摘要
This research applies aggregate and cumulative risk assessment considerations to intakes of compounds acting through the sodium-iodide symporter mechanism to produce iodide uptake inhibition into the thyroid. Four approaches to setting regulatory limits considered here based on NOELs/LOELs yield the following estimates of the safe levels of perchlorate in water (when perchlorate in water is the sole intake) or total goitrogens (PEC) acting through the same mechanism: 1) Approach 1: 18 μg/L;2) Approach 2: 400 μg/L (50% required inhibition) or 38 μg/L (5% required inhibition);3) Approach 3: 338 μg/L (without serum half-life correction) or 573 μg/L (with serum half-life correction);4) Approach 4: 737 μg/L (without serum half-life correction) or 973 μg/L (with serum half-life correction) for 50% required inhibition;375 μg/L (without half-life) or 735 μg/L (with half-life) for 5% required inhibition. Where water is not the sole route of exposure and perchlorate is not the sole goitrogen acting through the sodium-iodide symporter mechanism, the results of Approaches 3 and 4 can be applied to mixtures of compounds that produce these values as PECs. Results of the analysis suggest that compound-by-compound regulatory limits may be better dealt with through a change to risk-based management strategies that are built around the concept of focusing limited regulatory resources on the main contributors to risks induced by the mechanism considered here.
This research applies aggregate and cumulative risk assessment considerations to intakes of compounds acting through the sodium-iodide symporter mechanism to produce iodide uptake inhibition into the thyroid. Four approaches to setting regulatory limits considered here based on NOELs/LOELs yield the following estimates of the safe levels of perchlorate in water (when perchlorate in water is the sole intake) or total goitrogens (PEC) acting through the same mechanism: 1) Approach 1: 18 μg/L;2) Approach 2: 400 μg/L (50% required inhibition) or 38 μg/L (5% required inhibition);3) Approach 3: 338 μg/L (without serum half-life correction) or 573 μg/L (with serum half-life correction);4) Approach 4: 737 μg/L (without serum half-life correction) or 973 μg/L (with serum half-life correction) for 50% required inhibition;375 μg/L (without half-life) or 735 μg/L (with half-life) for 5% required inhibition. Where water is not the sole route of exposure and perchlorate is not the sole goitrogen acting through the sodium-iodide symporter mechanism, the results of Approaches 3 and 4 can be applied to mixtures of compounds that produce these values as PECs. Results of the analysis suggest that compound-by-compound regulatory limits may be better dealt with through a change to risk-based management strategies that are built around the concept of focusing limited regulatory resources on the main contributors to risks induced by the mechanism considered here.
