Agricultural Pesticide Applications Research Articles

Functional paraoxonase 1 variants modify the risk of Parkinson's disease due to organophosphate exposure

BackgroundWe previously demonstrated that carriers of the “slower metabolizer” MM genotype of paraoxonase (PON1) who were also exposed to ambient organophosphate (OP) pesticides at their residences were at increased risk of developing Parkinson's disease (PD). Here, with a larger sample size, we extend our previous investigation to consider additional sources of ambient exposure and examined two additional functional PON1 variants. MethodsFrom 2001 to 2011, we enrolled incident cases of idiopathic PD and population controls living in central California. We genotyped three well-known functional PON1 SNPs: two exonic polymorphisms (PON1L55M and PON1Q192R) and the promoter region variant (PON1C-108T). Ambient exposures to diazinon, chlorpyrifos, and parathion at residential and workplace addresses were assessed using a validated geographic information system-based model incorporating records of agricultural pesticide applications in California. ResultsThe odds ratio (OR) for Caucasians exposed to OPs at either residential or workplace addresses varied by PON1 genotype; for exposed carriers of the “faster” metabolizer genotypes, ML or LL, we estimated lower odds ratios (range, 1.20–1.39) than for exposed carriers of the “slower” metabolizer genotype MM (range, 1.78–2.45) relative to unexposed carriers of the faster genotypes. We observed similarly increased ORs for exposure across PON1Q192R genotypes, but no differences across PON1C-108T genotypes. The largest ORs were estimated for exposed carriers of both PON1192QQ and PON155MM (OR range, 2.84–3.57). ConclusionsSeveral functional PON1 variants may act together to modify PD risk for ambient OP exposures. While either PON1L55M or PON1Q192R may be sufficient to identify increased susceptibility, carriers of both slow metabolizer variants seem most susceptible to OP exposures.

Sulfur management and miticide use in winegrapes grown in California

AbstractProper sulfur management in winegrapes may potentially reduce both insecticide/miticide use and the human/social problems associated with sulfur's impacts on air quality and odors, particularly in wine tourism regions. Data from California's unique Pesticide Use Report (PUR) database, which records agricultural pesticide applications on all crops throughout the state, are used to determine if either winegrape grower's choice of sulfur formulation (dust only, wettable only, or a combination) or overall sulfur use rates (pounds per acre planted) correlate with annual miticide and insecticide use in Fresno and Madera (hotter–drier) and Napa and Sonoma counties (cooler–damper). Annual sulfur use has declined by 36–55% in these counties from 1993 to 2009. In 2000, the greatest number of growers in each county were combination users; wettable users were higher in Napa (38%) and Sonoma (34%) than in Fresno (24%) and Madera (10%); and dust-only users varied little (15–19%) across the four counties. Data for 2005 and 2009 showed similar trends. The use of high-toxicity insecticides in Fresno was 387% higher than in Napa–Sonoma in 2000, but was 25 and 8% lower in 2005 and 2009, respectively. In Fresno, wettable sulfur users used less high-toxicity insecticides; while in Fresno and Madera dust users used less lower-risk insecticides than combination or wettable sulfur users. No significant differences in insecticide use were evident between the three sulfur use categories in Napa–Sonoma (P = 0.97). On average, dust users in Fresno–Madera used more high-toxicity miticides than combination or wettable sulfur users in 2000. That trend decreased in the data for 2005 and 2009. Average miticide use in Fresno–Madera was higher than in Napa–Sonoma by 1349% in 2000, 1103% in 2005 and 146% in 2009. Higher sulfur use intensities among individual growers in Fresno–Madera were positively correlated with greater use of high-toxicity miticides in 2000 and 2005, but not 2009. The comparable results for Napa–Sonoma were less clear. Since PUR data represent statewide information on pesticide use decisions in real-world farming scenarios, it can complement data from field and laboratory studies. Expanding these analyses to compare pesticide use by individual growers across years, or to correlate pesticide usage with any published mite field surveys may shed more light on the enigmatic relationship between sulfur fungicide use and mite outbreaks in winegrapes.

