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Iodine Research
Resource Network of The Iodine Movement
IODINE AND OTHER HALOGENS
PERCHLORATE
BLOUNT
Urinary Perchlorate and Thyroid Hormone Levels in Adolescent and Adult Men and Women Living
in the United States
Benjamin C. Blount, James L. Pirkle, John D. Osterloh, Liza Valentin-Blasini and Kathleen L.
Caldwell
Online 5 October 2006
Background: Perchlorate is commonly found in the environment and known to inhibit thyroid
function at high doses. Assessing the potential effect of low-level exposure to perchlorate on
thyroid function is an area of ongoing research.
Objectives: Evaluate the potential relationship between urinary levels of perchlorate and serum
levels of thyroid stimulating hormone (TSH) and total thyroxine (T4) in 2299 men and women, aged
12 and older, participating in the National Health and Nutrition Examination Survey (NHANES)
during 2001-2002.
Methods: Multiple regression models of T4 and TSH that included perchlorate and covariates
known or likely to be associated with T4 or TSH levels: age, race/ethnicity, body mass index,
estrogen use, menopausal status, pregnancy status, premenarche status, serum C-reactive
protein, serum albumin, serum cotinine, hours of fasting, urinary thiocyanate, urinary nitrate, and
selected medication groups.
Results: Perchlorate was not a significant predictor of T4 or TSH levels in men. For women overall,
perchlorate was a significant predictor of both T4 and TSH. For women with urinary iodine < 100
μg/L, perchlorate was a significant negative predictor of T4 (p < 0.0001) and a positive predictor of
TSH (p = 0.001). For women with urinary iodine ≥ 100 μg/L, perchlorate was a significant positive
predictor of TSH (p = 0.025), but not T4 (p = 0.550).
Conclusions: These associations of perchlorate with T4 and TSH are coherent in direction and
independent of other variables known to affect thyroid function, but are at perchlorate exposure
levels unanticipated based on previous studies.
DE GROEF
Perchlorate versus other environmental sodium/iodide symporter inhibitors: potential thyroid-
related health effects.
De Groef B, Decallonne BR, Van der Geyten S, Darras VM, Bouillon R.
Eur J Endocrinol. 2006 Jul;155(1):17-25. Review.
[abstract only]
OBJECTIVE: Perchlorate is a known competitive inhibitor of the sodium/iodide symporter (NIS).
Possible thyroid-related effects of environmental perchlorate have created great health concerns,
especially in the US, resulting in a debated reference dose (RfD) of 0.0007 mg/kg per day in
drinking water recommended by the National Academy of Sciences (NAS). However, the impact of
other environmental NIS inhibitors and the role of iodine seem to have received little attention in the
whole debate.
METHODS: We performed a PubMed search for articles published up to February 2006, using the
key terms perchlorate, nitrate, thiocyanate, iodine, NIS, RfD, thyroid (alone or in combinations), with
particular attention for human studies. In parallel, we critically analysed the January 2005 NAS'
report, entitled 'Health implications of perchlorate ingestion'.
RESULTS: The relative potencies of prevalent environmental NIS inhibitors (nitrate, thiocyanate
and perchlorate) to inhibit iodine uptake have been estimated repeatedly with robust results. Our
calculations show that nitrate and thiocyanate, acquired through drinking water or food, account for
a much larger proportion of iodine uptake inhibition than perchlorate. Furthermore, the iodine
uptake inhibitory effects of nitrate and thiocyanate - as defined by their legally accepted maximal
contaminant levels in drinking water - exceed the potential effect of the proposed RfD for
perchlorate by far.
CONCLUSIONS: Iodine uptake inhibition and any potential downstream effect by perchlorate are
highly dependent on the presence of other environmental NIS inhibitors and iodine intake itself.
These potential confounders should therefore be considered in future studies and calculations for
risk assessment.
Thiocyanate, having a half-life of approximately 6 days as compared to 8 and 5 h for perchlorate
and nitrate respectively, remains in the serum 18-29 times longer than the other anions. Based on
these differences in half-lives, the perchlorate equivalency ratios of thiocyanate and nitrate in
terms of ingested-weight basis have been recalculated to be 0.5 and 240 respectively.
The concentration of nitrate allowed in drinking water would cause an I- uptake inhibitory effect that
is 12 times greater than that of perchlorate.
