The Science o f the Total Em'ironment, 3 (1975) 275-277 © Elsevier Scientific Publishing Company, Amsterdam - Printed in Belgium

T H E R E L A T I O N S H I P B E T W E E N M E R C U R Y LEVELS IN M A T E R N A L A N D C O R D B L O O D C. A. R. DENNIS and F. FEHR Prairie Institute o f Enciromnental l-[ealth, 2220 Lorne Street, Regina, Saskatchewan (Canada)

IReceived August 30th. 1974)

ABSTRACT The object of the study was to discover the relationship between mercury levels in maternal and cord blood. Paired whole blood samples, maternal and cord blood were analysed for total mercury content; 45 paired samples from non-fish-eating women in southern Saskatchewan demonstrated no significant differences in mercury levels between maternal and cord blood; 43 paired samples from fish-eating women in northern Saskatchewan demonstrated a significant difference, cord blood levels being higher. The significance is discussed.

INTRODUCTION A literature review indicated that the foetus may concentrate mercury and that the newborn child may be at greater risk of clinical damage than its mother 1-3. The object of the study, carried out in 1973, was to discover the relationship between mercury levels in maternal and cord blood. METHODS A survey 4 of whole blood mercury levels in Saskatchewan (1972) indicated that higher levels were to be found in persons living in northern Saskatchewan. Doctors from four centres in the north: Uranium City, La Ronge, Flin Flon and Nipawin, and from Regina in the south, participated in the study. Doctors were asked to submit paired blood samples of maternal and cord blood taken at the time of delivery. The method of collection and analysis for the blood samples was the same as in the 1972 survey. The Student's t test was used for statistical tests of significance. RESULTS Paired samples were submitted: 43 from the north and 45 from the south. With few exceptions subjects from the north ate locally caught fresh-water fish while subjects from the south did not. 275

Values for the mean mercury levels of maternal and cord blood (Table 1) indicate that the difference between maternal and foetal levels from the south was not significant, while there was a significant difference (P < 0.01) between paired specimens from the north (Fig. I). There was a positive correlation between maternal and cord blood mercury levels in both regions: r = 0.45 in the south and r = 0.87 in the north. TABLE I MERCURY IN RESIDENTS

MATERNAL

North

AND

number

mean ng mercury/ml range* [median

l

South

number

Imean ng mercury/ml ]range* I median

FOETAL

WHOLE

BLOOD

Maternal

Foetal

43

43

15,0 1-53 9

26.7 2-95 17

45

45

6.8 1-27 5

7.5 1-22 6

OF

SASKATCHEWAN

* Limit of detectability 1 ng/ml.

80

70 60 0 o

~L 4 0

oo

o 0 o

o

0 0

~o 1~

0

-2%- % Moter

Zo

~o

~o

r~oI

Fig. I. Mercury in maternal and foetal whole blood (ng/ml~ of residents of northern Saskatchewan. v = 0.0038.~-z + 1.3151 x + 5.0670.

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DISCUSSION It should be stressed that the paired samples subjected to analysis were not intended to be representative of the population: indeed, selection from the north intentionally identified persons with a high fish intake when the opportunity arose. The results suggest that when the maternal blood level is minimally influenced by mercury absorbed from fish then cord blood levels are not significantly different from maternal blood levels, but that when maternal blood mercury levels are elevated then higher cord blood levels are found. The values from northern Saskatchewan did not show a strictly linear relationship but suggest rather that foetal levels rise more sharply than associated maternal levels. If it were known that maternal levels were uniform throughout the year, then a clear relationship between maternal and foetal blood levels might be predicted. However, the 1972 survey indicated that higher blood mercury levels were associated with the open water fishing season and that levels were lower at other times. As the paired samples were taken during the months September to December inclusive, it is possible that the higher foetal levels were associated with higher levels of maternal mercury absorption during the earlier months of pregnancy, i.e. during the open water fishing season. Otherwise the evidence would seem to add support to the hypothesis that the foetus concentrates mercury in some way, either by selective concentration or possibly by an inability of mercury to recross the placental barrier. Until proven otherwise the foetus carried by a mother who is a high fish consumer must be considered the critical member of the Saskatchewan population potentially at risk from the adverse effects from mercury. ACKNOWLEDGEMENTS The authors wish to acknowledge the active co-operation of the Research Comittee of the Saskatchewan Chapter of the College of Family Physicians without whose assistance this research study would not have been possible. We also gratefully acknowledge the help of physicians and staff members from the obstetrical units of the following hospitals: Flin Flon, La Ronge, Nipawin Union, Uranium City Municipal and Regina General. Mercury analysis was carried out by Mr. H. Wooley under the direction of Mr. G. Scattergood, senior occupational hygienist--Government of Saskatchewan and Mr. G. Spencer was the computer programmer-analyst. The report is part of a study financed by the Public Health Research Grant, Number 607-7-171, of the National Health Grants Program. REFERENCES 1 D.J. Clegg. Mereuo' in Man's Enriromnent, Royal Society of Canada. Ottawa, 1971, p. 141. 2 Report from an Expert Group, Nord. hryg. Tidskr., (1971) 202. 3 P. E. Pierce J. F. Thompson, W. H. Likosky, L. N. Nickey, W. F. Barthel and A. R. Hinman, J. Amer. Med. Ass., 220 (1972~ 1439. 4 C. A. R. Dennis and F. Fehr, Sci. Total Environm., 3 (1975) 267.

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The relationship between mercury levels in maternal and cord blood.

The object of the study was to discover the relationship between mercury levels in maternal and cord blood. Paired whole blood samples, maternal and c...
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