep was associated with elevated ORs for screen-positive neuropathy (ORadi 1.57 95%CI 0.97-2.54) and Parkinsonism (ORadj 1.56 95%CI 0.95-2.56) but not depression or dementia. In those participants who had handled the pesticide concentrate, seeking advice for pesticide poisoning was associated with screen-positive depression (Odds ratio, ORadj=9.97 95%CI 4.76-20.8 ), dementia (OR=6.94 95%CI 3.44-14.0), Parkinsonism (ORadj=4.77 95% 2.39-9.52), and neuropathy (ORadj=4.77 95%CI 2.39-9.52). Adjustment for somatic severity score modified little the associations with pesticide handling in those not acutely exposed but reduced the ORs for seeking advice for pesticide poisoning in those exposed chronically. Furthermore, stratification of results based upon somatic severity score indicated that the highest ORs for handling the pesticide concentrate associated with neuropathy and Parkinsonism were found in those participants whose somatic score was minimal.

CONCLUSIONS

Results are consistent with low-dose exposure to pesticides being associated with screen-positive neuropathy and Parkinsonism but the stronger associations between seeking advice for pesticide poisoning and screen-positive ill-health suggest that acute pesticide exposure remains an important determinant of ill-health. Further work is required to better delineate to what extent low dose exposures may contribute to ill-health in populations without acute exposures. Somatising tendency does not appear to play an important role in this population.

Prevalence of Parkinson disease among the Navajo: a preliminary examination

BACKGROUND

The prevalence of Parkinson disease (PD) varies by geographic location and ethnicity, but has never been studied among the Navajo.

METHODS

Period prevalence was calculated using the number of people diagnosed with PD in the Shiprock Service Unit Indian Health Service database during 1995-1999, 2000-2004, and 2005-2009 as the numerator, and the number seen for any reason as the denominator. Age-standardized rates were calculated using the 2000 US population.

RESULTS

During 2005-2009, 126 people were seen with PD (crude prevalence = 203.7/100,000 population). The age-adjusted rate was 335.9 (95% C. I. 277.8-394.0) overall, 438.5 (95% C.I. 336.5-540.5) in men and 259.7 (95% C.I. 192.8-326.7; p = 0.004) in women. The adjusted rate increased with age: 788.8 (95% C.I. 652.0-925.7) for age 40 and above to 1964.9 (95% C.I. 1613.7-2316.1) for age 60 and above. Adjusted rates were 246.6 (95% C.I. 187.2-306.0) in 1995-1999 and 284.7 (95% C.I. 227.0-342.4) in 2000-2004.

CONCLUSION

Parkinson disease appears common among the Navajo. Estimates increased with age and time, and were higher in men. In-person interviews are needed to confirm these estimates, and to determine incidence, quality of care, and risk factors for PD among the Navajo.

Dermal exposure associated with occupational end use of pesticides and the role of protective measures

BACKGROUND

Occupational end users of pesticides may experience bodily absorption of the pesticide products they use, risking possible health effects. The purpose of this paper is to provide a guide for researchers, practitioners, and policy makers working in the field of agricultural health or other areas where occupational end use of pesticides and exposure issues are of interest.

METHODS

This paper characterizes the health effects of pesticide exposure, jobs associated with pesticide use, pesticide-related tasks, absorption of pesticides through the skin, and the use of personal protective equipment (PPE) for reducing exposure.

CONCLUSIONS

Although international and national efforts to reduce pesticide exposure through regulatory means should continue, it is difficult in the agricultural sector to implement engineering or system controls. It is clear that use of PPE does reduce dermal pesticide exposure but compliance among the majority of occupationally exposed pesticide end users appears to be poor. More research is needed on higher-order controls to reduce pesticide exposure and to understand the reasons for poor compliance with PPE and identify effective training methods.

Acute ill-health in sheep farmers following use of pesticides

BACKGROUND

Sheep farmers often complain of acute ill-health, known colloquially as 'dipper's flu', immediately after treating sheep with pesticides. There have been few prospective epidemiological studies to determine it's nature and incidence. Aims To determine the nature and frequency of symptoms occurring in farmers treating sheep for ectoparasites.

