Lead-associated deficits in stature, mental ability and behaviour in children in Karachi

This study was conducted to evaluate the cumulative and steady-state lead burden in children from Karachi, an area of high lead exposure, and to assess the degree of damage to physical growth and mental ability related to lead exposure. A cross-sectional survey was conducted in seven primary schools from around Karachi. Shed primary teeth and blood samples were collected from students of grades I to III (age range 6-10 years) and were analysed for lead by atomic absorption spectrophotometry. Haemoglobin concentration, height, weight and head circumference were measured. IQ was estimated using Raven's Standard Progressive Matrices. Classroom behaviour was rated by teachers and school performance was estimated from the percentage mark in a school examination taken just before the date of the IQ test. Complete data were available for 138 children. Over 80% of children had lead levels above the safety limit set by the United States Centers for Disease Control and Prevention. The blood lead levels in boys did not differ significantly from that in girls. Significant differences were observed between the schools. Univariate analysis showed negative association of blood lead with haemoglobin, IQ and height. Tooth lead was negatively associated with height, classroom behaviour and performance. When adjusted for other confounding variables, blood lead was negatively associated with haemoglobin and IQ, whereas tooth lead was negatively associated only with classroom behaviour. Height was negatively associated with blood or tooth lead. These results were further supported when the upper and lower quintiles for blood or tooth lead were compared. Tooth lead level was not a better marker of lead poisoning than blood lead level in our study population. These data demonstrate the association of increased lead with impaired learning and adverse behaviour in Karachi children and call for strict government regulations to limit environmental lead burden.