The thyrotoxic potential of perchlorate cannot be seen separately from the effects of other NIS
inhibitors such as nitrate and thiocyanate."
Perchlorate only accounts for a small portion (<10%) of the exposure from drinking water.
In addition to drinking water, food also contains considerable amounts of nitrate and thiocyanate.
Using milk and lettuce as examples, it becomes evident that the contamination of monovalent
anions in food expressed as PECs is much higher than what is actually present in the contaminated
drinking water sources.... Food contamination is predominantly due to the high levels of nitrate and
thiocyanate that would account for 98.83 and 99.98% of the total NIS I- uptake inhibition caused by
milk and lettuce respectively. These numbers hardly change when a 50% absorption of
thiocyanate in the gut is taken into account: 97.84 and 99.97% for milk and lettuce respectively.
Eating just 50 g lettuce would cause an I- uptake inhibition exceeding the effect of the maximum
allowed concentration of 24.5 p.p.b. perchlorate in drinking water by 140 times. By drinking just
100 ml milk, an average 70-kg adult has already been exposed to an equivalent of the perchlorate
RfD.
Considering all these data, it is obvious that either the RfD for perchlorate is unrealistically strict, or
the MCLs for nitrate and thiocyanate are far too high and should be revised accordingly. The latter
is hardly possible, as the natural nitrate content of a crop like lettuce or spinach -- even grown
without fertilizer -- would already exceed such an RfD.
Dietary iodine. An important issue in environmental exposure to NIS inhibitors is the modulation of
inhibition by dietary iodine. The model of competitive inhibition developed by Tonacchera et al.
predicts that thyroidal I- uptake is approximately proportional to iodide nutrition for any fixed
underlying goitrogen load. Unfortunately, little or no data are available on the daily-required dose
of dietary I- to withstand inhibition of NIS I- uptake by perchlorate nitrate and thiocyanate present in
drinking water and food. The model of Tonacchera et al does not predict the levels of dietary I-
and goitrogen load at which effects on thyroid economy will occur.... Iodine supplementation should
be given to any person showing iodine deficiency, irrespective of whether there is significant
exposure to environmental perchlorate, nitrate, thiocyanate or foods that naturally contain these
anti-thyroid compounds or their precursors.
Other more prevalent NIS competitors such as nitrate and thiocyanate are not acknowledged, while
the effect of perchlorate cannot be seen separately from the effects of these anions. Taking into
account their individual I- uptake inhibition potential at the level of NIS, which can be considered as
robust since several studies agree on the perchlorate equivalence ratios, our calculations show
that perchlorate accounts for less than 10% of possible thyroidal effects resulting from the
exposure from drinking water; in food, its share is even negligible. The enormous discrepancy
between the safe NOEL-based RfD for perchlorate (in the context of iodine uptake inhibition) and
the disproportionately high -- legally binding -- LOEL-based RfD for nitrate (in the context of
acquired methaemoglobinaemia) is not logical, and measures should be taken accordingly. Due to
heterogeneity at several levels (inclusion of prevalent NIS inhibitors, type of exposure, populations
exposed and measures of exposure) a meta-analysis of available human data -- if at all possible --
would probably not reveal new conclusions, underlining the need for scientific evidence from
carefully designed human clinical studies evaluating the effects of nitrate and thiocyanate (along
with dietary iodine) on I- uptake inhibition, in order to determine RfDs for all prevalent NIS inhibitors
in drinking water and food. Moreover, further animal studies are needed, investigating not only
thyroidal, but also neurodevelopmental endpoints in circumstances of controlled intake of iodine,
perchlorate, nitrate and thiocyanate..
WOLFF
Perchlorate and the thyroid gland.
Wolff J.
Pharmacol Rev. 1998 Mar;50(1):89-105. Review.
