Applied Geochemistry, Vol. 4, pp. 203-208, 1989
0883-2927/89$3.00 + .(X) Pergamon Press plc
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Iodine in waters: possible links with endemic goitre RONALD FUGE Centre for Applied Geochemistry, Institute of Earth Studies, University College of Wales, Aberystwyth, Dyfed SY23 3DB, U.K. (Received 9 September 1988; accepted in revised form 20 January 1989)
Abstract--Iodine analyses of surface waters from various areas of the U.K. (0.40-15.6/~g/1 I) and N. America (0.47-13.3/~g/l I) reveal considerable regional differences. Some variation is due to contaminant I deriving from urban, industrial and agricultural sources and drainage from abandoned metalliferous mines. However, it is significantthat the geology of the areas with higher I levels is dominated by limestone bedrocks. The I content of domestic supplies reflect their source, sub-surface waters containing appreciably more than those from surface sources; in addition, I in waters for domestic use is reduced during purification treatment. It is unlikely that drinking waters provide more than 10% of the daily human I requirement. Whereas the I content of surface waters can give a general indication of the I status of the local environment, the highest levels were recorded for Missouri (~ = 8.03/~g/l) and northern England (2 = 3.71), areas where endemic goitre was prevalent and soil I is generally low.
INTRODUCTION Ix HAS long been suggested that a low I content in drinking water is a contributory factor to occurrences of endemic goitre in man and animals. The idea that water is an important source of dietary I is historical and would seem to be due, in part, to an over estimation of I levels in this medium. Much of the early data on I in waters is reviewed by McCLENDON (1939) and it was the same author ( M c C L E N D O N and WILLIAMS, 1923) who suggested that levels of less than 3-5/~g/11 in a water supply are goitrogenic. The contribution of drinking water to dietary I has been variously assessed. STANBURY(1967) suggests that 20% of man's I requirement derives from this source while ELEMENTS (1976) prefers a figure of 10°//o. STANBURY a n d RAMALINGASWAMI (1964) state that water must make a significant but minor contribution to dietary I, a view echoed by BECKERSand DELANGE (1980) who stress the role of food as the main I source. UNDERWOOD(1977) and KOUTRASet al. (1980) list examples where low I water supplies have been a major cause of endemic goitre but suggest that in most areas the proportion of I intake derived from this source is low. Many workers, on the other hand, have commented on the marked inverse correlation between the I content of drinking water and the prevalence of endemic goitre. VONFELLENBURG(1933) found this in Switzerland, BRUSH and ALTLAND (1952) in Michigan, U.S.A., WILSON (1954) in Nigeria and Sri Lanka, HUGHES et al. (1959) in north Oxfordshire, U.K., COBLEetal. (1968) in Egyptian oases, KAMBAL et al. (1969) in Sudan, KARMARKARet al. (1974) in t h e Himalayas and, most recently, ROSENXHAL and MATES (1986) in Israel. PEREL'MAN (1977) rejects the idea that drinking water is a major source of I in the human diet but 203
suggests that low I contents in surface waters indicate a deficiency in the local environment. The negative correlation between goitre occurrence and I in water is, according to KOtJTRAS(1986), merely an index of the element in locally produced food. This paper presents data on I in surface, spring and reservoir waters and domestic supplies in areas with a history of endemic goitre together with other areas where no such problems have been noted. The regions studied are mainly in the U.K. but a smaller number of samples from N. America are included. The link between I in waters and the occurrence of endemic goitre is considered in the light of the present data and that from the literature. The analyses have been performed by automated photometric methods as previously outlined (FUGEet al., 1978, 1985).
IODINE GEOCHEMISTRY
Iodine in the primary environment is generally low with igneous rocks containing an average of 0.25 ppm (FtJGE and JOHNSON, 1986). Sedimentary rocks can contain appreciably more I, particularly if they are organic rich. However, it is apparent that most I in soils is derived from the atmosphere which is enriched in that element (GOLDSCHMIDT,1954; RANKAMAand SAHAMA, 1950; PEREL'MAN, 1977). Atmospheric I derives from sea water which contains 58/~g/1 (a mean of all reliable literature values--FUGE and JOHNSON, 1986). Iodine from the oceans is volatilised into the atmosphere possibly as I vapour (MIYAKE and TSUNOGAI, 1963) or as CH3I (WHITEHEAD, 1984) and is then carried onto the land masses where it is deposited in wet and dry precipitation. SUGAWARA (1967) has suggested that about half of the I deposited in this way is carried off in surface drainage.
