Perchlorate The State of the Science Human Studies Offie Porat Soldin, Ph.D. Consultants in Epidemiology and Occupational Health, Inc. Washington, D.C. 12-12- 2001

Outline Thyroid Occupational NIS Environmental Neonatal Perchlorate Exposure ranges Occupational Environmental Neonatal Pediatric Adult Cancer Clinical studies

Perchlorate (ClO4-) ion Characteristics A halogen Oxyanion: ClO4-1 Perchlorate One “extra” oxygen atom Tetrahydron ClO3 –1 Chlorate Most common form ClO2-1 Chlorite One less oxygen atom ClO-1 Hypochlorite Two fewer oxygen atoms

Perchlorate (ClO4-) ion properties High chemical stability. The reduction of Cl from a +7 oxidation state to –1 as a chloride requires energy or a catalyst and does not occur spontaneously Hygroscopic. Highly water soluble (AP is 20g/100g solution @ 25oC) Exceedingly mobile in aqueous systems Density nearly twice that of water Can persist for decades due to kinetic barriers to its reactivity with other constituents

The Sodium-Iodide Symporter (NIS) Controls the uptake of iodine by the thyroid An intramembrane protein of 65kD Co-transports iodide (I-) with two sodium (Na+) ions against an electrochemical gradient Iodine thyroid/plasma gradient equals 25: 1 to 500: 1

The Sodium-Iodide Symporter

Iodine Age Group Recommended I2 intake (μg/day) Adults 150 Pregnant women Lactating women 175 200 Adolescents Children 90-120 Fetus in uteri, Neonates and infants 90

Effects of Iodine Deficiency Disorders Adult Goiter with its Complications Thyroid Deficiency Impaired Mental Function Child Goiter Thyroid Deficiency Impaired School Performance Retarded Physical Development Neonate Neonatal Goiter Brain Damage Neurobehavioral Fetus Abortion Stillbirths Brain Damage - Cretinism

Pregnancy and Thyroid Function – The Mother Iodine clearance by the kidney increases - increased glomerular filtration Iodine and iodothyronines transferred to fetus Women living in low iodine intake areas may develop iodine deficiency and enlarged thyroid The hypothalamic-pituitary-thyroid axis functions normally in pregnant women with adequate iodine

Thyroid Adequacy Maternal Fetal Outcome + Good - Good if treated early May not be good Bad

Pregnancy and Thyroid Function – Fetus / Neonate I Maternal hypothyroidism can be associated with neonatal defects (mental deficiency/ neurological defects/ low or normal IQs) If infants have low T3 and T4 levels and elevated TSH levels, early appropriate treatment results in a normal intellect

Pregnancy and Thyroid Function – Fetus / Neonate II NIS presence in mammary glands leads to secretion of iodine in milk, which is probably important for thyroid function in neonates Prolactin stimulates NIS production which is inhibited by most anti-thyroidal agents, but not by perchlorate

ClO4- in water - Detection 1997 – Ion chromatography, assay sensitivity improved from 400ppb to 4 μg/L (4 ppb) Public water supplies found to contain perchlorate ions: S California - 5-8 ppb; S Nevada - 5-24 ppb Method modified for ClO4- detection in urine (LOD 500 ppb) and serum (LOD 50 ppb) Electrospray ionization (ESI/MS/MS) (LOD 0.5 ppb) Less signal suppression by nitrate, bicarbonate and sulfate

Perchlorate Potential Exposure Potential Risk Pathologic Therapeutic Pharmacology Occupational Environmental Neonatal Pediatric Adult Cancer

Reported Deaths from Bone Marrow Toxicity among Perchlorate-treated Thyrotoxicosis Patients Study Daily Dosage (mg/day) Body Weight Adjusted Daily Dosage (mg/kg/day) Length of Treatment for each case   Effects Hobson 1961 800 600 11 9 14 weeks 20 weeks Fatal aplastic anemia Johnson & Moore 1961 1000 14 3 months 1 month  Fatal aplastic anemia Fawcett & Clark 1961 400 6 5 months 1-2 months Krevans et al. 1962 450 2 weeks 2 months Gjemdal 1963 Barzilai and Sheinfeld 1966 Few Months Fatal agranulocytosis