Controlling Sugar Beet Mortality Disease by Application of New Bioformulations

There is growing interests in the use of biological approaches to replace or reduce the application of chemical pesticides in modern agriculture. In this regard, antagonistic fungi and particularly bacteria have proved to be potential candidates. In the search for efficient alternative biofungicides, eight new Bioformulations were developed and prepared using two strains of Pseudomonas fluorescens (B1) and Bacillus coagulans (B2) isolated from different rhizospheric soils and plant roots of Iranian sugar beet fields. Biofor- mulations were developed using procedures described in the literature. Bioformulations included a talc-based powder and bentonite- based powder as inorganic carriers, and peat and rice bran as organic carriers. The results of our greenhouse experiment, where these bioformulations were applied to sugar beet seeds to control seedling mortality disease, showed that most of the treatments at different intervals (15, 30, 45 and 60 days after sowing) were effective in reducing the disease (compared to the untreated control). According to the results, six out of eight of the developed bioformulations, including Peat-B1, Peat-B2, R.B.-B2, Bent.-B1, Talc-B1 and Talc-B2, were more effective than commonly used fungicides (Carboxin-thiram) in controlling sugar beet mortality disease. Yet, two bioformula- tions (R.B.-B1 and Bent.-B2) were less effective than carboxin-thiram in the reduction of the disease incidence.

Measuring the effects of pesticides on bacterial communities in soil: A critical review

Extensive application of industrially-produced pesticides in agriculture has resulted in contamination of soil ecosystems. A variety of both cultivation-dependent and cultivation-independent methods can be applied to measure and interpret the effects of pesticide exposure. We review here the expanding panel of these methods in the specific context of responses of the soil bacterial microflora to pesticide exposure, and of ongoing advances in microbial molecular ecology, including metagenomics and new approaches for DNA sequencing. Several issues still need to be addressed in order to routinely evaluate the effect of pesticides on bacterial communities in soil in the future, and to make way for a widely accepted framework for risk assessment in agro-ecosystems that include bacterial indicators.

Determination of accuracy level of agricultural spraying application in Sanliurfa/ Turkey

When calibration, spraying height, applied pressure, volume rate, nozzle type and application time of equipment used in pesticide applications are incorrect, this causes the amount of agricultural pesticide applied per unit area to be more or less needed. A survey study was carried out on farmers in order to determine whether or not they adjust application pressure of pesticide equipment, nozzle type, volume rate, spraying height and calibration of spraying equipment needed for pesticide application to have values, and also whether or not they carry out agricultural pesticide application in accurate weather conditions such as wind speed, air temperature, relative humidity, temperature and application time. This research was conducted in 2008 by randomly determining 110 agricultural organizations located in villages in the center of Sanliurfa/Turkey and its districts. Survey study was carried out by taking data from pesticide applications processes made on products such as cotton, wheat, barley, lentils and corn which have been intensely produced in the region. It was determined that in general, farmers operated field sprayer at very high pressures in agricultural pesticide application and they did not adjust travel speed of boom sprayer based on the calibration of pesticide application equipment. Moreover, based on data obtained from survey studies,application operators and farmers did not know values of wind speed, temperature and relative humidity required for agricultural pesticide applications. Key words: Pesticide spraying applications, survey, accuracy level, spraying parameters.

