Effects of low mercury vapour exposure on the thyroid function in chloralkali workers

Abstract

Forty‐seven chloralkali workers exposed to mercury vapour for an average of 13.3 years were compared with 47 referents matched for age in a cross‐sectional study of thyroid function. The mean urinary mercury concentration in the exposed workers was low compared with other studies of chloralkali workers: 5.9 nmol mmol−1 creatinine (range 1.1–16.8) vs 1.3 nmol mmol−1 creatinine (range 0.2–5.0) in the reference group. The median serum concentration of reverse triiodothyronine (rT3) was statistically significantly higher in the exposed subjects compared with the referents (268 pmol l−1 and range 161–422 vs 240 pmol l−1 and range 129–352; P = 0.009). The difference between the exposed subjects and the referents was most pronounced in the highest exposed sub‐groups. The free thyroxine (T4)/free T3 ratio was also higher in the highest exposed subgroups compared with the referents. The median serum concentration of tumour necrosis factor alpha (TNF‐α) was lower in the exposed subjects (7.3 pg ml−1 and range 4.4–69.7 vs 8.0 pg ml−1 and range 6.0–34.6; P = 0.004). Exposed subjects with the lowest urinary iodine (<67.8 nmol mmol−1 Cr) had higher serum concentrations of reverse T3 and a higher free T4/free T3ratio than the other subjects, suggesting that a low concentration of iodine in urine may be a risk factor for increased serum concentrations of reverse T3 and the free T4/free T3 ratio in subjects exposed occupationally to mercury vapour. The study could indicate a slight effect of low mercury vapour exposure on the function of the enzyme type I iodothyronine deiodinase, possibly modified by comparatively low urinary iodine concentrations. Copyright © 2000 John Wiley & Sons, Ltd.

Mercury derived from dental amalgams and neuropsychologic function.

“…Dentists and dental workers have lower UHg (range, 2.0-45 µg/g creatinine) Cianciola et al 1997;Naleway et al 1985Naleway et al , 1991Ritchie et al 1995;Steinberg et al 1995;Woods et al 1993) than workers in chloralkali or other factories that use mercury (range, 50-116 µg/g creatinine) Buchet et al 1980;Ellingsen et al 2000Ellingsen et al , 2001Hansteen et al 1993;Lauwerys and Buchet 1973;Roels et al 1985). Occupational studies that include unexposed employees as controls have found UHg similar to ours (range, 0.9-1.4 µg/g creatinine) Buchet et al 1980;Ellingsen et al 2000;Hansteen et al 1993;Lauwerys and Buchet 1973;Roels et al 1985). In a healthy male military population with an average age of 53 years, UHg was also comparable (1.8 µg/g creatinine) (Kingman et al 1998).…”

Autism: Transient in utero hypothyroxinemia related to maternal flavonoid ingestion during pregnancy and to other environmental antithyroid agents

“…Moreover, inorganic mercuric chloride (HgCl 2 ) is also a strong inhibitor of thyroid peroxidase, an effect not observed with methylmercury chloride [128,129]. Human exposure to low levels of metallic mercury vapors produces decrease in T3 [130,131] confirming the inhibition of 5′-deiodinase type I in vivo; enzyme inhibition was higher in those with low urinary iodine excretion [131]. During pregnancy, Takser et al [132] found a significant correlation between inorganic mercury levels in umbilical cord and lower maternal serum free thyroxin (T4) levels and concluded that even low levels of exposure to persistent environmental contaminants interfere with thyroid status during pregnancy.…”

An in vitro approach to assess the toxicity of certain food contaminants: Methylmercury and polychlorinated biphenyls

“…A somewhat surprising finding was the high susceptibility of TT cells toward MeHg toxicity. However, there are reports indicating that mercury can affect thyroid function, both during development and in adults (Watanabe et al, 1999;Ellingsen et al, 2000;Takser et al, 2006).…”