Perchlorate competitively blocks iodide from entering the thyroid by an effect on the Na+/I-
symporter thus preventing the further synthesis of thyroid hormone but has no effect on the
iodination process itself. It is concentrated by thyroid tissue in a manner similar to iodide but is not
significantly metabolized in the gland or peripherally. What is not settled is whether there are
additional perchlorate effects on iodide transport. Perchlorate has a fast turnover in the body and
requires frequent daily doses for therapy of thyrotoxicosis. Perchlorate appears to be substantially
more effective against large iodide loads than the thionamides, and, with long-term iodide
contamination, combined therapy of perchlorate (with < or = 1 g/day) and thionamides is
recommended for the more severe cases of thyrotoxicosis that may result from excess iodide or
iodide-generating organic compounds, as for example with amiodarone. After approximately 30
days, the perchlorate dosage can be tapered or stopped, continuing with thionamides alone. This
markedly increases its safe use. Despite serious side effects during its early use, lower dosages
and shorter treatment periods appear to have prevented such reactions in its recent reintroduction,
mostly for amiodarone-induced thyroid dysfunction. Perchlorate can also protect against inhibition
of thyroid function and the resulting hypothyroidism caused by excess iodide, presumably by
reducing the formation of an iodinated inhibitor. The reduction of the iodide pool by perchlorate
thus has dual effects--reduction of excess hormone synthesis and hyperthyroidism, on the one
hand, and reduction of thyroid inhibitor synthesis and hypothyroidism on the other. Perchlorate
remains very useful also as a single dose application in tests measuring the discharge of
radioiodide accumulated in the thyroid as a result of many different disruptions in the further
metabolism of iodide in the thyroid gland.
CROHN
Perchlorate Controversy Calls for Improving Iodine Nutrition
Crohn DM
Vegetarian Journal 2006 Issue 2
Depending on the amount ingested, perchlorate may affect the body in a number of ways, but it is
normally expected to interfere with the thyroid first. The thyroid is a small butterfly-shaped gland at
the front of the neck. It uses iodine to produce the only biologically active compounds in the body
that contain iodine, the hormones T3 and T4. To produce these hormones, the thyroid must collect
and concentrate iodine from the bloodstream. When perchlorate is present, the thyroid will collect
both iodine and perchlorate so that the amount of iodine that can be concentrated is reduced.
Perchlorate is seldom a significant problem for people with adequate iodine in their diets because
the thyroid still absorbs enough to meet the body's hormone production needs. If a person is
already iodine deficient, however, perchlorate can further impair their ability to produce T3 and T4.
To be fair, perchlorate is not the only chemical that interferes with the thyroid's iodide collection. At
least two other compounds common in the American diet, nitrate and thiocyanate, can also
interfere with iodine collection. Nitrate, the most widely occurring groundwater pollutant, results
from over-fertilization with nitrogen fertilizer or manures. Nitrate concentrations are regulated in
drinking water because it can contribute to a type of anemia in infants known as 'blue baby
syndrome,' not because of its possible effect on thyroid function. Thiocyanate occurs naturally in
certain vegetables, such as broccoli, cauliflower, cabbage, turnips, and Brussels sprouts. Although
perchlorate interferes more strongly with thyroid function than thiocyanate or nitrate, these last two
compounds are more common in most people's diets.
Perchlorate is, therefore, a concern because it intensifies problems resulting from iodine
deficiency. Iodine deficiency is already the world's leading cause of avoidable intellectual
impairment. The damage that this deficiency precipitates is permanent, but most damage is mild to
moderate. Nonetheless, damage can be severe, depending on the timing and intensity of the
deficiency. Typical iodine consumption in the United States has fallen significantly since the early
1970s, leading to concerns that iodine deficiency problems in the public at large, and particularly in
nursing mothers, may be increasing. This decrease in iodine intake in the United States is likely
associated with changes in the manufacturing of bread and milk that have lowered their iodine
contents. In addition, processed foods, which have become more popular, frequently are
manufactured with non-iodized salts.
Perchlorate should interest Journal readers because risk assessments suggest that the babies of
pregnant and nursing vegan mothers are, theoretically, at greatest risk for perchlorate toxicity.
Vegans are perceived to be at greater risk than the general public, including lacto-vegetarians,
because plant-based diets are generally relatively low in iodine. Evidence for this comes from
knowledge of the iodine content of different foods rather than from direct measurements of iodine
levels in vegans. The iodine content of most fruits, nuts, and vegetables is low but can vary
depending on soil iodine content, irrigation, and fertilization practices.