Genetic variation in nucleotide excision repair pathway genes, pesticide exposure and prostate cancer risk

Previous research demonstrates increased prostate cancer risk for pesticide applicators and pesticide manufacturing workers. Although underlying mechanisms are unknown, human biomonitoring studies indicate increased genetic damage (e.g. chromosomal aberrations) with pesticide exposure. Given that the nucleotide excision repair (NER) pathway repairs a broad range of DNA damage, we evaluated interactions between pesticide exposure and 324 single-nucleotide polymorphisms (SNPs) tagging 27 NER genes among 776 prostate cancer cases and 1444 male controls in a nested case-control study of white Agricultural Health Study pesticide applicators. We determined interaction P values using likelihood ratio tests from logistic regression models and three-level pesticide variables (none/low/high) based on lifetime days of use weighted to an intensity score. We adjusted for multiple comparisons using the false discovery rate (FDR) method. Of the 17 interactions that met FDR <0.2, 3 displayed a monotonic increase in prostate cancer risk with increasing exposure in one genotype group and no significant association in the other group. Men carrying the variant A allele at ERCC1 rs2298881 exhibited increased prostate cancer risk with high versus no fonofos use [odds ratio (OR) 2.98; 95% confidence interval (CI) 1.65-5.39; P(interact) = 3.6 × 10(-4); FDR-adjusted P = 0.11]. Men carrying the homozygous wild-type TT genotype at two correlated CDK7 SNPs, rs11744596 and rs2932778 (r(2) = 1.0), exhibited increased risk with high versus no carbofuran use (OR 2.01; 95% CI 1.31-3.10 for rs11744596; P(interact) = 7.2 × 10(-4); FDR-adjusted P = 0.09). In contrast, we did not observe associations among men with other genotypes at these loci. While requiring replication, our findings suggest a role for NER genetic variation in pesticide-associated prostate cancer risk.

Living near agricultural pesticide applications and the risk of adverse reproductive outcomes: a review of the literature

ObjectivesThis systematic review evaluates the current epidemiological evidence on the association between living near agricultural pesticide applications and adverse reproductive outcomes, including congenital malformations, stillbirth, intrauterine growth retardation (IUGR), low...

Generalized Haber's Law for Exponential Concentration Decline, with Application to Riparian‐Aquatic Pesticide Ecotoxicity

A simple analytic solution to the dynamic version of Haber's law was derived, conditional on a specified toxic load exponent (n) and on exponential decline in environmental toxicant concentration. Such conditions are particularly relevant to assessing ecotoxicity risk posed (e.g., to juvenile salmonids) by agricultural organophosphate (OP) pesticides that are subject to degradation and/or dissipation. A dynamic Haber's law model was fit to previously published detailed data on lethality for two aquatic species induced by six agricultural OP pesticides, and more crude fits were obtained to less detailed data on five other OP and on two non-OP pesticides, indicating that for lethality, a range of 0.5 ≤ n ≤ 1.5 may be typical for OP pesticides. The AgDRIFT(®) stream deposition model was next used to establish that first-order or exponential loss, with dilution half-times on the order of ≤0.01 days, pertains approximately to pesticide residues in streams that arise after aerial application of agricultural pesticides 100 feet upwind. The analytic model was then applied to demonstrate that pesticide concentrations deposited in downwind streams following an aerial application are effectively diluted by about 50- to 300-fold from their initial concentration. Riparian ecotoxicity risk assessment models that ignore this effective dilution, and base pesticide-specific estimates of reduced survival on the initial concentrations, are therefore unrealistically conservative.

Evaluation of Chemical and Natural Resistance Inducers against Downy Mildew (Plasmopara viticola) in Grapevine

