This study also highlights the importance of traditional management systems and of smallholder agriculture for the conservation of bee communities in transitioning tropical agroecosystems. Manganese is a naturally occurring element found in soil, food, and water. It is mined for use in metal industries, as a gasoline additive, and as an agricultural fungicide. Mn is an essential nutrient but at high doses it is neurotoxic and can result in a syndrome of neurologic deficits called manganism.There is a growing body of evidence that early life exposure to Mn, at much lower doses than those that cause manganism, may have detrimental effects on the developing organism. In school-aged children, lower cognitive scores have been associated with higher levels of Mn in water, in blood and in hair.Pregnancy and the first year of life are potentially vulnerable periods of exposure because Mn crosses the placenta during pregnancy, and young children have increased absorption efficiency and reduced excretion via bile compared to adults.Occupational studies have generally found no association between Mn inhalation exposure and urinary Mn concentrations.Blood Mn has been the most commonly used biomarker of exposure, but the short half-life of Mn in blood may miss periods of peak exposure and Mn is well regulated by homeostatic mechanisms in adults.Higher hair Mn levels have been observed in children living near environmental sources of Mn. However,plants in pots ideas hair is susceptible to exogenous contamination and methods used for cleaning hair samples prior to analysis may affect the accuracy of Mn measurement in hair.Mn levels in nails may be a valid biomarker of cumulative occupational Mn exposure 7–12 months earlier.
In a rodent study, Mn levels in nail clippings were strongly correlated with Mn levels in the brain.Available biomarkers have a limited ability to assess prenatal exposure to the fetus. Even maternal blood Mn levels measured during pregnancy do not accurately reflect exposure to the fetus as cord blood Mn concentrations are consistently much higher than concentrations in maternal delivery blood Mn.Measurement of Mn in deciduous teeth offers a promising biomarker to characterize prenatal and early postnatal Mn exposure. Mn is incorporated directly into developing dentin and current analytical techniques allow for detailed Mn measurements that can be related to specific time periods of neonatal development beginning in the second trimester of pregnancy for incisors and ending 10–11 months after birth for primary coronal dentin in molars.In this study, we analyzed Mn in prenatal dentin of shed teeth from children enrolled in the Center for the Health Assessment of Mothers and Children of Salinas study, a birth cohort of children living in the Salinas Valley. The fungicides maneb and mancozeb contain approximately 21% Mn by weight. Agricultural use of these Mn fungicides averages 160 000 kg per year in the Salinas Valley of California and more than 90% is used on lettuce.Our goal was to determine whether Mn levels in dentin during the entire prenatal period were related to environmental, occupational and dietary sources of Mn exposure. We evaluated the contribution to MnPN from nearby agricultural Mn fungicide use, soil type, estimated concentrations of Mn in ambient air, farm work by the mother or other members of the household, Mn levels in house dust samples, and estimated prenatal Mn intake from maternal diet and tap water consumption. Between September 1999 and November 2000, the CHAMACOS study enrolled 601 pregnant women from health clinics in the Salinas Valley primarily serving low-income families. Participants were eligible if they spoke English or Spanish and qualified for state funding of well-pregnancy care .
A total of 537 liveborns were followed to delivery, of which 353 participated in a visit when the child reached 7-years. We collected 324 teeth from 282 children. We analyzed 237 of these teeth for Mn that were free of obvious defects such as caries and extensive attrition. Analyses for this paper include children who provided a shed incisor with Mn levels measured in prenatal dentin . Written informed consent was obtained from all participants and all research was approved by the University of California, Berkeley Committee for the Protection of Human Subjects prior to commencement of the study. Mothers were interviewed twice during pregnancy and shortly after delivery. Trained bilingual bicultural interviewers obtained information on maternal age, country of birth, education level, and household poverty level. Information was also obtained regarding potential sources of Mn exposure including maternal farm work during pregnancy, number of farm workers in the home, number of farm workers that stored their clothes or shoes indoors and glasses per day of tap water consumed by the mother. We abstracted information on the mother’s hematocrit to hemoglobin ratio from prenatal medical records for a subset of participants to assess maternal iron status during pregnancy. We conducted a home inspection during pregnancy . We collected latitude and longitude coordinates using global positioning system units and evaluated housekeeping characteristics. We also collected house dust samples described in more detail elsewhere.Briefly, we collected dust from one square meter area of the residence using a high volume surface sampler which allows for the calculation of dust loading in grams per square meter of floor area to better characterize Mn in dust available for contact by children.We collected deciduous teeth beginning with the 7-year visit. Participants either mailed or brought in teeth as they were naturally exfoliated. The method for measuring Mn in human teeth has been described in detail elsewhere.Briefly, teeth are sectioned in a vertical plane, and microscopy is used to visualize the neonatal line and incremental markings in sectioned teeth samples. We determined the concentrations and spatial distribution of Mn using laser ablation inductively coupled plasma mass spectroscopy.