PERCHLORATE
- Blount, et al, report on the 2006 study of effects of environmental perchlorate on thyroid
hormones of US men and women. - De Groef has compared the effects of perchlorate vs. other environmental NIS inhibitors
(nitrate and thiocyanate), concluding that perchlorate is not the biggest problem. - Wolff has written a review article on the effects of perchlorate on the thyroid gland.
- Crohn has written an article for Vegetarian Times on perchlorates and how vegetarians can
get adequate iodine.
BLOUNT
Urinary Perchlorate and Thyroid Hormone Levels in Adolescent and Adult Men and Women Living
in the United States
Benjamin C. Blount, James L. Pirkle, John D. Osterloh, Liza Valentin-Blasini and Kathleen L.
Caldwell
Online 5 October 2006
Background: Perchlorate is commonly found in the environment and known to inhibit thyroid
function at high doses. Assessing the potential effect of low-level exposure to perchlorate on
thyroid function is an area of ongoing research.
Objectives: Evaluate the potential relationship between urinary levels of perchlorate and serum
levels of thyroid stimulating hormone (TSH) and total thyroxine (T4) in 2299 men and women, aged
12 and older, participating in the National Health and Nutrition Examination Survey (NHANES)
during 2001-2002.
Methods: Multiple regression models of T4 and TSH that included perchlorate and covariates
known or likely to be associated with T4 or TSH levels: age, race/ethnicity, body mass index,
estrogen use, menopausal status, pregnancy status, premenarche status, serum C-reactive
protein, serum albumin, serum cotinine, hours of fasting, urinary thiocyanate, urinary nitrate, and
selected medication groups.
Results: Perchlorate was not a significant predictor of T4 or TSH levels in men. For women overall,
perchlorate was a significant predictor of both T4 and TSH. For women with urinary iodine < 100
μg/L, perchlorate was a significant negative predictor of T4 (p < 0.0001) and a positive predictor of
TSH (p = 0.001). For women with urinary iodine ≥ 100 μg/L, perchlorate was a significant positive
predictor of TSH (p = 0.025), but not T4 (p = 0.550).
Conclusions: These associations of perchlorate with T4 and TSH are coherent in direction and
independent of other variables known to affect thyroid function, but are at perchlorate exposure
levels unanticipated based on previous studies.
DE GROEF
Perchlorate versus other environmental sodium/iodide symporter inhibitors: potential thyroid-
related health effects.
De Groef B, Decallonne BR, Van der Geyten S, Darras VM, Bouillon R.
Eur J Endocrinol. 2006 Jul;155(1):17-25. Review.
[abstract only]
OBJECTIVE: Perchlorate is a known competitive inhibitor of the sodium/iodide symporter (NIS).
Possible thyroid-related effects of environmental perchlorate have created great health concerns,
especially in the US, resulting in a debated reference dose (RfD) of 0.0007 mg/kg per day in
drinking water recommended by the National Academy of Sciences (NAS). However, the impact of
other environmental NIS inhibitors and the role of iodine seem to have received little attention in the
whole debate.
METHODS: We performed a PubMed search for articles published up to February 2006, using the
key terms perchlorate, nitrate, thiocyanate, iodine, NIS, RfD, thyroid (alone or in combinations), with
particular attention for human studies. In parallel, we critically analysed the January 2005 NAS'
report, entitled 'Health implications of perchlorate ingestion'.
RESULTS: The relative potencies of prevalent environmental NIS inhibitors (nitrate, thiocyanate
and perchlorate) to inhibit iodine uptake have been estimated repeatedly with robust results. Our
calculations show that nitrate and thiocyanate, acquired through drinking water or food, account for
a much larger proportion of iodine uptake inhibition than perchlorate. Furthermore, the iodine
uptake inhibitory effects of nitrate and thiocyanate - as defined by their legally accepted maximal
contaminant levels in drinking water - exceed the potential effect of the proposed RfD for
perchlorate by far.
CONCLUSIONS: Iodine uptake inhibition and any potential downstream effect by perchlorate are
highly dependent on the presence of other environmental NIS inhibitors and iodine intake itself.
These potential confounders should therefore be considered in future studies and calculations for
risk assessment.
Thiocyanate, having a half-life of approximately 6 days as compared to 8 and 5 h for perchlorate
and nitrate respectively, remains in the serum 18-29 times longer than the other anions. Based on
these differences in half-lives, the perchlorate equivalency ratios of thiocyanate and nitrate in
terms of ingested-weight basis have been recalculated to be 0.5 and 240 respectively.