Chemical and natural resistance-inducing substances may be used to decrease the susceptibility of plants to various pathogens, thus reducing the application of pesticides in agriculture. This study evaluated the potential of biocontrol products and of plant extracts. The invoked mode of induced resistance was verified to control downy mildew on grapevine plants using leaf discs and potted vines. Induced resistance was determined by the increase of pathogenesis-related (PR) proteins, including peroxidase, polyphenol oxidase, β-1,3-glucanase, phenylalanine ammonia-lyase, stilbene synthase, β-1,3-glucanase, PR-1 protein, and caffeoyl-coenzyme A 3-<i>O</i>-methyltransferase. Candidate resistance inducers, including <i>Solidago canadensis</i> (CanG) extract<i>,</i> mycelium extract of <i>Penicillium crysogenum</i> (PEN), linoleic acid (LIN), and biocontrol agent <i>Aureobasidium pullulans</i> (Aureo), and chemical elicitors 3-dl-β-aminobutyric acid (BABA) and benzothiadiazole (BTH) were tested against <i>Plasmopara viticola</i> in potted vines grown outdoors. BABA, BTH, and CanG provided a protection of more than 80%, whereas PEN, LIN, and Aureo provided minimal protection. BABA and Aureo were not able to inhibit zoospores, whereas a concentration-dependent inhibition of zoospore mobility was observed for all other tested substances. BTH, CanG, PEN, and LIN induced the production of a broad spectrum of resistance-related metabolites, whereas Aureo did not cause any response. BABA provoked formation of necrotic spots and PR proteins immediately after inoculation. These results indicate the potential to partly induce natural resistance metabolites to enhance tolerance of grapevine plants to <i>P. viticola</i>, thus offering a synergistic effect when used with fungicides and aiding in reducing their ecological burden, even if they are not effective enough to replace them fully.

Determinants of Agricultural Pesticide Concentrations in Carpet Dust

Background: Residential proximity to agricultural pesticide applications has been used as a surrogate for exposure in epidemiologic studies, although little is known about the relationship with levels of pesticides in homes.Objective: We identified determinants of concentrations of agricultural pesticides in dust.Methods: We collected samples of carpet dust and mapped crops within 1,250 m of 89 residences in California. We measured concentrations of seven pesticides used extensively in agriculture (carbaryl, chlorpyrifos, chlorthal-dimethyl, diazinon, iprodione, phosmet, and simazine). We estimated use of agricultural pesticides near residences from a statewide database alone and by linking the database with crop maps. We calculated the density of pesticide use within 500 and 1,250 m of residences for 180, 365, and 730 days before collection of dust and evaluated relationships between agricultural pesticide use estimates and pesticide concentrations in carpet dust.Results: For five of the seven pesticides evaluated, residences with use of agricultural pesticides within 1,250 m during the previous 365 days had significantly higher concentrations of pesticides than did residences with no nearby use. The highest correlation with concentrations of pesticides was generally for use reported within 1,250 m of the residence and 730 days before sample collection. Regression models that also accounted for occupational and home use of pesticides explained only a modest amount of the variability in pesticide concentrations (4–28%).Conclusions: Agricultural pesticide use near residences was a significant determinant of concentrations of pesticides in carpet dust for five of seven pesticides evaluated.

Living near agricultural pesticide applications and the risk of adverse reproductive outcomes: a review of the literature

Over the last decade, there has been growing concern about the possible health effects, including a number of adverse reproductive outcomes, from pesticide exposure of people living near agricultural fields. This systematic review evaluates the current epidemiological evidence on the association between living near agricultural pesticide applications and adverse reproductive outcomes, including congenital malformations, stillbirth, intrauterine growth retardation (IUGR), low birthweight, preterm birth and miscarriage. We identified and reviewed 25 studies from a systematic search of the main scientific databases and other sources published in 1950-2007. Study methods and main results were summarised and tabulated according to the year of study, design and type of adverse reproductive outcome. The levels of evidence for reproductive toxicity in humans contributed by each study were assessed and the main limitations associated with these studies discussed. Residential proximity to agricultural pesticide applications may be an important source of ambient environmental exposure, but because of the underlying methodological difficulties, the strength of evidence for its relationship with adverse reproductive outcomes is generally weak and varied between outcomes. The evidence suggested an association for congenital malformations, but because of methodological limitations, such as poor exposure measurement and potentially inadequate control of confounding, a firm conclusion remains beyond reach. For the other outcomes (stillbirth, IUGR, low birthweight, preterm birth and miscarriage) the evidence for any associations was equivocal at best, but some leads warrant further investigation. Improved exposure assessment methods are needed to obtain a more reliable assessment of any risks.

