Pesticides as a source of developmental disabilities

Modeling the Dietary Pesticide Exposures of Young Children

A stepped approach was used to assess the exposures of 1 1/2-4 1/2-year-old children in the United Kingdom to residues of pesticides (dithiocarbamates; phosmet; carbendazim) found in apples and pears. The theoretical possibility that the acute reference dose (ARD) was being exceeded for a particular pesticide/fruit was tested by applying a combination of maximal variability and maximum measured residue relative to an average-body-weight consumer. The actual risk was then quantified by stochastically modeling consumption, from dietary survey data, with individual body weights, against published residue results for 2000-2002 and the variability of residue distribution within batches. The results, expressed as numbers of children per day likely to ingest more than the ARD, were in the range of 10-226.6 children per day, depending upon the pesticide and year of sampling. The implications for regulatory action are discussed.

[Chemical methods for determination of hydroxylated metabolites of polycyclic aromatic hydrocarbons and polychlorinated biphenyls in biological material]

This review presents methods for the analysis of hydroxylated metabolites of polycyclic aromatic hydrocarbons and polychlorinated biphenyls in humans and animals. These metabolites serve as biomarkers of human and animal exposure to the mentioned pollutants, but some metabolites also have toxic properties. Most are analysed in urine, which is the most accessible sample, but they can also be analysed in human and animal liver, bile, and adipose tissue.Their analysis is important for assessing bioavailability of aromatic pollutants and their toxicity in human organism, but also the toxicity of metabolites themselves. Advancements in analytical methods have made it possible to analyse multiple metabolites in a sample at the same time. New extraction techniques and more precise and selective qualitative and quantitative analyses can now detect very low metabolite concentrations. An extra advantage is that these simple techniques require less chemicals and time.

Testicular toxicity of chlorpyrifos (an organophosphate pesticide) in albino rat

Organophosphates are among the most widely used synthetic insect pesticides. The widespread use of organophosphates has stimulated research into the possible existence of effects related with their reproductive toxic activity. Present study was therefore, undertaken to assess the effects of chlorpyrifos on testes, the main organ of male reproduction. Chlorpyrifos at the dose levels of 7.5, 12.5 and 17.5 mg/kg b. wt./day was administered orally to male rats of Wistar strain for 30 days to evaluate the toxic alterations in testicular histology, biochemistry, sperm dynamics and testosterone levels. The body weight of animals did not show any significant change, however, a significant reduction was observed in testes. Chlorpyrifos also brought about marked reduction in epididymal and testicular sperm counts in exposed males and a decrease in serum testosterone concentration. Histopathological examination of testes showed mild to severe degenerative changes in seminiferous tubules at various dose levels. Fertility test showed 85% negative results. A significant reduction in the sialic acid content of testes and testicular glycogen was noticed, whereas the protein and cholesterol content was raised at significant levels. All these toxic effects are moderate at low doses and become severe at higher dose levels. From the results of the present study it is concluded that chlorpyrifos induces severe testicular damage and results in reduction in sperm count and thus affect fertility. Small changes in sperm counts are known to have adverse affects on human fertility. Therefore, application of such insecticide should be limited to a designed programme.

The effects of organophosphate pesticide exposure on Hispanic children's cognitive and behavioral functioning

OBJECTIVE

This study investigates the effects of Organophosphate (OP) pesticides exposure on the cognitive and behavioral functioning of Hispanic children living in an agricultural community.

METHODS

Forty-eight children were administered a battery of cognitive measures, and their parents and teachers completed behavior rating scales. Children provided a urine sample for analysis of OP pesticides metabolites.

RESULTS

All children had a detectable level of at least one OP pesticide metabolite. Higher OP pesticide metabolite concentration levels were significantly correlated with poorer performance on some subtests of the Wisconsin Card Sorting Test. However, the significance of this association was dependent upon the inclusion of two samples with noticeable higher OP pesticide metabolite concentration levels.

CONCLUSIONS

Short-term OP pesticide exposure seems to have deleterious effects on children's speed of attention, sequencing, mental flexibility, visual search, concept formation, and conceptual flexibility. This study is among a relatively small number of studies investigating an extremely complex problem. Limitations and suggestions for future studies are discussed.

Polypyrrole-polyvinyl sulphonate film based disposable nucleic acid biosensor

Double stranded calf thymus deoxyribonucleic acid entrapped polypyrrole-polyvinyl sulphonate (dsCT-DNA-PPy-PVS) films fabricated onto indium-tin-oxide (ITO) coated glass plates have been used to detect organophosphates such as chlorpyrifos and malathion. These disposable dsCT-DNA-PPy-PVS/ITO bioelectrodes have been characterized using cyclic voltammetry, Fourier-transform-infra-red (FTIR) spectroscopy and atomic force microscopy (AFM), respectively. These biosensing electrodes have a response time of 30s, are stable for about 5 months when stored in desiccated conditions at 25 degrees C and can be used to amperometrically detect chlorpyrifos (0.0016-0.025 ppm) and malathion (0.17-5.0), respectively. The additive effect of these pesticides on the amperometric response of the disposable dsCT-DNA-PPy-PVS/ITO bioelectrodes has also been investigated.