METHODS

In a longitudinal study, farmers who planned to treat their sheep for ectoparasites were recruited. Farmers kept a symptom diary for 7 days after starting pesticide treatment. Symptoms reported on days 1-6 were compared to those reported on day 7 via the McNemar's test and with previously published literature definitions of dipper's flu. A principal component analysis (PCA) was carried out on new symptoms occurring on days 1 and 2.

RESULTS

Of 781 farmers recruited, 352 farmers (45%) completed the symptom diary. In the 7 days after starting pesticide treatment, symptom complex reporting typically peaked on day 2, but few farmers (7 or less; <2%) were identified as having dipper's flu using literature definitions. However, PCA identified two new patterns of symptom complexes that accounted for 35% of the variance. A pyrexial factor consisted of four symptom complexes (feeling generally ill; feeling sweaty, shivery, feverish, hot or cold; feeling unusually tired; and having a headache) and a respiratory factor consisted of three symptom complexes (runny, stuffy, blocked or irritated nose; cough, shortness of breath or wheeze; and eye irritation).

CONCLUSIONS

Existing definitions of dipper's flu do not adequately describe symptoms that occur following the treatment of sheep for ectoparasites.

Systematic review of biomonitoring studies to determine the association between exposure to organophosphorus and pyrethroid insecticides and human health outcomes

For the appropriate protection of human health it is necessary to accurately estimate the health effects of human exposure to toxic compounds. In the present review, epidemiological studies on the health effects of human exposure to organophosphorus (OP) and pyrethroid (PYR) insecticides have been critically assessed. This review is focused on studies where the exposure assessment was based on quantification of specific biomarkers in urine or plasma. The 49 studies reviewed used different epidemiological approaches and analytical methods as well as different exposure assessment methodologies. With regard to OP pesticides, the studies reviewed suggested negative effects of prenatal exposure to these pesticides on neurodevelopment and male reproduction. Neurologic effects on adults, DNA damage and adverse birth outcomes were also associated with exposure to OP pesticides. With regard to exposure to PYR pesticides, there are currently few studies investigating the adverse health outcomes due to these pesticides. The effects studied in relation to PYR exposure were mainly male reproductive effects (sperm quality, sperm DNA damage and reproductive hormone disorders). Studies' findings provided evidence to support the hypothesis that PYR exposure is adversely associated with effects on the male reproductive system. The validity of these epidemiological studies is strongly enhanced by exposure assessment based on biomarker quantification. However, for valid and reliable results and conclusions, attention should also be focused on the validity of the analytical methods used, study designs and the measured toxicants characteristics.

Gene-environmental interactions and organophosphate toxicity

Organophosphates (OPs) are an important class of insecticides that in the UK have been widely used for treating sheep for ectoparasites as well as in other sectors of the farming industry. Health problems associated with acute OP toxicity are well defined but, ill-health induced by chronic exposures to OPs remains controversial. A substantial number of sheep farmers complain of chronic ill-health which they attribute to repeated exposure to OPs. If OPs were associated with chronic ill-health then individuals with specific defects in OP metabolism might be expected to be at greater risk of ill-health following exposure. To examine such a hypothesis, the characterisation of both OP exposure and those pathways which lead to the formation and removal of the active OP metabolites becomes important. A wide range of OPs have previously been used to treat sheep but currently the only OP licenced for treating sheep is diazinon. Immediately after treatment, farmers' urines contain detectable levels of OP metabolites but few farmers have a significant decrease in plasma cholinesterase activity. Diazinon, like chlorpyrifos, is an organothiophosphate which is metabolised, particularly by cytochrome p450s, to the corresponding active oxon form. CYP metabolism also leads to the inactivation of the parent compound and the relative balance of inactivation and activation can depend upon the specific OP and the CYP isoform. OP oxons are inactivated by serum paraoxonase (PON1) and mice lacking PON1 activity are susceptible to oxon and parent OP induced toxicity. PON1 polymorphisms at positions 192 (R form with arginine at 192 and Q with glutamine) and 55 (L form with a leucine and a M form with methionine) influence paroxonase activity. The effect of the Q192R polymorphism is substrate specific with reports indicating that diazoxon is metabolised less by the R isoform. In a study of sheep farmers within the UK, the R allele was associated with an increased risk of self-reported chronic ill-health, a result consistent with the hypothesis that this ill-health may have been caused by OPs. Studies in other populations exposed to pesticides also show associations between ill-health and PON1 Q192R polymorphisms but not consistently so. This is not surprisingly given that exposure is often poorly characterised. In vivo models also suggest that PON1 genotypes may have little influence on susceptibility at low doses of the parent OP. Hence further work is required not only to better characterise OP exposure in humans populations but also to identify those populations susceptible to OP toxicity.