Pesticide Analysis of Bee and Bee Product Samples

Bee products possess therapeutic properties and are the source of many essential trace elements, which is why they are regarded as valuable food products. Honey bees may bring to the hive numerous contaminants deposited on the plants they visit, including pesticide without xenobiotics. The large-scale application of pesticides in agriculture and horticulture can lead to mass mortality among bees, and the chemicals find their way into bee products. The presence of xenobiotics in these products can lower their quality and cause their properties to deteriorate, which in consequence may endanger human health. All this means that the analysis of bees, honey and other bee products is becoming a matter of increasing urgency. In this context new analytical methodologies are needed, enabling a wide spectrum of analytes to be assayed in a single sample and during one analytical run. Attention is focused on new techniques of sample preparation and extract cleanup prior to the final determination step. Besides characterizing the honey bee and bee products, the article analyzes the literature data on the latest methodological developments for determining levels of a wide range of pesticides.

Simulating and Characterizing Agricultural Ground Applications for Soil VOC Deposition Studies

Abstract Reactive volatile organic compounds (VOCs) play a major role in the formation of photochemical oxidants in the atmosphere by reacting with oxides of nitrogen and solar ultraviolet energy producing ozone, which is a criteria pollutant regulated under the National Ambient Air Quality Standards. The United States is one of the most agriculturally productive countries in the world due in part to the use of chemical pesticides that consist of active ingredients that are typically non-volatile or semi-VOCs and inert ingredients such as solvents, emulsifiers, and diluents that may also be volatile. Presently, the VOC determination of emission factors from agricultural pesticide applications assumes that all of the inert VOC ingredients volatilize. This research focuses on the development of a laboratory methodology for applying agricultural spray formulations in accurate and measurable levels to support VOC deposition onto and loss from soil surfaces. Adapting a laboratory spray table system with a modified spray and deposition sampling scheme resulted in repeatable spray applications, with the deposition pattern being mapped across the treatment area. These mapped deposition values allow for measurements from soil samples to be correlated with actual spray deposition. This methodology provides for a rapid and repeatable means for surveying VOC deposition and losses from a variety of spray formulations under varying spray rates and spray droplet sizes.

Risk assessment induced by knapsack or conventional motor sprayer on pesticides applicators and farm workers in cotton season

Fakous Province in the Sharkia Governorate constitutes one of the largest agricultural areas in Egypt. The majority of people in this province rely on subsistence agriculture. In the cotton cultivation season the continuous application of pesticides is commonly used to increase agricultural productivity, using different types of spraying equipment. In this study a cohort of 210 intensive agricultural pesticide applicators and farm workers from Sawada and Akyad Elkepplia villages in Fakous Province were assessed according to the type of spraying equipment they used. Conventional motor (300 l/feddan or 0.42 ha) and knapsack motor sprayer (20 l/feddan) were commonly used by farmers. Contamination on applicators was detected on head, body (thorax/abdomen) and legs at different percentages according to the spraying tools. The recorded results revealed that contamination with pesticides due to knapsack motor sprayers 0.76% on head, 4.8% on body and 5.8% on legs; however, conventional motor sprayers induce contamination of 3.6% on head, 23.7% on body and 29.1% on legs. Several criteria for estimating pesticide contamination by previous delivery systems were used. The most important reference biomarker was serum acetyl cholinesterase (AchE) depression. Sprayers showed changes in serum glucose levels as well as reduced erythrocytic glutathione levels (GSH). However, an increase in both total serum protein and albumin was recorded also, alongside elevation in lipid peroxidation biomarker malondialdehyde (MDA). Changes in serum biochemistry regarding enzymes reflecting cytotoxicity were also recorded, such as inhibition of alanine aminotransferase (ALT) and glutathione-S-transferase (GST). An increase in aspartate aminotransferase (AST) and glutathione reductase (GR) was observed particularly in conventional motor sprayers. Changes in enzymes activities found in this study are linked to the adverse health effects related to chronic pesticide toxicity that may lead to pathophysiological diseases, cancer or neurodegenerative disorders, which warrants further investigation.