Levels of tooth Mn were characterized by normalizing to measured tooth calcium levels to provide a measure independent of variations in tooth mineral density. Values are the area under the curve for points measured during the second trimester and third trimesters separately,container size for blueberries and combined into a prenatal average value . The coefficient of variation for five teeth measured on three different days ranged from 4.5% to 9.5% indicating good reproducibility of 55Mn:43Ca dentin measurements. Of the 207 children with a tooth analyzed for Mn, 131 had dust samples collected from the maternal residence during pregnancy. We stored dust samples at −80 °C for approximately ten years before shipping them on dry ice for analysis. We passed the dust samples through a 150 μm sieve and digested them overnight in 7.5 N nitric acid. We quantified Mn concentrations in dust using inductively coupled plasma optical emission spectroscopy with a limit of detection of 0.1 μg Mn/g dust. We calculated Mn dust loading by multiplying the Mn concentration by the dust loading obtained by weighing the sieved dust sample and dividing by the area sampled. The California Department of Pesticide Regulation maintains the comprehensive California Pesticide Use Report system.Pesticide applicators are legally required to report the active ingredient, quantity applied, acres treated, crop treated, date and location to one square mile in area for all agricultural pesticide applications. We used geographic information system software to geocode residential locations using the latitude and longitude coordinates and to calculate kilograms of maneb and mancozeb reported in the PUR data for combinations of distance from the residence and trimester of pregnancy based on gestational age . We weighted fungicide use near homes based on the proportion of each square-mile Section that was within the buffer around a residence.To account for the potential downwind transport of fungicides from the application site, we obtained data from the five closest meteorological stations in the study area on wind direction to determine the percentage of time during each trimester that the wind blew from each of eight directions. We determined the direction of each section centroid relative to residences and weighted fungicide use in a Section by the percentage of time that the wind blew from that direction for each trimester. Since 90% of agricultural Mn fungicides are used on lettuce in the Salinas Valley, we used Monterey County crop maps for spring, summer, and fall of 199724 to estimate the acres of lettuce within 1, 3, and 5 km of residences during each trimester.
We linked the geocoded residential locations to the appropriate drinking water system using customer service area boundaries provided by local drinking water companies and the state of California.Public drinking water systems provide monitoring data on Mn concentrations sampled at water distribution points.However, Mn was not frequently detected in the study area during the pregnancy period for our cohort. Therefore, we used the average Mn concentration of all available samples from a water system to estimate long-term average concentrations of Mn in tap water. We estimated tap water consumption using questionnaire data on the number of glasses of tap water consumed per day . We multiplied consumption by the average Mn concentration to estimate the average daily Mn intake from tap water during each trimester. Mothers were interviewed about their dietary intake at the time of the second prenatal interview using a modified Spanish-language Block food frequency questionnaire specifically adapted for this study population.For each food item, frequency of consumption and usual portion size were assessed for the previous year. We estimated the mean Mn concentration for each food/beverage item and the daily Mn intake for each women using the average frequency and portion-size of each food and beverage reportedly consumed in a day in combination with food-specific Mn estimates from the total diet study data from 1991 to 2005.We also included Mn intake from dietary supplements. Because iron deficiency might increase Mn uptake, we also estimated daily iron intake using similar methods for use as a covariate in the models.For a subset of participants , we also had hematocrit to hemoglobin ratios as a measure of anemia. We estimated exposure to other potential sources of Mn, including soil type at the residence, estimated Mn concentration in outdoor air, and motor vehicle traffic. To account for variations in soil Mn concentrations, we linked each residence, based on latitude and longitude coordinates, to detailed soil maps.To account for exposure via air inhalation, we assigned residences to a 2000 census tract and linked them to estimated 2002 Mn concentrations in ambient air from U.S. EPA.We also estimated Mn emissions from vehicle traffic at each residence by calculating the traffic density using previously published methods that involve summing vehicle kilometers traveled for all major roads by the length of the road segments within 500 m of the residence.We used ANOVA for bivariate analysis of categorical predictor variables and the Spearman correlation coefficient to evaluate continuous predictor variables We identified potential explanatory variables for inclusion in multi-variable regression models that were associated with MnPN levels with p < 0.2. Mn tooth levels were skewed to the right and we natural log transformed the values to normalize the distributions for regression models. We used manual forward selection to derive final multi-variable linear regression models to determine which Mn exposure sources were significantly associated with Mn levels in dentin during the prenatal period. We also used backward elimination as an alternative method to identify significant predictor variables. We estimated the percentage change associated with each exposure source by exponentiating the regression coefficients, subtracting one and multiplying by 100. We evaluated outliers and reran models excluding one participant with a studentized t-score >3 that also had the lowest measured MnPN level . Our final models included one using data available for all children with MnPN measured in teeth and another for the subset that had both tooth and house dust Mn measurements . We evaluated model fit using residual plots, log likelihood tests and Aikake’s Information Criterion. We investigated nonlinear relationships between continuous predictor variables and tooth Mn levels using penalized splines with 3 degrees of freedom in general additive models. We used Moran’s Global I to assess residual spatial auto correlation of MnPN levels for the final models. We compared Mn levels in prenatal dentin from the second trimester to levels from the third trimester using a paired t test and ran separate regression models by trimester to evaluate significant predictors by trimester.