Beneficial effects of breast milk in the neonatal intensive care unit on the developmental outcome of extremely low birth weight infants at 18 months of age

OBJECTIVE

Beneficial effects of breast milk on cognitive skills and behavior ratings have been demonstrated previously in term and very low birth weight infants. Extremely low birth weight infants are known to be at increased risk for developmental and behavior morbidities. The benefits of breast milk that is ingested in the NICU by extremely low birth weight infants on development and behavior have not been evaluated previously.

METHODS

Nutrition data including enteral and parenteral feeds were collected prospectively, and follow-up assessments of 1035 extremely low birth weight infants at 18 months' corrected age were completed at 15 sites that were participants in the National Institute of Child Health and Human Development Neonatal Research Network Glutamine Trial between October 14, 1999, and June 25, 2001. Total volume of breast milk feeds (mL/kg per day) during hospitalization was calculated. Neonatal characteristics and morbidities, interim history, and neurodevelopmental and growth outcomes at 18 to 22 months' corrected age were assessed.

RESULTS

There were 775 (74.9%) infants in the breast milk and 260 (25.1%) infants in the no breast milk group. Infants in the breast milk group were similar to those in the no breast milk group in every neonatal characteristic and morbidity, including number of days of hospitalization. Mean age of first day of breast milk for the breast milk infants was 9.3 +/- 9 days. Infants in the breast milk group began to ingest non-breast milk formula later (22.8 vs 7.3 days) compared with the non-breast milk group. Age at achieving full enteral feeds was similar between the breast milk and non-breast milk groups (29.0 +/- 18 vs 27.4 +/- 15). Energy intakes of 107.5 kg/day and 105.9 kg/day during the hospitalization did not differ between the breast milk and non-breast milk groups, respectively. At discharge, 30.6% of infants in the breast milk group still were receiving breast milk. Mothers in the breast milk group were significantly more likely to be white (42% vs 27%), be married (50% vs 30%), have a college degree (22% vs 6%), and have private health insurance (34% vs 18%) compared with the no breast milk group. Mothers who were black, had a low household income (< or = dollar 20000), or had higher parity were less likely to provide breast milk feeds. The analysis of outcomes between the any human milk and no human milk groups were adjusted for maternal age, maternal education, marital status, race/ethnicity, and the other standard covariates. Children in the breast milk group were more likely to have a Bayley Mental Development Index > or = 85, higher mean Bayley Psychomotor Development Index, and higher Bayley Behavior Rating Scale percentile scores for orientation/engagement, motor regulation, and total score. There were no differences in the rates of moderate to severe cerebral palsy or blindness or hearing impairment between the 2 study groups. There were no differences in the mean weight (10.4 kg vs 10.4 kg), length (80.5 cm vs 80.5 cm), or head circumference (46.8 cm vs 46.6 cm) for the breast milk and no breast milk groups, respectively, at 18 months. Multivariate analyses, adjusting for confounders, confirmed a significant independent association of breast milk on all 4 primary outcomes: the mean Bayley (Mental Development Index, Psychomotor Development Index, Behavior Rating Scale, and incidence of rehospitalization). For every 10-mL/kg per day increase in breast milk ingestion, the Mental Development Index increased by 0.53 points, the Psychomotor Development Index increased by 0.63 points, the Behavior Rating Scale percentile score increased by 0.82 points, and the likelihood of rehospitalization decreased by 6%. In an effort to identify a threshold effect of breast milk on Bayley Mental Development Index and Psychomotor Development Index scores and Behavior Rating Scale percentile scores, the mean volume of breast milk per kilogram per day during the hospitalization was calculated, and infants in the breast milk group were divided into quintiles of breast milk ingestion adjusted for confounders. Overall, the differences across the feeding quintiles of Mental Development Index and Psychomotor Development Index were significant. There was a 14.0% difference in Behavior Rating Scale scores between the lowest and highest quintiles. For the outcomes (Mental Development Index, Psychomotor Development Index, Behavior Rating Scale, and Rehospitalization <1 year), only the values for the >80th percentile quintile of breast milk feeding were significantly different from the no breast milk values. In our adjusted regression analyses, every 10 mL/kg per day breast milk contributed 0.53 points to the Bayley Mental Development Index; therefore, the impact of breast milk ingestion during the hospitalization for infants in the highest quintile (110 mL/kg per day) on the Bayley Mental Development Index would be 10 x 0.53, or 5.3 points.

