Robert B. Gunier

Autism spectrum disorders in relation to distribution of hazardous air pollutants in the san francisco bay area.

Objective To explore possible associations between autism spectrum disorders (ASD) and environmental exposures, we linked the California autism surveillance system to estimated hazardous air pollutant (HAP) concentrations compiled by the U.S. Environmental Protection Agency. Methods Subjects included 284 children with ASD and 657 controls, born in 1994 in the San Francisco Bay area. We assigned exposure level by census tract of birth residence for 19 chemicals we identified as potential neurotoxicants, developmental toxicants, and/or endocrine disruptors from the 1996 HAPs database. Because concentrations of many of these were highly correlated, we combined the chemicals into mechanistic and structural groups, calculating summary index scores. We calculated ASD risk in the upper quartiles of these group scores or individual chemical concentrations compared with below the median, adjusting for demographic factors. Results The adjusted odds ratios (AORs) were elevated by 50% in the top quartile of chlorinated solvents and heavy metals [95% confidence intervals (CIs), 1.1–2.1], but not for aromatic solvents. Adjusting for these three groups simultaneously led to decreased risks for the solvents and increased risk for metals (AORs for metals: fourth quartile = 1.7; 95% CI, 1.0–3.0; third quartile = 1.95; 95% CI, 1.2–3.1). The individual compounds that contributed most to these associations included mercury, cadmium, nickel, trichloroethylene, and vinyl chloride. Conclusions Our results suggest a potential association between autism and estimated metal concentrations, and possibly solvents, in ambient air around the birth residence, requiring confirmation and more refined exposure assessment in future studies.

Traffic density in California: Socioeconomic and ethnic differences among potentially exposed children

Motor vehicles are the main source of many hazardous air pollutants in California. Previous studies have shown that low-income and minority populations are more likely to live near industrial sources of pollution and in areas that do not meet national air quality standards. We estimated neighborhood exposures to motor vehicle emissions from a road network with daily traffic counts using a geographic information system. To calculate traffic density, we summed the average daily vehicle miles of travel per square mile of land area for each census block group in the state. We used 1990 census data to characterize the population by age, race and socioeconomic status in block groups with high traffic density. Block groups with more than 500,000 vehicle miles of travel per square mile were defined to be high traffic density. Statewide, about 5% of all block groups met this criterion and more than 215,000 children under 15 years of age lived in these high traffic density areas. Block groups in the lowest quartile of median family income were three times more likely to have high traffic density than block groups in the highest income quartile. The percentage of children living in high traffic density block groups increased with decreasing median family income for all race and ethnicities except White. Overall, children of color were about three times more likely to live in high-traffic areas than were white children. Based on this analysis, low-income and children of color have higher potential exposure to vehicle emissions. Future exposure assessment studies should target the highest traffic density areas, and health studies should consider the differences by income and race or ethnicity during design.

Nitrogen dioxide prediction in Southern California using land use regression modeling: potential for environmental health analyses.

We modeled the intraurban distribution of nitrogen dioxide (NO2), a marker for traffic pollution, with land use regression, a promising new exposure classification technique. We deployed diffusion tubes to measure NO2 levels at 39 locations in the fall of 2003 in San Diego County, CA, USA. At each sample location, we constructed circular buffers in a geographic information system and captured information on roads, traffic flow, land use, population and housing. Using multiple linear regression, we were able to predict 79% of the variation in NO2 levels with four variables: traffic density within 40–300 m of the sampling location, traffic density within 300–1000 m, length of road within 40 m and distance to the Pacific coast. Applying this model to validation samples showed that the model predicted NO2 levels within, on average, 2.1 p.p.b for 12 training sites initially excluded from the model.Our evaluation of this land use regression model showed that this method had excellent prediction and robustness in a North American context. These models may be useful tools in evaluating health effects of long-term exposure to traffic-related pollution.

Prenatal and early childhood bisphenol A concentrations and behavior in school-aged children

INTRODUCTION Early life exposure to bisphenol A (BPA), an endocrine disrupting chemical used in some food and beverage containers, receipts, and dental sealants, has been associated with anxiety and hyperactivity in animal studies. A few human studies also show prenatal and childhood BPA exposure to be associated with behavior problems in children. METHODS We measured BPA in urine from mothers during pregnancy and children at 5 years of age (N=292). Child behavior was assessed by mother and teacher report at age 7 years and direct assessment at age 9 years. RESULTS Prenatal urinary BPA concentrations were associated with increased internalizing problems in boys, including anxiety and depression, at age 7. No associations were seen with prenatal BPA concentrations and behaviors in girls. Childhood urinary BPA concentrations were associated with increased externalizing behaviors, including conduct problems, in girls at age 7 and increased internalizing behaviors and inattention and hyperactivity behaviors in boys and girls at age 7. CONCLUSIONS This study adds to the existing literature showing associations of early life BPA exposure with behavior problems, including anxiety, depression, and hyperactivity in children. Additional information about timing of exposure and sex differences in effect is still needed.