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Ronald Fuge
Limited information is available on the I content of precipitation but a wide range of values seems likely (FuGE and JOHNSON, 1986). Recently, FUGE et al. (1987) have shown that I contents of rainfall are highest in near coastal environments (2.i/~g/1 at the Welsh coast) but decrease with increasing distance inland (1.0/~g/1-84 km from the coast). In addition, data for rainwater from central Missouri, more than 800 km from the nearest coast, show I to be <1 #g/l (FUGE, 1987).
RESULTS AND DISCUSSION
The data from this study are presented in Table 1 and in histogram form in Fig. 1.
S u r f a c e wafers
There is an apparent regional variation in the I content of river and stream waters of the U.K., the
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Iodine c o n t e n t in ~Jg/I
FIG. 1. Histograms of I concentrations in: (i) spring and well waters, (ii) domestic water supplies, and (iii) river and stream waters, from the U.K.
samples from northern England being somewhat higher than those from elsewhere. WHITEHEAD(1979) also noted a regional variation in river waters of the U.K. but suggested that the high levels of I he found for rivers in S.E. England and the W. Midlands are due to urban contamination, mainly from sewage effluent. The same author found consistently low I levels in rivers and lakes of rural areas. The surface waters analysed in this study are generally in the same range as those listed by WHITEHEAD (1979) but the majority are from rural areas. The northern England samples are mainly from Northumberland, Durham, Yorkshire and Derbyshire, an area which is dominated by Carboniferous limestone. Most other U.K. samples were collected from areas where there are few calcareous rocks. FUGE and JOHNSON (1986) note that limestones are generally richer in I than most other rock types and list literature values ranging up to 29 ppm. Analyses of limestones from northern England give values of up to 2.23 ppm in outcropping rocks with weathered limestones from soil profiles containing up to 6.62 ppm I (FUGE and LONG, 1988). It is possible, therefore, that the higher levels of I in surface waters from northern England reflect the geology. Although most of the samples analysed in this work are from rural regions, it is likely that some of the higher values are due to contamination. Some streams in Wales draining predominantly agricultural areas are somewhat enriched in I (up to 3.5/~g/1). This probably reflects the use of I-containing sterilants and detergents for dairy equipment, while some herbicides etc. are I-based. In addition, farmyard manure can also contain appreciable I and this could add significantly to some streams and rivers. Three of the highest I values for river waters from Wales (4.0-6.2 #g/l) were found in samples collected from within 1 km of the sea. These samples are also rich in C1 (>20 mg/l) and it is likely that the main source of these two halogens is sea spray. The effluent from disused metal mines can contain up to 5.5pg/l I (FuGE et al., 1978: JOHNSON,1980) and this together with tailings drainage could be a source of the element in surface run-off. This may be important in parts of north- and mid-Wales where there are many abandoned mine workings. Several of the lake waters analysed in the present study are enriched in I, most of these have been found to contain relatively high levels of organic matter, some of which may be derived from contamination. However, many of these lakes occur in upland regions and it is possible that much of the drainage is from peaty areas. Most peats are strongly enriched in I and the data of WHITEHEAD (1979) and JOHNSON (1980) suggest that waters draining peats are also enriched. Most of the reservoir waters analysed in this study are from upland regions and are surrounded by peaty ground which could explain their higher I levels. It is also of note that the highest value for a reservoir water (4.48#g/1 I) is that for Calcleugh
205
Iodine in waters: possible links with endemic goitre Table 1. Iodine in surface, spring and reservoir waters and domestic supplies Iodine content ~g/1) No. of samples
Range
Mean
Stream and river waters S. Scotland, U.K. N. England, U.K. S. England, U.K. Wales, U.K. Missouri, U. S.A. British Columbia and Alberta, Canada
5 35 10 47 10 5
0.88-3.60 1.18-15.6 1.75-5.54 0.40-7.80 3.17-13.30 0.47-2.48
3.71 2.96 2.13 8.03 0.94
Lake waters British Isles
12
1.47-12.60
4.77
9
2.50-4.84
3.33
11 3 16
1.66--14.0 2.12-4.88 1.18-7.30
4.30 3.33 4.17
9 7 9 1 1 1
1.30-3.73 1.95-11.90 0.50-3.80 -
1.82 5.52 1.89 <0.10 6.42 7.68
Sample type and source
Reservoir waters British Isles Spring and well waters N. England, U.K. S.W. England, U.K. Wales, U.K. Domestic supplies N. England, U.K. E. and S. England, U.K. Wales, U.K. Calgary, Alberta, Canada Rolla, Missouri, U.S.A. Phoenix, Arizona, U.S.A.
