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Letters |
1
Lab. Service Branch,
2
Public Health Branch, Ontario Ministry of Health, Toronto, Ontario, Canada,
a Address for correspondence: 81 Resource Rd., Etobicoke, Ontario, Canada M9V 3T1.
To the Editor:
Since 1980, the Ontario government has conducted several blood lead screening surveys in children in several cities and regions of Ontario, Canada (1)(2). The blood lead concentrations in Ontario children has declined in both rural and urban areas over the past decade, this decline coinciding with the complete phasing out of lead in gasoline in 1990. Here, we evaluate this decline in terms of the geometric mean of the blood lead concentrations of 6014 children.
The collection procedure of capillary finger-prick blood samples and the method for blood lead analysis by Zeeman graphite furnace atomic absorption spectrophotometry were described previously (3) and were used identically in all our blood lead analyses. The blood lead screening and surveys evaluated were done in the Toronto Western Health Unit in 1984, 1985, and 1988; the Peel Region, 1987; the Niagara Region, 1987; Southern Ontario, covering more-urban areas (Toronto, Windsor, etc.), 1984 (1); and Northern Ontario, covering the less-settled areas (e.g., Thunder Bay and Moosonee), 1987 and 1992 (2)(4).
Gasoline sales data in Ontario were taken from Statistics Canada (Ottawa, ON), and the annual estimates of the lead content (g/L) of leaded gasoline in Ontario were provided by Ethyl Canada (Mississauga, ON). Thus the total lead in leaded gasoline consumption in Ontario was calculated as the product of grams of lead per liter of gasoline times the liters of leaded gasoline sold. In 1982, 2.6 x 109 g of lead was consumed in Ontario; by 1990, this had declined to 1.9 x 107 g.
The geometric mean of the blood lead concentrations and the total
amount of lead in leaded gasoline consumed in each year from 1983 to
1992 are shown in Fig. 1
. The linear regression analysis of the 22 blood lead summaries
determined during that time shows a decline of 0.05 µmol/L per year
(r = 0.8505, n = 22; 1 mol = 207.2 g). In a
high-risk area of the Toronto Eastern Health Unit, the rate of decrease
was 0.07 µmol/L per year (r = 0.9264, n = 10).
It declined at 0.04 µmol/L per year (r = 0.8287,
n = 3) for the Toronto Western Health Unit from 1984 to 1988, and
at 0.06 µmol/L per year (r = 0.9441, n = 4) for
the City of Toronto from 1984 to 1992. The lead in leaded gasoline
declined by an average of 3.6 x108 g per year between 1982
and 1990 (r = 0.9604, n = 8). Moreover, the
regression analysis showed that the decline in blood lead
concentrations overall was closely correlated to the decrease in the
previous years' consumption of leaded gasoline (r =
0.9323, n = 13). This close correlation was evident in the Toronto
Eastern Health Unit (r = 0.9646, n = 8), the
Toronto Western Health Unit (r = 0.9999, n = 3),
and the City of Toronto (r = 0.9881, n = 4).
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Our results are similar to the close correlation reported for blood lead in the US population for 1976–1991 (5). That study concluded that the major cause of the observed decline in blood lead was most likely the removal of 99.8% of lead from gasoline (5). Moreover, the blood lead values reported previously correlated well with air lead concentrations in the environment in previous studies (1). Lead additives in gasoline were shown (1) to be the most significant single determinant of Ontario children's blood lead concentrations.
We had some difficulty interpreting data in the early studies and
explaining why the blood lead concentrations in 1985 were higher than
in the previous year, despite having been determined with exactly the
same analytical techniques. This became clear when the leaded gasoline
consumed in Ontario was considered along with the blood lead values.
The consumption of lead in leaded gasoline indeed increased in 1984,
and then gradually declined in the following years (Fig. 1
).
The geometric means of the blood lead concentrations of 227 Toronto children and 395 children in Moosonee (4) were 0.17 and 0.15 µmol/L, respectively, in 1992—slightly higher than the 0.08 µmol/L measured in cord blood from 95 Toronto newborns (a different sampling technique) (6). The blood lead concentrations in Ontario children decreased to 0.15 µmol/L, similar to the US geometric mean of 0.17 µmol/L for children ages 1 to 5 years during 1988–1991 (5) and to the British geometric mean of 0.11 µmol/L for boys in 1995 (7). This value is in keeping with current guidelines by Health Canada and by the US Centers for Disease Control and Prevention in preventing lead poisoning in young children. The further decrease in blood lead concentrations of Ontario children will be affected by the way we remove the major blood lead risk factors identified in the previous studies, e.g., lead contamination in soil, drinking water, lead-based paint, industrial lead emission, lead shot, and lead solder in several consumer products (1)(2)(4).
References
The following articles in journals at HighWire Press have cited this article:
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  E. Weir Identifying and managing adverse environmental health effects: a new series Can. Med. Assoc. J., April 1, 2002; 166(8): 1041 - 1043. [Full Text] [PDF]
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; blood lead concentrations in the
Toronto Eastern Health Unit (
), in the Toronto Western Health Unit
(*), in the City of Toronto (
), and in other regions of Ontario,
(•).