Residential exposure to traffic in California and childhood cancer.

Background: Motor vehicle emissions are a major source of air pollution in California. Past studies have suggested that traffic-related exposures can increase the risk of childhood cancer, particularly leukemia. Methods: From California’s statewide, population-based cancer registry, we identified cancers diagnosed in children younger than 5 years of age between 1988 and 1997. We matched these cases to California birth certificates. For each case, we randomly selected 2 control birth certificates, matched by birth date and sex. For each mother’s residential address at the time of her child’s birth, we calculated road density by summing the length of all roads within a 500-foot radius of the residence. Traffic density was based on road lengths and vehicle traffic counts for highways and major roads. Results: The distributions of road and traffic density values were very similar for the 4369 cases and 8730 matched control subjects. For all cancer sites combined, the odds ratio (OR) for the highest road density exposure category, compared with the lowest, was 0.87 (95% confidence interval [CI] = 0.75–1.00). For all sites combined and for leukemia, the ORs were also below 1.0 for the highest traffic density exposure category (0.92 for both). For central nervous system tumors, the OR was 1.22 (CI = 0.87–1.70). Conclusions: In a large study with good power, we found no increased cancer risk among offspring of mothers living in high traffic density areas for all cancer sites or leukemia.

Maternal Urinary Bisphenol A during Pregnancy and Maternal and Neonatal Thyroid Function in the CHAMACOS Study

Background: Bisphenol A (BPA) is widely used in the manufacture of polycarbonate plastic bottles, food and beverage can linings, thermal receipts, and dental sealants. Animal and human studies suggest that BPA may disrupt thyroid function. Although thyroid hormones play a determinant role in human growth and brain development, no studies have investigated relations between BPA exposure and thyroid function in pregnant women or neonates. Objective: Our goal was to evaluate whether exposure to BPA during pregnancy is related to thyroid hormone levels in pregnant women and neonates. Methods: We measured BPA concentration in urine samples collected during the first and second half of pregnancy in 476 women participating in the CHAMACOS (Center for the Health Assessment of Mothers and Children of Salinas) study. We also measured free thyroxine (T4), total T4, and thyroid-stimulating hormone (TSH) in women during pregnancy, and TSH in neonates. Results: Associations between the average of the two BPA measurements and maternal thyroid hormone levels were not statistically significant. Of the two BPA measurements, only the one taken closest in time to the TH measurement was significantly associated with a reduction in total T4 (β = –0.13 µg/dL per log2 unit; 95% CI: –0.25, 0.00). The average of the maternal BPA concentrations was associated with reduced TSH in boys (–9.9% per log2 unit; 95% CI: –15.9%, –3.5%) but not in girls. Among boys, the relation was stronger when BPA was measured in the third trimester of pregnancy and decreased with time between BPA and TH measurements. Conclusion: Results suggest that exposure to BPA during pregnancy is related to reduced total T4 in pregnant women and decreased TSH in male neonates. Findings may have implications for fetal and neonatal development.

Residential exposure to polychlorinated biphenyls and organochlorine pesticides and risk of childhood leukemia.

Background Incidence of childhood leukemia in industrialized countries rose significantly during 1975–2004, and the reasons for the increase are not understood. Objectives We used carpet dust as an exposure indicator to examine the risk of childhood leukemia in relation to residential exposure to persistent organochlorine chemicals: six polychlorinated biphenyl (PCB) congeners and the pesticides α- and γ-chlordane, p,p′-DDT (dichlorodiphenyltrichloroethane), p,p′-DDE (dichlorodiphenyldichloroethylene), methoxychlor, and pentachlorophenol. Methods We conducted a population-based case–control study in 35 counties in northern and central California in 2001–2006. The study included 184 acute lymphocytic leukemia (ALL) cases 0–7 years of age and 212 birth certificate controls matched to cases by birth date, sex, race, and Hispanic ethnicity. We collected carpet dust samples from the room where the child spent the most time before diagnosis (similar date for controls) using a specialized vacuum. Results Detection of any PCB congener in the dust conferred a 2-fold increased risk of ALL [odds ratio (OR) = 1.97; 95% confidence interval (CI), 1.22–3.17]. Compared with those in the lowest quartile of total PCBs, the highest quartile was associated with about a 3-fold risk (OR = 2.78; 95% CI, 1.41–5.48), and the positive trend was significant (p = 0.017). Significant positive trends in ALL risk were apparent with increasing concentrations of PCB congeners 118, 138, and 153. We observed no significant positive associations for chlordane, DDT, DDE, methoxychlor, or pentachlorophenol. The associations with PCBs were stronger among non-Hispanic whites than among Hispanics despite similar distributions of PCB levels among controls in each racial/ethnic group. Conclusions Our findings suggest that PCBs, which are considered probable human carcinogens and cause perturbations of the immune system, may represent a previously unrecognized risk factor for childhood leukemia.