Therapeutic use of ClO4- Indication Dosage Hyperthyroidism 600-900 mg/day Hyperthyroidism in pregnancy 600-1000 mg/day Amiodarone induced (treatment for resistant tachyarryhthmias) 800-1000 mg/day then 1-6 months at lower doses Contains about 40% iodine by weight – I2/Amiodarone induced hypothyroidism or thyrotoxicosis

Perchlorate Pharmacology I rapidly absorbed excreted intact in the urine half-life: 5-8 hr (humans) 95% recovered in urine over 72 hr similar ionic size to iodide competitive inhibitor of NIS

Perchlorate Pharmacology II May not be translocated into the thyroid cell Ki is estimated as 0.4-24 μM May inhibit iodide accumulation → goiter1 and lead to hypothyroidism if iodine intake low < 50-150 μg/day May inhibit organic binding of iodine by affecting thyroid peroxidase (not proven) 1 Toxic multinodular goiter (Plummer’s disease) refers to an enlarged multinodular goiter commonly found in areas of iodine deficiency in which patients with long-standing non-toxic goiter develop thyrotoxicosis  

Perchlorate Diagnostic Use The perchlorate discharge test - detect iodide organification defects (1000 mg) Pertechnetate (Tc 99m) radiological studies to image brain, blood pool, localize the placenta. Pretreatment: 200-400 mg ClO4- minimizes pertechnetate in thyroid, salivary glands and choroid plexus Perchlorate is used to block the gastric uptake of Tc 99m in the investigation of GI bleeding tracer radioiodine ± 500 μg stable iodide. 3 hr thyroid radioiodine uptake, followed by 1 gm of ClO4, radioiodine uptake 1 hr later. Decrease in the thyroid iodine uptake @ 4 hrs > 15% of the 3 hr uptake is a positive test indicating an iodide organification defect

Perchlorate Epidemiological Studies Occupational Exposure To determine exposure levels and potential health effects need to estimate a safe working level of perchlorate Much higher than environmental Exposure: inhalation, ingestion, or dermal contact Significant systemic absorption likely because of the high aqueous solubility at body temperature USA: No occupational standard for perchlorate OSHA regulates perchlorate as a nuisance dust (limit of 15 mg/m3 (time-weighted average) Safety concerns – it has explosive potential

Occupational Studies Gibbs et al. (1998) Nevada Cumulative exposure Average lifetime dose: 38 mg/kg No adverse effects on thyroid Shift exposure Inhaled dose: 0.2-436 g/kg (ave 36 g/kg) Lamm et al. (1999) Utah Cross sectional Individual exposure Pre- post-shift urine Group exposure 3 exposures & control group Urine: 0.9 – 34 mg/shift (LOD=500 ppb) Serum: 110 – 1600 ppb (LOD 50 ppb) No adverse effects on thyroid function 0.01-34 mg/day

Perchlorate Exposure Environmental Clinical Studies Neonatal Pediatric Adult Cancer Clinical Studies

Neonatal Studies Environmental exposure Neonatal screening routine in most of the developed world Congenital hypothyroidism (CH) treatable if caught early enough 3. Neonatal TSH - Las Vegas (+ ClO4-) neonates compared with Reno (-) Perchlorate exposure had no effect 4.Chile – neonatal TSH (n=9,784). (100-120 ppb compared to low exposures 5-7 and <4ppb) No differences found in TSH levels 1. CH data – no CH increase in exposed areas 2. T4 - Las Vegas (+ ClO4- 15ppb) neonates compared with Reno(-) No ClO4- effect Brechner -Arizona

