Basis of the Massachusetts reference dose and drinking water standard for perchlorate.
OBJECTIVE
Perchlorate inhibits the uptake of iodide in the thyroid. Iodide is required to synthesize hormones critical to fetal and neonatal development. Many water supplies and foods are contaminated with perchlorate. Exposure standards are needed but controversial. Here we summarize the basis of the Massachusetts (MA) perchlorate reference dose (RfD) and drinking water standard (DWS), which are considerably lower and more health protective than related values derived by several other agencies. We also review information regarding perchlorate risk assessment and policy.


METHODS
MA Department of Environmental Protection (DEP) scientists, with input from a science advisory committee, assessed a wide range of perchlorate risk and exposure information. Health outcomes associated with iodine insufficiency were considered, as were data on perchlorate in drinking water disinfectants.


RESULTS
We used a weight-of-the-evidence approach to evaluate perchlorate risks, paying particular attention to sensitive life stages. A health protective RfD (0.07 microg/kg/day) was derived using an uncertainty factor approach with perchlorate-induced iodide uptake inhibition as the point of departure. The MA DWS (2 microg/L) was based on risk management decisions weighing information on perchlorate health risks and its presence in certain disinfectant solutions used to treat drinking water for pathogens.


CONCLUSIONS
Current data indicate that perchlorate exposures attributable to drinking water in individuals at sensitive life stages should be minimized and support the MA DEP perchlorate RfD and DWS. Widespread exposure to perchlorate and other thyroid toxicants in drinking water and foods suggests that more comprehensive policies to reduce overall exposures and enhance iodine nutrition are needed.
Zewdie
Tsedash
T
Massachusetts Department of Environmental Protection, Office of Research and Standards, Boston, Massachusetts 02108, USA.
Smith
C Mark
CM
Hutcheson
Michael
M
West
Carol Rowan
CR
D003247:Conservation of Natural Resources; D006077:Government Agencies; D006801:Humans; D007454:Iodides / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D008404:Massachusetts; D010472:Perchlorates / Q000032:analysis / Q000592:standards* / Q000633:toxicity*; D018570:Risk Assessment; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000592:standards* / Q000633:toxicity*; D014881:Water Supply / Q000592:standards*
D007454:Iodides; D010472:Perchlorates; D014874:Water Pollutants, Chemical; C494474:perchlorate