Agricultural pesticide use and childhood cancer in California.

Background: Household pesticide use has been associated with higher risk for several childhood malignancies, but few studies have evaluated risks associated with residential proximity to agricultural pesticide use. We conducted a population-based case-control study of early childhood cancer (age 0–4 years) among California children born between 1990 and 1997 and mothers residential proximity to agricultural applications of pesticides at the time of the childs birth. Methods: Included in the study were 2189 case children and 4335 controls matched for birth date and sex. We estimated the in utero exposure potential from specific chemicals and chemical groups used in the 9 months before birth within a half mile of the maternal residence. We computed odds ratios (ORs) using conditional logistic regression. Results: No striking patterns emerged. There were modestly elevated ORs for leukemias associated with probable and possible carcinogen use, and with nearby agricultural applications of organochlorines and organophosphates during pregnancy. Two commonly used pesticides were associated with higher leukemia risk when comparing the highest and lowest categories: metam sodium (OR = 2.05; 95% confidence interval = 1.01–4.17) and dicofol (1.83; 1.05–3.22). Conclusions: The few elevated risk associations in this study are consistent with chance, given the large number of comparisons, but they may deserve more careful consideration. Future studies that integrate specific temporal and spatial exposure potential for targeted pesticides will be important in further evaluating risks associated with childhood cancer.

Traffic patterns and childhood cancer incidence rates in California, United States

Objective: Some studies have suggested that residential proximity to high traffic areas is associated with increased risk of childhood cancer, although the epidemiologic evidence to date has been mixed. This study takes advantage of available information on population-based cancer reporting and various spatially assigned indices of traffic in a sufficiently large and heterogeneous area to obtain reasonably stable estimates of risk associations. Methods: The time period 1988–1994 included a total of 7143 newly diagnosed cases of childhood cancer and 46 million child-years of observation in California. Rate ratios, estimated via Poisson regression (with adjustment for age, sex, and race/ethnicity), were computed for estimated traffic level as measured by spatial information on neighborhood vehicle density, road density, and traffic density. Results: Compared to area air monitoring data, traffic density estimates were the most strongly correlated with measures of benzene and 1,3-butadiene. Rate ratios at the 90th percentile of traffic density (neighborhoods with over 320,700 vehicle miles traveled per day per square mile) were 1.08 (95% CI 0.98–1.20) for all cancers in children, 1.15 (95% CI 0.97–1.37) for the leukemias, and 1.14 (95% CI 0.90–1.45) for the gliomas. There was also little or no evidence for rate differences in areas characterized by high vehicle or road density. Conclusion: These data suggest that childhood cancer rates are not higher in high traffic neighborhoods, but future studies which can better refine timing and measures of exposure are needed to more directly address the question of etiologic risks.

Correlating Agricultural Use of Organophosphates with Outdoor Air Concentrations: A Particular Concern for Children

For the organophosphate pesticide chlorpyrifos, median inhalation noncancer, acute children’s exposures in agricultural communities are elevated above reference doses; for diazinon, similar exposures are nearly elevated. We used multivariate linear regression analysis to examine the temporal and spatial associations between agricultural use and measured air concentrations of chlorpyrifos, chlorpyrifos oxon, diazinon, and malathion. Agricultural use within a 3-mile radius on the monitoring day and use on the 2–4 prior days were significantly associated with air concentrations (p < 0.01) for all analytes except malathion; chlorpyrifos oxon showed the strongest association (p < 0.0001). In the final models, which included weather parameters, the proportion of variance (r 2, adjusted for the number of model variables) for all analytes ranged from 0.28 (p < 0.01) for malathion to 0.65 (p < 0.0001) for diazinon. Recent cellular, animal, and human evidence of toxicity, particularly in newborns, supports the public health concern indicated by initial risk estimates. Agricultural applications of organophosphates and their oxon products may have substantial volatization and off-field movement and are a probable source of exposures of public health concern.