Pesticides and Autism: Incorporating Temporal Vulnerability as an Unknown Parameter

ISEE-0333 Background and Objectives: Investigators have suggested that exposure to diverse pesticides during gestation could be associated with development of autism spectrum disorders (ASD) in childhood. Because little is known about ASD pathophysiology, investigation of this possibility requires a priori specification of hypothesized temporal periods of vulnerability of the embryo/fetus. This necessity may decrease the sensitivity of hypothesis tests, require unwieldy numbers of tests, or underestimate parameter variances for associations. We formulated day-specific vulnerability as a vector in a hierarchical Bayesian model to examine temporal patterns of associations of maternal residential proximity to agricultural applications of several pesticides with ASD in children. Methods: 465 children with ASD born in California's Central Valley were matched with 6975 controls based on date of mother's last menstrual period. Day-specific agricultural pesticide applications within 500 meters of mother's residence at time of birth were quantified from 10 months preconception to the postnatal period. The conditional logistic regression model was specified as having coefficients normally distributed about a locally weighted temporal average with variance described using a non-informative prior. The structure of the local weighting function was selected by minimizing the Deviance Information Criterion. Significance was ascertained through Monte Carlo simulations. Results: Residential proximity to organochlorine pesticide applications was associated with ASD risk during the first trimester (postconception days 27-60 [P < 0.01] or 14-77 [P < 0.05]). A period of association during the second trimester (days 108-165) only intermittently attained significance. Averaging coefficients over each time period yielded odds ratios for ASD comparing proximity to 50 pounds of pesticide to no exposure of 1.54, 1.47, and 1.18, respectively. Conclusions: This approach allowed us to incorporate uncertainty regarding temporal periods of vulnerability into our estimates of associations. This method may be broadly applicable to the environmental epidemiology of conditions for which little is known about temporal vulnerability.

Residential proximity to agricultural pesticide applications and childhood acute lymphoblastic leukemia

Ambient exposure from residential proximity to applications of agricultural pesticides may contribute to the risk of childhood acute lymphoblastic leukemia (ALL). Using residential histories collected from the families of 213 ALL cases and 268 matched controls enrolled in the Northern California Childhood Leukemia Study, the authors assessed residential proximity within a half-mile (804.5m) of pesticide applications by linking address histories with reports of agricultural pesticide use. Proximity was ascertained during different time windows of exposure, including the first year of life and the child's lifetime through the date of diagnosis for cases or reference for controls. Agricultural pesticides were categorized a priori into groups based on similarities in toxicological effects, physicochemical properties, and target pests or uses. The effects of moderate and high exposure for each group of pesticides were estimated using conditional logistic regression. Elevated ALL risk was associated with lifetime moderate exposure, but not high exposure, to certain physicochemical categories of pesticides, including organophosphates, chlorinated phenols, and triazines, and with pesticides classified as insecticides or fumigants. A similar pattern was also observed for several toxicological groups of pesticides. These findings suggest future directions for the identification of specific pesticides that may play a role in the etiology of childhood leukemia.