Fenamiphos and related organophosphorus pesticides: environmental fate and toxicology

In this review, we emphasize recent research on the fate, transport, and metabolism of tree selected organophosphorus pesticides (fenamiphos, isofenphos, and coumaphos) in soil an water environments. This review is also concerned with the side effects of these pesticides on nontarget organisms. Despite the fact that fenamiphos is not very mobile, its oxides have been detected in the groundwaters of Western Australia. Most organophosphorus pesticides generally are chemically unstable and underfo microbial degradation in soil and water environments. Enhanced biodegradation of many organophosphorus pesticides upon their repeted applications to soil and water is well established. Myriads of soil microorganisms, bacteria in particular, exhibit an exceptional capacity to transform many organophosphorus pesticides. Fenamiphos can undergo rapid microbially mediated degradation via oxidation to its oxides (sulfoxide and sulfone) and eventually to CO2 and water in soils, or via hydrolysis, in cultures of the soil bacterium, Brevinbacterium sp. There is evidence for enhanced biodegradation of (i) isofenphos in soils with a long history of use and (ii) coumaphos in cattle dip by bacterial cultures to chlorferon and diethylthiophosphoric acid.

Neurobehavioural effects of pesticides with special focus on organophosphorus compounds: which is the real size of the problem?

The risk of neurobehavioural impairment as a consequence of a prolonged, low dose exposure to neurotoxic pesticides is not clearly demonstrated despite numerous publications addressing the topic. We reviewed the 24 papers published on human neurobehavioural effects of organophosphorus and/or carbamates pesticides up to May 1st 2008. Variables evaluated were compound/s addressed, number of subjects, approach to measure or estimate exposure, characteristics of control groups and presence of confounders, methodological approach, and type of alteration, taking into account cognitive, sensory-motor, psychological, and psychomotor measures. A total of 6 papers considered the whole spectrum of functions, the studies yielding positive or uncertain results were 13 (68%) for cognitive function, 11 (69%) for psychomotor function, 11 (65%) for sensory-motor function, and 11 (65%) for psychological function impairment. In 46% of the positive studies a previous severe acute poisoning was reported. Exposure levels were measured only in 5 studies, and very often there were problems in the selection of controls, and firm conclusions on the risk of neurobehavioural effects cannot be reached yet. The main limits of the available data are: limited number of studies and compounds addressed, significant differences in the approach among studies, poor concordance of the results of different studies, and difficulties in controlling confounding factors. Nevertheless, there are sufficient data to conclude that neurobehavioural impairment might be the consequence of an acute poisoning, and possibly the consequence of relatively high and prolonged exposures.

The paraoxonase (PON1) Q192R polymorphism is not associated with poor health status or depression in the ELSA or INCHIANTI studies

BACKGROUND

The human paraoxonase (PON1) protein detoxifies certain organophosphates, and the PON1 Q192R polymorphism (rs662) affects PON1 activity. Groups with higher dose exposure to organophosphate sheep dips or first Gulf War nerve toxins reported poorer health if they had 192R, and these associations have been used to exemplify Mendelian randomization analysis. However, a reported association of 192R with depression in a population-based study of older women recently cast doubt on the specificity of the higher dose findings. We aimed to examine associations between the PON1 Q192R polymorphism and self-reported poor health and depression in two independent population-based studies.

METHODS

We used logistic regression models to examine the associations in men and women aged 60-79 years from the English Longitudinal Study of Ageing (ELSA, n = 3158) and InCHIANTI (n = 761) population studies. Outcomes included the Center for Epidemiologic Studies Depression (CES-D) scale, self-rated general health status and (in ELSA only) diagnoses of depression.

