INCREASED THYROID VOLUME AND PREVALENCE OF THYROID-DISORDERS IN AN AREA HEAVILY POLLUTED BY POLYCHLORINATED-BIPHENYLS

Objective: To evaluate whether long-term exposure to heavy environment al pollution with polychlorinated biphenyls (PCBs) could result in imp airment of thyroid status as evaluated by an epidemiological field sur vey. Methods: Thyroid volume (ThV) was measured by ultrasound in 238 e mployees of a factory (EMP) which previously produced PCBs and 454 ado lescents from the surrounding area polluted by PCBs. Controls (C) were 572 adults and 965 adolescents from much less polluted areas. In the 238 EMP and various numbers (shown in parentheses) of adult C the leve rs of thyroid-stimulating hormone (TSH) (n=498), thyroxine (n=498), th yroglobulin (n=278) and thyroid antibodies (anti-peroxidase (TPO Ab), n=517: anti-thyroglobulin (Tg Ab), n=455: anti-TSH receptor (TSHR Ab), n=238) were estimated in serum, while only TSH and TPO Ab were measur ed in 269 and 171 adolescents from polluted and control areas respecti vely. In several subjects in whom thyroid disease was suspected, total tri-iodothyronine or free thyroxine and tri-iodothyronine were measur ed. In a total of 362 adults and adolescents the urinary iodine was es timated. Results: Using the Mann-Whitney test, ThV in EMP (mean +/- S. E. = 18.85 +/- 0.69 ml, median = 17.3 ml, upper quartile=22.9ml, n=238 ) was significantly higher (P<0.001) than that in C (13.47 +/- 0.48 mi , 11.5ml, 15.3 mi, n=486 respectively). Similarly, ThV in adolescents from the polluted area (9.37 +/- 0.17ml, 8.9 mi, 11.0 mi, rr = 454 res pectively) was significantly higher (P < 0.001) than that in C (8.07 /- 0.10 mi, 7.6 mi, 9.6 mi, n = 965 respectively). In adults, a signif icantly increased prevalence of TPOAb (P<0.05) was found (using the ch i-square test) in EMP women of all. ages (54/190) vs C women (70/282), in EMP women aged 31-50 years (40/117 vs 70/282 respectively) and tho se aged 41-50 years (28/77 vs 54/215 respectively). Compared with C, t here was also a higher prevalence of Tg Ab in EMP women aged 31-60 yea rs (36/169 vs 50/342 respectively) and of TSHR Ab IP < 0.001) in the g roup of EMP men and women (25/238) vs sex- and age-matched C (6/238), No difference between EMP and C was found in the level of thyroxine (m ean+/-S.D,= 116.1 +/- 31.2 nmol/l, n = 238 vs 112.2 +/- 37.0 nmol/l, n = 460 respectively), TSH in the range 0.1-4.5 mU/l (1.56 +/- 0.86 mU/ l, n = 219 vs 1.51 +/- 0.84 mU/l. n = 460 respectively), prevalence of TSH: >4.5 (14/238 vs 28/498 respectively) and <0.1mU/l (25/238 vs 10/ 498 respectively). The prevalence of individuals without any defined c linical or laboratory signs of thyroid disorders among EMP who had cor ked in the factory for 21-35 years (43/128, 33.6%) was significantly l ower than that in twice as many matched C (118/256, 46.1%, P < 0.025) or in EMP who had worked for only 11-20 years (36/73, 49.3%, P < 0.05) . In adolescents, no difference was found in the prevalence of TPO Ab or TSH >4.5 mU/I between the polluted (17/269, 6.3% and 2/243, 0.8% re spectively) and C areas (15/171, 8.5% and 4/140, 2.8% respectively). T he median values of urinary iodine were in the optimal range (mu g per dI/number of cases) and about the same in polluted (12.6/90 and 11.4/ 55) and C areas (14.1/80, 13.2/82 and 13.4/55). Conclusions: Since iod ine intake in Slovakia is considered sufficient as a result of 45 year s of well-monitored iodine prophylaxis, the increased ThV and prevalen ce of thyroid disorders in the polluted areas presumably results from long-term exposure to toxic substances rather than from a difference i n life-long iodine intake. The increased prevalence of some thyroid an tibodies may be related to the known immunomodulatory effects of PCBs.