reservoir in Northumberland which contains extremely peaty water. The results for the N. American river water samples show those from Missouri to be relatively I-rich. Some of the high values are probably due to contamination; the highest values of 11.3 and 13.3 btg/1 I were obtained for the Missouri and Osage rivers, respectively, which are likely to be affected by industrial and urban effluent. However, even disregarding the two highest values the remaining samples range up to 9.10/~g/11 with a mean of 7.0/~g/1. The Missouri waters were collected during the summer of 191~6 following a period of drought and the high I values may, in part, reflect the low flow. However, many of the samples derive from rivers draining areas of calcareous rock and, as in the case of northern England, the higher values may reflect the geology. In addition, several of the rivers have an appreciable input of subsurface water which may be a significant source of I, particularly during a period of drought. Of the Canadian samples analysed only one has a relatively high value 2.48/zg/l, the other four containing <0.70/~g/l. The higher figure was obtained for a sample from the Red Deer River near Brooks, Alberta, an extremely muddy river which drains organic-rich Cretaceous rocks. This sample also contains 2.15 mg/1 C1, which is more than twice the level in the other samples, thus it is probable that halogens are being derived from the Cretaceous rocks. The I values obtained in this study for surface
1.96
run-off from most areas are lower than much of the data listed in the literature. FUGE (1974) and FUGE and Jonr~soN (1986) have compiled literature data for I in river and stream waters and the latter have proposed an average of 5/~g/l I. The value obtained in the present study for U.K. waters (~ = 2.42/~g/l) is close to the mean value for Japanese waters (2.2 ,ugttI'-'-SUGAWARA,1967) and waters from N. Israel (2-2.5/tg/I--ROSENTHAL and MATES, 1986). It is possible that previous estimates of average I in surface run-off are somewhat high due to the inclusion of data for waters contaminated from urban, industrial and agricultural sources.
Spring and well waters Whereas the range of values for these waters is similar to that for surface samples, the mean value (4.11 gg/1) suggests that the subsurface waters are generally richer in I. There is no obvious regional variation of I content in spring and well waters. Literature data suggest that subsurface waters are frequently enriched in I (FuGE and JOHr~SON, 1986), generally containing much higher values than those recorded in this study. The relatively low I content of most of the spring and well waters recorded here probably reflects fairly shallow water penetration and short residence times. The highest I values were recorded for samples which are solute-rich.
2(16
Ronald Fuge
Table 2. Variations in iodine contents of river and spring water with rate of flow Iodine content t ttg/[) Sample
Low flow
Average flow
High llow
1.~2 t. 53 1.62
1.7t~ -1.02 !1.97 i 5.~ 4.7S
River 1, mid Wales, U.K. River 2, mid Wales, U.K. River 3. mid Wales, U. K River 4, mid Wales, U.K.
2.52 2.65
River 1, N.E. England, U.K. River 2, N. England, U.K.
5.12 I S6
--
Spring, mid Wales, U .K. Spring, N. England, U.K, Spring. Missouri, U.S.A.
7,3(I 2,82 Ytl5
-1.42
Temporal variation of iodine in surjace and spring wagers
KAMENEV (1968) recorded higher I contents for Russian rivers in summer than in spring or winter, but RYKHILOV (1970) found no such variation. WHiTEHEAD (1979) suggests that several of his values for I in river waters may be high because they were collected after dry weather. The samples analysed in this study were collected at various times of the year and states of flow. No significant variation was observed on a seasonal basis, however, there were marked differences in the I content of run-off during wet and dry periods (Table 2). It is apparent that the I levels of both river and spring waters are strongly influenced by the volume of flow. H o w e v e r , the effect of increased flow is not uniform, In the mid Wales and Missouri samples the I level decreases with increasing flow but in the northern England samples the opposite is true. The reason for this variation is not immediately apparent but the high flow samples from northern England were collected during very heavy rain in early summer following a period of drought. It is likely that during rainfall, I levels of surface waters could vary markedly over a short time span because the corresponding levels in rainwater have been shown by FUGE et al. (1987) to vary through one event from 0.89 to 4.1 ~tg/1 I (at a coastal site). In such a rainfall event there is initially a considerable washout ("flushing") effect resulting in elevated I levels, followed by a dilution effect. There would be a corresponding influence on surface run-off which might explain the variable effect of flow rate on I content. In the author's opinion, however, the very marked increase of I levels from low to high flow rates in the northern England rivers is likely to be due largely to the sudden "flushing" of soluble I from soils and plant surfaces, etc. This source of I would probably have been fairly rich due to dry deposition during the preceding period of drought. In addition, the samples were collected from rivers draining high ground with areas of peat which following desiccation could be more prone to lose I.
