This paper applies cumulative and aggregate risk methods and weight of evidence determination to re-analysis of epidemiological and clinical studies of exposure to perchlorates. The implications of cumulative and aggr...This paper applies cumulative and aggregate risk methods and weight of evidence determination to re-analysis of epidemiological and clinical studies of exposure to perchlorates. The implications of cumulative and aggregate risk are considered for 28 epidemiological studies on IUI, serum thyroid hormone levels and clinical indicators. Consideration is given to simultaneous exposures to perchlorates, nitrates, thiocyanates and organohalogens in the study populations. The elevation of effects by perchlorates alone is found only in the studies that use urinary perchlorate as the metric of exposure. These studies are beset by a problem with use of urinary perchlorate concentration in that there is large inter-subject variability in the relationship between intake and urinary concentration due to differences in metabolism and disposition of the compounds following ingestion. As a result, an individual placed into the “high urinary concentration” group may be there due to high values of exposure, to long biological clearance halflives, or due to high transfer fractions from the serum into the urine. The influence could be removed by correcting urinary levels by measured clearance half-times for individuals in a study, but that has not been done in the case of the studies examined here. It is of interest therefore that the studies that use direct measures of intake of perchlorates rather than urine concentration fail to display the hormone effects. The current study uses a “weight of evidence” approach for perchlorates, employing all 28 studies. The result is a slope of the exposure response curve (percentage change in hormone effect per unit exposure) of 0.3% per μg/kg-day, with 95% confidence interval of (?0.05%, 1%). This confidence interval for the slope encompasses 0, indicating no statistically significant slope when all data are combined in a weight of evidence determination. This is consistent with the conclusions of the USEPA and EFSA that the epidemiological studies do not provide compelling evidence f展开更多
文摘This paper applies cumulative and aggregate risk methods and weight of evidence determination to re-analysis of epidemiological and clinical studies of exposure to perchlorates. The implications of cumulative and aggregate risk are considered for 28 epidemiological studies on IUI, serum thyroid hormone levels and clinical indicators. Consideration is given to simultaneous exposures to perchlorates, nitrates, thiocyanates and organohalogens in the study populations. The elevation of effects by perchlorates alone is found only in the studies that use urinary perchlorate as the metric of exposure. These studies are beset by a problem with use of urinary perchlorate concentration in that there is large inter-subject variability in the relationship between intake and urinary concentration due to differences in metabolism and disposition of the compounds following ingestion. As a result, an individual placed into the “high urinary concentration” group may be there due to high values of exposure, to long biological clearance halflives, or due to high transfer fractions from the serum into the urine. The influence could be removed by correcting urinary levels by measured clearance half-times for individuals in a study, but that has not been done in the case of the studies examined here. It is of interest therefore that the studies that use direct measures of intake of perchlorates rather than urine concentration fail to display the hormone effects. The current study uses a “weight of evidence” approach for perchlorates, employing all 28 studies. The result is a slope of the exposure response curve (percentage change in hormone effect per unit exposure) of 0.3% per μg/kg-day, with 95% confidence interval of (?0.05%, 1%). This confidence interval for the slope encompasses 0, indicating no statistically significant slope when all data are combined in a weight of evidence determination. This is consistent with the conclusions of the USEPA and EFSA that the epidemiological studies do not provide compelling evidence f