RESULTS

The PON1 Q192R polymorphism was not associated with self-reported poor health {meta-analysis: odds ratio (OR) = 1.01 [confidence interval (CI) 0.91-1.13], P = 0.80} or depressive symptoms in either study or in meta-analyses [CES-D: OR = 1.01 (CI 0.87-1.17), P = 0.90]. There was also no association with histories of diagnosed depression in ELSA [OR = 1.03 (CI 0.82-1.30), P = 0.80].

CONCLUSIONS

We found no evidence of an association between the PON1 Q192R polymorphism and poor general or mental health in two independent population-based studies. Neither the claimed Q192R association with depression in the general population nor its theoretical implications were supported.

A cohort study of pesticide poisoning and depression in Colorado farm residents

PURPOSE

Depressive symptoms have been associated with pesticide poisoning among farmers in cross-sectional studies, but no longitudinal studies have assessed the long-term influence of poisoning on depressive symptoms. The purpose of this study was to describe the associations between pesticide poisoning and depressive symptoms in a cohort of farm residents.

METHODS

Farm operators and their spouses were recruited in 1993 from farm truck registrations using stratified probability sampling. The Center for Epidemiologic Studies-Depression scale was used to evaluate depression in participants using generalized estimating equations. Baseline self-reported pesticide poisoning was the exposure of interest in longitudinal analyses.

RESULTS

Pesticide poisoning was significantly associated with depression in three years of follow-up after adjusting for age, gender, and marital status (odds ratio [OR] 2.59; 95% confidence interval [CI] 1.20-5.58). Depression remained elevated after adjusting for health, decreased income, and increased debt (OR 2.00; CI 0.91-4.39) and was primarily due to significant associations with the symptoms being bothered by things (OR 3.29; CI 1.95-5.55) and feeling everything was an effort (OR 1.93; CI 1.14-3.27).

CONCLUSIONS

Feeling bothered and that everything was an effort were persistently associated with a history of pesticide poisoning, supportive of the hypothesis that prolonged irritability may result from pesticide poisoning.

Exposure profiles of pesticides among greenhouse workers: implications for epidemiological studies

The aim of this study was to assess exposure to pesticides for a longitudinal epidemiological study on adverse reproduction effects among greenhouse workers. Detailed information on pesticide use among greenhouse workers was obtained on a monthly basis through self-administered questionnaires and subsequent workplace surveys. Questionnaires were filled in for a whole year. Dermal exposure rankings were developed for each task using the observational method Dermal Exposure Assessment Method (DREAM). Exposure scores were calculated for each worker for each month during the year, taking into account frequency, duration and exposure intensity for each task. A total number of 116 different active ingredients were used in the population, whereas a mean number of 15 active ingredients were applied per greenhouse. DREAM observations provided insight into the exposure intensity of 12 application techniques and three mixing and loading activities. Relatively high DREAM scores were obtained for scattering, fogging, dusting, and mixing and loading of powders. Observations with DREAM indicated that application with a horizontal ground-boom, motor driven boom, and bulb shower resulted in low dermal exposure. Exposure scores showed substantial variation between workers and over the year. It can be concluded that exposure variation between- and within greenhouses is very large, both in terms of chemical composition and exposure intensity. This may be a significant contributor to the inconsistent results of studies evaluating health effects of pesticide exposure.

Acute symptoms following work with pesticides

BACKGROUND

Serious accidental poisoning by pesticides is rare in the UK, but more minor pesticide-related illness may be under-reported. Anecdotally, use of sheep dip has been linked with flu-like symptoms.

AIM

To explore the frequency, nature and determinants of acute symptoms following work with pesticides.

METHODS

A postal survey of men in three rural areas of England and Wales provided data on occupational use of five categories of pesticide, occurrence of 12 specified symptoms within 48 h of using pesticides and tendency to somatize. Risk factors for pesticide-related symptoms were assessed by modified Cox regression.

RESULTS

Of 10 765 responders (response rate = 31%), 4108 had at some time used pesticides occupationally, including 935 (23%) who reported symptoms following such work on at least one occasion. In two areas, acute symptoms were most frequent following use of sheep dip (29 and 32% of users), but in the third area the rate was significantly lower (13% of users). The relative frequency of symptoms was similar for all five categories of pesticide, and flu-like symptoms did not cluster unusually among users of sheep dip. Risk of pesticide-related symptoms increased with somatizing tendency (prevalence ratio for highest versus lowest category 2.4, 95% confidence interval 2.0-3.0) and was higher in men who had used pesticides most often or handled concentrate.