-
2.00 3.8 I
The increase of I with increased flow in the spring samples from northern England is harder to explain but could be due to the higher concentration in surface water which subsequently mixed with subsurface water prior to its issue from the spring.
Domestic supplies The range of values is similar to those of the surface and subsurface samples. It is apparent that there is a marked regional variation in I content which seems to reflect the source of the waters. Most domestic supplies in a large part of England and Wales are obtained from surface waters either from reservoirs or directly by abstraction from rivers or river gravels. This is reflected in the general low levels of I in most of the U . K . domestic waters analysed in this study (~ 1.92/~g/l for Wales and 1.85 Ftg/1 for northern England). The higher values are found mainly in waters from east and southeast England (~ = 5.52 1~g/l) where much of the domestic supply is derived from subsurface sources. The high value recorded for the London domestic supply (7.68/~g/1 I) may reflect its derivation from re-cycled water. The water supply of both Rolla, Missouri and Phoenix, Arizona is from subsurface sources and is enriched in I. H o w e v e r , the water supply for Calgary, Alberta, which is extremely low in I (<0.1/~g/l) is derived from the Bow and Elbow rivers; the former of these was found to contain 0.64/~g/l I. Similar results were obtained by DEAN (1963) in a study of domestic waters in New Zealand. DEAN records a similar range of I values (0.7-14.8¢tg/1) with the highest being those from artesian and bore sources (2 = 5.29 llg/1 for 10 samples). Supplies derived from upland surface sources (2 = 4.55 ~g/l for 11 samples) contained more I than those from river sources (2 = 2.72/~g/l for 11 samples). It seems likely that the I content of waters for domestic use are decreased during treatment; comparison of the values for surface, reservoir and domestic waters of several areas reveals I to be lowest in the domestic supplies (Table 3).
Iodine in waters: possible links with endemic goitre
207
It is therefore apparent that while some waters derived from subsurface sources can provide a major component of dietary I in limited areas, in the vast Mean I content (#g/l) majority of cases water for domestic use supplies only Domestic a small percentage of the I requirement for man and Area River Reservoir supply animals. It seems likely that most 1-rich waters from subsurface sources will be solute-rich and as such N. England, U.K. 3.71 3.58 1.85 would be somewhat unpalatable. S.W. England, U.K. 2.35 2.50 1.95 The idea that the I content of surface waters is an Wales, U.K. 2.13 3.25 1.92 index of that element in the environment as suggested Calgary, Alberta, 0.64" -<0.10 Canada by PEREL'MAN (1977) and KOUTRAS (1986) and, moreover, can be used as a measure of the likelihood *This value is for the Bow River which provides about of the occurrence of I-deficiency diseases, has some half of the domestic supply. merit. Many researchers have found links between the I content of local waters and the severity of goitre; KAMBALet al. (1969) demonstrated this in Sudan and MALAMOSet al. (1971) in Greece. DAY and POWELLENDEMIC GOITRE AND IODINE IN WATERS JAcrsor~ (1972) have shown that I contents of surface As outlined above, several workers have suggested waters in the Himalayas, an area of extreme endemic that drinking water is an important dietary source of goitre, are all
Table 3. Comparison of I contents of river, reservoir and domestic supplies
Table 4. Comparison of I contents of soils and surface waters Mean I content (No. of samples)
Wales, U.K. Wales, U.K. Derbyshire, N. England, U.K. Missouri, U.S.A. *FUGE(1987). t FUGE(unpublished data). ~:FUGEand LONG(1989).
