Browsing by Author "Simmonds, P. Lynne"
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- Examination of dietary methylmercury exposure in the Casa Pia study of the health effects of dental amalgams in childrenPublication . Evens, Carina C.; Martin, Michael D.; Woods, James S.; Luís, Henrique Soares; Bernardo, Mário; Leitão, Jorge; Simmonds, P. Lynne; Liang, Lian; DeRouen, TimothyThis study examined methylmercury concentrations in blood of children participating in the Casa Pia Study of the Health Effects of Dental Amalgams in Children over a 1-yr period and related them to their diets in terms of fish and other seafood consumption. One hundred and fifty children between the ages of 8 and 10 yr who were residents of the Casa Pia School System of Lisbon, Portugal, participated. Parents or caregivers completed a food frequency questionnaire designed specifically for this study at baseline. Children provided urinary and blood samples for mercury determinations at baseline and at 1 yr following placement of dental tooth fillings. Mercury levels in fish samples from children’s diets were also obtained. Mercury determinations in urine, blood, and fish were performed using cold vapor atomic fluorescence spectroscopy. The mean value of baseline methylmercury concentrations in blood increased as the report of seafood consumption increased, although not statistically significantly. However, blood methylmercury and total mercury concentrations were significantly lower at 1-yr follow-up than at baseline. Sixty-one percent of parents/ caregivers reported that their children consumed fish on a weekly basis. The fish offered at a sample of the schools contained low levels of methylmercury ( range 13.9–23.6 ng/ g) . Thus, children participating in the Casa Pia dental amalgam study are exposed to low dietary levels of methylmercury by way of fish consumption, and this finding was reflected in the low mean blood methylmercury concentrations observed. The present findings indicate that dietary methylmercury is not a significant source of mercury exposure and is not likely to confound the association of dental amalgam mercury with potential health effects in the present study.
- The contribution of dental dmalgam to urinary mercury excretion in childrenPublication . Woods, James S.; Martin, Michael D.; Leroux, Brian G.; DeRouen, Timothy A.; Leitão, Jorge G.; Bernardo, Mario F.; Luís, Henrique S.; Simmonds, P. Lynne; Kushleika, John V.; Huang, YingBACKGROUND: Urinary mercury concentrations are widely used as a measure of mercury exposure from dental amalgam fillings. No studies have evaluated the relationship of these measures in a longitudinal context in children. OBJECTIVE: We evaluated urinary mercury in children 8–18 years of age in relation to number of amalgam surfaces and time since placement over a 7-year course of amalgam treatment. METHODS: Five hundred seven children, 8–10 years of age at baseline, participated in a clinical trial to evaluate the neurobehavioral effects of dental amalgam in children. Subjects were randomized to either dental amalgam or resin composite treatments. Urinary mercury and creatinine concentrations were measured at baseline and annually on all participants. RESULTS: Treatment groups were comparable in baseline urinary mercury concentration (~ 1.5 μg/L). Mean urinary mercury concentrations in the amalgam group increased to a peak of ~ 3.2 μg/L at year 2 and then declined to baseline levels by year 7 of follow-up. There was a strong, positive association between urinary mercury and both number of amalgam surfaces and time since placement. Girls had significantly higher mean urinary mercury concentrations than boys throughout the course of amalgam treatment. There were no differences by race in urinary mercury concentration associated with amalgam exposure. CONCLUSIONS: Urinary mercury concentrations are highly correlated with both number of amalgam fillings and time since placement in children. Girls excrete significantly higher concentrations of mercury in the urine than boys with comparable treatment, suggesting possible sex-related differences in mercury handling and susceptibility to mercury toxicity.
- Urinary porphyrin excretion in children with mercury amalgam treatment: findings from the Casa Pia children’s dental amalgam trialPublication . Woods, James S.; Martin, Michael D.; Leroux, Brian G.; DeRouen, Timothy A.; Bernardo, Mário F.; Luís, Henrique S.; Leitão, Jorge G.; Simmonds, P. Lynne; Echeverria, Diana; Rue, Tessa C.Increases in the urinary concentrations of pentacarboxyl- and coproporphyrins and the appearance of the atypical precoproporphyrin have been defined in relation to mercury (Hg) body burden in animal studies, and this change in the porphyrin excretion pattern has been described as a biomarker of occupational Hg exposure and toxicity in adult human subjects. In the present studies, urinary porphyrins were determined in relation to Hg exposure in children and adolescents, 8–18 yr of age, over the 7-yr course of a clinical trial designed to evaluate the neurobehavioral and renal effects of dental amalgam in children. Subjects were randomized to either dental amalgam or composite resin treatments. Urinary porphyrins and creatinine concentrations were measured at baseline and annually in all subjects. Results were evaluated using linear regression analysis. No significant differences between treatment groups (amalgam versus composite) were found when comparing all subjects for any of the porphyrins of interest. However, incipent amalgam treatment-specific increases were observed in the mean concentrations of penta-, precopro- and coproporphyrins especially when the analyses were restricted to younger subjects (8 to 9 yr old at baseline), and these increases were most apparent during yr 2 through 3 of follow-up, the period of highest mercury exposure from amalgam treatment. Based on the mean number of amalgam fillings received by children in this group (17.8), the renal Hg concentration associated with incipient increases in urinary porphyrins was estimated to be approximately 2.7 μg/g renal cortex. This value corresponds to an observed mean urinary Hg concentration of 3.2 μg/g creatinine, which is approximately fivefold less than that at which renal damage from Hg exposure is estimated to occur in children. These findings are consistent with growing evidence supporting the sensitivity of urinary porphyrins as a biological indicator of subclinical Hg exposure in children.
- Urinary porphyrin excretion in normal children and adolescentesPublication . Woods, James S.; Martin, Michael D.; Leroux, Brian G.; DeRouen, Timothy A.; Bernardo, Mario F.; Luis, Henrique S.; Leitão, Jorge G.; Simmonds, P. Lynne; Rue, Tessa C.Background—Urinary porphyrins are diagnostic of various metabolic disorders and xenobiotic exposures, but comprehensive normative data for urinary porphyrin concentrations in children are currently unavailable. Methods—Subjects were participants in a prospective, randomized, controlled clinical trial of dental materials safety, 8 to 12 y at inception, who were followed longitudinally for 7 y after baseline with an extensive battery of neurobehavioral, neurological, renal function and urinary porphyrin assessments. Porphyrins were quantified by HPLC. Linear regression analyses were used to measure associations of porphyrin levels with age and gender. Results—Mean concentrations, 95% confidence intervals, and 10th 50th, and 90th percentiles for all 5 typically excreted urinary porphyrins are presented by year of age and by gender. Unadjusted urinary concentrations (μg/l) of all 5 porphyrins remained relatively constant throughout the age range of 8–18 y for both males and females. In contrast, creatinine-adjusted urinary porphyrin concentrations (μg/g) declined significantly throughout this age range in both genders. Boys had significantly higher pentacarboxyl- and copro- porphyrin levels compared with girls both before and after creatinine adjustment. Conclusions—Normative longitudinal data provided herein may facilitate the clinical assessment of pediatric metabolic disorders and may be of particular relevance in evaluating porphyrin changes as a biological indicator of disease or xenobiotic exposures among children and adolescents.