CONCLUSION

Acute symptoms are common following work with pesticides, but in many cases the illness may arise through psychological rather than toxic mechanisms.

Neuropsychiatric symptoms in past users of sheep dip and other pesticides

OBJECTIVES

To explore the prevalence and pattern of neuropsychiatric symptoms in past users of sheep dip and other pesticides.

METHODS

From a postal survey of men born between 1933 and 1977 and resident in three rural areas of England and Wales (response rate 31%), data were obtained on lifetime history of work with pesticides, neurological symptoms in the past month, current mental health and tendency to be troubled by non-neurological somatic symptoms (summarised as a somatising tendency score). Risk factors for current neuropsychiatric symptoms were assessed by modified Cox regression.

RESULTS

Data were available for 9844 men, including 1913 who had worked with sheep dip, 832 with other insecticides but not sheep dip and 990 with other pesticides but never with sheep dip or insecticides. Neurological symptoms were consistently 20-60% more common in past users of sheep dip than in men who had never worked with pesticides, but their prevalence was also higher in men who had worked only with pesticides other than sheep dip or insecticides. They clustered strongly within individuals, but this clustering was not specific to men who had worked with sheep dip. Reporting of three or more neurological symptoms was associated with somatising tendency (prevalence ratio (PR) 15.0, 95% CI 11.4 to 19.5, for the highest vs the lowest category of somatisation) and was more common in users of sheep dip (PR 1.3, 95% CI 1.0 to 1.6), other insecticides (PR 1.4, 95% CI 1.0 to 1.8) and other pesticides (PR 1.3, 95% CI 1.0 to 1.7) than in non-users. Among users of sheep dip, prevalence was higher in men who had dipped most often, but not in those who had worked with sheep dip concentrate. Past use of pesticides was not associated with current anxiety or depression.

CONCLUSION

Neurological symptoms are more common in men who have worked with sheep dip, but the association is not specific to sheep dip or insecticides. A toxic cause for the excess cannot be ruled out, but several features of our observations suggest that psychological mechanisms have a role.

Association of pesticide exposure with neurologic dysfunction and disease

Poisoning by acute high-level exposure to certain pesticides has well-known neurotoxic effects, but whether chronic exposure to moderate levels of pesticides is also neurotoxic is more controversial. Most studies of moderate pesticide exposure have found increased prevalence of neurologic symptoms and changes in neurobehavioral performance, reflecting cognitive and psychomotor dysfunction. There is less evidence that moderate exposure is related to deficits in sensory or motor function or peripheral nerve conduction, but fewer studies have considered these outcomes. It is possible that the most sensitive manifestation of pesticide neurotoxicity is a general malaise lacking in specificity and related to mild cognitive dysfunction, similar to that described for Gulf War syndrome. Most studies have focused on organophosphate insecticides, but some found neurotoxic effects from other pesticides, including fungicides, fumigants, and organochlorine and carbamate insecticides. Pesticide exposure may also be associated with increased risk of Parkinson disease; several classes of pesticides, including insecticides, herbicides, and fungicides, have been implicated. Studies of other neurodegenerative diseases are limited and inconclusive. Future studies will need to improve assessment of pesticide exposure in individuals and consider the role of genetic susceptibility. More studies of pesticides other than organophosphates are needed. Major unresolved issues include the relative importance of acute and chronic exposure, the effect of moderate exposure in the absence of poisoning, and the relationship of pesticide-related neurotoxicity to neurodegenerative disease.

Health Effects of Chronic Pesticide Exposure: Cancer and Neurotoxicity

Pesticides are widely used in agricultural and other settings, resulting in continuing human exposure. Epidemiologic studies indicate that, despite premarket animal testing, current exposures are associated with risks to human health. In this review, we describe the routes of pesticide exposures occurring today, and summarize and evaluate the epidemiologic studies of pesticide-related carcinogenicity and neurotoxicity in adults. Better understanding of the patterns of exposure, the underlying variability within the human population, and the links between the animal toxicology data and human health effects will improve the evaluation of the risks to human health posed by pesticides. Improving epidemiology studies and integrating this information with toxicology data will allow the human health risks of pesticide exposure to be more accurately judged by public health policy makers.

