Volume 188 - Issue 1
Toxic levels of mercury in Chinese infants eating fish congee
Authors: Stephen J Corbett and Christopher C S Poon
Med J Aust 2008; 188 (1): 59-60. || doi: 10.5694/j.1326-5377.2008.tb01512.x
Published online: 7 January 2008
Published online: 7 January 2008
To the Editor: We report elevated mercury levels in three infants, each the only child of Chinese parents living in Sydney. All three children had eaten fish congee (a rice and fish porridge) as a weaning food and ate fish regularly as toddlers. Their parents had sought medical advice for either developmental delay or neurological symptoms in the children.
A 2-year-old boy had demonstrated increasingly aggressive behaviour for the past 6 months. A general practitioner had diagnosed mercury poisoning in the boy’s father 2 months earlier, following investigation for complaints of allergies, rashes, abdominal pain and diarrhoea. The family ate fish (usually salmon, barramundi or snapper) at least five times a week, and had used unspecified herbal medicines in the past. The child had eaten fish regularly since weaning. The boy’s blood mercury level was 158 nmol/L (normal range [NR], < 50 nmol/L), a random urine mercury/creatinine (Hg/Cr) ratio was 9 nmol/mmol (NR, < 6 nmol/mmol*), and his hair mercury level was 1.42 mg% (NR, < 0.18 mg%). The boy’s father and mother (who was pregnant) also had elevated hair mercury levels, of 4.3 mg% and 6.0 mg%, respectively. The father and child were treated with chelation therapy elsewhere.
A boy aged 2 years and 10 months presented with delayed speech and some autistic features. Since weaning, he had eaten fish (barramundi, sea perch, salmon and rock cod) up to eight times a week. He had no history of herbal medicine use, and his thyroid function, blood lead level, and a DNA screen for fragile X syndrome were normal. The child’s blood mercury level was 350 nmol/L and urine Hg/Cr ratio was 14 nmol/mmol (NR, < 10 nmol/mmol*). The boy’s father did not eat fish, and his blood mercury level was 19 nmol/L. The child’s mother did eat fish, and had a blood mercury level of 27 nmol/L. Two weeks after removing fish from the diet, the child’s blood mercury level had fallen to 99 nmol/L and his urine Hg/Cr ratio to 7 nmol/mmol. However, his behaviour did not improve, and he was subsequently diagnosed with classical autism.
A 15-month-old boy presented with delayed development since birth. Fish had been introduced to his diet at 8 months of age, and he had since continued to consume fish four to five times a week. He had recently eaten either ling or salmon. The boy’s mother had consumed ling three to four times a week after the fifth month of her pregnancy. The child’s thyroid function, DNA screen for fragile X syndrome, chromosome karyotype, and urinary metabolic screen were normal. His blood mercury level was 143 nmol/L, but fell to 19 nmol/L over a period of 1 year after ceasing fish intake. His longer-term developmental status is unknown.
Fish congee, made with either freshwater species or locally caught fish, is a common weaning food in coastal regions of southern China and South-East Asia.1 Adding fish to the weaning diet has health benefits,1,2 such as reducing anaemia, and is actively promoted. However, fish, particularly the large pelagic (open ocean) species more likely to be bought in Australia, may also contain mercury. Excessive consumption of mercury has been associated with neurological impairment.3-5
The Box shows that the consumption by infants of fish congee made from portions of large fish species may exceed the provisional tolerable weekly intake (PTWI)7 for methylmercury of 1.6 μg/kg bodyweight/week (the limit considered sufficient to protect a developing fetus). Food Standards Australia New Zealand’s most recent risk assessment concluded that median-level consumers of fish are unlikely to exceed the PTWI for methylmercury,6 but frequent consumers might if all their consumption is of predatory or long-lived fish species, which tend to acccumulate higher concentrations of mercury.
It has been previously noted in the Journal that public health policy regarding fish consumption needs to balance the health benefits for cardiovascular disease and anaemia with the possible ill effects of mercury on neurological development in infants.8
We recommend that multilingual information about fish and mercury be made available to pregnant women and mothers, especially targeting groups who are likely to be frequent consumers of fish and who use fish in weaning and infant foods. Regulatory and health promotion activities could also be informed by surveillance of blood or hair mercury levels in infants from ethnic groups at high risk of mercury intoxication, and of the frequency of fish consumption in this age group (by type of fish).
Estimated weekly mercury intake in infants consuming fish congee
Child’s estimated weekly mercury intake† (μg/kg bodyweight/week) |
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* For species consumed in Australia.6 † For a 12-month-old child weighing 10 kg; weekly fish consumption is estimated to be 0.25 kg, assuming 50 g servings five times per week. Provisional tolerable weekly intake for methylmercury = 1.6 μg/kg bodyweight/week.7 ‡ Average concentrations of all fillets purchased. | |||||||||||||||
References
- Leung SSF, Lui SSH. Nutritive value of Hong Kong Chinese weaning diet. Nutr Res 1990; 10: 707-715.
- Leung SS, Lee WT, Lui SS, et al. Fat intake in Hong Kong Chinese children. Am J Clin Nutr 2000; 72 (5 Suppl): 1373S-1378S. 0_i1091912
- Grandjean P, White RF, Weihe P, Jørgensen PJ. Neurotoxic risk caused by stable and variable exposure to methylmercury from seafood. Ambul Pediatr 2003; 3: 18-23. 0_i1091914
- Harada M. Minamata disease: methylmercury poisoning in Japan caused by environmental pollution. Crit Rev Toxicol 1995; 25: 1-24. 0_pgfId-1512193
- Kjellström T, Kennedy P, Wallis S, et al. Physical and mental development of children with prenatal exposure to mercury from fish. Stage II: interviews and psychological tests at age 6. Stockholm: National Swedish Environmental Protection Board, 1989. 0_i1091917
- Food Standards Australia New Zealand. Final assessment report. Proposal P265 — Primary production and processing standard for seafood. Canberra: FSANZ, 2005. 0_i1091919
- Joint FAO/WHO Expert Committee on Food Additives. Evaluation of certain food additives and contaminants. Sixty-first report of the Joint FAO/WHO Expert Committee on Food Additives. WHO Technical Report Series No. 922. Geneva: WHO, 2004. 0_i1091921
- Bambrick HJ, Kjellström TE. Good for your heart but bad for your baby? Revised guidelines for fish consumption in pregnancy [editorial]. Med J Aust 2004; 181: 61-62. 0_CBBHHIDC