The concentration of nitrate allowed in drinking water would cause an I- uptake inhibitory effect that
is 12 times greater than that of perchlorate.
The thyrotoxic potential of perchlorate cannot be seen separately from the effects of other NIS
inhibitors such as nitrate and thiocyanate."
Perchlorate only accounts for a small portion (<10%) of the exposure from drinking water.
In addition to drinking water, food also contains considerable amounts of nitrate and thiocyanate.
Using milk and lettuce as examples, it becomes evident that the contamination of monovalent
anions in food expressed as PECs is much higher than what is actually present in the contaminated
drinking water sources.... Food contamination is predominantly due to the high levels of nitrate and
thiocyanate that would account for 98.83 and 99.98% of the total NIS I- uptake inhibition caused by
milk and lettuce respectively. These numbers hardly change when a 50% absorption of
thiocyanate in the gut is taken into account: 97.84 and 99.97% for milk and lettuce respectively.
Eating just 50 g lettuce would cause an I- uptake inhibition exceeding the effect of the maximum
allowed concentration of 24.5 p.p.b. perchlorate in drinking water by 140 times. By drinking just
100 ml milk, an average 70-kg adult has already been exposed to an equivalent of the perchlorate
RfD.
Considering all these data, it is obvious that either the RfD for perchlorate is unrealistically strict, or
the MCLs for nitrate and thiocyanate are far too high and should be revised accordingly. The latter
is hardly possible, as the natural nitrate content of a crop like lettuce or spinach -- even grown
without fertilizer -- would already exceed such an RfD.
Dietary iodine. An important issue in environmental exposure to NIS inhibitors is the modulation of
inhibition by dietary iodine. The model of competitive inhibition developed by Tonacchera et al.
predicts that thyroidal I- uptake is approximately proportional to iodide nutrition for any fixed
underlying goitrogen load. Unfortunately, little or no data are available on the daily-required dose
of dietary I- to withstand inhibition of NIS I- uptake by perchlorate nitrate and thiocyanate present in
drinking water and food. The model of Tonacchera et al does not predict the levels of dietary I-
and goitrogen load at which effects on thyroid economy will occur.... Iodine supplementation should
be given to any person showing iodine deficiency, irrespective of whether there is significant
exposure to environmental perchlorate, nitrate, thiocyanate or foods that naturally contain these
anti-thyroid compounds or their precursors.
Other more prevalent NIS competitors such as nitrate and thiocyanate are not acknowledged, while
the effect of perchlorate cannot be seen separately from the effects of these anions. Taking into
account their individual I- uptake inhibition potential at the level of NIS, which can be considered as
robust since several studies agree on the perchlorate equivalence ratios, our calculations show
that perchlorate accounts for less than 10% of possible thyroidal effects resulting from the
exposure from drinking water; in food, its share is even negligible. The enormous discrepancy
between the safe NOEL-based RfD for perchlorate (in the context of iodine uptake inhibition) and
the disproportionately high -- legally binding -- LOEL-based RfD for nitrate (in the context of
acquired methaemoglobinaemia) is not logical, and measures should be taken accordingly. Due to
heterogeneity at several levels (inclusion of prevalent NIS inhibitors, type of exposure, populations
exposed and measures of exposure) a meta-analysis of available human data -- if at all possible --
would probably not reveal new conclusions, underlining the need for scientific evidence from
carefully designed human clinical studies evaluating the effects of nitrate and thiocyanate (along
with dietary iodine) on I- uptake inhibition, in order to determine RfDs for all prevalent NIS inhibitors
in drinking water and food. Moreover, further animal studies are needed, investigating not only
thyroidal, but also neurodevelopmental endpoints in circumstances of controlled intake of iodine,
perchlorate, nitrate and thiocyanate..
WOLFF
Perchlorate and the thyroid gland.
Wolff J.
Pharmacol Rev. 1998 Mar;50(1):89-105. Review.