Distance from coast (km)
Soils (ppm)
Surface waters (#g/l)
<20 20--40 >80 >800
14.7 (424)* 11.9 (120)t 5.41 (28)~ 1.26 (92)*
2.35 (15) 2.11 (32) 3.94 (8) 8.03 (10)
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Ronald Fuge
Acknowledgements--The author is extremely grateful to Dr Bobby Wixson of the University of Clemson, S. Carolina, and Dr Nord Gale of the University of Missouri-Rolla, for their help and advice on sampling in the U.S.A. Editorial handling: Brian Hitchon.
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KAMBALA., RAHMANI. A., GREIGW. R., GRAYH. W. and McGIRR E. M. (1969) Endemic goitre in the Sudan. Lancet 1,233-235. KAMENEV V. F. (1968) The content of iodine and other halogens in the soil, water and plants within the UlanUde area. Vop Pitaniya 27, 77-78 (in Russian). KARMARKAR M. G., DEO M. G., KOCHUPILLA1 N. and RAMALINGASWAMI V. (1974) Pathophysiology of Himalayan endemic goiter. Am. J. clin. Nutr. 27, 96-103. KELLY F. C. and SNEDDEN W. W. (1960) Prevalence and geographical distribution of endemic goitre. In Endemic Goitre, pp. 27-233. WHO, Geneva. KOUTRAS D. A. (1986) Iodine: distribution, availability, and effects of deficiency on the thyroid. In Towards the Eradication o f Endemic Goiter, Cretinism, and Iodine Deficiency (eds J. T. DUNN, E. A. PRETELL, C. H. DAZA and F. E. VITERI) pp. 15--26. Pan American Health Organisation, Washington, DC. KOUTRASD. A., MATOVINOVICJ. and VOUGHTR. (1980) The ecology of iodine. In Endemic Goiter and Endemic Cretinism. Iodine Nutrition in Health and Disease (eds J. B. STANBDRVand B. S. HETZEL) Chap. 9. Wiley. MALAMOS B., KOUTRASD. A., RIGOPOULOSG. A., PAPAPETROU P. D., GOUGASE., KELPERI n . , MORAITOPOULOS C., DAVI E. and LEONARDOPOULOS J. (1971) Endemic goiter in Greece: some epidemiologic studies. J. clin. Endocrinol. 32, 130-139. MCCLENDON J. F. (1939) Iodine and the Incidence of Goitre. Oxford University Press. McCLENDON J. F. and WILIJAMS A. (1923) Simple goiter as a result of iodine deficiency. J. Am. reed. Ass. 80, 60(}601. MIYAKE Y. and TSUNOGAIS. (1963) Evaporation of iodine from the ocean. J. geophys. Res. 68, 3989-3993. PERLE'MAN A. I. (1977) Geochemistry o f Elements in the Supergene Zone. Keterpress Enterprises, Jerusalem. RANKAMA K. and SAHAMA Z. G. (1950) Geochemistry. University Press, Chicago. ROSENTHAL E. and MATESA. (1986) Iodine concentrations in groundwater of northern Israel and their relation to the occurrence of goiter. Appl. Geochem. 1,591-600. RHKHILOV G. P. (1970) Level of fluorine, bromine and iodine in the water of the Irtysh and Om rivers. Mikroelem. Sib. 7, 22-26 (in Russian). STANBURYJ. B. (1967) Inherited and environmental factors in thyroid disease. In Modern Trends in Endocrinology, Vol. 3 (ed. H. GAgDENER-HILL) Chap. 3. Butterworths. STANBURYJ. B. and RAMALINGASWAMIV. (1964)Iodine. In Nutrition, Vol. 1. Macronutrients and Nutrient Elements (eds G. H. BEATON and E. W. MCHENRY) Chap. 7. Academic Press. SUGAWARAK. (1967) Migration of elements through phases of the hydrosphere and atmosphere. In Chemistry o f the Earth's Crust (ed. A. P. VINOGRADOV)Vol. 2, pp. 501510. Program for Scientific Translations, Jerusalem. UNDERWOOD E. J. (1977) In Trace Elements in Human and Animal Nutrition, Chap. 1 l, 4th Edn. Academic Press. WHITEHEAD D. C. (1979) Iodine in the U.K. environment with particular reference to agriculture. J. appl. Ecol. 16, 269-279. WHITEHEAD D. C. (1984) The distribution and transformations of iodine in the environment. Environ. Int. 10, 321-339. WILSON D. C. (1954) Goitre in Ceylon and Nigeria. Hr. J. Nutr. 8, 90-99.