Voir page 774 le resume en francais. En la pagina 774 figura un resumen en espanol.
Lead is a pervasive chemical that is well known for its toxicity (1). Lead causes neurological, physiological and behavioural problems in children, ranging from raised hearing threshold and decrease in intelligence quotient (IQ) at low blood lead concentrations to acute encephalopathy, memory loss and death at high blood lead concentrations (2). The harmful effects of lead, at even relatively low levels of exposure, have led WHO and the US Centers for Disease Control and Prevention (CDC) to consider lead concentrations in blood [greater than or equal to] 10 [micro]g/dl as elevated (2). Sources of lead in the environment that have been shown to contribute greatly to elevated blood lead concentrations include petrol, paint, water, food, cosmetics and lead-glazed ceramics (3, 4).
Automobile emissions are recognized as an important source of lead exposure for urban residents, particularly in areas with congested traffic. The lead from emissions is deposited in dust, soil and other ecosystems (5) and subsequently ingested by children (6, 7). Nutritional deficiencies of iron, zinc, copper, calcium and phosphorus enhance the absorption of lead (8, 9).
Leaded paint is another well-established cause of lead poisoning and elevated blood lead concentrations in children, often in association with pica (10). In New Zealand, the blood lead concentrations fell by 42% between 1978 and 1985 after lead-based paints and varnishes were abandoned and lead-soldered food and drinks cans were replaced by seamless-welded containers (11).
Two studies from Glasgow and Canada identified drinking-water as a potential source for elevated blood lead concentrations (12, 13). Although concentrations of lead levels in ground and surface water are typically low (14), levels may increase after water from surface drainage enters the distribution system. The type of utensils and containers used for storing and boiling water or for cooking and storing food can also contribute to elevated blood lead concentrations in children (6).
Traditional remedies or cosmetics can also be important sources of lead exposure. "Surma" and "kohl", which are preparations of powders, gels or water-based fluids used for eye make-up, contain 16-80% lead (15). A study in Faisalabad, Pakistan, in 1988 reported that 80% of 20 samples of surma had a lead content >65% (16). In Israel, blood lead concentrations were significantly higher in infants to whom kohl was applied than in those who did not have kohl applied (11.2 vs 4.3 [micro]g/dl). Among infants not directly exposed to kohl, blood lead concentrations were significantly higher in infants whose mothers used kohl than in those whose mothers did not (5.2 vs 2.8 [micro]g/dl) (17).
Family members of workers exposed to lead at their workplace are believed to be at additional risk of elevated blood lead concentrations. For example, blood lead concentrations of up to 280 [micro]g/dl were reported in workers at a lead-smelting plant in the USA (7) and concentrations of 28-70 [micro]g/dl were found among families living next to a battery factory in Bombay, India (18).
In 1989, Manser et al. reported mean blood lead concentrations of 38 [micro]g/dl among children at the Karachi Grammar School and 38.2 [micro]g/dl among children at a school in a less congested area of the city (19). In contrast, a study conducted in Bombay, India, in 1991, reported a mean blood lead concentration in children of 11.3 [micro]g/dl (20). These differences and the similarities between Karachi and Bombay in terms of concentrations of lead in the air derived from petrol, sociocultural status and socioeconomic status raise a few research issues, including the need to reassess blood lead concentrations in children from Karachi and the need to identify factors associated with high concentrations. …