Perchlorate competitively blocks iodide from entering the thyroid by an effect on the Na+/I-
symporter thus preventing the further synthesis of thyroid hormone but has no effect on the
iodination process itself. It is concentrated by thyroid tissue in a manner similar to iodide but is not
significantly metabolized in the gland or peripherally. What is not settled is whether there are
additional perchlorate effects on iodide transport. Perchlorate has a fast turnover in the body and
requires frequent daily doses for therapy of thyrotoxicosis. Perchlorate appears to be substantially
more effective against large iodide loads than the thionamides, and, with long-term iodide
contamination, combined therapy of perchlorate (with < or = 1 g/day) and thionamides is
recommended for the more severe cases of thyrotoxicosis that may result from excess iodide or
iodide-generating organic compounds, as for example with amiodarone. After approximately 30
days, the perchlorate dosage can be tapered or stopped, continuing with thionamides alone. This
markedly increases its safe use. Despite serious side effects during its early use, lower dosages
and shorter treatment periods appear to have prevented such reactions in its recent reintroduction,
mostly for amiodarone-induced thyroid dysfunction. Perchlorate can also protect against inhibition
of thyroid function and the resulting hypothyroidism caused by excess iodide, presumably by
reducing the formation of an iodinated inhibitor. The reduction of the iodide pool by perchlorate
thus has dual effects--reduction of excess hormone synthesis and hyperthyroidism, on the one
hand, and reduction of thyroid inhibitor synthesis and hypothyroidism on the other. Perchlorate
remains very useful also as a single dose application in tests measuring the discharge of
radioiodide accumulated in the thyroid as a result of many different disruptions in the further
metabolism of iodide in the thyroid gland.
CROHN
Perchlorate Controversy Calls for Improving Iodine Nutrition
Crohn DM
Vegetarian Journal 2006 Issue 2
Depending on the amount ingested, perchlorate may affect the body in a number of ways, but it is
normally expected to interfere with the thyroid first. The thyroid is a small butterfly-shaped gland at
the front of the neck. It uses iodine to produce the only biologically active compounds in the body
that contain iodine, the hormones T3 and T4. To produce these hormones, the thyroid must collect
and concentrate iodine from the bloodstream. When perchlorate is present, the thyroid will collect
both iodine and perchlorate so that the amount of iodine that can be concentrated is reduced.
Perchlorate is seldom a significant problem for people with adequate iodine in their diets because
the thyroid still absorbs enough to meet the body's hormone production needs. If a person is
already iodine deficient, however, perchlorate can further impair their ability to produce T3 and T4.
To be fair, perchlorate is not the only chemical that interferes with the thyroid's iodide collection. At
least two other compounds common in the American diet, nitrate and thiocyanate, can also
interfere with iodine collection. Nitrate, the most widely occurring groundwater pollutant, results
from over-fertilization with nitrogen fertilizer or manures. Nitrate concentrations are regulated in
drinking water because it can contribute to a type of anemia in infants known as 'blue baby
syndrome,' not because of its possible effect on thyroid function. Thiocyanate occurs naturally in
certain vegetables, such as broccoli, cauliflower, cabbage, turnips, and Brussels sprouts. Although
perchlorate interferes more strongly with thyroid function than thiocyanate or nitrate, these last two
compounds are more common in most people's diets.
Perchlorate is, therefore, a concern because it intensifies problems resulting from iodine
deficiency. Iodine deficiency is already the world's leading cause of avoidable intellectual
impairment. The damage that this deficiency precipitates is permanent, but most damage is mild to
moderate. Nonetheless, damage can be severe, depending on the timing and intensity of the
deficiency. Typical iodine consumption in the United States has fallen significantly since the early
1970s, leading to concerns that iodine deficiency problems in the public at large, and particularly in
nursing mothers, may be increasing. This decrease in iodine intake in the United States is likely
associated with changes in the manufacturing of bread and milk that have lowered their iodine
contents. In addition, processed foods, which have become more popular, frequently are
manufactured with non-iodized salts.
Perchlorate should interest Journal readers because risk assessments suggest that the babies of
pregnant and nursing vegan mothers are, theoretically, at greatest risk for perchlorate toxicity.
Vegans are perceived to be at greater risk than the general public, including lacto-vegetarians,
because plant-based diets are generally relatively low in iodine. Evidence for this comes from
knowledge of the iodine content of different foods rather than from direct measurements of iodine
levels in vegans. The iodine content of most fruits, nuts, and vegetables is low but can vary
depending on soil iodine content, irrigation, and fertilization practices.
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