Well-Water Consumption and Parkinson’s Disease in Rural California

IntroductionInvestigators have hypothesized that consuming pesticide-contaminated well water plays a role in Parkinson’s disease (PD), and several previous epidemiologic studies support this hypothesis.ObjectivesWe investigated whether consuming water from private wells located in areas with documented historical pesticide use was associated with an increased risk of PD.MethodsWe employed a geographic information system (GIS)–based model to estimate potential well-water contamination from agricultural pesticides among 368 cases and 341 population controls enrolled in the Parkinson’s Environment and Genes Study (PEG). We separately examined 6 pesticides (diazinon, chlorpyrifos, propargite, paraquat, dimethoate, and methomyl) from among 26 chemicals selected for their potential to pollute groundwater or for their interest in PD, and because at least 10% of our population was exposed to them.ResultsCases were more likely to have consumed private well water and to have consumed it on average 4.3 years longer than controls (p = 0.02). High levels of possible well-water contamination with methomyl [odds ratio (OR) = 1.67; 95% confidence interval (CI), 1.00–2.78]), chlorpyrifos (OR = 1.87; 95% CI, 1.05–3.31), and propargite (OR = 1.92; 95% CI, 1.15–3.20) resulted in approximately 70–90% increases in relative risk of PD. Adjusting for ambient pesticide exposures only slightly attenuated these increases. Exposure to a higher number of water-soluble pesticides and organophosphate pesticides also increased the relative risk of PD.ConclusionOur study, the first to use agricultural pesticide application records, adds evidence that consuming well water presumably contaminated with pesticides may play a role in the etiology of PD.

Samsun Yöresinden Toplanan Çiğ Süt Örneklerinde Bazı Pestisid Kalıntılarının Araştırılması

Summary The widespread application of pesticides in veterinary medicine, agriculture and public health can result in the accumulation of pesticides in the environment. Their residues may easily concentrate in foods (such as milk). These toxicants get into the human body through the food chain, and cause serious health problems. In this study, method adaptation for multiresidue analysis of some organochlorine (OC) and synthetic pyrethroid pesticides in raw milk samples, which were collected from Samsun province, determination of amounts and regional distributions of the residues and as a result, evaluation of probable hazards of determined residues for human health, were aimed. One hundred cow milk samples were collected from Samsun province, and analyzed for nine OC and five synthetic pyrethroid pesticides. Average recovery for OC and synthetic pyrethroid pesticides were in the range of 33-81% and 60-136%, respectively. The limit of detections (LODs) for OC and synthetic pyrethroid pesticides were determined 5-82 and 162-281 ng/kg (ppt), respectively. The limit of quantifications (LOQs) for OC and synthetic pyrethroid pesticides were measured 17-271 and 535-926 ng/kg, respectively. Any investigated pesticide residue was not detected in the all examined raw milk samples.

Assessment of environmental exposures from agricultural pesticides in childhood leukaemia studies: challenges and opportunities

Pesticides are ubiquitous in environments of many rural communities due to drift from agricultural applications and home/garden use. Studies of childhood leukaemia predominantly relied on retrospective pesticide exposure assessment and parental recall of use or proximity to fields or pesticide applications. Sample size requirements mostly preclude the collection of individual-level exposure information, biomarkers or environmental measurements of pesticides prospectively in cohorts. Yet such measures can be used in nested case-control approaches or for validating exposure models that can be applied to large populations. Recently developed models incorporate geographic information system technology and environmental databases of pesticide and/or crop data to assess exposure. Models developed in California to estimate residential exposures are presented by linking addresses to agricultural pesticide application data and land-use maps. Results from exposure validation and simulation studies and exposure measurement error issues are discussed.

Agricultural pesticides and risk of childhood cancers

Agricultural pesticide applications have the potential for significant drift beyond the target spray area and may result in exposure to non-farming residents in surrounding communities. Using geographic information system (GIS) methods, 1778 childhood cancer cases and 1802 controls born in Texas between 1990 and 1998 were assigned probable agricultural pesticide exposure based on proximity of birth residence to crop fields. Multivariate modeling was used to estimate odds ratios and 95% confidence intervals for selected cancers. For most childhood cancers, we found no evidence of elevated risk associated with residential proximity at birth to cropland. There was an overall pattern of increased risk for germ-cell tumors but the odds ratios were based on few number of exposed cases. There was also some indication of increased risk for non-Hodgkin lymphoma (NHL) and Burkitt lymphoma, but point estimates were imprecise and not statistically significant. Previous studies have assessed pesticide exposure primarily based on parental occupational history or household use, while our focus was on agricultural pesticides and so may represent a different array of chemical agents occurring at lower doses.