ENVIRONMENTAL MERCURY EXPOSURE IN
CHILDREN WITH AUTISM:
A CASE-CONTROL STUDY
Ip P, Ho HK,
Lee J*, Wong VCN
Division of Neurodevelopmental Paediatrics, Department of
Paediatrics;
*Clinical Biochemistry Department, Queen Mary Hospital, The University
of Hong Kong, Hong Kong SAR, China
Objective: Chronic
low level of mercury exposure had been reported of harmful effect on
neurodevelopment of children. There was so far no scientific data on the
relationship between mercury exposure and autism. We evaluated blood and
hair mercury level in our patients with autism and compared them with age
and sex matched normal controls.
Methods: Simultaneous
hair and blood mercury levels were checked. The hair and blood mercury
levels were measured by Atomic Absorption Spectroscopy(AAS). Questionnaires
on family sociodemographic data and various risk factors for environmental
mercury exposure were completed. Statistical analysis including Student
t-test, Chi-square test, correlation analysis and analysis of variance procedure
were employed.
Results: 137 Hong
Kong children were enrolled in the study. 82 children (M:F=73:9; mean age
7.2 +/- 0.2year) fulfilled DSM-IV diagnostic criteria for autism and 55
normal children (M:F=46:9; mean age 7.8 +/- 0.4yr) were recruited as control. The mean hair mercury level (n=137) was 2.18 +/-
0.33ppm, exceeding the potentially harmful level of 2.1ppm as recommended
by US Environmental Protection Agency and it was also higher than levels of
European(1.2ppm) and US(1.5ppm) adults. The mean blood mercury level (n=137)
was 17.93 +/- 0.22nmol/L (WHO recommendation <45nmol/L). The mean hair mercury level of autistic group was
2.26 +/- 0.26ppm as compared with control group of mean 2.07 +/- 0.42ppm(p=0.79). The mean blood mercury
level of autistic group was 19.53 +/-0.49nmol/L as
compared with control group of mean 15.67 +/- 0.38nmol/L(p=0.13). 3.6% of our
subjects(5/137) had blood mercury level >45nmol/L, the WHO recommended
safety level(4/82= 4.9% autistic group vs
1/55=1.8% control group p=0.33).
Hair mercury level was correlated well (r=0.86) with blood mercury level in
our study (n=137). The frequency of fish consumption was the only
independent variable positively associated with both hair and blood mercury
level (r=0.5). Children consumed fish more than 3 times per week (n=52) had
doubled their hair and blood mercury levels as compared to those had less
than 3 times per week (n=85).
Conclusions: The mean hair and blood mercury levels of autistic group are at 9%
and 20% higher than the control group but the differences are not
statistically significant. The frequency of fish consumption in our
subjects has a positive correlation with hair and blood mercury level
hinting a highly possible means of environmental mercury exposure to Hong
Kong children. Our subjects in general having higher mean hair mercury level as compared with the
Western data.