Pediatric Studies Environmental exposure Children and adolescents at greatest risk for low I2 Crump et al. studied school-age children (n = 162) 100-120 ppb, 5-7ppb and < 4ppb ClO4- in their drinking water No differences found in TSH, FT4 and goiter prevalence

Adult Studies Environmental exposure Nevada Medicaid database (1997-1998) Prevalence of thyroid diseases in areas exposed to ClO4- vs. areas unexposed The prevalence rates of thyroid diseases was no greater in areas exposed to ClO4- in drinking water

Thyroid Cancer Studies Environmental exposure Risk measures of thyroid cancer Prevalence, Mortality, Incidence All 3 measures showed no association with ClO4- exposure ClO4- is non-mutagenic

Prospective Volunteer Studies I 900 mg/day ClO4- for 4 wks – FT4 decreased; thyroid gland not depleted of iodine (Brabant et al. 1992) Iodine uptake inhibition studies (Lawrence et al. 2001) Thyroid function studies and iodine-uptake studies (prior/ during 2 wk exposure (3 mg or 10 mg ClO4-)/ 2 wks post-exposure No effect on thyroid function studies (T4, T3, FTI, thyroid hormone binding ratio & TSH) 10 mg/day dosage 38 % inhibition of iodine uptake Serum ClO4- levels: 0.6 μg/ml (6 μM) 3 mg/day dosage Serum ClO4- levels: below detection limit A linear-log regression predicted a no-effect level of 2 mg/day Linear-log extrapolation of the iodine uptake inhibition data would predict a no-effect level of about 2 mg/day.

Prospective Volunteer Studies II Greer et al. (2000) 35 mg/day, 7 mg/day, 1.4 mg/day and 0.5 mg/day Found a significant inhibition of iodine uptake A linear-log regression predicted a no-effect level of 0.5 mg/day 0.5 mg/day had no effect on iodine uptake The data indicated a no-effect on iodine uptake level equivalent to an environmental ClO4- drinking water level of 250 μg/L

Body-Weight Adjusted Daily Dose i Perchlorate dose-response in humans exposed therapeutically, occupationally, in clinical studies or environmentally via drinking water   Effect / endpoint Daily Dose Body-Weight Adjusted Daily Dose i Fatal hemotoxicity (aplastic anemia) 1000 - 2000 mg 15-30 mg/kg Non-fatal hemotoxicity (blood-dyscrasias, including agranulocytosis) 600–1000mg 400 mg agranulocytosis 8.5-14 mg/kg 5.7 mg/kg Therapeutic Effect Range for Amiodarone treatment 1000 mg start followed by 100 mg 12.8 mg/kg then 1.4 mg/kg Pharmacological Effect Range (normalization of thyroid function in hyperthyroid patients) 200-1000 mg 2.8 – 14 mg/kg Calculated Safe Occupational Average (BMDL) 50 mg 0.7 mg/kg Demonstrated Safe Occupational Average ii Per shift average 2.5 mg 34 mg 0.036 mg/kg 0.48 mg/kg No-effect level for TSH elevation in newborns iii (Environmental Level 5-25 ppb) Amount in 2L drinking water 200 μg 20 μg 2.9μg/kg 0.29μg/kg i Based on a 70-kg adult ii No-effect level for tests of thyroid function in occupationally exposed iii Exposed in utero via maternal consumption of drinking water

Model - Human Health and Perchlorate Exposure Ranges

Summary I Thyroid - the critical effect organ of perchlorate toxicity Perchlorate blocks iodide uptake by NIS Assuming intake of 2 liters of water per day, the highest known level of ClO4- in public drinking water (24 μg/L) would yield a daily exposure of less than 50 μg/day – 700 times lower than the no effect level

Summary II Absence of an observed effect on neonatal thyroid, thyroidal diseases, or thyroidal cancer in areas with ClO4- in drinking water is epidemiologically consistent with human toxicological and pharmacological observations

Summary III Methods for measurement of ClO4- in urine, serum, solid matrix, and soil will need to be standardized in order to allow a better analysis and interpretation of data