CONCLUSIONS

An increase of 5 points potentially would optimize outcomes and decrease costs by decreasing the number of very low birth weight children who require special education services. The societal implications of a 5-point potential difference (one third of an SD) in IQ are substantial. The potential long-term benefit of receiving breast milk in the NICU for extremely low birth weight infants may be to optimize cognitive potential and reduce the need for early intervention and special education services.

Principles and practices of neurodevelopmental assessment in children: lessons learned from the Centers for Children's Environmental Health and Disease Prevention Research

Principles and practices of pediatric neurotoxicology are reviewed here with the purpose of guiding the design and execution of the planned National Children's Study. The developing human central nervous system is the target organ most vulnerable to environmental chemicals. An investigation of the effects of environmental exposures on child development is a complex endeavor that requires consideration of numerous critical factors pertinent to a study's concept, design, and execution. These include the timing of neurodevelopmental assessment, matters of biologic plausibility, site, child and population factors, data quality assurance and control, the selection of appropriate domains and measures of neurobehavior, and data safety and monitoring. Here we summarize instruments for the assessment of the neonate, infant, and child that are being employed in the Centers for Children's Environmental Health and Disease Prevention Research, sponsored by the National Institute of Environmental Health Sciences and the U.S. Environmental Protection Agency, discuss neural and neurobiologic measures of development, and consider the promises of gene-environment studies. The vulnerability of the human central nervous system to environmental chemicals has been well established, but the contribution these exposures may make to problems such as attention deficit disorder, conduct problems, pervasive developmental disorder, or autism spectrum disorder remain uncertain. Large-scale studies such as the National Children's Study may provide some important clues. The human neurodevelopmental phenotype will be most clearly represented in models that include environmental chemical exposures, the social milieu, and complex human genetic characteristics that we are just beginning to understand.

Environmental Toxicants and Developmental Disabilities: A Challenge for Psychologists

Developmental, learning, and behavioral disabilities are a significant public health problem. Environmental chemicals can interfere with brain development during critical periods, thereby impacting sensory, motor, and cognitive function. Because regulation in the United States is based on limited testing protocols and essentially requires proof of harm rather than proof of lack of harm, some undefined fraction of these disabilities may reflect adverse impacts of this "vast toxicological experiment" (H. L. Needleman, as quoted in B. Weiss & P. J. Landrigan, 2000, p. 373). Yet the hazards of environmental pollutants are inherently preventable. Psychologists can help prevent developmental disabilities by mobilizing and affecting public policy, educating and informing consumers, contributing to interdisciplinary research efforts, and taking action within their own homes and communities to reduce the toxic threat to children.

Pesticides

Pesticides are a broad group of heterogeneous chemicals that have a significant public health benefit by increasing food production productivity and decreasing food-borne and vector-borne diseases. However, depending on the agent and the exposure, they may pose health risks. Because of their behavior, acute accidental toxic exposures occur more commonly in children. Because of the dietary habits and greater intake of foods per kilogram in children and because some infants are breastfed, there is also concern about the effects on them of low-level environmental exposures. In the absence of direct conclusive evidence, consistent and relevant observations have led some investigators to infer that chronic low-dose exposure to certain pesticides might pose a potential hazard to the health and development of infants and children. Other investigators have concluded that such inferences can be neither supported nor refuted at the present time. The pediatrician has a role to play in recognizing the symptoms of acute exposure and to be able to provide appropriate treatment. It is essential to study whether there are subtle neurologic effects that may result from low-level pesticide exposures in individual patients.

Repeated exposures to subthreshold doses of chlorpyrifos in rats: hippocampal damage, impaired axonal transport, and deficits in spatial learning

Organophosphorus (OP) compounds are detectable in the environment for years after use and endanger many populations. Although the effects of acutely toxic doses of many OP compounds are well described, much less is known about repeated low-level exposures. The purpose of these studies was to further evaluate potential toxicological effects of the extensively used OP pesticide chlorpyrifos (CPF) in rats. CPF, across a range of subthreshold doses (i.e., for acute toxicity), reduced rearing and sniffing activity and the magnitude of weight gain over 14 days of repeated exposure. Performance in a spatial learning task was impaired after 14 days of exposure to CPF (18.0 and 25.0 mg/kg) when testing was initiated 24 h after the last injection but not after a 14-day washout. However, inhibition of both fast anterograde and retrograde axonal transport was observed for up to 20 days after exposure to 25.0 mg/kg CPF. Studies using hippocampal cultures indicated that 8 days of continuous exposure to the parent compound, CPF (> or =100 micro M), resulted in cell toxicity and death. Furthermore, a dose (2.5 mg/kg) of CPF that had no effects on weight gain or memory performance when administered 5 days per week over 38 days impaired forelimb grip strength in the later days of testing. Collectively, these results indicate that repeated exposures to subthreshold doses of CPF may lead to growth retardation, behavioral abnormalities, and muscle weakness. Some of these symptoms may be attributed to effects of the OP on axonal transport.