Neurobehavioral effects of pesticides: state of the art

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.

Di-alkyl phosphate biomonitoring data: assessing cumulative exposure to organophosphate pesticides

The 1996 Food Quality Protection Act (FQPA) requires the evaluation of both aggregate and cumulative health risks from pesticides (FFDCA 408(b)(2)(D)(v) and (vi).) Organophosphate (OP) pesticides are the first class of chemicals to undergo FQPA mandated aggregate and cumulative assessments. In this report, summary data on biomonitoring for urinary levels of six alkyl phosphate (AP) metabolites of OPs, as reported in the initial, March 2001, U.S. Centers for Disease Control and Prevention's (CDC) "National Report on Human Exposure to Environmental Chemicals," are compared to EPA modeled estimates of OP exposure reported in Registration Eligibility Decision documents (REDs), Interim REDs and to currently reported cumulative exposure estimates in the EPA's Cumulative Risk Assessment of the Organophosphate Pesticides. This comparison indicates that EPA's aggregate exposure estimates (dietary, drinking water, and non-dietary residential exposures) for many individual OPs were greater than the cumulative estimate for all OPs combined based on the CDC AP biomonitoring data. The results also suggest that EPA's screening level assessments of OPs, while being qualitative indicators of the relative importance of various exposure sources, are not good quantitative indicators of actual exposures. However, the mean biomonitoring estimate of cumulative OP exposure appears to exceed the EPA's subsequent preliminary estimate of cumulative OP exposure by as much as the REDs appear to overestimate the biomonitoring results. While the conservatism, tendency to overestimate exposure, in the individual REDs is readily acknowledged, the conservatism and limitations of applying currently available CDC AP biomonitoring data to evaluate human exposure to OPs are not as readily apparent. We postulate that oral absorption of non-anti cholinergic, pre-hydrolyzed OPs, sources of APs other than pesticides, and the conservative result of summing exposure from each AP at the geometric mean contribute to non-quantified overestimates of absorbed dosage from the CDC biomonitoring data reported in March 2001. CDC AP biomonitoring data may serve a useful purpose in providing an upper bound estimate of absorbed dosage for "ground truthing" aggregate exposure estimated from first tier models used in REDs, but at best may provide only a credible "target" for the complex cumulative exposure assessment models currently under development. The reliability of quantitative estimates of OP exposure levels will improve as cumulative risk exposure models are validated over time and under use conditions prevalent at the time the AP biomonitoring samples are collected. Analyses contained herein should be revisited and compared to the CDC Second National Report on Human Exposure to Environmental Chemicals ( http://www.cdc.gov/exposurereport), released to the public on January 31, 2003, and the final EPA OP Cumulative Risk Assessment.

Immunotoxicity of organophosphorous pesticides

This study reviews the toxic effects of organophosphate (OP) pesticides on the immune systems and immune functions of invertebrates, fish, and higher vertebrate wildlife. The fundamental features and mechanisms of OP-induced immunotoxicity are illustrated with reference to parathion, chlorpyrifos, malathion, and diazinon. Immunotoxicity may be direct via inhibition of serine hydrolases or esterases in components of the immune system, through oxidative damage to immune organs, or by modulation of signal transduction pathways controlling immune functions. Indirect effects include modulation by the nervous system, or chronic effects of altered metabolism/nutrition on immune organs. Immunotoxicities are varied and include pathology of immune organs, and decreased humoral and/or cell mediated immunity. Altered non-specific immunity, decreased host resistance, hypersensitivity and autoimmunity are also features of immunotoxicity; although not all of these have been conclusively demonstrated in terms of pollutant exposure and immunotoxic effects in wildlife within individual experiments. Immunotoxicological biomarkers and biological monitoring tools are urgently needed to assess the extent of immunotoxicity in wildlife. Selection of universal biomarkers is hampered by the physiological diversity of immune systems in animals. However, by drawing on evidence from human epidemiology and tiered approaches in mammalian immunotoxicity evaluation, a selection of generic biomarkers of immunotoxicity in animals is suggested. Priorities for future research are also identified.

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

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 effect of low dose cumulative exposure to OPs. It is suggested that long term health effects may occur in at least some sheep dippers exposed to OPs over a working life, although the mechanisms are unclear.